First Aid MCQs: Musculoskeletal

The correct answer is A. This patient has symptoms and signs consistent with vitamin D-deficient rickets, which results from the decreased or absent mineralization of osteoid (bone matrix) secondary to decreased serum calcium and/or phosphorous levels. Vitamin D normally promotes absorption of calcium and phosphorous from the GI tract. In vitamin D-deficient patients, areas of bone growth (eg, wrists, ankles, costochondral junctions) contain patches of unmineralized, soft osteoid that give rise to the classically reported signs, including widened wrists and/or ankles and enlarged costochondral junctions (rachitic rosary). In cases of severe vitamin D deficiency, laboratory studies typically demonstrate decreased serum calcium, decreased serum phosphorous, decreased serum 1,25-dihydroxycholecalciferol, increased serum alkaline phosphatase, and increased serum intact PTH levels.

A 1-year-old adopted, darkly pigmented boy is brought to the pediatrician for his first wellchild check-up. The adoptive parents do not know any of the infant's past medical history or family history. Physical examination reveals an unusual widening of the child's wrists and ankles and marked enlargement of the child's costochondral junctions. What is a characteristic laboratory finding used to support the most likely diagnosis? (A) Increased intact parathyroid hormone level (B) Increased serum 1,25-dihydroxycholecalciferol level (C) Increased serum 25-hydroxycholecalciferol level (D) Increased serum calcium level (E) Increased serum phosphorus level

The correct answer is C. This patient has acute osteomyelitis and a history of sickle cell disease as evidenced by her multiple hospitalizations (likely for episodes of painful crises) and medication (hydroxyurea reduces the incidence of painful crises in sickle cell disease by increasing the amount of fetal hemoglobin). Osteomyelitis is an infection of the bone tissue. It is common in young children and usually results from the hematogenous spread of organisms from another site of infection (upper respiratory infection in this case). Salmonella species are the most common organisms responsible for osteomyelitis in patients with sickle cell disease.

A 12-year-old African-American girl is brought to the physician with complaints of fever, malaise, and pain in her left forearm for the past four days. Her mother reports no history of trauma or fracture, but recounts an upper respiratory infection a few days ago. The patient has been hospitalized three times for abdominal pain, for which she takes hydroxyurea. Her temperature is 39.8°C (103.6°F) and the rest of her vital signs are stable. On examination the left forearm is erythematous, warm, and tender to palpation. Blood samples for culture are drawn. Which of the following organisms is most likely to be isolated from this patient's blood? (A) Escherichia coli (B) Pseudomonas aeruginosa (C) Salmonella species (D) Staphylococcus aureus (E) Streptococcus pyogenes

The correct answer is A. The common peroneal nerve courses around the neck of the fibula, making it vulnerable to damage by a fracture at the fibular neck. It is the most frequently lesioned nerve in the lower limb. Patients experience foot drop, which results from a loss of dorsiflexion at the ankle, and a loss of eversion. Patients will have pain and paresthesia in the lateral leg and dorsum of the foot. Patients with foot drop may also have a steppage gait, as described in the vignette. Common peroneal nerve injury can occur with fracture to the fibular neck and patients will present with an inability to dorsiflex or evert, as well as a foot drop gait.

A 15-year-old boy presents to the emergency department after falling off his skateboard. On physical examination he is unable to dorsiflex or evert at the ankle. In addition, the patient reports pain and numbness in the lateral leg and dorsum of the foot. When asked to walk, he raises his affected leg high off the ground and his foot slaps the ground when walking. He is diagnosed with a fracture. Which of the following structures is most likely to be compromised by this fracture? (A) Common peroneal nerve (B) Femoral nerve (C) L4 nerve root (D) Obturator nerve (E) Tibial nerve

The correct answer is A. The lateral ligaments of the foot are more commonly injured that the medial ligaments, since they are weaker. The anterior talofibular ligament is the most common of the lateral ligaments to be injured. Injuries to the ligaments about the ankle usually result from inversion and internal rotation of the foot combined with ankle plantar flexion. With complete disruption of the anterior talofibular ligament, forward displacement of the talus in the ankle mortise is present. Lateral ankle sprains represent 16%-21% of all sports-related traumatic lesions. The anterior talofibular ligament is the weakest ligament and therefore the most frequently torn. There is usually a predictable pattern of injury involving the anterior talofibular ligament followed by the calcaneofibular ligament and the posterior talofibular ligament. First-degree sprain is characterized by a partial or complete tear of the anterior talofibular ligament. In seconddegree sprain both the anterior talofibular and calcaneofibular ligaments are either partially or completely torn. Third-degree sprain consists of injuries to the anterior talofibular, calcaneofibular, and posterior talofibular ligaments.

A 16-year-old gymnast presents to the emergency department after landing awkwardly on her ankle subsequent to dismounting from the parallel bars. She reports that she felt her ankle "roll inward," essentially inverting her ankle as a result of a misaligned axial load. On physical examination of the injured ankle, there appears to be a forward displacement of the talus. Which of the following ligaments has she most likely injured? (A) Anterior talofibular ligament (B) Calcaneofibular ligament (C) Talonavicular ligament (D) Tibiocalcaneal ligament (E) Tibiotalar ligament

The correct answer is E. Osteosarcoma is the most common primary malignant bony tumor. These tumors are seen predominantly in males <20 years old and occur at the metaphyseal region of long bones. Plain films of the affected bone often reveal a characteristic "sunburst" pattern. Genetic mutations of the Rb gene are associated with both osteosarcoma and retinoblastoma, which was likely present in this patient's sister Answer A is incorrect. Chondrosarcomas are malignant cartilaginous tumors that occur most commonly in men 30-60 years old, usually in the pelvis, spine, scapula, humerus, tibia, or femur. Answer B is incorrect. Enchondromas are benign cartilaginous tumors found in intramedullary bone, and are most often found in the distal extremities. Answer C is incorrect. Ewing sarcoma is the second most common primary bone cancer. Most patients present at the onset of puberty (average is between 10 and 15 years old). Ewing sarcoma most commonly occurs in the diaphyses of long bones, pelvis, scapula, and ribs. Answer D is incorrect. Osteochondromas are benign growths that are often first diagnosed in late adolescence or early adulthood. They are the most common benign bone tumor.

A 17-year-old boy presents to his pediatrician with pain in his right leg. Biopsy reveals a malignancy in the distal femur. He has a family history of "eye cancer" in a younger sister. Which of the following is the most likely diagnosis? (A) Chondrosarcoma (B) Enchondroma (C) Ewing sarcoma (D) Osteochondroma (E) Osteosarcoma

The correct answer is C. This patient has systemic lupus erythematosus (SLE), which is diagnosed by the presence of four of the following 11 findings designated by the American Rheumatism Association, and summarized by the mnemonic "BRAIN SOAP, MD:" Blood dyscrasias (such as hemolytic anemia or thrombocytopenia), Renal disorder, Arthritis (in two or more peripheral joints), Immunologic disorder (such as anti-DNA antibody and anti- Smith antibody), Neurologic disorder, Serositis (such as pleuritis or pericarditis), Oral ulcers, Antinuclear antibody (elevated titers in the absence of drugs associated with drug-induced lupus syndrome), Photosensitivity, Malar rash, and Discoid rash. Many patients with SLE have antiphospholipid antibodies, which actually are believed to be antibodies against proteins that complex to phospholipids. Because these antibodies also bind to the cardiolipin antigen used in syphilis serology, patients with SLE may have a false-positive result for syphilis. Whereas antinuclear antibodies are sensitive for SLE, anti-Smith and anti-doublestranded DNA are the most specific. Many other autoantibodies may be present in SLE that are not necessarily sensitive or specific for the condition.

A 17-year-old girl complains of a painful, swollen left elbow and fever. In the previous few days her right knee was also swollen and slightly painful. The physician notices several oral ulcers and an edematous and tender left elbow. Laboratory tests are notable for weakly positive antinuclear antibodies and anemia, and the results of Venereal Disease Research Laboratory testing are positive. The patient is shocked when informed of her positive result for syphilis, stating that she has no sexual history. Which of the following is the most specific antibody for the patient's condition? (A) Anti-IgG (B) Anti-Jo-1 (C) Anti-Smith (D) Anticentromere (E) Antimicrosomal

The correct answer is B. The infection caused by Actinomyces israelii typically presents as a chronic, slowly progressing mass that eventually evolves into a draining sinus tract. Characteristic sulfur granules are seen in the thick yellow exudate. Penicillin G is the first-line treatment.

A 20-year-old man presents to the physician with a nontender indurated mass over his mandible. He has had this mass for four months after undergoing oral surgery and decided to come to the physician because the mass started to ooze a thick yellow exudate. Yellow granules are seen on microscopic examination of the discharge and an antibiotic is prescribed. Which of the following best describes the mechanism of action of the antibiotic most likely prescribed? (A) Binds ergosterol, forming pores in the membrane (B) Block bacterial cell wall synthesis by inhibiting transpeptidase crosslinking (C) Block bacterial nucleotide synthesis (D) Block bacterial protein synthesis (E) Inhibits ergosterol synthesis

The correct answer is A. This patient has Guillain-Barré as a result of his gastroenteritis. The important message here is that Guillain- Barré syndrome is thought to be primarily an autoimmune disorder against peripheral nerves and the cells that myelinate them (Schwann cells). Thus, it makes sense that an excessive immune response to an infection (such as from a pathogen like Campylobacter jejuni) can lead to an autoimmune process. Histologically, this disease is characterized by perivenular and endoneurial infiltration with lymphocytes, macrophages, and plasma cells. Answer B is incorrect. Guillain-Barré syndrome is a disease that primarily attacks peripheral nerves and Schwann cells. The ascending paralysis and muscle weakness that occur as a consequence are secondary to the neuropathy. Answer C is incorrect. The mechanism suggested in this answer choice is not thought to be the primary disease process in Guillain- Barré syndrome. Answer D is incorrect. Guillain-Barré syndrome is a disease that primarily attacks peripheral nerves and Schwann cells. The ascending paralysis and muscle weakness that occur as a consequence are secondary to the neuropathy. Answer E is incorrect. While Campylobacter jejuni does produce an enterotoxin, the mechanism described in this answer choice is not the major hypothesized pathogenesis of Guillain-Barré syndrome.

A 22-year-old college student presents to the school health service complaining of worsening weakness in his arms and legs. He says that over the past day he has also begun to feel weakness in his chest and back. He mentions that he thinks he had food poisoning earlier in the week, which caused stomach pain and bloody diarrhea. Physical examination reveals that the deep tendon reflexes in his lower extremities are absent. His physician sends his stool to be cultured. The results show infection with Campylobacter jejuni. Which one of the following statements is most consistent with the disease process connecting the patient's gastrointestinal infection and his neurological symptoms? (A) An excessive immune response to a gastrointestinal Campylobacter jejuni infection led to an autoimmune inflammation of peripheral nerves (B) Dissemination of Campylobacter jejuni gastrointestinal infection led to infiltration of peripheral muscle cells with C jejuni (C) Dissemination of Campylobacter jejuni gastrointestinal infection led to infiltration of peripheral nerves with C jejuni (D) Toxins secreted by Campylobacter jejuni infiltrated into peripheral muscle cells (E) Toxins secreted by Campylobacter jejuni infiltrated into peripheral nerves, causing their destruction

The correct answer is C. This woman has a positive purified protein derivative test, signifying possible exposure to TB and latent disease. To decrease her risk of developing an active TB infection, a 6- to 12-month regimen of isoniazid is indicated. Isoniazid causes a decrease in the synthesis of mycolic acids that make up the unique cell envelope of mycobacterium TB. One of the possible adverse effects of isoniazid is a lupus-like syndrome. Drug-induced lupus is characterized by an abrupt onset of symptoms, which may include fever, arthritis, pleural pericarditis, and rash, along with the development of anti-nuclear antibodies. Other medications that may cause a similar lupuslike syndrome include procainamide, hydralazine, minocycline, and penicillamine

A 22-year-old emergency room nurse has a positive purified protein derivative test. Results of radiography of the chest are unremarkable. She begins a nine-month prophylaxis regimen, but two months into treatment she complains of the sudden onset of fever, rash, and swelling of her joints. What is the mechanism of the medication that caused these adverse effects? (A) Decreases synthesis of folate (B) Decreases synthesis of messenger RNA (C) Decreases synthesis of mycolic acids (D) Decreases synthesis of peptidoglycan (E) Increases synthesis of cGMP

The correct answer is B. This patient suffers from lateral epicondylitis, better known as tennis elbow. This condition stems from overuse of the superficial extensor muscles of the forearm and wrist, including the extensor carpi radialis muscle. This muscle also inserts at the lateral epicondyle. The repeated forced extension and flexion of the forearm at the elbow causes an inflammation of the common extensor tendon. Patients exhibit pain over the lateral epicondyle that may radiate down the posterior aspect of the forearm. Treatment options include rehabilitation, which may include exercises, motion analysis, and straps or braces; medication; open surgery; and arthroscopic (minimally invasive) surgery. Answer A is incorrect. The biceps muscle functions to supinate and flex the forearm. Answer C is incorrect. The extensor carpi ulnaris muscle functions to extend and adduct the hand at the wrist but does not extend the forearm. Answer D is incorrect. The flexor carpi ulnaris muscle functions to flex and abduct the hand at the wrist. Answer E is incorrect. The pronator teres muscle functions to pronate and flex the forearm

A 22-year-old woman who is a professional tennis player presents to her physician because of pain on the lateral aspect of her elbow radiating down her forearm. She describes the pain as shooting and constant. Repetitive use of which of the following muscles most likely led to this patient's condition? (A) Biceps (B) Extensor carpi radialis (C) Extensor carpi ulnaris (D) Flexor carpi ulnaris (E) Pronator teres

The correct answer is D. Polyarteritis nodosa (PAN) is a vasculitis (ie, inflammation of a blood vessel) characterized by inflammation affecting small to medium-sized arteries, particularly the renal, cardiac, and GI-tract vessels (usually not the pulmonary vasculature). As many as 30% of patients have had prior hepatitis-B infections. Answer A is incorrect. Buerger disease, also known as thromboangiitis obliterans, is a vasculitis that mostly affects arteries and veins of the extremities. As such, patients often have intermittent claudication and Raynaud phenomenon. The majority of patients are men who are heavy smokers and show hypersensitivity to tobacco injected into the skin. Answer B is incorrect. Giant cell (temporal) arteritis is a type of vasculitis that affects the arteries of the head, especially, of course, the temporal arteries. The highlights of this disease can be remembered by the mnemonic, JOE: patients get Jaw pain and Ocular disturbances from ischemia to the arteries supplying them. Patients also often have markedly elevated Erythrocyte sedimentation rates. The disease is often associated with the presence of polymyalgia rheumatica. Answer C is incorrect. Kawasaki disease is a self-limited vasculitis that normally occurs in infants and children and is characterized by conjunctival and oral erythema, fever erythema and edema of the palms and soles, generalized rash, and cervical lymph node swelling. About 20% of patients may go on to develop coronary artery inflammation and/or aneurysm. Answer E is incorrect. Takayasu arteritis is a vasculitis characterized by fibrotic thickening of the aortic arch (it also affects the pulmonary arteries, the branches of the aortic arch, and the rest of the aorta in up to one-third of patients). Clinically, patients often have lower blood pressure and weaker pulses in the upper extremities than in the lower extremities; some patients have ocular disturbances as well.

A 25-year-old man develops acute onset of fever, malaise, muscle pain, hypertension, abdominal pain, bloody stool, and prerenal failure six months after recovering from an acute hepatitis B infection. Which of the following disease processes is most likely responsible for the patient's findings? (A) Buerger disease (B) Giant cell (temporal) arteritis (C) Kawasaki syndrome (D) Polyarteritis nodosa (E) Takayasu arteritis

The correct answer is C. This patient has fractured his distal humerus, which is a common way to injure the ulnar nerve. Remember, the ulnar nerve courses through the medial epicondyle of the humerus just below the skin, so it is not well-protected at all. This vulnerability is famous with the so-called "funny bone" injuries. Our patient's radiograph shows a much more serious injury—a completely fractured humerus, so it should come as no surprise that muscles innervated by the ulnar nerve would have decreased function. Of the muscles listed here, only the flexor carpi ulnaris is innervated by the ulnar nerve, and on exam the patient would not be able to flex his fingers.

A 32-year-old man is brought into the emergency department by ambulance after falling from a ladder while cleaning his roof gutters. His vital signs are stable, he is fully alert and oriented, and he reports having no past medical problems. He is in excruciating pain, which he states is located in his left arm. An x-ray of the left upper extremity is shown in the image. If left untreated, which of the following muscles is at risk of losing function due to this injury? (A) First and second lumbricals (B) Brachioradialis (C) Flexor carpi ulnaris (D) Opponens pollicis (E) Palmaris longus (F) Pronator teres

The correct answer is B. This patient has osteomyelitis, most commonly caused by Pseudomonas aeruginosa in intravenous drug users. The image shows a bone abscess with polymorphonuclear leukocytes and foci of degraded bone collagen. Treatment would require several weeks of antipseudomonal antibiotics such as ticarcillin or piperacillin. Answer A is incorrect. Chronic corticosteroid use can lead to immunosuppression and osteoporosis, but does not predispose one to pseudomonal osteomyelitis.. Answer C is incorrect. Patients with miliary Mycobacterium tuberculosis infection are at risk for vertebral osteomyelitis, known as Pott disease. It is uncommon for tubercular osteomyelitis to affect the humerus. Answer D is incorrect. Multiple sexual partners would put the patient at increased risk of Neisseria gonorrhoeae infection, which can cause osteomyelitis. More commonly, the patient would have urethritis, epidydimitis, or perhaps Fitz-Hugh-Curtis syndrome, which is the formation of postinfection adhesions on the liver capsule, leading to chronic upper right quadrant pain. Answer E is incorrect. Patients with sickle cell anemia are at risk for osteomyelitis due to Salmonella or Staphylococcus, but not to pseudomonal osteomyelitis.

A 27-year-old homeless man presents to the clinic because of a five-day history of pain and swelling in his right upper arm. MRI of the area reveals diffuse soft tissue and bone inflammation. Results of bone biopsy are shown in the image. Blood cultures grow Pseudomonas. Which of the following would a complete history of this patient most likely reveal? (A) Corticosteroid use (B) Intravenous drug use (C) Miliary tuberculosis (D) Multiple sexual partners (E) Sickle cell anemia

The correct answer is A. This patient has ankylosing spondylitis, a chronic inflammatory disease of the spine and sacroiliac joints that often leads to the stiffening or consolidation of the bones that make up the joints. Common findings are low back pain, stiffness for over three months, pain and stiffness in the thoracic region, limited movement in the lumbar area, and limited chest expansion. Around 90% of patients are positive for human leukocyte antigen (HLA) B27, and common complications include uveitis and aortic regurgitation. Answer B is incorrect. Antinuclear antibodies are most commonly found in systemic autoimmune diseases such as lupus, scleroderma, Sjögren syndrome, and rheumatoid arthritis. Answer C is incorrect. Antineutrophil cytoplasmic antibodies (ANCA) are associated with the vasculitides, including Wegener granulomatosis and Churg-Strauss syndrome. Answer D is incorrect. IgM antibodies to B burgdorferi are suggestive of acute Lyme disease, which is transmitted by a bite from an Ixodes tick. Initially patients suffer from a local skin infection (often in a bull's-eye pattern) arthat can be followed by arthralgias and arthritis (usually monoarticular). The late sequelae of Lyme disease include myocardial, pericardial, and neurologic changes. Answer E is incorrect. Rheumatoid factor is positive in about 80% of patients with rheumatoid arthritis; it can also be positive in those with other rheumatic disorders such as Sjögren syndrome and lupus, as well as in healthy people. Rheumatoid arthritis is an autoimmune disorder of synovial joints and often presents with morning joint stiffness, subcutaneous joint nodules (particularly in the proximal interphalangeal joints), and symmetric joint involvement. The disease may also include systemic symptoms such as fever, pleuritis, and pericarditis. Answer F is incorrect. Vertebral compression fractures are a complication of osteoporosis and present with acute back pain, loss of height, and kyphosis.

A 27-year-old man comes to the physician's office with a six-month history of low back pain and stiffness that wakes him up during the night and is worst in the morning. The patient was diagnosed with bilateral sacroiliitis four months ago because of his tenderness to percussion of the sacroiliac joints and pain on springing the pelvis up. He has severe limitation of motion of his lumbar spine. Laboratory tests are most likely to be positive for which of the following? (A) Human leukocyte antigen B27 (B) Antinuclear antibodies (C) Anti-neutrophil cytoplasmic antibodies (D) IgM antibodies to B burgdorferi (E) Rheumatoid factor (F) Vertebral compression fractu

The correct answer is B. This patient has erythema nodosum, an inflammation of subcutaneous fat that is often accompanied by fever and malaise that is described clinically and pathologically in this vignette. The exact mechanism is unknown, but it often occurs together with inflammatory-bowel diseases (IBDs) such as Crohn disease or ulcerative colitis (UC); sarcoidosis; certain drugs (such as oral contraceptives and sulfonamides); certain malignant neoplasms; and certain infections (such as tuberculosis (TB), b-hemolytic streptococci, coccidioidomycosis, histoplasmosis, and leprosy).

A 27-year-old man presents to his dermatologist with several red, tender nodules on his lower legs. On histopathology, there is inflammation of the subcutaneous fat, tissue septal widening, neutrophilia, and fibrin exudation. Which of the following diseases often goes along with these skin findings? (A) Acne vulgaris (B) Crohn disease (C) Eczema (D) Pancreatitis (E) Psoriasis

The correct answer is C. Osteogenesis imperfecta, or "brittle bone disease," is a group of hereditary disorders characterized by abnormal type I collagen synthesis. In this disease a number of mutations can result in either defective synthesis or secretion of type I collagen. The result is increased bone fragility, abnormal dentition, hearing loss, and a blue appearance to the sclera, as seen in this child.

A 3-year-old boy is brought to the pediatrician by his mother, who notes that, despite no history of trauma, her son has been crying, rubbing his forearm, and guarding this area. This child's medical history is significant for normal, full-term birth and satisfactory achievement of developmental milestones, but poor dentition and two previous instances of skeletal fracture. The posterior area of the forearm is tender and erythematous. There is a bluish discoloration to the sclera and diminished auditory acuity. Which of the following is the most likely diagnosis? (A) A defect in dystrophin (B) A defect in fibrillin (C) A defect in type I collagen (D) A defect in type III collagen (E) Child abuse (F) Hemophilia A

The correct answer is D. Conjunctivitis in a patient who has had both urethritis (or cervicitis) and arthritis for at least one month is suggestive of reactive arthritis. Most patients are in their 20s or 30s, and 80% are positive for HLAB27. Reactive arthritis is thought to be caused by an autoimmune reaction to a gastrointestinal (GI) or genitourinary infection. Answer A is incorrect. Ankylosing spondylitis is an inflammatory disease of the spine and sacroiliac joints causing stiffening of the back, and it often is accompanied by uveitis and aortic regurgitation. It is strongly associated with the HLA-B27 allele. Answer B is incorrect. Lyme arthritis, usually caused by a bite from a tick harboring the spirochete Borrelia burgdorferi, presents with a local skin rash followed by arthralgias and arthritis (usually mono-articular). Its late sequelae include myocardial, pericardial, and neurologic changes. Answer C is incorrect. Patients with psoriatic arthritis can have joint pain and conjunctivitis, but the diagnosis requires the presence of psoriasis, which is characterized by nonpruritic scaly or silvery erythematous plaques with welldefined borders. Answer E is incorrect. SLE is diagnosed by the presence of four of the 11 symptoms summarized by the mnemonic "BRAIN SOAP, MD:" Blood dyscrasias (such as hemolytic anemia or thrombocytopenia), Renal disorder, Arthritis, Immunologic disorder (such as anti- DNA antibody and anti-Smith antibody), Neurologic disorder, Serositis (such as pleuritis or pericarditis), Oral ulcers, Antinuclear antibody (elevated titers in the absence of drugs associated with drug-induced lupus syndrome), Photosensitivity, Malar rash, and Discoid rash.

A 31-year-old man comes to the clinic complaining of red and itchy eyes for the past eight hours. The patient has had pain on urination and diffuse joint pain for 1 month, but tested negative for gonorrhea and chlamydial infection on a previous visit three weeks ago. He has also tested negative for rheumatoid factor, and his human leukocyte antigen (HLA) status is HLA-B27. When asked about any recent illnesses, the patient recalls going to the emergency department two months ago for a bad case of diarrhea. Which of the following is the most likely diagnosis? (A) Anklyosing spondylitis (B) Lyme arthritis (C) Psoriatic arthritis (D) Reactive arthritis (E) Systemic lupus erythematosus

The correct answer is A. The main adverse reactions to cyclosporine therapy are renal dysfunction, tremor, hirsutism, hypertension, and gum hyperplasia. Cyclosporine can damage renal tubules irreversibly, thus decreasing the kidney's ability to excrete potentially toxic metabolites. This patient is suffering from acute gouty arthritis secondary to impaired renal excretion of uric acid and thus increased serum levels of urate, which can precipitate as monosodium urate crystals in joints. Gout classically presents with a warm, red, painful joint. The most common joint affected in gout is the great toe. Other potential adverse effects of cyclosporine that occur secondary to renal failure include hyperkalemia, hypophosphatemia, hypomagnesemia, hypercalciuria, and metabolic acidosis. Allopurinol is used to prevent gouty arthritis by inhibiting xanthine oxidase, an enzyme involved in uric acid synthesis. The mainstay of therapy for acute gout is nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids.

A 32-year-old man recently underwent a liver transplant and was prescribed cyclosporine to reduce the chance of immune rejection. After a few weeks of taking the drug, he started experiencing acute pain, tenderness, warmth, and swelling of his right great toe. His physician takes a fluid sample from the affected area. Examination of the contents reveals the presence of intracellular crystals. Which of the following medications would prevent this problem from recurring? (A) Allopurinol (B) Calcitonin (C) Collagenase (D) Furosemide (E) Warfarin

The correct answer is A. This patient has symptoms and signs consistent with a diagnosis of myasthenia gravis (MG). MG is an autoimmune disorder characterized by the presence of acetylcholine receptor antibodies, which cause impaired signal transmission at the neuromuscular junction. Patients typically present with characteristic ocular (ptosis, diplopia) and musculoskeletal (facial muscle weakness, proximal muscle weakness) symptoms, which are classically worsened by repetitive use of the involved muscles (which is why symptoms are worse by the end of the day). Thymomas (evidenced by the widened superior mediastinum in the image) occur in approximately 10% of patients with MG. The diagnosis of MG can be confirmed by measuring acetylcholine receptor antibodies and performing electromyography (EMG) and/or a Tensilon (edrophonium) test. Treatment generally consists of an acetylcholinesterase inhibitor such as pyridostigmine.

A 32-year-old woman is incidentally found to have a mediastinal mass (see image) while having a plain film x-ray of the chest performed. She subsequently reports that lately she has been "feeling more fatigued, especially at the end of the day." In the office, she has difficulty rising from her chair to move to the examination table. On physical examination the patient has asymmetric left-sided ptosis, a subjective feeling of "blurred vision" when reading the eye chart on the wall, and a facial droop bilaterally. What test would confirm the most likely diagnosis in this patient? (A) Acetylcholine receptor antibody assay (B) Complete blood cell count (C) Parathyroid hormone level (D) Thyroid stimulating hormone level (E) Urine catecholamine levels

The correct answer is C. This woman has sustained an injury to her long thoracic nerve, which innervates the serratus anterior muscle, as a complication of her surgery. The function of the serratus anterior muscle is to anchor the scapula against the thoracic cage. When the long thoracic nerve is damaged, the scapula moves away from the thoracic cage, resulting in what is referred to as winging of the scapula. Long thoracic nerve injury is an occasional complication of mastectomy. The long thoracic nerve originates from the brachial plexus, specifically from C5, C6, and C7.

A 45-year-old woman who recently underwent a left mastectomy and axillary dissection for breast cancer now presents to her physician with a chief complaint that she feels like her shoulder blade sticks out sometimes. She denies any pain. This patient's injured nerve originates at which spinal levels? (A) C3, C4, and C5 (B) C5 and C6 (C) C5, C6, and C7 (D) C7 and C8 (E) C7, C8, and T1

The correct answer is C. This patient has RA, which is characterized by systemic symptoms of fever, fatigue, pleuritis, and pericarditis. Women are affected by RA more frequently than men. Patients with RA classically experience symmetric morning stiffness of joints that improves with use. Patients may also have subcutaneous rheumatoid nodules, ulnar deviation of the fingers, and joint subluxation. RA is mediated by a type III hypersensitivity reaction in which immune complexes form and activate complement. In RA, rheumatoid factor is an IgM autoantibody that is directed against the Fc region of the patient's IgG antibody, leading to immune complex formation and deposition. Rheumatoid factor antibodies are present in a number of asymptomatic patients; more recently, anti-CCP (citrulline-containing protein) antibodies have become more popular as sensitive and specific serological diagnostic indicators of RA.

A 36-year-old woman presents to the clinic with a new complaint of fatigue of several months' duration. She also reports stiffness in both hands that is worse in the morning and decreases after soaking them in her warm morning bath each day. Physical examination reveals a low-grade fever. Subcutaneous nodules are palpated along her forearm bilaterally. What type of hypersensitivity reaction is causing this patient's arthritis? (A) Arthus reaction (B) Delayed cell-mediated hypersensitivity reaction (C) Immune complex hypersensitivity reaction (D) Type I hypersensitivity reaction (E) Type II hypersensitivity reaction

The correct answer is F. Molluscum contagiosum is a member of the poxvirus family that causes a localized infection consisting of nonerythematous, pearly, dome-shaped papules on the skin of an infected individual. Children and immunosuppressed patients are often infected with this virus. The infection is usually self-limited and spontaneously resolves after a few months. Answer A is incorrect. Adenovirus is a common cause of upper respiratory infections. Answer B is incorrect. Hepadnavirus causes hepatitis B with jaundice being a possible dermatologic sequela. Answer C is incorrect. The various herpes simplex viruses (HSVs) cause several different diseases resulting in rash. HSV-1 and HSV-2 cause genital herpes and cold sores. Varicellazoster virus causes chickenpox, which can reactivate and result in shingles. The lesions are painful vesicles with an erythematous base. Answer D is incorrect. Papillomavirus causes warts, which can be flat, raised, or resemble a cauliflower. Answer E is incorrect. Reactivation of polyomavirus results in progressive multifocal leukoencephalopathy in immunosuppressed patients.

A 37-year-old man presents to his physician with a rash. Physical examination reveals the lesions shown in the image; the man says the lesions do not itch. Which family of viruses is responsible for causing this rash? (A) Adenovirus (B) Hepadnavirus (C) Herpes simplex virus (D) Papillomavirus (E) Polyomavirus (F) Poxvirus

The correct answer is B. This patient has psoriatic arthritis, which presents with psoriasis (nonpruritic scaly or silvery erythematous plaques with well-defined borders) and joint symptoms that are of acute onset in one-third of patients. Psoriatic arthritis is an inflammatory arthritis and signs of inflammation, such as an elevated ESR, are commonly seen in patients with this condition. More than 50% of patients have an asymmetric distribution of joint swelling in the distal interphalangeal joints of the hands and feet. Some patients may develop a sausage-like finger from inflammation of the digital tendon sheaths.

A 38-year-old man comes to the clinic with a swollen, sausage-like left middle finger along with diffuse joint swelling of his left hand and right foot over the past three days. The patient also has scaly plaques with well-defined borders along the skin just distal to both elbows. His uric acid level is within normal limits. Which of the following is most likely to be seen in this patient? (A) Antigliadin antibodies (B) Elevated erythrocyte sedimentation rate (C) Negatively birefringent crystals in joint fluid (D) Positive rheumatoid factor (E) Weakly positively birefringent crystals in joint fluid

The correct answer is B. Anti-Jo-1 antibody is a myositis-specific antibody most commonly associated with polymyositis and dermatomyositis. Polymyositis and dermatomyositis are diagnosed if five criteria are met: symmetric proximal muscle weakness; characteristic heliotrope rash; elevated serum muscle enzymes; myopathic changes on EMG; and muscle biopsy abnormalities with the absence of histopathologic signs of other myopathies. This patient presented with the heliotrope rash, a skin manifestation that is highly specific for dermatomyositis. Answer A is incorrect. Anti-dsDNA autoantibodies are associated with SLE. Answer C is incorrect. Anti-IgG autoantibodies are associated with rheumatoid arthatthritis. Anti-IgG is also known as rheumatoid factor. Answer D is incorrect. Anti-microsomal autoantibodies are associated with Hashimoto thyroiditis, not polymyositis or dermatomyositis. Answer E is incorrect. Anti-mitochrondrial auto-antibodies are associated with primary biliary cirrhosis, not polymyositis or dermatomyositis.

A 38-year-old woman presents to the emergency department complaining of increasing muscle weakness and pain. She first noticed the muscle weakness approximately one month ago, and it has gradually worsened since then. During the same time she has had increasing difficulty swallowing her meals. Two weeks prior to this visit, she recalls swelling and a rash over her eyelids. On physical examination, deltoid and quadriceps strength are 2/5 bilaterally. Creatine kinase, lactate dehydrogenase, and aldolase levels are elevated. Which auto-antibody would diagnostic testing find to be elevated? (A) Anti-dsDNA (B) Anti-Jo-1 (C) Anti-IgG (D) Anti-microsomal (E) Anti-mitochondrial

The correct answer is D. This patient has Sjögren syndrome. The vast majority of patients with this syndrome are women between the ages of 35 and 45, and the disease is characterized by dry eyes (keratoconjunctivitis sicca), dry mouth (xerostomia), and one other connective tissue or autoimmune disease (such as rheumatoid arthritis). The eye and mouth dryness is from autoimmune destruction of the lacrimal and salivary glands.

A 42-year-old woman comes to the clinic complaining of blurry vision. She states that for the past three weeks her eyes have been very dry and itchy, and she is unable to make tears. She also states that she has had a very dry mouth despite drinking adequate fluids. Physical examination reveals bilateral dry, ulcerated corneas and fissures on the sides of her lips. In addition, both of her knees are erythematous and swollen. When asked about her knees, she says, "Yes, my knees and wrists tend to be swollen and stiff in the morning, but my mom had arthritis." Testing for several autoantibodies reveals she is rheumatoid factor-positive and antibody-SS-B (La)-positive. Which of the following is the most likely diagnosis? (A) CREST syndrome (B) Cystic fibrosis (C) Sicca syndrome (D) Sjögren syndrome (E) Sjögren-Larsson syndrome

The correct answer is E. Rheumatoid factor would most likely be positive in this woman, who is suffering from RA. Eighty percent of patients with RA have positive rheumatoid factor (anti-IgG antibody). This autoimmune condition causes a marked influx of inflammatory cells into the joint synovium, as seen here, resulting in destructive change, pannus formation, and eventually joint deformity. The disease is more common in women, and classically symmetrically affects the proximal interphalangeal joints, as described here.

A 42-year-old woman has had increasing pain and swelling of the joints of her hands and feet for several months. It is becoming very difficult for her to perform common household tasks. A microscopic image of the synovium of a proximal interphalangeal joint in her hand is shown in the image. Which of the following laboratory serologic findings would most likely be positive in this patient? (A) Anti-centromere antibody (B) Anti-nuclear antibody (C) Borrelia burgdorferi antibody (D) HLA-B27 (E) IgM anti-IgG

The correct answer is C. The subscapularis muscle is one of the muscles that comprise the rotator cuff. It medially rotates and adducts the arm. It is the only rotator cuff muscle that acts to medially rotate the arm. Answer A is incorrect. The deltoid muscle is not a muscle that comprises the rotator cuff Answer B is incorrect. The infraspinatus is an adductor of the arm and a lateral rotator of the glenohumoral joint. Answer D is incorrect. The supraspinatus is the most often injured rotator cuff muscle. It is typically described as being the initiator of abduction for the first 15° of the arc. The deltoid muscle becomes the main propagator for abducting the arm beyond 15 degrees. Answer E is incorrect. The teres minor is a narrow, elongated muscle of the rotator cuff that works to adduct and laterally rotate the arm.

A 49-year-old man is lifting a heavy box above his head when he experiences a sudden tearing sensation and pain that travels along his left arm. When he attempts to move his arm he is not able to medially rotate it. Which of the following muscles is most likely injured? (A) Deltoid muscle (B) Infraspinatus muscle (C) Subscapularis muscle (D) Supraspinatus muscle (E) Teres minor

The correct answer is E. Yersinia pestis is the organism responsible for the plague, also known as the Black Death. The bacterium can be spread to humans by fleas from rodents, especially prairie dogs in the United States. The disease develops after two-eight days of incubation and is characterized by the presence of exquisitely tender lymph nodes called buboes Unlike in the case of anthrax, the skin ulcers seen in Y pestis infection are painful. Furthermore, prolonged infection and spread of Y pestis can lead to disseminated intravascular coagulation Answer A is incorrect. Babesia microti is transmitted to humans through the bite of a tick. It causes a sickness similar to malaria with symptoms of fever and anemia. Answer B is incorrect. Bacillus anthracis can cause cutaneous anthrax, which is characterized by a painless ulcer with a black scab. Answer C is incorrect. Leishmania donovani is transmitted through the bite of a sandfly and causes visceral leishmaniasis. This disease is characterized by abdominal pain and distention, anorexia, weight loss, and fever. Answer D is incorrect. A person infected with Trichinella spiralis presents with fever, periorbital and facial edema, myalgia, and eosinophilia.

A 50-year-old man who recently returned from visiting family in northern New Mexico comes to the physician with exquisitely tender and enlarged lymph nodes. He also complains of fever, chills, and general weakness. On physical examination, the physician notes a painful ulcer surrounded by dark, hemorrhagic purpura on the right arm in the area where, according to the patient, a flea had bitten him five days ago. After being admitted to the hospital, the patient soon develops abnormal coagulation times and is quickly started on a regimen of streptomycin and tetracycline. Which of the following organisms is most likely responsible for this patient's symptoms? (A) Babesia microti (B) Bacillus anthracis (C) Leishmania donovani (D) Trichinella spiralis (E) Yersinia pestis

The correct answer is C. This patient is suffering from pemphigus vulgaris, an autoimmmune blistering disorder. This disease most commonly presents in the fourth to sixth decades of life. It is characterized by fragile blisters over the face, axilla, trunk, and mucosa. Large lesions can jeopardize fluid balance and temperature regulation, and can be sources of infection; thus severe cases may be lifethreatening. The disease is caused by an autoimmune reaction against desmoglein 3, a component of desmosomes (also called macula adherens). Desmosomes are "spot-junctions" that attach epithelial cells to one another. Immunoglobulin is deposited in a net-like pattern surrounding keratinocytes. This condition is treated with corticosteroids and other immunosuppressive medications.

A 52-year-old woman presents to her physician with three weeks of skin blisters. She says when these blisters rupture they leave painful ulcerations. On examination, tender ulcerations are found on her back and trunk. Biopsy is performed and direct immunofluorescence of the lesion reveals a net-like deposit of immunoglobulin surrounding keratinocytes. What aspect of epithelial cell junctions is targeted by autoantibodies in this condition? (A) Gap junctions (B) Hemidesmosomes (C) Macula adherens (D) Zona adherens (E) Zona occludens

The correct answer is D. The supraspinatus muscle is the most frequently injured rotator cuff muscle. Patients often report pain anteriorly and superiorly to the glenohumeral joint during abduction. The primary motion of the supraspinatus is the first 15 degrees of abduction of the arm, at which point the deltoid muscle continues the motion of abduction. Therefore, as long as a patient can assist the injured rotator cuff at the beginning of abduction, he or she will be able to continue the motion unassisted thereafter. This muscle and its tendon can be torn traumatically, but it is most often injured in a more insidious manner because of repetitive movement, as is the likely cause in this case.

A 57-year-old automotive factory worker with no significant past medical history reports to the clinic complaining of weakness and pain in his right shoulder with any movement. He says that for the past two weeks he has had trouble lifting his right arm above his head. He reports using his left arm to lift his right arm slightly, and then he can lift his right arm the rest of the way without help. Which of the following muscles is most likely injured in this patient? (A) Deltoid (B) Infraspinatus (C) Subscapularis (D) Supraspinatus (E) Teres minor

The correct answer is C. Poliovirus infects the Peyer patches of the intestine and the motor neurons. It is passed by the fecal-oral route and can present as a spectrum of severity, depending on the age of the patient. Younger children and infants often have a nonclinical infection or mild fever with diarrhea. Older children who have not previously been infected can develop meningitic signs. The most severe complications are respiratory muscle failure, paraplegia, and quadriplegia. Answer A is incorrect. The neuron loss that occurs affects the motor neurons in the anterior horns, not the posterior horns. Answer B is incorrect. Because this is a lower motor neuron disease, reflexes are lost in the affected limbs, and the limbs atrophy. Answer D is incorrect. The poliovirus infects the motor neurons, leaving sensation spared. Answer E is incorrect. Poliovirus does not affect short-term memory or cortical functioning. It can affect the cranial nerves, however.

A 6-year-old child is brought to the emergency department by his parents after they all returned from a trip to East Africa. His parents report that approximately two weeks ago he had a fever and diarrhea that resolved. However, he now has a fever and weakness of his left leg. On further questioning, his parents state that he is home-schooled and that he has never received vaccinations. Which of the following sequelae is most likely to result in this patient? (A) Neuron loss in the posterior horns (B) Reflex preservation in affected limbs (C) Respiratory muscle paralysis (D) Sensory loss in affected limbs (E) Short-term memory loss

The correct answer is C. A sarcomere, the basic functional unit of skeletal muscle, extends from one Z line to an adjacent Z line. Upon muscle contraction, the power stroke results from actin sliding on myosin, causing Z lines to move closer together. The absolute length of the thin (actin) and thick filaments (myosin) in a myofibril does not change during contraction, but rather the overlap of the filaments increases. Thus, the A band, which is the length of myosin, does not change upon contraction. The H band and I band are the two areas where there is no overlap of actin and myosin; both bands will then decrease when the overlap increases with contraction. Answer A is incorrect. The A band, which is composed of myosin, does not change with contraction. H shortens and I shortens. Answer B is incorrect. This is what will occur upon relaxation. The A band will again remain the same length, but as myosin and actin decrease their overlap, both the H and I bands will increase in length. Answer D is incorrect. The A band, which is composed of myosin, does not change with contraction. H shortens and I shortens. Answer E is incorrect. The A band, which is composed of myosin, does not change with contraction. H shortens and I shortens.

A 63-year-old man and known alcoholic has been unable to afford alcohol. He now presents with hypertension and profuse sweating, and is agitated because he believes that insects are crawling all over his skin. During the examination, he loses consciousness and begins to seize on the stretcher. The seizure-induced muscle contractions result in which of the following changes in length within each sarcomere? (A) Lengthening of A band; no change in H band; shortening of I band (B) No change in A band; lengthening of H band; lengthening of I band (C) No change in A band; shortening of H band; shortening of I band (D) Shortening of A band; no change in H band; shortening of I band (E) Shortening of A band; shortening of H band; no change in I band

The correct answer is B. Osteoarthritis is a disease of wear and tear leading to destruction of articular cartilage, subchondral bone formation, osteophytes, sclerosis, and other degenerative changes. It is common and progressive, and becomes more so with age. It classically presents in weight-bearing joints as pain after use, improving with rest. It commonly affects the distal interphalangeal joints as well. Common imaging findings include narrowing of the joint space, sclerosis, and the presence of osteophytes. The image reveals Heberden's nodes, representing bony enlargement of the distal interphalangeal (DIP) joints.

A 64-year-old woman with no prior medical history has had increasing back pain and right hip pain for the past decade. The pain is worse at the end of the day. On physical examination, she has bony enlargement of the distal interphalangeal joints (see image). Which of the following diseases is most likely the cause of this patient's symptoms? (A) Gout (B) Osteoarthritis (C) Osteomyelitis (D) Pseudogout (E) Rheumatoid arthritis

The correct answer is B. Direct inguinal hernias protrude directly through the abdominal wall in Hesselbach's triangle, which is bordered by the inguinal ligament (inferiorly), rectus abdominis muscle (medially), and inferior epigastric vessels (laterally). Direct versus indirect distinguishes where the hernia enters the inguinal canal, either through the internal ring (indirect) or straight through the abdominal wall (for direct hernias, think directly through the wall). In this case the abdominal contents pierced through the abdominal wall and through the external inguinal ring. Direct hernias often are discovered in older patients as a result of pressure and tension exerted over time that eventually leads the abdominal wall to give way. Direct hernias are less common and have less risk of strangulation than indirect hernias.

A 76-year-old man is scheduled to undergo elective repair of an abdominal hernia that is easily reducible. During the repair, the surgeon sees that the sac protrudes directly through the external inguinal ring without coursing through the inguinal canal. Which of the following types of hernia does this patient most likely have? (A) Diaphragmatic hernia (B) Direct inguinal hernia (C) Femoral hernia (D) Hiatal hernia (E) Indirect inguinal hernia

The correct answer is A. The image demonstrates osteoblastic lesions of the pelvis secondary to metastatic cancer. Prostate cancer, the most common cause of cancer in men, is notorious for producing osteoblastic lesions upon metastasis. Prostate cancer may often be detected on physical examination through the use of a digital rectal examination. Digital rectal examination can also be useful in detecting a small number of colorectal cancers, though most bony lesions of metastatic colorectal cancer are osteolytic. Answer B is incorrect. Palpation of the abdomen may assist in the detection of leukemia or lymphoma, as splenomegaly is a common presenting symptom. These cancers occur much less frequently than prostate cancer, and more often produce osteolytic lesions. Answer C is incorrect. Signs of renal cell cancer include flank pain (noted upon palpation of the costovertebral angle), the presence of a flank mass, hematuria, and/or weight loss. Renal metastases are more commonly osteolytic Answer D is incorrect. Palpation of the neck may be helpful in detecting thyroid cancer. Thyroid metastases are more often lytic.

A 68-year-old man presents to his physician's office with diffuse pelvic pain. X-ray of the abdomen is shown in the image. Which of the following would help diagnose the primary tumor most commonly responsible for these radiologic findings? (A) Digital rectal examination (B) Palpation of the abdomen (C) Palpation of the costovertebral angle (D) Palpation of the neck (E) Thorough skin examination

The correct answer is D. The patient has a classic case of chronic gout, with intermittent attacks eventually giving rise to disfiguring tophi. Gouty arthritis is a common manifestation of hyperuricemia, and tophi form as a result of the accumulation of monosodium urate crystals surrounded by reactive fibroblasts and chronic inflammatory cells in the joints and soft tissues. Common extra-articular sites of tophus formation include the Achilles tendon and the helix of the external ear. Aspiration of the tophus usually reveals the presence of neatively birefringent needle-shaped crystals seen in the question image, which are characteristic of gout. The best therapy of chronic gouty arthritis aims to lower the levels or uric acid. Allopurinol blocks xanthine oxidase and thus reduces the generation of uric acid. Therefore it should be used in patients who overproduce uric acid and in patients at risk of tumor lysis syndrome to prevent renal toxicity during therapy for malignancies. It is the most effective urate-lowering agent. However, alcohol can interfere with the effectiveness of allopurinol. Probenecid increases excretion of uric acid by the kidneys and can therefore also be used in treatment of chronic gout.

A 70-year-old man complains of a long history of pain in his ankles, toes, and fingers. He has experienced intermittent acute attacks of exquisite pain every few months, followed by completely asymptomatic periods. In recent years, he has had near-constant discomfort at baseline, and now has permanent "swelling" in many of the joints of his fingers and toes. Joint fluid is aspirated, and the fluid is examined under polarized light (shown in the image). Treatment is initiated, and the patient's uric acid levels gradually fall. What is the mechanism of action of the best treatment? (A) Binds tubulin (B) Blocks formation of prostaglandins and thromboxane from arachidonic acid (C) Inhibits release of phospholipase A2 (D) Inhibits xanthine oxidase (E) Selective, competitive angiotensin II receptor inhibition

The correct answer is A. The genitofemoral nerve arises from the L1 and L2 nerve roots. In male subjects its genital branch travels through the superficial inguinal ring along with the spermatic cord, and supplies the cremaster and the scrotal skin. Severing the genitofemoral nerve during a hernia repair leads to numbness of the scrotum and/or inner thigh. The genitofemoral nerve and the ilioinguinal nerve have overlapping territory. Thus, severing one only leads to transient anesthesia. Answer B is incorrect. The lateral femoral cutaneous nerve originates from the L2-L3 roots of the lumbar plexus, passes deep to the inguinal ligament, and innervates the skin on the lateral aspect of the thigh. Answer C is incorrect. The posterior femoral cutaneous nerve originates from the S1-S3 roots of the sacral plexus, passes through the greater sciatic foramen, and innervates the skin overlying the buttock, the posterior aspect of the thigh, and the popliteal fossa. Answer D is incorrect. Nerve roots S2-S4 are associated with the pudendal nerve, which innervates the external genitals. Injury to this nerve would be associated with bowel or bladder incontinence and possible anesthesia in the perineum. This nerve is injured most commonly during childbirth or saddle injury. The pudendal nerve is not near the inguinal ligament

A 74-year-old man presents to his physician with a bulge in his scrotum. He is diagnosed with an inguinal hernia on his left side, and undergoes surgery two days later to repair the hernia. On postoperative day two he complains of numbness and tingling of his scrotum. Which nerve root contributes to the affected nerve? (A) L1-L2 (B) L2-L3 (C) S1-S3 (D) S2-S4

The correct answer is C. This child has achondroplasia, which is the most common inherited form of dwarfism. This autosomal dominant disease results in a disturbance of endochondral bone formation due to a mutation in the fibroblast growth factor receptor-3 (FGF-3 gene). This change results in abnormal growth plates and impaired cartilage maturation.

A 9-month-old girl presents to her pediatrician because of abnormal stature and growth. The child displays short stature, shortening of the proximal limbs, short fingers, and frontal bossing. Which of the following is the most likely etiology of this infant's condition? (A) Bone resorption (B) Collagen formation (C) Endochondral ossification (D) Mucopolysaccharide degradation

The correct answer is D. A spiral fracture is one that is caused by a twisting, rotational force to the bone. While child abuse may manifest with any kind of fracture, a spiral fracture should raise increased suspicion of intentionally inflicted injury. The mechanism of injury is usually the twisting of the bone by an angry adult.

A couple brings their 3-year-old son to the emergency department, reporting that he fell down the stairs and broke his arm. The boy has a tearful face and gingerly holds his right arm by the elbow, but refuses to look the physician in the eye or to answer any questions. An x-ray of the boy's arm is performed. Which of the following types of fracture is most likely to suggest an etiology of child abuse? (A) Bowing fracture (B) Buckle fracture (C) Greenstick fracture (D) Spiral fracture

The correct answer is A. The most likely diagnosis is Ewing sarcoma. Made up of anaplastic, small blue cells, Ewing sarcoma is classified as one of the primitive neuroectodermal tumors. This patient's presentation is typical in that 80% of tumors are found in patients <20 years old. Most of these are between the ages of 2 10 and 15 years. Males are at slightly greater risk than females, and a great proportion of patients are white. Plain film x-ray classically reveals a lytic lesion with "onion skinning" of the periosteum. This reactive process occurs as the tumor arises out of the medullary cavity and new layers of bone are deposited around it by the periosteum (hyperlucent layers seen in the radiograph). Microscopic analysis of biopsy specimens reveals sheets of uniform, small, round cells that are slightly larger than lymphocytes. Rosette formations may be seen as cells arrange themselves around a central fibrous space. Otherwise, there is very little stromal space and no normal bony matrix material.

A mother brings her 12-year-old son to the pediatrician's office because he is complaining of leg pain. The pain is located at the distal right tibia and has persisted over the past two weeks. The mother also notes that the child has had intermittent fevers during this time. On examination, the site is erythematous and swollen. A plain film x-ray is taken, the results of which are shown in the image. Biopsy of the site shows sheets of many uniform cells with scant, clear cytoplasm and no evidence of normal bony matrix. Which of the following is the most likely diagnosis? (A) Ewing sarcoma (B) Giant cell tumor (C) Osteochondroma (D) Osteomyelitis (E) Osteosarcoma

The correct answer is D. This image depicts a berry aneurysm. Berry aneurysms are congenital and associated with several syndromes. In this patient, the combination of a berry aneurysm, work as a contortionist (implying hyperextensible joints), and a history of easy bruising and bleeding suggests a collagen disorder, specifically Ehlers-Danlos syndrome (EDS). EDS is a group of disorders resulting from defects in collagen synthesis and processing. This patient likely had vascular EDS (type IV), which is associated with a defect in type III procollagen, a precursor of the collagen found in many tissues.

A previously healthy 30-year-old woman who performs as a contortionist in the circus is found unconscious in her dressing room. By the time she receives medical attention, she cannot be revived. An autopsy is performed and an abnormality is discovered in the circle of Willis, as shown in the image. The patient was also reported to have a history of easy bruising and bleeding. Which of the following proteins was most likely defective in this patient? (A) Fibrillin-1 (B) Keratin 14 (C) Type I procollagen (D) Type III procollagen (E) Type IV collagen

The correct answer is C. This patient most likely has a "boxer's fracture," which occurs when individuals strike a blow with a closed fist against a hard, unyielding object. The most commonly injured sites for experienced boxers are the first and second metacarpals, whereas for others, the neck of the fifth metacarpal is the most common site of injury. The metacarpals have a good blood supply and thus heal rapidly. Answer A is incorrect. A complete transverse fracture of the distal radius is called Colles' fracture. This occurs most commonly in the elderly after forced dorsiflexion. It results in avulsion of the styloid process from the shaft of the radius. The radius may be shortened, and the styloid process of the ulna may project farther distally than the styloid process of the radius. The forearm and hand may exhibit a "dinner fork" deformity as a result of the posterior displacement of the distal part of the radius. Answer B is incorrect. Fracture of the hamate is not common but can be complicated, as the ulnar nerve can often be injured. Patients with an ulnar nerve lesion at the wrist may have an ulnar claw hand, which is caused by a weakness of the medial two lumbricals that flex at the metacarpophalangeal joints and extend at the interphalangeal joints of the ring and little fingers. Patients will also experience weakness in the ability to abduct or adduct fingers or adduct the thumb at the metacarpophalangeal joints (interosseous muscles and adductor pollicis). They are unable to hold a piece of paper between the thumb and index finger or between adjacent fingers. Weakness of the interosseous muscles may also result in a slight clawing of the index and middle fingers. The muscles in the hypothenar eminence may also be affected; patients experience weakness in flexion, abduction, and opposition of the fifth finger. Altered sensation in skin of the medial aspect of the hand and medial digits may be evident. There are healing difficulties associated with this type of fracture. Answer D is incorrect. Fracture of the phalanges is a common injury and is often due to crushing or hyperextension injuries. Answer E is incorrect. Fracture of the scaphoid commonly occurs when individuals fall onto an outstretched hand. The scaphoid is the most commonly fractured carpal bone, and patients may exhibit pain and tenderness localized over the anatomic snuffbox.

A visibly upset 15-year-old boy is brought to the emergency department because he punched a wall and now has pain in his hand. The physician tells the patient that he has broken his hand. Which of the following is the most likely site of this patient's fracture? (A) Distal radius (B) Hamate (C) Metacarpals (D) Phalanges (E) Scaphoid

The correct answer is B. Four muscles are involved in jaw movement: the lateral pterygoid, masseter, temporalis, and medial pterygoid. The lateral pterygoid opens the jaw, and the other three close the jaw. One can remember this with the mnemonic "M's Munch" and "Lateral Lowers." All four muscles are innervated by the mandibular branch of the trigeminal nerve (V3).

A young man complains of difficulty eating. His neurologic examination reveals a symmetric smile, symmetric palate elevation, midline tongue, as well as good shoulder shrug and head turning strength. However, he has difficulty opening his mouth and biting down firmly. Damage to what cranial nerve could explain his condition? (A) V2 (B) V3 (C) VII (D) X (E) XII

The correct answer is B. Anterior cruciate ligament (ACL) injuries are common injuries in sports and frequently occur without contact when people change direction on a planted foot. ACL tears are commonly associated with other injuries and occur in isolation <10% of the time. The most common association is with the lateral meniscus and medial collateral ligament (MCL), which together with the ACL are referred to as the "unhappy triad" of knee injury. Answer A is incorrect. The valgus force of the injury described in the question is unlikely to put tension on the lateral collateral ligament, so it is less likely to be injured. Answer C is incorrect. Although it is possible to injure the medial meniscus, a medial meniscus injury is less likely to be associated with a concurrent MCL and ACL injury. Answer D is incorrect. The patellar ligament is a thick strong ligament that is unlikely to be injured in this type of mechanism. Answer E is incorrect. The posterior cruciate ligament is a strong ligament, but it can be injured, especially in association with collateral ligament tears; however, it is less likely to be injured via this mechanism.

An 18-year-old man is injured during a soccer game when the goalie dives for the ball but tackles the player on the lateral aspect of his leg. He is helped off the field and brought to the emergency department, where he tells the physician that he heard a pop when he was tackled. Physical examination reveals an anterior drawer sign and MRI reveals a torn anterior cruciate ligament and medial collateral ligament. Which one of the following structures is also likely to be injured? (A) Lateral collateral ligament (B) Lateral meniscus (C) Medial meniscus (D) Patellar ligament (E) Posterior cruciate ligament

The correct answer is C. C is the epidermis. Pemphigus vulgaris is an autoimmune disorder in which pathogenic antibodies are directed against a cell-cell adhesion protein, desmoglein-3, which is expressed by the keratinocytes of the epidermis. The destruction of desmoglein leads to intraepidermal acantholysis with sparing of the basal layer. Physical exam typically shows flaccid epidermal bullae that easily slough off leaving large denuded areas of skin (Nikolsky sign), subject to secondary infection. Treatment is usually steroids Answer A is incorrect. A is the stratum corneum, which is composed of enucleated, keratinized, flat keratinocytes. The autoantibodies that mediate pemphigus vulgaris are directed cell-cell adhesion within the other layers of the epidermis, not within the stratum corneum. Answer B is incorrect. B is the dermoepidermal junction. The autoantibodies that mediate this disease are directed against a protein expressed in the epidermis. Answer D is incorrect. D is the dermis. The autoantibodies that mediate this disease are directed against a protein expressed in the epidermis. Answer E is incorrect. E is the hypodermis. The autoantibodies that mediate this disease are directed against a protein expressed in the epidermis.

The diagram shows a cross-section of normal human skin. Pemphigus vulgaris patients suffer from production of autoantibodies against which of the following labeled layers in this image? (A) A (B) B (C) C (D) D (E) E