Neuroscience Block 2

b. S1-S2 The patient arrives at the office with issues concerning her right foot, which feels weak to her. The exam reveals tingling and reduced sensation, especially on the median and lateral sides. The Achilles tendon reflex test is performed to determine whether the S1 and S2 nerve roots are intact. The patient's diminished deep tendon reflex indicates a lower motor neuron injury. Remember that you count up the clinical reflexes: S1-S2 — "buckle my shoe" (Achilles reflex) L2-L4 — "kick the door" (patellar reflex) C5-C6 — "pick up sticks" (biceps reflex) C7-C8 — "lay them straight" (triceps reflex) Other reflexes include: L1-L2 — "testicles move" (cremaster reflex) S3-S4 — "winks galore" (anal wink reflex)

A 24-year-old woman presents to the office complaining of weakness in her right foot. She also says that her right calf muscle looks smaller than her left calf muscle. Physical examination reveals tingling and diminished sensation of the right foot, especially on the medial and lateral sides. There is minimal plantar flexion when her Achilles tendon is tapped with a reflex hammer. Other deep tendon reflexes of her right leg are within normal limits. Which nerve root corresponds to the most likely lesion in this patient? Select one: a. L3-L4 b. S1-S2 c. C5-C6 d. S3-S4 e. C7-C8

a. Medial longitudinal fasciculus This patient presents with internuclear ophthalmoplegia (INO), an example of a dysconjugategaze disorder in which the two eyes cannot move together in the same direction. In young patients, bilateral INO is highly indicative of multiple sclerosis (MS). MS is a chronic neurologic disorder affecting the white matter of the central nervous system (CNS). This disease typically affects young women (20-30 years old) and commonly manifests first with ocular problems. Other symptoms include unilateral optic neuritis, cerebellar dysfunction (ataxia, nystagmus, vertigo), bowel and bladder dysfunction, tingling or numbness, and muscle weakness. These symptoms can be exacerbated by heat since it slows the rate of conduction through demyelinated nerves even more, which explains why this patient experienced worsening weakness and fatigue after being in a sauna (Uhthoff phenomenon). When a healthy patient gazes to one side, lower motor neurons in the abducens nucleus send fibers via CN VI to the ipsilateral lateral rectus muscle, causing the ipsilateral eye to abduct. Simultaneously, interneurons in the abducens nucleus send their fibers across the midline to enter the contralateral medial longitudinal fasciculus (MLF) and synapse on neurons in the oculomotor nucleus that innervate the medial rectus muscle and cause the opposite eye to adduct. Through this mechanism, both eyes move conjugately in the horizontal plane. In MS, demyelination of the MLF secondary to the underlying disease process results in the failure of either eye to abduct on attempted horizontal gaze. The contralateral abducting eye may demonstrate a horizontal nystagmus. The underlying mechanism for the nystagmus is uncertain, but it may be explained by the Heringlaw of equal innervation, which states that conjugate eye movements occur because yoke muscles (eg, the medial and lateral recti for horizontal eye movements) receive equal and simultaneous innervation. In INO, attempts to increase innervation to the weak medial rectus muscle are accompanied by a commensurate increase in innervation to its yoke muscle (the contralateral lateral rectus), producing nystagmus. Lesions of the other areas of the brain would produce different symptoms: The arcuate fasciculus connects the Broca and Wernicke language areas in the dominant (usually left) hemisphere. Damage results in a language impairment known as conduction aphasia. The Edinger-Westphal nucleus supplies parasympathetic innervation to the pupil and ciliary muscle, but not to the somatic fibers involved in ocular movement. The medial lemniscus is a brainstem fiber pathway that carries somatosensory information from the extremities to the brain. Lesions here produce a loss of fine touch, conscious proprioception, and vibratory sense from the contralateral side of the body. The frontal eye field (FEF) is located near the intersection of the middle frontal gyrus with the precentral gyrus. Irritative lesions to the FEF (eg, seizure) cause horizontal conjugate deviation of the eyes away from the lesion, whereas destructive lesions of the FEF (eg, stroke) produce horizontal conjugate gaze toward the side of the lesion

A 24-year-old woman with no significant medical history complains of double vision that began 2 weeks ago. However, it only occurs when she looks to either side. Additionally, she reports feeling weak and fatigued after using the sauna at her local gym over the last few months. On neurologic examination, when the patient attempts to look to the left, her right eye does not adduct past the midline, and her left eye exhibits beating horizontal movements. When she looks to the right, her left eye exhibits the same signs while the right eye "beats." Her physician suspects a particular condition, and decides to order an MRI of the brain. The MRI would most likely reveal a lesion in which of the following locations? Select one: a. Medial longitudinal fasciculus b. Frontal eye field c. Bilateral lesion of Edinger-Westphal nuclei d. Arcuate fasciculus e. Medial lemniscus

b. L1 The patient arrives after suffering a herniated disc, which refers to herniation of the nucleus pulposus from the intervertebral disc. This is often precipitated by some trauma and can cause nerve root impingement. Disc herniation below the level of the C7 vertebra affects the nerve root associated with the inferior intervertebral disc. For example, T12-L1 disc herniation would affect the L1 nerve root, as seen in this patient. Disc herniation above the level of C7 also follows the same rule, but for a different reason: there are 7 cervical vertebrae and 8 cervical nerves. The C1 spinal nerve exits above the C1 vertebra, whereas the C2 spinal nerve exits between the C1 and C2 vertebrae (and is consequently affected in C1/C2 disc herniation). The hallmark of acute or chronic nerve root compression is pain. Pain due to nerve root compression has certain characteristics: It tends to follow a dermatomal distribution and it often results in radiculopathy. It may be accompanied by paresthesia, sensory loss, and/or hyporeflexia affecting a dermatome. There may be weakness in the muscles innervated by the nerve. Some alarming signs in a patient with acute back pain include bowel or bladder incontinence, saddle anesthesia, and/or focal neurologic deficits. These signs indicate cord compression and require emergent surgical intervention. Disc herniation in the lumbosacral levels would elicit a positive straight-leg test on exam. Diagnosis is made by MRI. As depicted in the illustration, the L1 dermatome is at the level of the inguinal ligament. This dermatome also includes the femoral triangle, the superolateral quadrant of the buttock, and the upper part of the medial thigh. Pain radiating to the groin and decreased sensation in the region around the inguinal ligament suggest L1 nerve root compression. Here is what you would expect from compression of the other listed nerve roots: The S1 dermatome involves the lateral malleolus, the lateral and plantar surface of the foot, and, occasionally, the heel. Patients with S1 nerve root impingement would have decreased Achilles tendon reflex and weakness with plantarflexion. The T7 dermatome is at the level of the xiphoid process, causing pain in the sternum. The T10 dermatome is at the level of the umbilicus. In patients with appendicitis, pain may begin here before moving to the more classically tested McBurney point (1/3 the distance between the right anterior superior iliac spine and the umbilicus), in the right lower quadrant of the abdomen. The L4 dermatome is at the level of the kneecaps. Patients with L4 nerve root impingement would have weakness with knee extension and little to no patellar deep tendon reflex on physical examination.

A 40-year-old man presents to his physician complaining of lower back pain. He was lifting some heavy boxes yesterday when the pain started. He reports the pain to be sharp, constant, and radiating to his groin. He denies bowel or bladder incontinence. On exam, he has decreased pinprick sensation around the inguinal ligament region, but a straight-leg test is positive. A herniated disk is suspected, and an MRI confirms the diagnosis. Which of the following nerve roots is most likely compressed by the herniated disc? Select one: a. S1 b. L1 c. T10 d. T7 e. L4

a. Anterior horn and lateral column degeneration with gliosis The patient has a long-term history of muscle weakness within his lower extremities, which has confined him to a wheelchair. His other symptoms, including dysarthria, tongue fasciculations, dysphagia, and extensor plantar responses, support a diagnosis of amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig disease. ALS usually begins in middle age and progresses to death over a period of a few years. ALS is characterized by the atrophy of the anterior horn cells and replacement of the large motor neurons by fibrous astrocytes (gliosis), which causes the affected anterior and lateral columns of the spinal cord to become hard (lateral sclerosis). This degenerative process is marked by the loss of upper and lower motor neurons, with sparing of sensory and autonomic neurons. The degeneration of the anterior horn results in progressive weakness that proceeds from neurogenic muscular atrophy to paralysis. The skeletal muscle fibers appear small and angular due to denervation atrophy. In this scenario, the patient developed lower motor neuron signs of weakness, atrophy, and fasciculations. Loss of neurons in the nuclei of cranial nerves V, IX, X, and XII can also be present, resulting in bulbar signs (dysarthria, dysphagia) from the lower motor neuron lesion. The patient also has a positive Babinski reflex (extensor plantar response), which is indicative of upper motor neuron lesions. Upper motor neuron signs are due to degeneration of the lateral corticospinal tract and mild atrophy of the prefrontal gyrus. Patients usually retain mental function over the course of the disease, and death is usually caused by paralysis of respiratory muscles. Irregularly scattered parenchymal and spinal cord lesions are consistent with multiple sclerosis (MS), a multifocal disease, marked by lesions in the brain and spinal cord that are separated in location and time. Demyelination of dorsal columns and spinocerebellar tracts is found in vitamin B12 neuropathy and Friedrich ataxia. Dorsal column and dorsal root degeneration is often seen in tabes dorsalis caused by tertiary syphilis. This results in impaired proprioception and balance. Physical examination would show decreased reflexes and positive Romberg sign. A whorled pattern of concentrically arranged spindle cells within the meninges describes the classic microscopic appearance of a meningioma. These neoplasms are slow growing and resectable, but may reach a large size before symptoms such as headaches and blurry vision lead to detection.

A previously healthy 54-year-old man presents with a 3-year history of progressive, symmetric muscle weakness in his extremities that has confined him to a wheelchair. Over the past week, the patient has experienced slurring of his speech and difficulty swallowing. He denies sensory deficits, myalgias, fever, or arthralgias, and his mental status is intact. Physical examination reveals muscle atrophy, tongue fasciculations, and extensor plantar responses. Which of the following histologic findings is most typical of this patient's underlying disease? Select one: a. Anterior horn and lateral column degeneration with gliosis b. Irregularly scattered parenchymal and spinal cord lesions c. Whorled pattern of concentrically arranged spindle cells within the meninges d. Dorsal column and dorsal root degeneration e. Demyelination of dorsal columns and spinocerebellar tracts

g. T4 The patient presents with paresthesia around the nipples, which is consistent with T4 nerve compression. The nipples are used as landmarks for the T4 dermatome. Remember "T4 at the teat pore." As an aside, the peritoneal cavity can extend as high as the 4th intercostal space (the nipple line). Therefore, trauma surgeons use the nipple line to approximate where the diaphragm divides the thorax from the abdomen. Any penetrating injury at or below this level has the potential to injure intra-abdominal organs, especially when the wound tracks inferiorly. Learn the trunk dermatomes: T2—level of sternal angle T4—level of nipples T6—level of xiphoid T10—level of umbilicus T12—level of the midpoint between umbilicus and pubic symphysis L1—level of pubic crest

56-year-old man complains of a strange tingling sensation around the chest that started a week ago. Neurologic examination reveals loss of sensation in the skin around the nipples. No rashes are noted. Disc herniation is suspected, and MRI confirms the diagnosis. Which of the following spinal nerves is being compressed by the herniated disc? Select one: a. T1 b. T7 c. C4 d. C3 e. C6 f. T10 g. T4

d. T10, T12 Distension of the GI tract causes referred pain. The crampy epigastric pain felt at the beginning of appendicitis occurs because the visceral sensory axons from the appendix have cell bodies located in the T10 dorsal root ganglion. Therefore the pain refers to the T10 dermatome, as shown in the diagrams. (Remember the mnemonic "T10 controls the belly but-ten.") Later in its course, the inflammation of the appendix irritates the local peritoneum, which is innervated by somatic pain fibers of T12. The McBurney point, as described in this vignette, lies in the T12 dermatome. For a visual representation of the superficial regions of the T10 and T12 dermatomes, along with all the other dermatomes, refer to the dermatome map.

A 22-year-old man with no significant past medical history presents to the emergency department because of right lower quadrant pain. The patient says the pain started as a crampy sensation in his upper abdomen, but in the past hour it has localized to a point about 2.5 cm superior and medial to his anterior superior iliac spine. Which of the following dermatomes are responsible for the patient's pain? Select one: a. L1, L2 b. L4, L5 c. T4, T6 d. T10, T12 e. S2, S4

e. Spinothalamic tract The MRI in the vignette shows a Chiari I malformation, which is an anatomic abnormality characterized by displacement of the cerebellar tonsils below the level of the foramen magnum. A common manifestation of Chiari I malformation is elevated intracranial pressure, which would explain this woman's position-dependent headaches. Chiari I malformations are often associated with syringomyelia, a disorder caused by a cystic cavity (syrinx) inside the spinal cord which most commonly affects the C8-T1 level. The syrinx can impinge upon fibers of the spinothalamic tract as they cross through the anterior white commissure, located medially and anterior to the center of the spinal cord. Involvement of the spinothalamic tract results in bilateral loss of pain and temperature sensation, usually seen in the upper extremities (with a syrinx located around C8-T1). The other parts of the spinal cord are not likely to be affected. Ventral horn damage can occur from poliomyelitis and ALS and results in motor damage rather than sensory impairment. Damage to the dorsal columns results from syphilis and vitamin B12 deficiency, which manifests with proprioceptive and vibratory sensation abnormalities. The dorsal root ganglion is damaged in Charcot-Marie-Tooth syndrome, which manifests as a loss of limb sensation. The spinocerebellar tract is damaged in Friedreich ataxia and manifests with balance impairment.

A 25-year-old woman presents to her primary care physician with frequent headaches that worsen when she bends over. She has looked up her symptoms online and is very worried that she has multiple sclerosis. She is particularly worried because she has lost some sensation in both of her hands, and a coworker she knew with MS had "problems with numbness." She is referred to a neurologist, who orders an MRI with the results shown. Which part of the spinal cord would most likely be affected in this patient? Select one: a. Ventral horn b. Dorsal columns c. Dorsal root ganglia d. Spinocerebellar tract e. Spinothalamic tract

e. Proprioception

A 34-year-old man is evaluated in the clinic due to dificulty walking over the past 2 weeks. His symptoms have resulted in several recent falls, but he has had no head trauma or loss of consciousness. He has never had these symptoms before. The patient is frustrated as he cannot carry out his duties as a mailman. He has a history of crack cocaine use in the distant past but no current ilicit drug use. The patient is in a monogamous relationship but previously had numerous sexual partners. The physician asks him to stand with his feet close together, arms to the sides, and eyes closed. This maneuver most likely tests for abnormalities in which of the following? Select one: a. Cortical sensory integration b. Gait c. Motor coordination d. Muscle strength e. Proprioception

c. Hypoperfusion of the anterior spinal artery Explanation: After a surgical procedure for a resection/debulking of a large tumor, the patient suddenly lost motor function below the waist and began losing pain and temperature sensation below the T4 dermatome while in recovery. The anterior (ventral) spinal artery (ASA) is of particular interest, since it arises from the vertebral arteries and provides circulation for the ventral two thirds of the spinal cord. Unlike the dorsal (posterior) cord, which is served by two posterior spinal arteries, the ventral cord relies on only one artery, making it more vulnerable to infarction than the posterior cord. Although the blood supply to the spinal cord is considered rich, the spinal canal is narrowest—and the blood supply is poorest—at T4-9. This is why it is deemed the critical vascular zone of the spinal cord, since interference with circulation is most likely to result in paraplegia. The upper thoracic ASA territory is considered a watershed area, with the artery of Adamkiewicz being one of the largest radicular arteries supplying the ASA. Anterior cord syndrome is caused by hypoperfusion of the anterior spinal artery, resulting from occlusion or infarction of the anterior cord (as shown with cross-hatching in the image). It causes bilateral deficits below the lesion affecting: Pain and temperature sensation (spinothalamic tract) Voluntary motor control (lateral corticospinal tract) Autonomic motor control (including bladder and bowel control) However, the dorsal columns (light touch, vibration, proprioception) are spared. This patient most likely had an anterior cord infarction at the level of T4 during a period of hemodynamic instability requiring transfusions. An autoimmune attack on central nervous system myelin is the cause of multiple sclerosis (MS), which can produce transverse myelitis. Compression of the spinal cord by a tumor in the spinal canal is unlikely to present as suddenly or to the extent seen in this patient. Hypoperfusion of the artery of Adamkiewicz is common during cardiac surgery, but the neurologic deficits would typically arise below the level of T8 and would not extend to the T4 level. Hypoperfusion of the posterior spinal arteries would cause selective damage to the dorsal columns, leading to loss of touch, position, and vibration sense bilaterally below the lesion. Traumatic hemisection of the spinal cord at T4, known as Brown-Séquard syndrome, would induce ipsilateral dorsal column deficits below the lesion, contralateral spinothalamic deficits and partial deficits on the ipsilateral side up to one dermatome above and below the lesion, and ipsilateral corticospinal tract and ventral horn deficits leading to loss of motor control.

A 25-year-old woman undergoes spine surgery for resection of a large tumor. A complication during the long operation necessitated transfusion of several units of blood. In the recovery room, the patient suddenly complains of loss of motor function below the waist bilaterally. The intern examining her finds that she has also lost pain and temperature sensation below the level of the T4 dermatome. Vibration, light touch, and position sense are intact. The intern is concerned that the patient will soon experience fecal incontinence and urinary retention. Which of the following is the most likely cause of neurologic damage in this patient? Select one: a. Hypoperfusion of the posterior spinal arteries b. Autoimmune attack on myelin in the cord c. Hypoperfusion of the anterior spinal artery d. Traumatic hemisection of the spinal cord at level T6 e. Compression of the spinal cord by a tumor in the spinal canal f. Hypoperfusion of the artery of Adamkiewicz

b. Right C6-C7 disc herniation This patient's right neck pain and tingling, along with right triceps weakness and absent right triceps reflex, is a typical presentation of a right C7 radiculopathy, the most common of the cervical radiculopathies. Because cervical nerve roots emerge above the corresponding vertebrae (unlike other nerve roots that emerge below), a right C6-C7 disc herniation would impinge on the right C7 nerve root. Motor deficits of C7 radiculopathies most commonly affect the triceps, resulting in weakened elbow extension and diminished triceps reflexes. There will also be weakness in the extension of wrist and fingers. Sensory abnormalities are localized to the C7 dermatome, causing pain and paresthesias of the middle finger. Although nerve roots exit below the corresponding vertebrae in thoracic and lumbar regions, the nerve root from the lower vertebrae is still the one affected, as seen with cervical herniations (eg, an L4-L5 herniation would impinge on the L5 nerve root). The reason for this anatomic oddity is that the nerve root from the upper vertebrae has already descended to a point at which it is closer to exiting the spine, making it less likely to be impinged on. In contrast, the nerve root from the lower vertebrae is also descending but is more medial in location, so it is more likely to be compressed by a herniated disc. An ulnar compression would result in loss of ulnar hand sensation and motor effects. Axillary nerve compression would result in deltoid atrophy and impaired shoulder abduction. Radial nerve compression would result in impaired wrist extension and loss of sensation on the dorsum of the wrist. A C4-C5 disc slip results in impaired arm flexion and abduction, while a C5-C6 disc slip results in extension impairment, as well as partial loss of arm flexion (loss of biceps reflex).

A 30-year-old man presents with complaints of right neck pain and tingling that radiates into the middle finger on his right hand. Neurologic examination reveals weakness of the right triceps and an absent right triceps reflex. His history is significant for a skiing accident in which he injured his neck a year earlier. Which of the following lesions is the most likely cause of his symptoms? Select one: a. Right radial nerve compression at the midshaft of the humerus b. Right C6-C7 disc herniation c. Right ulnar nerve compression at the elbow d. Right C5-C6 disc herniation e. Right C4-C5 disc herniation f. Right axillary nerve compression at the humeral head

c. Right C6-C7 disc herniation This patient's right neck pain and tingling, along with right triceps weakness and absent right triceps reflex, is a typical presentation of a right C7 radiculopathy, the most common of the cervical radiculopathies. Because cervical nerve roots emerge above the corresponding vertebrae (unlike other nerve roots that emerge below), a right C6-C7 disc herniation would impinge on the right C7 nerve root. Motor deficits of C7 radiculopathies most commonly affect the triceps, resulting in weakened elbow extension and diminished triceps reflexes. There will also be weakness in the extension of wrist and fingers. Sensory abnormalities are localized to the C7 dermatome, causing pain and paresthesias of the middle finger. Although nerve roots exit below the corresponding vertebrae in thoracic and lumbar regions, the nerve root from the lower vertebrae is still the one affected, as seen with cervical herniations (eg, an L4-L5 herniation would impinge on the L5 nerve root). The reason for this anatomic oddity is that the nerve root from the upper vertebrae has already descended to a point at which it is closer to exiting the spine, making it less likely to be impinged on. In contrast, the nerve root from the lower vertebrae is also descending but is more medial in location, so it is more likely to be compressed by a herniated disc. An ulnar compression would result in loss of ulnar hand sensation and motor effects. Axillary nerve compression would result in deltoid atrophy and impaired shoulder abduction. Radial nerve compression would result in impaired wrist extension and loss of sensation on the dorsum of the wrist. A C4-C5 disc slip results in impaired arm flexion and abduction, while a C5-C6 disc slip results in extension impairment, as well as partial loss of arm flexion (loss of biceps reflex).

A 30-year-old man presents with complaints of right neck pain and tingling that radiates into the middle finger on his right hand. Neurologic examination reveals weakness of the right triceps and an absent right triceps reflex. His history is significant for a skiing accident in which he injured his neck a year earlier. Which of the following lesions is the most likely cause of his symptoms? Select one: a. Right ulnar nerve compression at the elbow b. Right axillary nerve compression at the humeral head c. Right C6-C7 disc herniation d. Right radial nerve compression at the midshaft of the humerus e. Right C5-C6 disc herniation f. Right C4-C5 disc herniation

e. T4

A 31-year-old man is brought to the emergency department after a motorcycle accident. The patient was texting on his cell phone while driving when he lost control of his bike and fell to the asphalt. He was found lying in the middle of the road by first responders, who placed him in a rigid cervical collar and put him on a backboard for spinal immobilization. The patient currently has severe pain in his neck and back. On physical examination, he is alert and fully oriented. There is no periorbital ecchymosis or hemotympanum, but there are several abrasions and lacerations located on the trunk and extremities. Neurologic examination suggests a spinal cord injury corresponding to the level shown in the illustration below. Which of the following spinal cord levels is most likely to be injured? Select one: a. C1 b. C7 c. L5 d. S2 e. T4

c. Damage to the central spinal cord extending bilaterally into anterior horn and white matter of lateral spinal cord (C5-T1)

A 32-year-old woman has a progressive loss of pain and temperature sensation across both hands and arms. Vibration and proprioceptive sense are intact. She begins to have weakness and fasciculations in both hands and lower arms. Further testing reveals hyperactive patellar and Achilles tendon reflexes in the right leg. Sensation is normal in both legs. Which of the following is the most likely cause of her symptoms? Select one: a. Bilateral damage to the posterior horn and adjacent white matter of lateral spinal cord (C5-T1) b. Bilateral damage to the anterior horn and adjacent white matter of anterolateral spinal cord (C5-T1) c. Damage to the central spinal cord extending bilaterally into anterior horn and white matter of lateral spinal cord (C5-T1) d. Bilateral damage to white matter of posterior and lateral spinal cord (C1-C3) e. Bilateral damage to white matter of anterior and lateral spinal cord (C1-C3)

e. Syringomyelia This patient is presenting with loss of pain and temperature sensation in a cape-like distribution, leading to her burn injuries, with preserved position and vibration sense. This localizes the pathology to the central cervical cord. These symptoms—along with the MRI findings (shown here)—are consistent with the diagnosis of syringomyelia. Syringomyelia consists of an enlargement of the central canal of the spinal cord, most commonly occurring at C8-T1. Crossing fibers of the spinothalamic tract are damaged (causing loss of pain and temperature sensation), but dorsal column function is preserved (intact position and vibration sense). Syringomyelia can be associated with a type 1 Chiari malformation of the posterior cranial fossa. Type 1 Chiari malformation leads to a downward herniation of the cerebellar tonsils into the foramen magnum, which can manifest with headaches, as seen in this patient. Acquired causes of syringomyelia include trauma, whiplash injury in the elderly, tumor, and inflammation. Communicating hydrocephalus is caused by impaired absorption of cerebrospinal fluid in the absence of any flow obstruction between the ventricles and subarachnoid space. It is typically associated with malfunctioning arachnoid villi. Congenital aqueductal stenosis is a common cause of congenital hydrocephalus, manifesting very early in life with symptoms of increased intracranial pressure, such as vomiting, altered mental status, and papilledema. Dandy-Walker syndrome is a congenital noncommunicating hydrocephalus typically associated with a cluster of abnormal findings that include abnormal formation of the cerebellar vermis. Lateral medullary syndrome, or Wallenberg syndrome, usually occurs as a result of occlusion of one of the posteroinferiorcerebellar arteries (PICA). It manifests with loss of pain and temperature sensations over the contralateral side of the body and the ipsilateral face, along with vertigo, dysarthria, dysphagia, and Horner's syndrome.

A 32-year-old woman presents to the physician with weakness of both upper extremities, headaches, and multiple second-degree burns on her hands. The patient has no prior significant medical history and cannot recall any recent episodes of trauma. Although physical examination uncovers no motor deficits in either upper extremity, it reveals the absence of pain and temperature sensation in the upper extremities bilaterally. Position and vibration sense are intact in the upper extremities, and there are no lower extremity abnormalities. An MRI of the spinal column shows dilation within the cervical spinal cord. Which diagnosis is consistent with this patient's findings? Select one: a. Wallenberg (lateral medullary) syndrome b. Dandy-Walker syndrome c. Congenital aqueductal stenosis d. Communicating hydrocephalus e. Syringomyelia

b. Amyotrophic lateral sclerosis Sporadic ALS is the most common acquired motor neuron disease, accounting for up to 80% of all such motor neuron diseases. It causes degeneration of both upper motor neurons (eg.pyramidal neurons of the cerebral cortex) and lower motor neurons (eg, anterior horn neurons of spinal cord). Degeneration of the motor neuron cell bodies leads to loss of corticospinal tracts and anterior spinal roots. The afflicted individual presents with both upper motor neuron signs (hyperreflexia, spasticity, Babinski sign) and lower motor neuron signs (fasciculations, weakness, muscle atrophy).

A 36-year-old man is seen because of repeated tripping and falling. The history reveals that he began to experience weakness in his left leg about 6 months ago and has recently begun to experience weakness in his right leg. He also reports twitching in his leg and arm muscles. Examination reveals weakness with hyperreflexia in leg and arm muscles. Fasciculations are observable in both thighs. Fasciculations and muscle atrophy are seen in the intrinsic hand muscles. There is no sensory involvement. Which of the following is the most likely cause of his symptoms? Select one: a. Schwannoma b. Amyotrophic lateral sclerosis c. Myasthenia gravis d. Lambert-Eaton myasthenic syndrome

c. Anterior horn of spinal cord Explanation:This patient presents with difficulty maintaining posture and head support, diminished deep tendon reflexes, and weak cry, all of which suggest a lower motor neuron (LMN) lesion. This patient most likely has spinal muscular atrophy (SMA) type 1, also known as Werdnig-Hoffmann disease, which is characterized by destruction of the anterior horn cells of the spinal cord. SMA is due to an autosomal recessive mutation in the SMN1 gene (survival motor neuron) that is thought to play a role in mRNA synthesis in motor neurons and inhibition of apoptosis. This condition affects only the LMN system, which includes the anterior horn cells of the spinal cord, ventral nerve root, peripheral nerve, neuromuscular junction, and skeletal muscle. Patients with LMN disease will experience muscle atrophy, proximal muscle weakness, fasciculations, hypotonia, and diminished deep tendon reflexes. Poliomyelitis infection could also cause isolated LMN disease. Injury to the cerebral cortex and lateral corticospinal tract would manifest with upper motor neuron signs, such as hypertonia, hyperreflexia, and spasticity. Damage to the dorsal root ganglion would result in absent sensation at the level of the lesion. Injury to the dorsal column of the spinal cord would lead to a sensory deficit below the lesion (absent vibration, fine touch, pressure) as well as absent proprioception and locomotor ataxia.

A 39-year-old mother presents to the clinic with her 1-month-old son with concerns that he is not reaching his developmental milestones. This is her first child, and he was born by an uncomplicated vaginal delivery. She reports difficulty with feedings and has noticed that he cannot keep his head supported while in the prone position. On examination, you notice the boy has a weak cry and difficulty maintaining posture. The infant also has generalized muscle atrophy and reduced ankle and brachial reflexes. This patient's condition can most likely be localized to which area of the nervous system? Select one: a. Cerebral cortex b. Lateral corticospinal tract c. Anterior horn of spinal cord d. Dorsal root ganglion e. Dorsal column of spinal cord

d. L3 and L4 In this video, the examiner is testing the patellar reflex by striking the patellar ligament of the quadriceps femoris muscle. The patellar reflex is mediated by innervation from the L3 and L4 spinal levels. Remember all the other clinical reflexes and their associated dermatomes by the rhymes in the table.

A 40-year-old man presents to the office because of progressively worsening pain and weakness in his legs over the past 4 months. Part of his physical examination is shown in the video clip. Which of the following spinal levels are tested in this examination? Select one: a. C5 and C6 b. C7 and C8 c. L1 and L2 d. L3 and L4 e. S1 and S2 f. S3 and S4

a. Decreased anal sensation The patient presents to the physician with erectile dysfunction that has plagued him over the past several months. Erection is mediated by the parasympathetic nervous system via the pelvic splanchnic nerves, which arise from S2-S4. Parasympathetic fibers, in general, exit from the cranial and sacral regions of the spinal cord. In the penis, the postsynaptic parasympathetic fibers release acetylcholine, increasing the production of nitric oxide (NO) and thereby raising the level of intracellular cGMP in the arterial smooth muscle cells. This results in arterial vasodilation along with compression of the tunicalveins, leading to pooling of the blood within the erectile tissue, which ultimately generates an erection. In addition to erection, S2-S4 fibers (through the pudendal nerve) are also responsible for anal and penile sensations (via inferior rectal and dorsal nerves, respectively). A useful mnemonic is "S2-3-4 keeps the penis off the floor." Decreased sensation at the lateral malleolus is due to issues affecting the S1 dermatome. Decreased sensation at the anterior upper thigh involving the knee caps results from issues with the nerve fibers arising from L3-L4. Decreased sensation at the inguinal crease is correlated to the L1 dermatome. Impaired emission and ejaculation are due to issues with nerve fibers from T10-L2.

A 42-year-old man is being evaluated following several months of erectile dysfunction. Along with difficulties achieving and maintaining erections, he has noticed that he gets morning erections less frequently. He decided to seek medical advice now because of the strain this is having on his marriage. His medical history is significant for an injury to his lower back 1 year ago. If the patient's erectile dysfunction is due to his previous back injury, which of the following additional findings is most likely? Select one: a. Decreased anal sensation b. Decreased sensation at the lateral malleolus c. Decreased sensation at the inguinal crease d. Impaired emission and ejaculation e. Decreased sensation at the anterior upper thigh involving the knee caps

b. Diminished ankle-jerk reflex The patient arrives in the ED with severe lower back pain, caused by a herniated disc which occurs while lifting a piano. A slipped disc at the L5-S1 level will typically compress the S1 nerve root. An S1 lumbar radiculopathy is characterized by decreased sensation of the posterior leg and lateral foot, a diminished ankle-jerk reflex, and weakness of plantarflexion, toe flexion, and foot inversion. In terms of spinal anatomy, the annulus fibrosis usually keeps the soft nucleus pulposus in place and protected, but damage to the fibrous tissues allows for herniation of the nucleus pulposus. Most herniations occur in the posterolateral direction, where the annulus is relatively thin and does not receive support from the posterior longitudinal ligament. If the nucleus pulposus breaks through the annulus enough to cause bulging, it may compress the ipsilateral nerve root as it exits from the dural sac. The nerve root that is compressed in this type of herniation corresponds to the lower vertebral body. Cervical nerve roots exit above their corresponding vertebral bodies, but in the thoracic, lumbar, and sacral regions, nerve roots exit below, not above, their corresponding vertebral bodies. However, the end result is the same. Using L5/S1 as an example, the nerve root from the lower body—in this case, S1—is compressed as it travels vertically to exit below S1. The L5 nerve root is not compressed because it exits the intervertebral foramina above the L5/S1 disc. The diminished knee-jerk reflex is caused by a radiculopathy in the L2-L4 region, and produces a similar weakness to knee extension, hip flexion, and hip adduction due to femoral nerve impairment. Diminished sensation to the medial aspect of the foot would be caused by an L4 radiculopathy. Dorsiflexion of the foot occurs via L5, due to the L4-L5 disc slip, not L5-S1 slip as seen in this patient.

A 42-year-old man presents to the emergency department with severe lower back pain. The pain started abruptly as he was lifting a piano while helping his daughter move into a new apartment. He describes the pain as sharp and shooting and says it radiates down his right leg. The patient has a history of hypertension and type 2 diabetes mellitus. On examination, there are no obvious signs of trauma. The pain is exacerbated while slowly lifting the leg while the leg is straight at the knee and the patient is supine. The patient describes the pain as excruciating at an angle of 45 degrees. After he is given medication for his pain, the patient undergoes CT of his lumbar region, which reveals a herniated disc at the L5-S1 level. Which is the most likely finding on neurologic examination? Select one: a. Weakness to knee extension b. Diminished ankle-jerk reflex c. Diminished knee-jerk reflex d. Weakness to dorsiflexion of foot e. Diminished sensation to the medial aspect of foot

e. S1

A 43-year-old woman comes to the office due to acute back pain after dragging a heavy box. The pain is located in her lower back and radiates down the right posterior thigh to the foot. The patient describes the pain as "shooting" and grades it 8/10 in intensity. She has no bowel or bladder symptoms. The patient has tried over-the-counter analgesics with limited symptomatic relief. Vital signs are within normal limits. On physical examination, straight leg raise testing is positive on the right. Right hip extension is weaker when compared to the left. Knee jerk reflexes are 2+ and bilaterally symmetric, but the right ankle jerk reflex is absent. Which of the following nerve roots is most likely affected in this patient? Select one: a. L2 b. L3 c. L4 d. L5 e. S1

d. Fasciculations Explanation: This patient presents with numerous indications of ALS, which is a progressive neurodegenerative disease that is diffuse (involving multiple limbs) and affects both upper and lower motor neurons (LMN). Fasciculations (twitching of the muscle as it loses innervation) are characteristic of LMN lesions. They are thought to be caused by release of acetylcholine from the degenerating nerve terminal at the neuromuscular junction. Brisk deep tendon reflexes are indicative of upper motor neuron lesions. LMN lesions result in decreased reflexes. Normal reflexes are graded as 2+; thus a 3+ reflex would be considered "brisk." The extensor plantar response (also known as the Babinski sign) refers to reflexive dorsiflexion (extension) of the big toe and fanning of the toes in response to stroking the lateral sole of the patient's foot. The normal response to this test is flexion of the toes, so an extensor response indicates upper motor neuron damage. Because upper motor neurons (UMN) provide an inhibitory influence on the motor unit, loss of UMNs results in increased activity at the neuromuscular junction, resulting in increased muscle tone, spasticity, and hyperreflexia. Paresis (weakness) is nonspecific in that it is seen in both upper and lower motor neuron lesions, and would not be unique to LMN deficits.

A 45-year-old man comes to his physician because of worsening weakness in his legs. He has also recently experienced difficulty chewing and moving his hands and fingers. Physical examination reveals fasciculations in his calves and atrophy of the calf and thigh muscles. Spasticity and hyperreflexia is noted in the upper extremities. After further testing, the physician concludes the patient has amyotrophic lateral sclerosis (ALS). Which of the following signs is specifically indicative of a lower motor neuron (LMN) lesion? Select one: a. Extensor plantar response (Babinski sign) b. 3+ knee jerk reflex c. Weakness d. Fasciculations e. Spasticity

a. Degeneration of the anterior horns and corticospinal tracts. Amyotrophic lateral sclerosis (ALS) is characterized by both upper and lower motor neuron signs. Lesions of the anterior horns of the gray matter lead to lower motor neuron signs (eg, muscle weakness, atrophy, and fasciculations), whereas lesions of the corticospinal tracts yield upper motor neuron signs (eg, hyperreflexia). The image shows degeneration of the lateral and anterior corticospinal tracts. The neuromuscular symptoms of tertiary syphilis, known as tabes dorsalis, are secondary to posterior column degeneration and include problems with gait and balance. Guillain-Barré doesn't lead to degeneration of the anterior white commissure. Guillain-Barré syndrome is characterized by loss of lower motor neuron and sensory nerve function, caused by demyelination of peripheral nerves. Degeneration of the posterior columns and corticospinal tracts is characteristic of pernicious anemia (vitamin B12 deficiency). Polio is characterized by degeneration of the anterior horn cells. Syringomyelia affects pain and temperature sensation and motor function in a cape-like distribution. Lesions are localized to the anterior white commissure.

A 45-year-old man comes to the clinic complaining of weakness of his left foot for the last 5 months. The patient explains that he usually trips over due to his foot weakness, he denies any numbness or tingling or weakness on the other foot. His past medical history is unremarkable and does not take any medication; family history is noncontributory. On physical examination, vital signs are normal; neurological examination shows left foot strength of 2/5, right foot strength 5/5. Strength in the upper extremities is normal. There is no decreased sensation but the physician notes mild atrophy of the left foot as well as fasciculations and spasticity on his right forearm. Which of the following pathological changes is most likely? Select one: a. Degeneration of the anterior horns and corticospinal tracts. b. Degeneration of the anterior horns. c. Degeneration of the anterior white commissure. d. Degeneration of the posterior columns and corticospinal tracts. e. Degeneration of the posterior columns.

a. Lateral corticospinal tract Explanation: This patient's complaints of lower limb weakness and violent shaking, combined with a positive family history, are consistent with hereditary spastic paraplegia. Hereditary spastic paraplegia is characterized by progressive lower limb weakness and spasticity due to degeneration of the lateral corticospinal tract, shown in the diagram. The lateral corticospinal tract controls descending voluntary movements of the contralateral limbs. The other portions of the spinal cord house different nerves: The anterior corticospinal tract is involved in controlling proximal muscles (eg, trunk) The anterior spinothalamic tract contains nerves that respond to crude touch and pressure. The lateral spinothalamic tract contains nerves that respond to pain and temperature. The dorsal column includes the fasciculus cuneatus and fasciculus gracilis, each of which contain sensory neurons involved in pressure, vibration, fine touch, and proprioception.

A 45-year-old man is seen in the clinic because of lower limb problems. He states that his legs "violently shake" when he walks. He also complains that his legs "feel weak and don't work well." His temperature is 36.7°C (98°F), pulse is 72/min, respiratory rate is 16/min, and blood pressure is 122/74 mm Hg. Upon further questioning about his family history, the patient reveals that his father and his uncle both had similar "problems moving around." The nerves most likely affected in this patient are found in which of the following portions of the spinal cord? Select one: a. Lateral corticospinal tract b. Dorsal column c. Lateral spinothalamic tract d. Anterior corticospinal tract e. Anterior spinothalamic tract

b. C5-C6

A 46-year-old man comes to the office with left upper limb weakness and numbness. He has had chronic neck pain since being involved in a motor vehicle collision 4 years ago. He has no other medical problems. Neurological evaluation reveals that the tendon reflex shown in the image below is absent. Reflexes in the right upper extremity and both lower extremities are normal. Imaging studies reveal degenerative changes in the spine causing mild spinal cord compression. Which of the following spinal segments is most likely affected in this patient? Select one: a. C3-C4 b. C5-C6 c. C7-C8 d. C8-T1 e. T1-T2

d. Neuronal loss in anterior horn cells and connecting pathways of the corticospinal tracts This patient presents with signs and symptoms consistent with amyotrophic lateral sclerosis (ALS), a neurodegenerative disease that affects both anterior horn cells (lower motor neurons) and corticospinal tract (upper motor neurons), as shown in the image. Consequently, ALS results in a combination of upper and lower motor neuron signs, although the deficits may be asymmetric. Lower motor neuron signs (fasciculations,weakness) are frequently the first noticed, with an eventual development of upper motor neuron signs (spasticity, hyperreflexia, Babinski sign). It typically affects adults over 40 years of age, with a higher incidence in men than women. Lifespan after symptom development is typically 3-5 years, with death frequently due to respiratory failure. Demyelination of axons in the dorsal columns and spinocerebellar tracts in the spinal cord occurs in subacute combined degeneration of the spinal cord, which is also known as vitamin B12 neuropathy. Demyelination of axons in the posterior limb of the internal capsule would cause contralateral spastic paralysis secondary to disruption of the descending fibers of the corticospinal tract, resulting in upper motor neuron signs. Neuronal loss in the region of the anterior horn cells and posterior columns in the spinal cord occurs in Charcot-Marie-Tooth disease, also known as peroneal muscular atrophy. Neuronal loss purely in the anterior horn cells of the spinal cord occurs in poliomyelitis, resulting in a flaccid paralysis (pure lower motor neuron disease). Demyelination of peripheral nerves occurs in diseases such as Guillain-Barré syndrome and manifests solely with lower motor neuron signs, such as hyporeflexia and weakness.

A 47-year-old man presents to his physician with frequent falls and an increasing sense of muscle weakness. He has no history of neurologic disease, recent illness, weight loss, or trauma. Mental status exam is normal, and cranial nerves are intact. Physical examination is notable for weakness in all extremities. Deep tendon reflexes are absent in the upper extremities and 3+ in the lower extremities, and fasciculations are present in the upper extremities. Gait exam is significant for a L foot drop. Babinski sign is upgoing bilaterally. The patient denies any sensory changes, and pinprick testing is unremarkable. Laboratory and imaging studies are all within normal limits. What findings would be expected on examination of the central nervous system? Select one: a. Neuronal loss purely in the anterior horn cells in the spinal cord b. Demyelination of axons in the dorsal columns and spinocerebellar tracts in the spinal cord c. Demyelination of peripheral nerves d. Neuronal loss in anterior horn cells and connecting pathways of the corticospinal tracts e. Neuronal loss in the anterior horn cells and posterior columns in the spinal cord f. Demyelination of axons in the posterior limb of the internal capsule

d. L5 and S1 The L5 nerve root exits here and supplies the sensory innervation of the lateral calf and dorsal root surface.

A 48-year-old woman is brought to the emergency department with episodes of intense, stabbing pain that radiates down her left leg. She is suffering from a cold, and the pain is made worse when she coughs. Upon questioning, she adds that the outside (lateral aspect) of her left calf intermittently tingles and feels numb. Examination reveals that passively raising the leg 30 degrees from the supine position elicits excruciating pain. The accompanying MRI confirms that she has a herniated disk. It is most likely that this disk is compressing the nerve root exiting between which of the following pairs of vertebrae? Select one: a. L2 and L3 b. L3 and L4 c. L4 and L5 d. L5 and S1 e. S1 and S2

e. Small angular muscle fibers This patient has progressive, asymmetric muscle weakness in his upper and lower extremities with no clear precipitant (eg, no recent trauma). Bowel and bladder function are intact. These are the classic characteristics of amyotrophic lateral sclerosis (ALS). Degeneration of the anterior horn and thinning of anterior roots contributes to the lower motor neuron (LMN) signs in ALS. Atrophy of the lateral corticospinal tract and precentral gyrus of the motor cortex manifests as the upper motor neuron (UMN) signs. The sensory and autonomic functions are spared. On a microscopic level, muscle biopsy reveals small, angular fibers indicative of muscular atrophy due to lack of neuronal input (denervation atrophy). The image shows small, angular fibers seen in ALS as opposed to the large, round fibers seen in a normal muscle biopsy. Creatine kinase may be slightly elevated in ALS due to muscle loss. Riluzole, a glutamate antagonist, is the treatment of choice, although the disease is ultimately fatal. Periodic acid-Schiff-positive remnants of autophagic vacuoles, or Buninabodies, are found in the anterior horn of the spinal cord in patients with ALS. An increase in fatty or fibrous tissue (representative of Duchenne muscular dystrophy) may occur in patients with ALS. This development, however, typically occurs only with significant muscle atrophy in long-standing ALS. The other explanations show biopsy specimens from polymyositis (increased endomysialinfiltration of lymphocytic cells), and rabies (eosinic intracytoplasmic inclusions).

A 50-year-old man comes to the physician complaining of weakness that started in his legs and has now progressed to include his arms. He first noticed the symptoms 3 months ago. He has no bowel or bladder changes. Physical examination reveals muscle wasting and fasciculations in the upper extremities. Motor strength is ⅖ in the upper extremities with +1 biceps reflex bilaterally. +3 patellar reflex and ⅗ motor strength are noted in the lower extremities bilaterally. The patient has no recent history of infections, animal bites, or trauma. Which of the following microscopic findings is most likely to be seen in a muscle biopsy of this patient's arms? Select one: a. Increase in fatty or fibrous tissue b. Increasedendomysialinfiltration of lymphocytic cells c. Eosinophilic intracytoplasmic inclusions d. Periodic acid-Schiff-positive remnants of autophagic vacuoles e. Small angular muscle fibers

h. Right spinothalamic Explanation:The patient is brought to the ED following a car accident, which left him with severe back pain. This patient likely has Brown-Séquard syndrome due to a hemisection of the spinal cord. Clinical manifestations of the syndrome include: Ipsilateral upper motor neuron (UMN) signs below the level of the lesion (corticospinal tract damage) Ipsilateral loss of tactile, vibration, and proprioception below the level of the lesion (dorsal column damage) Contralateral loss of pain and temperature one to two dermatome levels below the lesion (spinothalamic tract damage) Ipsilateral loss of all sensation at the level of the lesion Ipsilateral lower motor neuron signs (LMN) at the level of the lesion. This patient complains of severe pain and exhibits sensory loss upon neurologic examination—a clinical presentation consistent with a right hemisection of the spinal cord. His left leg sensory aberration is due to contralateral damage to the right spinothalamic tract. The right spinothalamic tract carries afferent pain and temperature sensation from one side of the body to the contralateral ventral posterolateral (VPL) nucleus and somatosensory cortex. Cell bodies of pain/temperature receptors are located in the dorsal root ganglia. Their axons enter the spinal cord, ascend one to two levels in the Lissauer tract, and synapse in the ipsilateral gray matter (dorsal horn) of the spinal cord. Second-order neurons decussate via the anterior white commissure and ascend in the contralateral spinothalamic tract, where they eventually synapse in the VPL nucleus of the thalamus. Third-order neurons then project to the primary somatosensory cortex. A lesion in the left spinothalamic tract would result in loss of pain and temperature sensations from the right side of the body, opposite of what is seen in the patient. The corticospinal tracts provide motor innervation to the ipsilateral alpha (α) motor neurons. Damage to these tracts would not result in the sensory deficits seen in this patient. Though lesions to the dorsal spinocerebellar tract would result in hyperreflexia, no symptoms of bulbar dysfunction (brainstem lesion) are present. The dorsal columns provide vibration and proprioceptive information and are intact in this patient.

A 50-year-old man presents to the emergency department after a motor vehicle collision. He denies loss of consciousness and is complaining of severe back pain. On initial survey, he has bilateral breath sounds and 97% oxygen saturation on room air. His blood pressure is 146/87 mm Hg, and he has equal pulses throughout. Neurologic examination reveals right lower extremity paralysis with a positive Babinski sign. His patellar and Achilles reflexes are hyperreflexive on the right side. Sensory examination of the right lower extremity reveals a loss of tactile, vibratory, and proprioceptive senses, and the left lower extremity does not respond to pain or cold stimuli. Transection of which fiber tract resulted in the left lower extremity sensory aberration? Select one: a. Left dorsal spinocerebellar b. Right dorsal spinocerebellar c. Right corticospinal d. Left corticospinal e. Right dorsal columns f. Left spinothalamic g. Left dorsal columns h. Right spinothalamic

a. Loss of sensation in the lateral forearm Following an incident with a nail gun, this patient presents with a puncture wound and an absent biceps reflex. Loss of biceps reflex with a proximal arm wound suggests an injury to the musculocutaneous nerve (C5-C7). The musculocutaneous nerve passes through the coracobrachialis muscle and innervates the coracobrachialis (which is involved in the adduction and extension of the shoulder) and the biceps and brachialis muscles (which are the muscles that flex the elbow). Sensation to the lateral portion of the forearm (which is supinated by the biceps) is also innervated by the musculocutaneous nerve. The biceps reflex also tests the C5-C6 nerve roots, but the lesion here is at the level of a peripheral nerve, not at the nerve root. Damage to the radial nerve would result in loss of hand extension and sensation to the dorsum of the thumb. Typically, the radial nerve is injured by a midshaft humeral fracture or improper use of crutches, leading to axillary compression. The ulnar nerve supplies sensation and motor innervation to the medial part of the hand (hypothenar); damage to the ulnar nerve can occur at the medial epicondyle of the humerus or hook of the hamate. The median nerve is responsible for innervation of the lateral portion of the hand; damage to this nerve can occur with a supracondylar fracture of the humerus. The axillary nerve is responsible for innervation of the deltoid. Damage to the axillary nerve can result in atrophy and difficulties with arm abduction.

A 52-year-old construction worker comes to the emergency department after being accidentally shot in the arm with a nail gun. She has no significant medical history. Her temperature is 36.8°C (98.3°F), blood pressure is 114/68 mm Hg, and pulse is 89/min. On physical examination, she has a clean puncture wound on her proximal arm. Biceps reflex is absent; all other reflexes are intact. Which of the following sensory deficits is most likely to accompany this injury? Select one: a. Loss of sensation in the lateral forearm b. Loss of sensation over the deltoid muscle c. Loss of sensation on the palmar aspect of the third finger d. Loss of sensation in the hypothenar eminence e. Loss of sensation in the dorsal thumb

b. Posterior and anterior roots Muscle atrophy indicates that muscle innervation has been lost. Fasciculations, the visible twitches of individual motor units, occur during ongoing damage to the anterior horn or anterior roots. Loss of sensation is explained by posterior root damage.

A 55-year-old woman is seen in the emergency department because of burning pain over the right shoulder and upper part of the right arm. The pain intensifies when she moves her neck or coughs. Examination reveals weakness and fasciculations in the right shoulder and upper arm muscles There is also a reduction in somatic sensation (fine touch, vibration, proprioception, pain, temperature, crude touch) along the right shoulder and the lateral aspect of the arm. There is atrophy in the right upper arm. Which of the following is the most likely damaged? Select one: a. Ventrolateral medulla b. Posterior and anterior roots c. Posterior limb of the internal capsule d. Contralateral side of the spinal cord e. Ipsilateral side of the spinal cord

b. Anterior roots at L2, L3, and L4 on the right side Axons of lower motor neurons travel through the anterior spinal roots. Damage to the axons results in LMN signs, including flaccid paralysis and areflexia. Over time, the denervated muscle will atrophy

A 57-year-old man is brought to the emergency department because of weakness in his right leg. Examination reveals flaccid paralysis and patellar reflex is absent on the right. Plantar reflex is normal. Sensory testing reveals sensitivity to pin-prick and vibration. Which of the following is the most likely site of damage given these findings? Select one: a. Lateral funiculus of spinal cord at midthoracic level on the right side b. Anterior roots at L2, L3, and L4 on the right side c. Medullary pyramids on the right side d. Posterior roots at L2, L3, and L4 on the right side e. Spinal cord hemisection at T12 on the right side

e. Neuron loss in the anterior horns With an unvaccinated child who has recent international travel, be prepared to consider infections that are not normally seen in the US. This child's neurologic findings are concerning for poliomyelitis, which is caused by infection with poliovirus. The last case of naturally occurring poliomyelitis (also called polio) in the US occurred in 1979, thanks to a very effective vaccine. However, the disease is still seen in Afghanistan, Pakistan, and some African countries, and unvaccinated US children visiting those countries can become infected. Poliovirus is passed by the fecal-oral route and initially infects the Peyer patches of the intestine and motor neurons. The disease can manifest with a spectrum of severity, as noted in the table. Replication of poliovirus in motor neurons of the anterior horn of the spinal cord results in cell destruction, which leads to the neurologic sequelae of poliomyelitis. There is no cure for polio and treatment is aimed at preventing complications, including paralysis, hypotonia, and hyperreflexia. Autoimmune central demyelination is seen in multiple sclerosis, which presents with neurologic symptoms separated in time and space. Autoimmune peripheral demyelination is the underlying mechanism of Guillain-Barre syndrome (GBS). GBS is most commonly seen in patients with ascending paralysis and weakness of bilateral lower limbs following a gastrointestinal bacterial or viral infection. Loss of neurons in the lateral funiculi (corticospinal tracts) would produce an upper motor neuron syndrome. Neuron loss in the posterior horns would cause a loss of fine touch, proprioception, and vibration.

A 6-year-old boy is brought to the emergency department by his parents because of a 4-hour history of abnormal behavior, fever, and weakness. Since awakening this morning, the patient has been unusually irritable. He also had trouble rising from his seat at the breakfast table, resulting in him falling to the floor. His parents report that this is the first episode of falling, but they have noticed that the patient "seems to be getting weaker" over the past couple of weeks. The patient and his family returned from a trip to Pakistan 1 month ago. On review of systems, the parents note that the child had a mild fever approximately 8 days ago. His past medical history is notable for vaccine nonadherence. Temperature is 39°C (102.2°F), pulse is 90/min, and blood pressure 128/93 mm Hg. On neurologic examination, the patient exhibits 3/5 weakness of left hip flexion and knee extension. Tone and reflexes are diminished bilaterally; sensation is intact throughout. Complete right knee extension cannot be attained when the hip is passively flexed to 90 degrees. Cerebrospinal fluid analysis shows elevated protein and pleocytosis. Nerve conduction study and electromyography reveal decreased action potential amplitude and decreased motor unit recruitment. Which of the following is the most likely pathophysiology of this patient's disease? Select one: a. Neuron loss in the posterior horns b. Autoimmune peripheral demyelination c. Neuron loss in the lateral funiculi d. Autoimmune central demyelination e. Neuron loss in the anterior horns

a. Medial lemniscus The patient has been dealing with a tingling sensation in his right leg, which has gradually worsened over the past 6 months. The video shows the patient undergoing the Romberg test, which evaluates the patient's balance in the absence of visual cues. A positive Romberg sign indicates a problem with proprioception or the vestibular apparatus. In this case, the patient's sensory deficits and paresthesias, in addition to his positive Romberg sign, suggest that the medial lemniscus is affected. The medial lemniscus is the pathway arising from the dorsal columns of the spinal cord that carries information about position sense, vibration, and light touch. A lesion of the medial lemniscus decreases contralateral proprioception, which produces the type of swaying and unsteadiness seen in this patient when his eyes are closed. This patient is also taking ranitidine, an H2 receptor antagonist, which results in decreased gastric acid secretion and can therefore impair vitamin B12 absorption. This patient likely has vitamin B12 deficiency, which, due to his age, places him at risk of pernicious anemia. Problems with the other neurologic structures listed would produce different results in a Romberg test: The basal ganglia play a role in motor control and motivation and would not affect somatic sensation or balance. Although a lesion in the cerebellum would disrupt the ability to maintain balance, it would be evident both before and after the patient closed his eyes for the Romberg test. The spinothalamic tract carries information about pain and temperature, and a lesion to it would not impair balance. The tectospinal tract is responsible for head movements in response to visual signals. A lesion here would not lead to a positive Romberg sign.

A 75-year-old man presents to his physician complaining of a tingling sensation in his lower right leg, which he first noticed about 6 months ago. He reports that it started gradually, and that sometimes he feels like his right leg is numb. He reveals that his father had Parkinson disease. His past medical history is significant for acid reflux, for which he takes ranitidine. Cranial nerve examination is normal. Muscle strength is intact throughout. The patient has not noticed trouble with balance, but an abnormality is noted in one part of the examination, as shown in the video clip. Which of the following neurologic structures is most likely affected in this patient? Select one: a. Medial lemniscus b. Spinothalamic tract c. Tectospinal tract d. Basal ganglia e. Cerebellum

d. Dorsal columns, lateral corticospinal tracts, and spinocerebellar tracts This patient has multiple risk factors and signs of vitamin B12 deficiency. Vitamin B12 is available only in animal products, making strict vegans susceptible to deficiency. The patient is also taking sulfasalazine, which is an anti-inflammatory drug used to treat inflammatory bowel disease. Crohn disease most commonly manifests as a terminal ileitis, and the terminal ileum is the site of vitamin B12-intrinsic factor absorption. Other possible risk factors for vitamin B12 deficiency include Helicobacter pylori or Diphyllobothrium latum infection, gastric bypass surgery, and poor dietary intake. The most prominent findings in vitamin B12 deficiency are glossitis (large, shiny tongue), macrocytic megaloblastic anemia with hypersegmentedneutrophils, and neurologic findings including dementia-like symptoms and ataxia. These neurologic findings are due to the degeneration of neurons and myelin in the dorsal columns, lateral corticospinal tracts, and spinocerebellar tracts (red arrow), indicative of B12 deficiency. The dorsal column and dorsal roots are affected in tabes dorsalis caused by tertiary syphilis. Degeneration of the ventral horn, precentral gyrus, and lateral corticospinal tract is seen in patients with amyotrophic lateral sclerosis. The anterior white commissure is affected in syringomyelia, in which a syrinx develops within the central canal of the spinal cord, typically at C8-T1 levels. The medial longitudinal fasciculus and periventricular white matter area are commonly involved in multiple sclerosis.

A 62-year-old woman is brought to the hospital by her daughter, who reports that her vegan mother has been feeling "tired all the time" and sometimes feels tingling in her hands and feet. Although the mother was previously very lively and active, she has been exhibiting depressed mood and memory issues for the past 6-7 months. The daughter has also noticed that her mother is often unsteady on her feet and has had multiple falls in the past few weeks. About a year ago, the patient was started on sulfasalazine for a gastrointestinal condition. Physical examination reveals conjunctival pallor, along with a shiny and enlarged tongue. Which of the following CNS regions is most likely abnormal in this patient? Select one: a. Anterior white commissure and ventral horn b. Medial longitudinal fasciculus and periventricular white matter area c. Dorsal column and dorsal roots d. Dorsal columns, lateral corticospinal tracts, and spinocerebellar tracts e. Lateral corticospinal tracts, precentral gyrus, and ventral horn motor neurons

b. Decreased proprioceptive sensation from the right leg Fasciculus gracilis, within the posterior columns, carries fine touch, proprioception, and vibration sensation from the ipsilateral lower body and leg (starting at about T6).

A 63-year-old man undergoes surgery to remove a benign tumor in the spinal canal. As a result of the surgery, there is damage to fasciculus gracilis on the right side at T7-T10. Following recovery, he has a limited neurologic deficit due to this damage. Which of the following is most likely given these findings? Select one: a. Decreased proprioceptive sensation from the left leg b. Decreased proprioceptive sensation from the right leg c. Decreased pain sensation from the right leg d. Dysmetria in the right arm e. Dysmetria in the left arm f. Decreased pain sensation from the left leg

c. Parasympathetic nervous system, nerves S2-S4 When a man is sexually stimulated, the penis becomes erect. This is due to parasympathetic stimulation via the cavernous nerves, which receive input from the pelvic splanchnic nerves that branch off the sympathetic chain from S2-S4. This stimulation induces vasodilation of arterioles and allows blood to flow into the corpora cavernosa, causing the penis to become erect. Emission, or the movement of semen into the urethra, is stimulated by sympathetic nerves, specifically, the hypogastric nerve from T11-L2. Peristaltic contractions of the vas deferens, seminal vesicles, and smooth muscles of the prostate facilitate emission. Ejaculation, or the release of semen from the penis, is under the control of visceral and somatic nerves, specifically the pudendal nerve. Rhythmic contractions of the perineal muscles moves the ejaculate through the urethra and out of the penis. Any significant lesion (ie, complication of surgery or trauma) to the parasympathetic nerves responsible for this mechanism could impair penile erectile function, as seen in this case. The mnemonic "Point, Squeeze, and Shoot" makes this information easier to remember: The Parasympatheticsmake the penis Point ; the Sympathetics Squeeze, causing semen to move into the urethra; and the Somatic nerves Shoot, ie, ejaculation. The somatic nervous system plays a role in both erection and ejaculation. The sympathetic nervous system plays a role in emission and ejaculation, but not in erection. Its role in ejaculation is contraction of the trigone and external urethral sphincter preventing backflow of semen into the bladder.

A 66-year-old man presents to his physician complaining of erectile dysfunction following surgery for prostate cancer. His temperature is 98.6°F (37°C), pulse is 90/min, and blood pressure is 130/86 mm Hg. On physical examination, sensation to light touch and vibration are intact in the genital region; the patient reports no paresthesias. Which of the following is most responsible for an erection? Select one: a. Somatic nervous system, serves S2-S4 b. Parasympathetic nervous system, nerves L1-L2 c. Parasympathetic nervous system, nerves S2-S4 d. Sympathetic nervous system, nerves S2-L4 e. Sympathetic nervous system, nerves L1-L2 f. Somatic nervous system, nerves L1-L2

e. T10 This patient's symptoms of periumbilical abdominal pain that has migrated to the right lower quadrant are consistent with acute appendicitis. The presence of nausea, vomiting, fever, and elevated WBC further supports this diagnosis. The absence of rebound tenderness, guarding, and negative Rovsingsign are reassuring that this patient does not have signs of peritonitis. Visceral abdominal pain is caused by activation of specialized axonal terminals stimulated by stretching of the walls or capsules of hollow or solid organs, and the embryologic origin of the involved organ determines the approximate localization of the pain. For example, foregut organs such as the stomach and biliary tract produce pain in the epigastric region. In this case the patient has appendicitis, in which visceral pain produced by distention of the lumen or smooth muscle spasm of the appendix is carried by axons through the superior mesenteric plexus and lesser splanchnic nerve to the T10 spinal cord segment. The T10 dermatome covers the umbilicus. The classic pain of appendicitis starts with visceral pain referred to the periumbilical region that later migrates to peritoneal pain if there is peritoneal inflammation at the site of the appendix, in this case, in the right lower quadrant. Neurons from the following spinal cord segments are not the source of this patient's referred pain: T8: This dermatome lies in the upper quadrants of the abdomen. T9: This dermatome lies just above the umbilicus. T11: This dermatome lies just below the umbilicus L1: This dermatome covers the inguinal and genital area.

A 7-year-old child presents to the emergency department complaining of abdominal pain that started 8 hours ago. The pain is dull and originated at the umbilicus; however, the pain is now present only in the right lower quadrant. He also feels nauseated and vomited several times since arriving at the emergency department. Vital signs are: Temperature, 101°F (38.33°C); heart rate, 101/min; blood pressure, 105/79 mm Hg; respiratory rate, 24/min; SpO2, 98% on room air. Physical exam shows a young boy in moderate distress. Abdominal exam is remarkable for tenderness to palpation in the right lower quadrant. There is no rebound or guarding. Rovsingsign is negative. Labs are remarkable for WBC count >15,000/mm3. Prior to localization of the pain to the right lower quadrant, activation of neurons from which of the following spinal cord segments produced the referred pain? Select one: a. T9 b. L1 c. T8 d. T11 e. T10

e. Decreased pain sensation; normal vibration sense Explanation:This patient is suffering from neurologic changes after a major surgery on his abdominal aorta. The aorta supplies blood to the spinal cord via the artery of Adamkiewicz, a major branch of which then provides circulation to the anterior spinal artery (ASA). Since the patient had to be stabilized for hemorrhage—and his lab values reflect a low hematocrit—his symptoms are most likely due to decreased blood supply to the anterior spinal cord via the ASA. This is called anterior spinal artery syndrome. Anterior spinal artery syndrome can affect all ascending and descending pathways except for the dorsal columns, which are located in the most posterior aspect of the spinal cord. Because the dorsal columns are used for proprioception and vibration, these functions should remain intact, whereas all others (pain, temperature, motor functions) should be decreased. This patient would then experience decreased pain sensation and normal vibration sense. Decreased pain sensation (spinothalamic tract) and decreased vibration sense (dorsal columns) could be seen together in a patient with both anterior and posterior spinal cord injury, such as occurs in Brown-Séquard syndrome. Patients will have ipsilateral loss of all sensation at the level of the lesion. Below the lesion, they also experience contralateral loss of pain and temperature sensation, whereas all other sensory/motor pathways are disrupted ipsilaterally. Decreased vibration sense (carried by the dorsal columns) with normal pain sensation (spinothalamic tract) could be seen in a patient with tabes dorsalis. This condition is a manifestation of tertiary syphilis, resulting from demyelination of the dorsal columns and roots. Normal sensory findings with abnormal motor exam (decreased strength) could be seen in amyotrophic lateral sclerosis or poliomyelitis. These disorders primarily affect motor neurons while sparing the sensory pathways of the spinal cord. Decreased ability to sense pain (spinothalamic tract) combined with a normal motor exam might be seen in a patient with syringomyelia. This condition occurs in the upper extremities due to the development of a cystic cavity in the spinal cord called a syrinx.

A 73-year-old male is admitted to the hospital to undergo correction of an abdominal aortic aneurysm, after having experienced back, flank, and abdominal pain over the past few weeks. His surgery is remarkable for hemorrhage, after which he is stabilized. In the recovery room, the patient has several complaints, including abnormal sensation in his legs. Laboratory studies show: WBC count: 4000/mm³ Hematocrit: 28% Hemoglobin: 9.3 g/dL Platelet count: 344,000/mm³ Na+: 143 mEq/L K+: 4.4 mEq/L Cl-: 103 mEq/L Blood urea nitrogen: 20 mg/dL Creatinine: 1.1 mg/dL Mean corpuscular volume: 85 fL Which of the following would be observed on physical examination of the lower extremities? Select one: a. Decreased strength; normal pain sensation b. Normal pain sensation; decreased vibration sense c. Decreased pain sensation; decreased vibration sense d. Normal strength; decreased pain sensation e. Decreased pain sensation; normal vibration sense

c. C2 dorsal root ganglion The elderly patient, who is undergoing chemotherapy treatment for late-stage breast cancer, presents with blistering lesions on her head, along with a vesicular rash on the back of her head. It indicates an acute infection with varicella-zoster virus (VZV), which can cause chickenpox and reactivate latent VZV (which causes shingles, also known as herpes zoster). After the primary infection, VZV establishes a latent infection in the dorsal (sensory) root ganglia of the host. In immunocompromised patients, like the one described here, reactivation of the virus may occur in sensory nerves along the corresponding dermatome. Indeed, the most common cause of death in immunocompromised patients is infection. This patient's lesion location implies dermatome C2, as shown in the image. It can be described as the "posterior half of a skull cap." There is no C1 dorsal root ganglion, as the nerves supply the suboccipital skeletal muscles. The C3 dorsal root ganglion presents closer to the neck area as indicated in the image, rather than the skull cap. The C4 dorsal root ganglion presents near the shoulder, collarbone, and shoulder blade, in the area of the "low-collar shirt." The C5 dorsal root ganglion covers the lateral aspect of the upper extremities at and above the elbow.

A 73-year-old woman presents with extremely painful blisters on her head. She does not recall having similar symptoms before. She is undergoing chemotherapy to treat late-stage breast cancer. Physical examination shows a vesicular rash above her left ear that extends from the vertex to the left side of the back of her head. What is the root ganglion associated with the most likely cause of the patient's dermatologic lesions? Select one: a. C3 dorsal root ganglion b. C5 dorsal root ganglion c. C2 dorsal root ganglion d. C1 dorsal root ganglion e. C4 dorsal root ganglion

c. 10 months The reflex elicited is known as the Babinski reflex. The infant responds to a stroke to the sole of the foot with dorsiflexion of the big toe and fanning of the rest of the toes. Although this reflex is a sign of neurologic pathology in adults, it is a normal finding in children before age 12-14 months due to the incomplete maturation and myelination of the corticospinal tract responsible for inhibiting this reflex. Babinski reflex commonly disappears by 12-14 months after birth. Other primitive reflexes present in children include the Moro (or startle) reflex, grasp reflex and rooting reflex. The primitive reflexes, present at birth, reflect the functional integrity of the child's central nervous system, and after the maturation of the appropriate central nervous system structures during the first year after birth, those primitive reflexes commonly disappear.

A pediatrician is conducting an examination on a child during a routine check-up. Stroking the bottom of the child's foot elicits a response that is very different from what would be expected in a normal adult. The pediatrician tells the infant's parents that this primitive reflex will eventually disappear as the child ages. What is the most likely age of this child? Select one: a. 42-48 months b. 24 months c. 10 months d. 14-20 months

d. Degeneration of the anterior horns and corticospinal tracts; the man had amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS) is characterized by both upper and lower motor neuron signs. Lesions of the anterior horns of the gray matter lead to lower motor neuron signs (eg, muscle weakness, atrophy, and fasciculations), whereas lesions of the corticospinal tracts yield upper motor neuron signs (eg, hyperreflexia). The image in the vignette shows degeneration of the lateral and anterior corticospinal tracts. Degeneration of the anterior horn cells is not a characteristic finding in a patient with tertiary syphilis. It is instead associated with polio. Degeneration of the anterior white commissure would not be seen in Guillain-Barré syndrome. Rather, it is the result of syringomyelia. Degeneration of the posterior columns and corticospinal tracts is not a characteristic finding of polio. Instead, it is characteristic of pernicious anemia (vitamin B12 deficiency). Degeneration of the posterior column is not a characteristic finding of syringomyelia. It is a classic finding in tertiary syphilis.

The body of a 68-year-old homeless man arrives at the medical examiner's office for autopsy. As part of the autopsy, examination of the spinal cord is performed. Since no clinical history is available, the medical examiner must make the diagnosis based solely on autopsy findings. Which combination of spinal cord autopsy findings and neurologic disease diagnosis is correctly paired? Select one: a. Degeneration of the anterior horns; the man had tertiary syphilis b. Degeneration of the posterior columns; the man had syringomyelia c. Degeneration of the anterior white commissure; the man had Guillain-Barré syndrome d. Degeneration of the anterior horns and corticospinal tracts; the man had amyotrophic lateral sclerosis e. Degeneration of the posterior columns and corticospinal tracts; the man had polio

C1-C7; C8 exits below the C7 vertebra, and all others exit below their corresponding vertebral levels

Which nerves exit the intervertebral foramina above the corresponding vertebrae?