EMG

61. A 55-year-old overweight man presents to clinic with co mp lai nts of numbness in his left leg. He reports that he does not exercise and has an office job. He is diagnosed with meralgia paresthetica. Which of the following is consistent with this diagnosis? (a) Peroneal motor F-wave study is abnormal. (b) Sensory nerve conduction studies reveal decreased am pli tu de on the affected side. (c) Electromyography findings show denervation in the va stu s lat eralis. (d) Exam reveals decreased sensation in the medial thigh .

"61 Answer: (b) Commentary: Meralgia paresthetica presents with paresthesias in the lat er al thigh. Sensory nerve conduction studies of the lateral femoral cutaneous nerve may show a drop in the sensory nerve action potential (SNAP) amplitude on the affected side compared to the asymptomatic, contralateral study. Symptoms are confined to below the inguinal ligament and above the knee. Peroneal motor nerve conduction studies and F waves should be normal and needle electromyography should not show acute or chronic axonal motor loss, because the lateral femoral cutaneous nerve is purely sensory. Reference: Craig EJ, Clinchot DM. Lateral femoral cutane ous n eur opathy. In: Frontera WR, Silver JK, Rizzo TD, editors. Essentials of physical medicine and rehabilitation. 2nd ed. Philadelphia: Saunders-Elsevier; 2008. p 283-9."

"94.

(This question has been eliminated from the exam, therefore, it was not scored. ) A 45 =-ye ar- old man pres ent s wit h d ipl opia and at ax ia 1 we ek after a viral infection. Physical examination reveals areflexia and ophthalmoplegia. Electrodiagnostic evaluation demonstrates reduced sensory nerve action potential amplitudes. Which course is expected in this disorder? (a) Need for ventilatory support (b) Muscle pain (c) Complete resolution (d) Improvement with plasma exchange" "94 (c) (This question has been eliminated from the exam, therefore, it was not scored.) The Miller-Fisher variant of Guillain-Barré syndrome consists principal ly of a tria d o f oph thalmoplegi a, ataxia, an d a refl exia . A ltered sensa tion in the h ands and a rou nd the m out h can als o o cc ur. Most patie nt s first not e the s udden on set o f dip lo pia . T his is g ene ral ly a ben ign co ndition and does not require specific immune therapy. Pure sensory and pure motor are other forms of Guillain-Barré syndrome."

"184. Electromyographic biofeedback for stroke patients i s most be nefi cial when

(a) proprioception is preserved. (b) used in the upper limb. (c) the patient is young. (d) the patient has flaccid paralysis." 184. (a) Hemiplegic stroke patients engaged in electromyography biofeedback training have a better functional outcome with lower extremity training than with upper extremity training. Further, their age and the duration of their hemiplegia have no effect on training outcome. Proprioceptive loss of the upper limb decreases the probability of making functional gains. Motivation by the patient is a necessity and is most beneficial when some voluntary activity is present.

"18. Which statement is TRUE about F-wave and H-reflex responses? (a) They both are obtained with supramaximal stimulation.

(b) F waves can only be obtained from posterior tibial and median ne rves. (c) They both involve conduction along motor and sensory fibers. ( d) They both can be he lpf ul in the diagnosis of S1 radiculopathy." 18. (d) The F-wave response is a pure motor response that is obtained with supramaximal stimulation and can be obtained from any motor nerve in an adult. The H reflex is usually obtained with submaximal stimulation and involves both sensory and motor fibers. Tibial and peroneal nerve F waves can be abnormal in L5-S1 radiculopathies and tibial nerve H reflex can be abnormal in S1 radiculopathies.

1. A 61-year-old woman reports tingling in the posterior aspect of her upper arm, f orea rm an d h and . She has no hist ory of trauma and r adio gra ph s are negative. Her physician has ruled out a cervical radiculopathy by electrodiagnostic studies, magnetic resonance imaging, and physical examination. The physician is suspicious that the cause of the patient's paresthesias is myofascial in nature. Which finding would be consistent with myofascial pain? (a) Positive sharp waves on electromyography at rest in trigger points (b) Reproduction of symptoms with palpation over the trigger point (c) Elevated serum creatine phosphokinase associated with prolonged muscle activity (d) Resolution of symptoms with isokinetic exercise of the affected muscle

1 (b) Moderate, sustained pressure on an irritable trigger point causes symptoms in the reference zone for that muscle. Myofascial trigger points are electric all y si lent and show no resting m uscle ac tiv ity on EMG. No elevation i n CPK is seen wit h this co ndition. Lo cal injec tio n and /or s pray a nd stretch of the mu scle are the treat me nts of cho ice. Is oki netic ex erc ise is not indicated as a treatment for this condition.

104. Muscle function changes after polio consist of all of the following EXCEPT (a) muscle fiber hypertrophy. (b) increase in motor unit size. (c) decreased jitter on single fiber electromyography. (d) increased fiber density on single fiber electromyography.

104 (c) Polio affects the anterior horn cells, resulting in motor axon dropout. Compensatory effects include individual muscle fiber hypertrophy of the survivin g m uscl e fib ers and increase in m otor uni t s ize due to spr outing and i nnervation of som e of t he surround ing denervat ed mu scl es. T here i s also an inc rease i n fiber densi ty as a re sul t of re- inn erv ation as we ll as atro phy and replacement of denervated muscles. This can be assessed by single fiber electromyography. Jitter also can be increased because of the re-innervated muscle fibers' instability.

108. The potentials above are (see pictures table) (a) complex repetitive discharges. (b) myotonic discharges. (c) neuromyotonia. (d) myokymia.

108 (b) The potentials noted are single-fiber discharges waxing and waning in frequency and amplitude. This is characteristic of myotonic discharges.

114. Which muscles are usual ly i nnerv ate d by t he median nerve?(a) Third and fourth lumbric als(b) Third and fourth dorsal inte rosse i(c) First and second lumbric als(d) First and second dorsal inte rosse i

114. (c) The ulnar nerve innervates all the dorsal interossei muscles and the third and fourth lumbricals. The median nerve innervates the first dorsal interosseus muscle in about 1% of the individuals. Rarely, the radial nerve innervates the first dorsal interosseus. The first and second lumbricals are innervated by the median nerve.

118. Comparing the results of electrodiagnostic studies on patients with clinical evidence of postpoliosyndrome and the results of those obtained in persons with a history of polio of similar severity and duration since polio onset but no clinical evidence of postpolio syndrome, you find (a) smaller motor units in the symptomatic group. (b) more polyphasic motor units in the symptomatic group. (c) more fasciculations in the symptomatic group. (d) no significant differences between the groups.

118 (d) There are no significant differences between the groups. Electrodiagnostic studies are not performed to confirm the diagnosis of postpolio syndrome; this is a clinical diagnosis. They are performed to rule out other disorders in the differential diagnosis.

118. A medical student has been practicing with the electromyography (EMG) machine. You n ote th at the c onve nti onal fil ter setting s h av e be en ch anged. The low frequency filter is now set at 200Hz and the high frequency filter is set at 1,000Hz. This will cause (a) a decreased common mode rejection ratio. (b) increased input impedance. (c) no significant changes. (d) distortion of recorded potentials.

118 (d) Typical settings are 20Hz for the low frequency filter and 10,000Hz for the high frequency filter. Allowing such a narrow bandwidth will cause distortio n o f th e rec ord ed po tentials. I t would ha ve no effe ct o n t he input imp edance or com mon mode r eje ction ra tio .

118. When performing needle electromyography in someone the ra peu tically anticoagulated with warfarin, which muscle would be the safest to examine? (a) Tibialis posterior (b) Paraspinal muscles (c) Deltoid (d) Flexor pollicis longus

118 Answer (c) Commentary: Although needle EMG is generally safe in pa tie nt s t aking warfarin, whenever bleeding risk is increased it is best to limit the needle examination to a few superficial muscles, where prolonged compression can be performed if necessary. The pronator teres and tibialis posterior are deep muscles in which, theoretically, a hematoma could develop. It is also best to avoid needle insertion into areas where possible hematoma could compress a nerve or artery, such as exiting spinal nerves near paraspinals or the radial artery near the flexor pollicis longus. Reference: Preston DC, Shapiro BE. Electrical safety an d i at rog enic complications of electrodiagnostic studies. In: Preston DC, Shapiro BE, editors. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations, 2nd ed. Philadelphia: Butterworth-Heinemann; 2005. p 658-9.

118. Which muscle is innerva ted by th e p eronea l division of the sciatic nerve?(a) Adductor magnus-anterior par t(b) Piriformis(c) Semimembranosus(d) Biceps femoris- short he ad

118. (d) The anterior part of adductor magnus is innervated by the obturator nerve. The piriformis receives its own branch off the lumbosacral plexus. The semimembranosus is innervated by the tibial division of the sciatic nerve. Only the short head of the biceps femoris is innervated by the peroneal division of the sciatic nerve.

128. Which electrodiagnostic finding is most consistent with neurogenic thoracic outlet syndrome? (a) Small median motor response from the thenar muscles (b) Abnormal response of the lateral antebrachial cutaneous nerve (c) Abnormal median sensory responses (d) Abnormal spontaneous activity in the pronator teres muscle

128 Answer: B Commentary: Neurogenic thoracic outlet syndrome involves the lower trunk of the brachial plexus; hence, sensory and motor loss develops in the C8-T1 distribution. Thumb abduction is often affected. Sensory changes are usually in the distribution of the ulnar and medial antebrachial cutaneous nerves. Ref:Preston DC, Shapiro BE. Brachial plexopathy. In: Preston DC, Shapiro BE, editors. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations. Boston: Butterworth-Heinemann; 1998. p 438.

128. Surface electrodes for reco rding an tidrom ic sural nerve conduction studies are best placed(a) posterior to the medial mall eolus . (b) posterior to the lateral mal leolu s. (c) anterior to the medial m alle olus. (d) anterior to the lateral mall eolus .

128. (b) The sural nerve travels posterior to the lateral malleolus and is best recorded over this area.

138. A 27-year-old woman noted the onset of paresthesias in the lateral 3 digits of the r igh t h and 6 mo nths ag o. In iti all y, these sy mp toms we re constant, lasting for about 1 week, and then resolved spontaneously. Over the 3 weeks prior to this consultation the paresthesias recurred and they are now present in both the right upper and lower extremities. Electromyogram of the right upper extremity is normal. Bilateral median, ulnar, and sural sensory nerve conduction studies were normal. Right peroneal motor nerve conduction study was normal. What electrodiagnostic study would be most appropriate to perform at this time? (a) Single-fiber electromyography (b) Somatosensory evoked potentials (c) Right median F wave (d) Electromyogram of the right lower extremity

138 (b) With all of the studies being normal a diagnosis of multiple sclerosis should be considered. Of those listed the only study that might provide any usefu l i nfor matio n w ould be the soma to sensory evo ked pot enti als .

138. In testing a patient with suspected myasthenia gravis, needle electromyography (EMG) of the rightupper extremity and orbicularis oculi is normal. Repetitive stimulation of the right ulnar nerve at a rate of 2/second shows no decrement before or immediately after 1 minute of exercise. A 4% decrement is noted 2 minutes after exercise. Your next electrodiagnostic step should be (a) EMG of the lower extremities. (b) EMG of the frontalis before and after edrophonium (Tensilon). (c) repetitive stimulation of recording from a proximal muscle. (d) ulnar somatosensory evoked potentials.

138 (c) In patients with myasthenia gravis, repetitive nerve studies recorded from proximal muscles are more sensitive, though technically more difficult.

138. What parameter of the motor unit action potential ( MUAP) is the most sensitive to the distance between the generator source and recording electrode? (a) Amplitude (b) Phases (c) Firing rate (d) Duration

138. (a) The amplitude is primarily influenced by the distance between the electrode's recording surface and the electrical generator. The duration is a highly stable and reliable parameter of the motor unit. The other parameters are not affected by the distance.

140. A patient presents to your clinic with a 1-month history of mild hand numbness and clumsiness without weakness. Electrodiagnosis confirms a primarily sensory median neuropathy at the wrist without axon loss. Symptoms are not interfering with work. What is the most appropriate treatment recommendation to provide short-term relief for this patient? (a) Immediate referral to surgery for carpal tunnel release (b) Neutral wrist splints to be worn at night (c) Thumb spica splint (d) Injection of platelet rich plasma into carpal tunnel

140 Answer (b) Commentary: Wrist splints are shown to effectively decrease symptoms of carpal tunnel syndrome in the short-term. Splints should be worn at night and during the day if possible. Brace should place wrist in neutral (up to 5o of extension): note that many off-the-shelf carpal tunnel braces place the wrist in excessive extensions. A thumb spica splint is not effective in treating carpal tunnel syndrome. Conservative treatment is essential in mild to moderate cases of carpal tunnel syndrome. Surgical referral should be considered for patients with weakness or worsening symptoms not improved with conservative treatment. Platelet rich plasma injections are not an effective treatment for carpal tunnel syndrome. Reference: a) Kelly BM, Patel AT, Dodge CV. Upper limb orthotic devices. In: Braddom RL, editor. Physical Medicine and Rehabilitation. 4th ed. Philadelphia: Elsevier Saunders; 2011:325326. b) Huistedde BM, Hoogvliet P, Randsdorp MS, Glerum S, Middelkoop M, Koes BW. Carpal tunnel syndrome. Part I. Effectiveness of nonsurgical treatments-a systematic review. Arch Phys Med Rehabil. 2010;91(7):981-1004.

148. In evaluating a hypotonic infant with electromyography you find low-amplitude, short-durationmotor units with early recruitment. Based on these findings, the LEAST likely diagnosis would be (a) central core disease. (b) nemaline myopathy. (c) type II glycogenosis (acid maltase deficiency). (d) infantile spinal muscular atrophy.

148 (d) The motor unit changes noted are typically seen in myopathies. Spinal muscular atrophy is an anterior horn cell disease.

148 Which muscle fiber is characterized by slow-twitch oxidative metabolic properties? (a) Type 2a (b) Type 1 (c) Type 2b (d) Type 3

148 Answer: (b) Commentary: There are 2 primary muscle fiber types in humans. They are categorized according to many different characteristics, including speed of contraction and sources of fuel. Type 1 muscle fibers are slow-twitch with oxidative metabolic pathways. Type 2 muscle fibers are fasttwitch fibers. The type 2 fibers can then be further divided into fast-twitch glyclolytic, and fasttwitch oxidative glycolytic. Ref: DeLateur BJ. Therapeutic exercise. In: Braddom RL, editor. Physical medicine and rehabilitation. 2nd ed. Philadelphia: WB Saunders; 2000. p 398.

151. A 37-year-old woman presents with complaints of paresthesias in the fourt h and fi fth digi ts of he r domin ant hand fo r the l ast 3 year s. Sh e h as vague co mpl ain ts of aching in and around her shoulder and neck. She reports great difficulty with overhead activities. She reports intermittent swelling and discoloration of her hand with these activities. She has no wasting of her muscles on exam, and Tinel's maneuver at the elbow is negative. You suspect (a) thoracic outlet syndrome (b) myofascial pain syndrome (c) rotator cuff tendonopathy (d) Raynaud's syndrome

151 (a) For a provocative test to be positive for thoracic outlet sy ndrome (TOS), the patient must volunteer that the maneuver exactly reproduces the symptoms. Adson's t est is performed by palpating the radial pulse while turning the patient's h ead to ward the affecte d si de, ex ten ding hi s/her neck, and holding the affected arm at the side. This will result in lo ss of the radial pulse. The costoclavicular maneuver is performed by having the patient mov e the shou lders b ack and down, resulting in a loss of the radial pulse. The elevated a rm str ess test (a/k/a Roos ' test ) i s perfo rmed by having t pat ie nt hol d hi s/ he r arms over head w hil e op enin g a nd clo sing th e ha nd s. A p ers on with TOS w ill repo rt pain and will fatigue within 30 seconds. A person without TOS will not report pain and will be able to perform the test for up to 3 minutes. Compression of the ulnar nerve is not a maneuver for the diagnosis of TOS. For a provocative test to be positive for thoracic outlet sy ndrome (TOS), the patient must volunteer that the maneuver exactly reproduces the symptoms. Adson's t est is performed by palpating the radial pulse while turning the patient's h ead to ward the affecte d si de, ex ten ding hi s/her neck, and

154. Which muscle fiber is characterized by fast-twitch oxidative met abolic properties? (a) Type 1 (b) Type 2a (c) Type 2b (d) Type 3

154 (b) Humans have 2 primary types of muscle fiber. They are divided according to many different characteristics, including speed of contraction and sources of fuel. Type 1 muscle fibers are slowtwitch with oxidative metabolic pathways. Type 2 muscle fibers are fast-twitch fibers. The type 2 fibers can then be further divided into fast-twitch oxidative (type 2a) and fast-twitch glyclolytic (type 2b). There are no muscle fibers designated as type 3.

158. A 35-year-old woman is sent to you for electrodiagnostic evaluation. Her symptoms include numb nes s in th e ri ght 4 th and 5t h dig its a nd in th e medial ha nd dis ta l to the wrist. Your primary diagnosis is MOST likely to be (a) ulnar neuropathy. (b) C8/T1 radiculopathy. (c) lower trunk plexopathy. (d) medial cord plexopathy.

158 (a) The distribution described is most consistent with involveme nt of the ulnar nerve proximal to the dorsal cutaneous branch. Involvement of the C8/T1 roo ts, lower trunk o f the brachial plexus, or medial cord of the brachial plexus would us ually result in some a ddit ional sen sory de ficits over the med ial f ore arm pro xi ma l to th e wr ist.

158. Studying F-wave responses would be most helpful in making an early diagnosis o f (a) cervical radiculopathy. (b) myotonic dystrophy. (c) multiple sclerosis. (d) Guillain-Barré syndrome.

158 (d) Guillain-Barré syndrome (acute idiopathic demyelinating polyradiculoneuropathy) commonly affects the most proximal portion of the nerve while sparing th e m ain nerve tr unk i n the early stages. While motor conduction velocities obtained with ordinary techniques may be normal, Fwave studies help detect proximal abnormalities.

167. Which condition is a cumulative trauma disorder tha t has bee n as sociated with intensive computer use? (a) Herniated thoracic disc (b) Shoulder adhesive capsulitis (c) Post-traumatic stress syndrome (d) Cervical myofascial pain

167. (d) The United States Department of Labor has determined that computer work is associated with a significant number of musculoskeletal disorders, many of which are considered cumulative trauma disorders. Examples include cervical and thoracic myofascial pain, rotator cuff tendonitis, medial and lateral epicondylitis, de Quervain tenosynovitis, and carpal tunnel syndrome.

168. In electromyographic testing of the ulnar nerve for entrapment at the elbow, t he p ri mar y r eas on fo r fl exi ng th e e lbo w to 45° or m ore is th at this position (a) causes the ulnar nerve to be more superficial and thus easier to stimulate. (b) allows more accurate assessment of the length of the nerve. (c) allows for the least possible stimulus overflow to the radial nerve. (d) causes increased compression of the nerve, thus improving the diagnostic yield.

168 (b) For testing of ulnar conduction around the elbow, flexion of 45° or greater is preferred because conduction studies frequently show slowing in the elbow se gmen t whe n t he fu lly extende d position is us ed. The dis crepancy is thought to ar ise from t he underest ima tion of t he ac tua l len gth of t he nerve wh en us in g surfac e dis tance m eas ure ment .

18. Which myopathy is most likely to demonstrate a "normal" EMG? (a) Myotonic dystrophy (b) Polymyositis (c) Steroid myopathy (d) Duchenne muscular dystrophy

18 (c) In steroid myopathy the only abnormalities are atrophy of the type II fibers. Since these fibers are recruited last, when the screen is full of motor un its , it is u sua lly d ifficult to a ppreciat e s ubt le a mpli tud e changes. T he other myop athi es not ed typicall y m ay exhibi t p os iti ve wa ves an d fibrillatio ns wi th motor u nit c hange s in the typ e I fib ers .

23. Which muscle fiber types are recruited first in isom etr ic co ntractions? (a) Type 1 (b) Type 1b (c) Type 2 (d) Type 2b

23 Answer: (a) Commentary: Fatigue-resistant type 1 fibers are recruit ed in iti ally followed by type 2b fibers. There are no type 1b fibers. Reference: Mysiw WJ, Jackson RD. Electrical stimulation . In : B raddom RL, editor. Physical medicine and rehabilitation. 3rd ed. Philadelphia: Saunders; 2007. p 479.

25 What do fibrillation potentials represent? a) Spontaneous depolarization of muscle fiber b) Demyelination of peripheral nerve c) Central nervous system pathology d) Activation of a motor unit

25 Reference(s) Dumitru D, Stegeman DF, Zwarts MJ. Electrical sources and volume conduction. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic medicine. 2nd e Philadelphia: Hanley & Belfus; 2002. p 47. Option a is correct. Fibrillation potentials are simply spontaneous depolarizations of a single muscle fiber seen in pathologic tissue and are often elicited with needle movemen t while performing electromyography (EMG ). Fibrillati on potential s are seen in neurogenic conditions with acute or chronic axonal loss, but also in myopathic disease. Fibrillations are not characteristic for central nervous system disease states or conduction block. Conduction block is evaluated on nerve conduction studies. However, fibrillations could be seen in cases of conduction block if axonal loss has occurred as well.

28. Which electrodiagnostic finding is more common in radiation plexopathy than in neop la sti c p lex opath y? (a) Myokymic discharges (b) Fibrillations (c) Decreased motor unit recruitment (d) Decreased amplitude of the sensory nerve action potential

28 (a) Myokymia is present in 50% of patients who have radiation plexopathy, but is rarely seen in neoplastic plexopathy. The other findings noted in both ple xop athi es, b ut predo minate in n ei ther.

28 Which characteristic best describes fasciculation potentials? (a) Semirhythmic in their firing pattern (b) Morphologically the same as motor unit potentials (c) Produced by ephaptic conduction between single muscle fibers (d) Randomly firing single muscle fibers

28 Answer: (b) Commentary: Fasciculation potentials are spontaneously firing motor unit potentials with the same morphologic characteristics as that of a motor unit or polyphasic action potential. They have an irregular firing pattern usually and the site of origin is unclear. Ephaptic conduction between single muscle fibers is thought to be the mechanism for complex repetitive discharges. Single muscle fiber potentials are much smaller and represent units such as a fibrillation potential. Ref: Dumitru D, Zwarts MJ. Needle electromyography. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 278-9.

28. Electrodiagnostic findings in a person with multiple myeloma monoclonal an tibody and amy loid depo sition mi ght i nclu de all of the following EXCEPT (a) distal symmetric axonal sensorimotor polyneuropathy. (b) mononeuropathy multiplex. (c) anterior horn cell disease. (c) demyelinating polyradiculoneuropathy. Clinical Activity 3.10

28. (c) Patients with multiple myeloma may commonly have distal demyelinating a nd axonal periph era l neuropath ies. Mo noneuropathy mult iplex with conduction blocks at a typ ical sit es is s ug ges tive of amy loid deposition. Amyloid deposition may also cause small fiber neuropathy, with normal nerve conduction study and electromyography results. Radiculopathy may be associated with pathologic spinal fracture or neuroforaminal stenosis. Multiple myeloma is not associated with isolated anterior horn cell disease.

28. A 27-year-old previously hea lthy wom an awo ke with severe right scapular and shoulder pain 4 weeks ago. There is no history of trauma. She has no constitutional symptoms. Three weeks ago, her pain began resolving and scapular winging developed. Electromyography (EMG) reveals 3+ positive waves and fibrillations with markedly decreased recruitment in the right serratus anterior. EMG of the right deltoid, biceps, pronator teres, abductor pollicis brevis, first dorsal interosseous, and cervical paraspinals is normal, as is EMG of the left serratus anterior. The most likely diagnosis is(a) systemic lupus erythemat osus . (b) compression neuropathy o f th e dor sal scapu lar nerve. (c) idiopathic brachial neur opat hy (n eur algic amyotrophy). (d) C5 radiculopathy due to cerv ical dis c hern iation.

28. (c) This is a classic history for neuralgic amyotrophy or idiopathic brachial plexopathy involving the long thoracic nerve. In 30% of patients with neuralgic amyotrophy, EMG abnormalities can be found in the asymptomatic upper extremity; however, the absence of such findings does not obviously exclude the diagnosis. The findings are inconsistent with the other diagnoses.

28. A 40-year-old man sustained an injury to his left ar m, 3 week s ag o, when he lost his balance and crashed into a bookshelf. His complaints include left arm pain, weakness with extension of his wrist and fingers, and decreased hand grip. He denies any numbness but has odd sensations over the dorsum of the left hand. Prior to any testing, which problem would you consider as the most likely? (a) Posterior interosseous neuropathy (b) C7 radiculopathy (c) Posterior cord brachial plexopathy (d) Radial neuropathy

28. (d) Based on the clinical presentation, radial nerve injury is the most likely cause of the patient's symptoms. Considering the location of the trauma the other possibilities seem less likely. In a posterior interosseous nerve injury one would not expect any sensory problems.

29 Small muscle motor units a. are recruited after large motor units. b. have fewer muscle fibers. c. have a higher threshold of recruitment. d. have larger cross sectional areas.

29 Option b is correct. The muscle motor unit size principle states that smaller motor units are recr uit ed pr io r t o l arg e m otor units . F ur ther , s mall er m otor u nits hav e few er muscl e f ibe rs, lo wer threshold of recruitment and smaller cross sectional areas.

30 When comparing the compound muscle action potential (CMA P) latency with the l ate ncy o f the F res pon se, which fin di ng i s m ost li ke ly to occu r as you mov e the st imu lat ing ele ctrode to a more proximal location in the limb? a. Both CMAP and F-response latency will decrease. b. Both CMAP and F-response latency will increase. c. CMAP latency will increase and F-response latency wil l decrease. d. CMAP latency will decrease and F-response latency wil l increase.

30 Option c is correct. The F response is a late response that becomes evident a fter the CMAP re spons e. The F r esp ons e i s d eriv ed fro m a n anti dro mic st im ulatio n of a p eriph era l ner ve tha t p rop agat es an impulse proximally to the anterior horn cells of the spinal cord and returns an orthodromic response to the distal muscle. The F response is a pure motor response creating a small action potential representing 1% to 5% of the muscle fibers. Moving the stimulator proximally shortens the distance to the spinal cord's anterior horn cells. Consequently, the F response latency decreases as you increase the distance from the distal muscle pick up site and the CMAP amplitude or direct motor potential latency increases.

34 Myotonic discharges produce a distinctive sound on electromyography (EMG). This sound results from a) spontaneous firing of motor unit action potentials (MUAPs). a. b) intermittent blocking of muscle fibers during voluntary activity. b. c) firing of just a few muscle fibers per motor unit during voluntary activity. c. d) spontaneous firing of muscle fibers.

34 Option d is correct. ommentary: The classic myotonic discharge of waxing and waning in frequency and amplitude is often described as either a dive-bomber or revving engine. T he so urc e generator of a myotonic potential is muscle fiber, and thus may take the form of either positive wave or a brief spike potential. Neuromyotonia and myokymia result in spontaneous firing of motor unit action potentials as opposed to muscle fiber action potentials. Intermittent blocking of some muscle fibers within a motor unit result in unstable MUAPs, which are characterized by changes in either amplitude or number of phases from potential to potential. Unstable MUAPs are seen in primary neuromuscular junction (NMJ) disorders or with new and immature NMJs, as can be seen in early reinnervation. Mypopathic MUAPs result from a decreased number of muscle fibers firing within a motor unit. These signals are seen as short-duration, small amplitude, and polyphasic potentials. Reference: (a) Myotonic muscle disorders and periodic paralysis syndromes. In: Preston DC, Shapiro BE, editors. Electromyography and neuromuscular disord ers. 2nd ed. Philadelphia: Butterworth-Heinemann; 2005. p 591. (b) Dumitru D, Zwarts MJ, Amato A, Peripheral nervous system's reaction to injury: electrodiagnostic medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 277-8.

38. Where do you place the cathode when performing a median motor nerve conduction stud y, st imu lat ing a t th e e lbow? (a) Lateral to the biceps tendon (b) Medial to the brachial artery (c) Lateral to brachioradialis (d) Medial to brachioradialis

38 (b) The median nerve is just medial to the brachial artery at the elbow.

38. A patient having difficulty late in the day getting up fr om a chair, going up or down stairs, and reaching with his arms presents for electrodiagnostic studies. Physical exam demonstrates normal deep tendon reflexes and normal findings on manual muscle testing. Standard sensory and motor nerve conduction studies are normal. Repetitive axillary nerve stimulation (RNS) performed at 2Hz demonstrates 20% decremental response. Immediately after exercise, the RNS decrement is no longer observed. Three minutes following exercise, however, the decrement is greater. Needle electromyography results are normal. Upon further investigation, you would most likely find w hat a ddi tional clinical finding? (a) Asthma (b) Dry mouth (c) Ptosis (d) Skin rash

38 Answer (c) Commentary: The patient presents with myasthenia gravis (M G) , a postsynaptic neuromuscular junction disorder. Ptosis and extraocular weakness often occur in MG. Lambert-Eaton myasthenic syndrome (LEMS), a presynaptic neuromuscular junction disorder, would demonstrate postexercise facilitation (at least 100% increase in first response CMAP immediately following exercise) and likely have low-amplitude baseline CMAP results. Autonomic symptoms such as dry mouth often accompany LEMS. Long-term steroid treatment for asthma may cause myopathy without significant needle EMG results, but RNS would be normal. Although dermatomyositis typically presents with proximal weakness, no abnormalities characteristic of an inflammatory myopathy were seen on needle electromyography. Reference: Preston DC, Shapiro BE. Neuromuscular junctio n d is ord ers. In: Preston DC, Shapiro BE, editors. Electromyography and neuromuscular disorders, 2nd ed. Philadelphia: ButterworthHeinemann; 2005. p 553-61.

38. Which modification can be used to increase the sensitivity of repetitive testing in neuromuscular junction disorders? (a) Decrease the muscle temperature below 30°C. (b) Allow the muscle to be rested for 6 minutes. (c) Test the most distal muscles in the feet. (d) Test the muscles after inducing ischemia.

38 Answer: (d) Commentary: In postjunctional disorders, such as myasthenia gravis, the proximal muscles seem to be more affected and it is thought that this difference is due to the increased temperature as one gets closer to the core of the body. The higher temperatures potentiate a reduced safety factor. Hence, the sensitivity of detecting a decrement response is higher with proximal muscle testing. Maximal exercise can help in demonstrating postactivation exhaustion. When repetitive stimulation is normal in both proximal and distal muscles, testing under ischemic conditions can demonstrate a decrement in the responses. Ref: Dumitru D, Amato AA. Neuromuscular junction disorders. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 1158-62.

40 While performing an electrodiagnostic study for suspecte d carpal tunnel syndr ome , y ou n oti ce tha t t he m edian, ul na r, a nd radi al s ensory ner ve c onduc tio n stu die s d emo nst rate prolonged peak latencies with increased sensory nerve action potential (SNAP) amplitudes and durations. What should be evaluated next? a. Additional nerve conduction studies of the lower extr emity b. F responses on the median and ulnar nerves c. Limb temperature d. Needle electromyography (EMG)

40 Option c is correct. Prolonged peak (or distal) latency with increased SNAP ( or CMAP) amplitu des m ay be an i ndi cat or of cool limb tem pe ratu res . Th is s hould not be c onfus ed with a d emy eli nat ing process affecting the peripheral nervous system. The effects of a cool limb include slowed nerve conduction velocity, prolonged distal and peak latencies, increased amplitude and duration of SNAPs and CMAPs, and increased duration, amplitude, and phases of motor unit action potentials (MUAP). Distal limb temperatures should be recorded and ideally maintained between 33 and 34 degrees Celsius. Additional nerve conduction studies of the lower limb, F responses of the upper limb, or needle electromyography (EMG) would not be the appropriate first intervention; however, these studies may be necessary if abnormalities exist even after temperature correction and if true peripheral nerve pathology is suspected.

41 Which phenomenon occurs when an axon is depolarized? a. The intracellular region becomes more negatively char ged. b. Sodium channels open, allowing sodium to rush out of the axon. c. Large anions and potassium permeate into the axon. d. Sodium movement is driven by electrical and concentra tion gradients.

41 Option d is correct. The resting potential is about -90 millivolts. With depo larization an in flux of sod iu m occ urs , d riv en b y both an e lect ric al a nd c oncent rati on g radie nt. This so diu m i nfl ux r esults in the axon becoming more positive internally. The axon membrane is impermeable to large negatively charged anions and relatively impermeable to sodium ions in the resting state. The concentration of sodium is higher outside the membrane, whereas the potassium concentration is higher inside.

42 Which electrodiagnostic finding would be most helpful in differentiating crit ica l i ll ne ss myo pat hy (CIM ) from cr it ical il lnes s po lyneur opat hy ( CIP)? a. Normal compound muscle action potential (CMAP) amplit udes b. Abnormal spontaneous activity c. Normal sensory nerve action potential (SNAP) amplitud es d. Decreased CMAP amplitudes

42 Option c is correct. Critical illness myopathy (CIM) presents as weakness in a patient in the inte nsi ve ca re un it (IC U). Cli nicall y i t may be diff ic ul t to d isti ngui sh CI M f rom C IP. A CIM pa tter n would have normal SNAP amplitudes, whereas CIP will show abnormalities on sensory nerve conduction studies consistent with an axonal loss pattern. Both CIM and CIP demonstrate decreased CMAPs and both may have abnormal spontaneous activity on needle examination.

42 Which statement is most correct regarding instrumentation for electrodiagnostic studies? a) Signals pass from the filters to the amplifiers. b) Cathode-ray tube subtracts common electrical activity. c) Electrical signals are transmitted from 2 surface electrodes. d) Filters are used to increase the electrical noise.

42 Reference(s) Malhotra G. Instrumentation. In: Visco C, Chimes G, editors. McLean course in electrodiagnostic medicine. New York; Demos Medical; 2011. p 9-11 . Electrical signals are transmitted from skin surface electrodes or through a needle. These electrodes are referred to as E1 and E2 or the active and the ref erence. Differential amplifiers elim inat e signal comm on to the 2 elect rodes. Filters are used to remove excessive electrical noise after signal amplification. Cathode-ray tube permits the visual display of the electrical signal as a waveform.

44 A 25 year old patient presents for electrodiagnostic testing after sustaining a right shoulder injury following a motorcycle crash 4 weeks ago. He has no ac tive elbow, wrist or finger extensio n. T he needle exa mi nation of the r adial innervated muscles shows normal insertional activity, no abnormal spontaneous activity and absent motor recruitment. In the Sunderland classification system, this nerve injury is best described as? a) myelin injury with no Wallerian degeneration b) Wallerian degeneration with preservation of endoneurium c) disruption of axon with intact perineurium d) complete discontinuity of the nerve

44 Reference(s) (1)Dumitru D, Zwarts MJ, Amato A Peripheral nervous system's reaction to injury. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic medicine. 2nd e Philadelphia: Hanley & Belfus; 2002. p 124-5. (2)Dumitru D, Zwarts MJ. Needle electromyography. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic medicine. 2nd e Philadelphia: Hanley & Belfus; 2002. p 275-6. Option a is correct. The injury described is limited to the myelin with preservation of the axon. This type of injury is classified as neurapraxia by the Seddon classification a nd as type 1 by the Sunderland class ific ation. In axo na l injury, one w ould typically observe positive sharp waves and fibrillation potential within 3 weeks after the injury. Sunderland type 2 and 3 are both forms of axonal injury and differ in their extent of injury to the supporting neural structures. Sunderland type 2 and 3 are classified as axonotmesis by the Seddon classification. Complete discontinuity of the nerve is classified as type 5 Sunderland and as neurotmesis by Seddon.

46 Following a crush injury with axonotmesis, the approximate growth regeneration rate at the wrist is 1 centimeter per a) day. a. b) week. b. c) month. c. d) year.

46 Option b is correct. Commentary: Regenerating axons grow approximately 1 millimeter a day, 1 centimeter a week, 1 inch a month, or 1 foot a year. The rate of axon regeneratio n dep end s chiefly on type of injury (crush or laceration) and whether the lesion is proximal or distal. Growth rate following a crush injury with axonotmesis in the upper arm is about 8 millimeters a day; in the upper forearm it is about 6 millimeters a day, at the wrist about 1-2 millimeters a day, and in the hand about 1.0-1.5 millimeters a day. Easier figures to remember, however, are 1mm/day, 1cm/week, or 1 inch/month. Reference: (a) Stewart, JD. Focal peripheral neuropathies. 3rd ed. Montreal (Quebec):McGill Univ; 2000. p 25. (b) Ref: Dumitru D, Zwarts MJ, Amato A, Peripheral nervous system's reaction to injury: electrodiagnostic medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2002. p -120 1

47 The definitive diagnostic test for inclusion body myositis is a) muscle enzyme serum levels. a. b) cerebrospinal fluid. b. c) muscle biopsy. c. d) electromyography.

47 Option c is correct. Commentary: Inclusion body myositis (IBM) is a slowly progressive myopathy that tends to affect middle-aged and older individuals. Clinical manifestations can include distal as well as prox imal wea kness, which can be asymmetrical. Muscle enzyme levels may be slightly elevated or normal. Myopathic motor units can be seen, although this finding is nonspecific, since it exists in other inflammatory myopathies, as well. Acquisition of cerebrospinal fluid is not part of the work-up for myopathy. Muscle biopsy is diagnostic with rimmed cytoplasmic vacuoles and cytoplasmic and nuclear inclusions. Reference: Kegan L. Inclusion body myositis. In: Kagen L, editor. The inflammatory myopathies. New York: Humana Press;2009. p 279-294.

78. A 55-year-old man presents with a 2-month history of progress ive weakness. On examination he has mild proximal weakness in the upper and lower limbs. His muscle tone and bulk are normal and he has no facial weakness. Sensation is normal and deep tendon reflexes are 1+ and symmetrical. Which finding on electrodiagnostic testing is most consistent with this patient's presentation? (a) Prolonged or absent F waves (b) Decreased recruitment ratio (c) Motor unit potentials with amplitudes of 10 millivol ts (d) Normal number of phases of the motor unit potentials

78. (b) The clinical presentation is most consistent with a myopathic picture. In myopathies the recruitment ratio is usually lower (<5). An increased recruitment ratio and large motor unit amplitude potentials are associated with a neurogenic process. The number of phases of the motor units is usually increased in myopathy and in different forms and stages of neuropathies. F waves are typically prolonged or absent in neuropathies, but not in myopathies.

48. A 22-year-old woman with complaints of fluctuating weakness and abnormal fatigability that improves with rest is sent for electrophysiologic testing. Which electrophysiologic finding on routine testing would be most consistent with this clinical presentation? (a) Small sensory nerve action potentials (b) Slow motor nerve conduction velocities (c) Variability in motor unit action potential amplitude (d) Small compound muscle action potentials

48 Answer: C Commentary: This patient's presentation is most consistent with myasthenia gravis. The incidence of this condition is bimodal and affects women more than men in the younger age group. When one suspects myasthenia gravis the test of choice is repetitive stimulation. However, it is still important to assess for other possible problems and routine nerve conduction and needle electromyographic examination should be performed. The sensory component of the peripheral nervous system lacks a neuromuscular junction and hence the sensory responses should be normal. Motor amplitudes can be small, but this is usually only in severe cases. Motor conduction velocities are normal, since this study assesses the conduction along the motor fibers. Motor unit action potential amplitude variability is a characteristic abnormality observed during routine electromyography in patients with neuromuscular junction disorders. This finding is due to the variability in the total number of single muscle fibers being activated at any single time. Ref: Dumitru D, Amato AA. Neuromuscular junction disorders. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2002.p 1149-50, 1153-4.

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48. What is the total duration of the motor uni t action potential shown above? (a) 8 ms (b) 12 ms (c) 18 ms (d) 22 ms" 48. (c) The total duration of a motor unit is measured from the initial deflection from baseline to the final return to baseline. Ref: Wiechers DO. Normal and abnormal motor unit potentials. In: Johnson EW, editor. Practical electromyography. 2nd ed. Baltimore: Lippincott Williams & Wilkins; 1988. p 28-9.

58. In a patient with a neuromuscular junction disorder, wh ic h e lectrodiagnostic results for compound muscle action potential (CMAP), motor unit action potential (MUAP) or nerve action potential (SNAP) may be misleading if the limb is cold? (a) Diminished CMAP decrement on repetitive nerve stimul ati on (b) Diminished polyphasia of the MUAP (c) Shortened distal latency of the CMAP (d) Decreased amplitude of the SNAP

58 Answer (a) Commentary: In neuromuscular junction (NMJ) disorders, c omp ou nd muscle action potential (CMAP) decrement may be diminished if the limb is cold, likely due to decreased functioning of acetylcholinesterase. Cool temperatures may alter results by slowing nerve conduction velocity, prolonging distal latency, increasing amplitude and duration of sensory nerve action potential (SNAP) and CMAP and motor unit action potential (MUAP), increasing phases of MUAP. Reference: Preston DC, Shapiro BE. In: Preston DC, Shap iro B E, editors. Electromyography and neuromuscular disorders, 2nd ed. Philadelphia: Butterworth-Heinemann; 2005. p 71, 87-9.

6 A 48-year-old man is undergoing rehabilitation after a heart transplant. His resting heart rate is consistently between 90 and 110 beats/minute. What is the most likely explanation for this? a) Prolonged bed rest post-operatively b) Low ejection fraction c) Denervation of the donor heart d) Anemia of chronic disease

6 Reference(s) Zafonte D, Pippin B, Munin M, Thai N. Transplantation medicine: a rehabilitation perspective. In: DeLisa JA, Gans BM, Walsh NE, editors. Physic al medicine and rehabilitation: principles and practice. 5th e Philadelphia: Lippincott Williams & Wilkins; 2010. p 1217-19. Option c is correct. Cardiac transplantation involves removing the diseased heart and leaving an atrial cuff which results in complete denervation of the donor heart, with loss of both afferent and efferent nerve conn ections. The do nor heart will not respond to vagolytic muscle relaxants, anticholinergics, anticholinesterases, digoxin, nifedipine or nitroprusside. The resting heart rate of a denervated heart varies between 90 and 110 beats/minute due to loss of vagal tone, leading to a small resting stoke volume.

62 Which finding is frequently associated with sensory neuronopathies? a) Symmetric onset b) Rheumatoid arthritis c) Paraneoplastic syndrome d) Impaired mobility secondary to weakness

62 Reference(s) Martinez A, et al. Sensory neuronopathy and autoimmune disease. Autoimmune Diseases 2012;1-6. Option c is correct. Sensory neuronopathies are uncommon and affect large sensory fibers. The onset is typically asymmetric and gait abnormalities are secondary to impaired prop rioception as opposed to weakness. T he d ifferential d ia gnoses inc lude paraneoplastic syndrome, toxins and Sjögren's syndrome but not rheumatoid arthritis.

64. A middle-aged man is evaluated 1 week after the onset of painless foot drop. On exam, 1/5 strength of ankle dorsiflexion and eversion is present. Electrodiagnostic testing demonstrates a 90% loss in the compound muscle action potential amplitude of the anterior tibialis without conduction block across the fibular head. Markedly reduced motor unit recruitment is present in the anterior tibialis. Of the following, the most appropriate recommendation is (a) observation and a temporary ankle-foot orthosis, as the prognosis is excellent. (b) a custom-molded ankle-foot orthosis with dorsiflexion assist. (c) functional electrical simulation of the anterior tibialis to facilitate recovery. (d) magnetic resonance imaging of the brain to rule out a lacunar stroke.

64 (b) The clinical features and electrodiagnostic studies are consistent with a peroneal neuropathy. The reduction in compound muscle action potential amplitude is indicative of significant axonal loss. In this situation, recovery is likely to be delayed and incomplete. The use of an ankle-foot orthosis to supply medial lateral stability and ankle dorsiflexion is appropriate. Functional electrical stimulation has not been shown to alter outcome after nerve injury.

8. Which radial innervated muscle is innervated by the C5 root? (a) Anconeus (b) Extensor carpi radialis longus (c) Brachioradialis (d) Triceps

8 (c) None of the other muscles listed receives C5 innervation. The supinator is the only other radial innervated muscle that has C5 innervation.

65 Positive sharp waves and fibrillation potentials are most likely to be seen in which condition? a) Anterior horn cell disease b) Steroid myopathy c) Small fiber neuropathy d) Cerebellar ischemia

65 Reference(s) Dumitru D, Zwarts MJ. Needle electromyography. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic med icine. 2nd e Philadelphia: Hanley & Belf us; 2002. p 2 74 -276 Option a is correct. Positive sharp waves (PSWs) and fibrillation potentials are seen in certain disorders of the muscles, neurogenic disease, and neuromuscular disorders. These may include but are not limited to infl ammatory myos it is, inclus ion b ody myositis, rhabdomyolysis, anterior horn cell disorders, radiculopathies, plexopathies, peripheral neuropathies, myasthenia gravis, and botulism. Steroid myopathy does not result in muscle necrosis and thus abnormal spontaneous activity is not observe Fibrillation potentials and PSWs are not characteristic for central nervous system pathology. Small fiber neuropathies will be undetected on needle EMG. Option b is correct.Interstitial lung disease occurs in up to 65% of patients with myositis and is a significant contributor to morbidity and mortality. Pat ients with myositis have further pul mona ry complicati on s with res pect to muscle weakness and vascular disease resulting in secondary complications of aspiration pneumonia, infection, respiratory muscle failure, pulmonary edema and pulmonary arterial hypertension. Spontaneous pn.

68. What is the earliest electrophysiologic abnormality seen in generalized myasthe nia gr avi s? (a) Increased jitter on single fiber electromyography of the extensor digitorum com muni s. (b) Blocking on single fiber electromyography of the extensor digitorum communis. (c) A 10% decrement of compound motor action potential (CMAP) amplitude with 2-3Hz repe ti tiv e s tim ulati on, rec ordin g f rom the abd uct or dig iti m inimi. (d) A 10% decrement of CMAP amplitude with 2-3Hz repetitive stimulation, recording from t he fro nta lis.

68 (a) Increased jitter on single-fiber electromyography is the earliest abnormality seen in myasthenia gravis. The other abnormalities noted are seen later in th e di sease pr ocess .

68. The number of phases of a motor unit is related to the (a) conduction time through collateral nerve sprouts. (b) sweep speed setting on the oscilloscope screen. (c) sensitivity (gain) setting on the oscilloscope screen. (d) central conduction time and the state of the upper motor neuron.

68 (a) The number of phases of the motor unit potential represents the synchronization of firing of the individual muscle fibers in a motor unit and is related to conduction time through collateral sprouts of the nerve. The number of phases is increased under conditions in which some sprouts are poorly myelinated and conduction is slow and less synchronous. The other factors do not affect the number of phases of a motor unit potential.

68. Which technique may redu ce s timul us artifa ct when performing sensory nerve conduction studies?(a) Increasing the impedance of the r eco rding electrodes(b) Increasing the stimulus dura tion(c) Rotating the anode aroun d th e cat hod e(d) Decreasing the low frequ ency filt er

68. (c) Rotating the anode around the cathode can decrease stimulus artifact. The other choices have no effect, or increase it.

78. During the electromyographic evaluation of a patient, you note discharges consistent with myotonia and small motor units in the distal muscles of the upper and lower extremities. The most likely diagnosis is (a) paramyotonia congenita. (b) myotonic dystrophy. (c) myotonia congenita. (d) hyperkalemic periodic paralysis.

78 (b) Although myotonic discharges may be seen in all of these disorders, myotonic dystrophy is the only one with low-amplitude motor units in the distal muscles.

78. Which compound muscle action potential (CMAP) finding is the mos t compati ble with myast hen ia gravis? (a) A 15% decrement in the amplitude between the 1st and 4th respons es with r epetitive stim ula tion at 3 hertz (b) A low amplitude response with supramaximal stimulation of the ul nar nerve and pick up o ver the hypothenar muscles (c) A 100% increase in the amplitude with stimulation of the spinal accessory nerve an d pic k-u p over the trapezius muscle immediately post exercise (d) A 50% increment in the amplitude between the 1st and 4th respons es with r epetitive stim ula tion at 30 hertz

78. (a) In myasthenia gravis there is a decrement in the amplitude and area of the compound muscle action potential (CMAP) with stimulation at low frequencies (2-3Hz). Stimulation at high rates of 20- 50Hz can result in pseudofacilitation with correction of the amplitude decrement in normal subjects as well as patients with neuromuscular junction disorders. A 100% or greater increase in the amplitude of the post exercise CMAP is usually associated with a presynaptic neuromuscular junction disorder such as Lambert-Eaton myasthenic syndrome (LEMS). Small CMAPs on routine nerve conduction studies are more characteristic of LEMS than of myasthenia gravis.

78. While recording an antidromic sensory nerv e a ct ion potential, you increase the distance between the active and reference electrode from 1cm to 4cm by moving the reference electrode. What is the effect on the onset latency and peak latency? Onset Latency Peak Latency (a) No change Increase (b) Increase No change (c) Decrease Decrease (d) Increase Increase

78. (a) Increasing the interelectrode distance from 1 cm to 4 cm does not alter the onset latency, but increases the peak latency and amplitude of the sensory response. The onset latency does not change because the active electrode position is not changed. The sensory nerve action potential amplitude increases because less of the information is eliminated by differential amplification. Similarly, the peak latency also is prolonged as less of the signal is eliminated. Ref: Dumitru D, Zwarts MJ. Instrumentation. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 73.

8. One advantage of a concentric needle compared to a monopolar needle is its (a) higher amplitude of motor unit action potentials(MUAPS). (b) decreased likelihood of electrical interference. (c) ability to vary the recording surface size. (d) longer duration of the MUAPs.

8 Answer: (b) Commentary: The shaft of a concentric needle serves as the reference electrode, whereas an additional electrode (typically a surface electrode) is needed as a reference when using a monopolar needle. MUAPs recorded from monopolar needles are slightly longer in duration and have higher amplitude, since they record from the entire area around the needle tip rather than only from the fibers facing the bevel. Because the concentric needle shaft serves as the reference electrode, the recording surface size is fixed and interference from surrounding muscles is minimized. Reference: (a) Daube JR, Rubin DI. AANEM Monograph #11: needle electromyography. Muscle Nerve. 2009;39:249. (b) Preston DC, Shapiro BE. basic overview of electromyography. In: Preston DC, Shapiro BE, editors. Electromyography and neuromuscular disorders. 2nd ed. Philadelphia: Butterworth-Heinemann; 2005. p 164.

8. Which safety practice is the most appropriate when performing an electrodiagnostic study on a patient in a hospital bed? (a) The device should be turned on after the placement of electrodes on the patient. (b) An insulated extension cord should be used to connect the power line. (c) More than 1 ground electrode should be attached to the patient. (d) All electrical devices in contact with the patient should share a common ground.

8 Answer: (d) Commentary: It is important to have all the electrical devices that are in contact with the patient plugged into the same outlet to share a common ground. Similarly, only 1 ground electrode should be used on the patient. To avoid power surges, the device should be turned on prior to the application of any electrodes to the patient and turned off after the removal of electrodes. Extension cords can increase leakage currents and should be avoided. Ref: Dumitru D, Zwarts MJ. Instrumentation. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 956.

8. Which hypothesis does NOT explain a normal electromyograph (EMG) in a patient who has a lumbar radiculopathy? (a) Involvement of only the sensory root (b) Limited sampling of musc les (c) Oxycodone taken prior to the stud y (d) Timing of the study

8. (c) Pain medication has no effect on EMG findings. All the other choices can be an explanation for a normal EMG in a patient who has a lumbar radiculopathy.

8. Which statement is TRUE about volume conduction as it relates to electroph ysiologic stud ies ? (a) Volume conduction is the transmission of an electrical potential through intracell ular tis sue. (b) Volume conducted potentials produce a biphasic waveform as an ad vancing a ction pot entia l a pproaches and then passes beneath a recording electrode. (c) The negative peak of a recorded waveform represents the time tha t the act ion poten tial is beneath the active electrode. (d) Volume conducted near field potential amplitudes does not charac teristica lly depen d on the distance between the recording electrode and the source.

8. (c) The characteristics of volume conducted near field responses are dependent on the distance from the recording electrode and the electrical source. The responses represent intracellular events transmitted through extracellular fluid and tissue. They usually produce a triphasic waveform and the negative phase is that time during which the advancing wave is directly underneath the recording electrode.

87 Which approach is shown to be efficacious in treating carpal tunnel syndrome? (a) Oral corticosteroids (b) Exercise therapy (c) Vitamin B6 (d) Botulinum toxin injection

87 Answer: (a) Commentary: Of the choices listed, only oral steroids have been shown to be efficacious in the treatment of carpal tunnel syndrome. In addition to oral steroids, local injection of corticosteroids and wrist splint are shown to be effective. Exercise therapy and botulinum toxin are ineffective in the treatment of carpal tunnel syndrome. Ref: Piazzini DB, Aprile I, Ferrara PE, Bertolini C, Tonali P, Maggi L, et al. A systematic review of conservative treatment of carpal tunnel syndrome. Clin Rehabil 2007;21;299.

88. Dorsal ulnar cutaneous nerve conduction studies are most useful in differentiating (a) ulnar neuropathy at the elbow from lower trunk plexopathy. (b) ulnar neuropathy at the elbow from ulnar neuropathy at the wrist. (c) lower trunk plexopathy from medial cord plexopathy. (d) ulnar neuropathy at the cubital tunnel from ulnar neuropathy at the ulnar groove.

88 (b) The fibers of the dorsal ulnar cutaneous nerve travel in the lower trunk and the medial cord of the brachial plexus. This nerve travels with the ulnar nerve to the forearm, where it branches off proximal to the wrist and supplies sensation to the ulnar aspect of the dorsum of the hand and wrist. The dorsal ulnar cutaneous sensory nerve action potential amplitude could be decreased with a lesion of the lower trunk, the medial cord, or the ulnar nerve at the elbow or proximal forearm, and would not be useful in differentiating among them. It should be normal in ulnar neuropathy at the wrist.

88. Which potentials have manifestations that CANNOT be observed on physical examin atio n? (a) Fasciculation potentials (b) Myokymic discharges (c) Complex repetitive discharges (d) Cramp potentials

88 (c) Complex repetitive discharges can only be detected with electromyography. The remainder of the discharges have manifestations that can be observed on ph ysi cal exami nat ion.

88. Which filter setting is usually considered to be appropriate for routine n eedle el ectromyo graph y? Low frequency High frequency (a) 2-10Hz 10,000Hz (b) 2-10Hz 2,000Hz (c) 20-30Hz 10,000Hz (d) 20-30Hz 2,000Hz

88 (c) There is no universally accepted guideline for filter settin gs. However, based on clinical experience certain ranges have been determined and are recom mended. Ea ch proc edure has particular filter settings, which are based on optimum fr eq uency content o f mean wave forms rou tinely observed. The re com men de d f ilt er s et ti ng for rout ine ne edl e el ectr omy ogr aph y is 20 -30 he rt z fo r t he low f ilt er an d 10k ilo hertz fo r the high filter.

88 Which electrodiagnostic criterion is included in the diagnosis of peripheral nerve demyelination? (a) Conduction velocity reduced in at least 4 nerves (b) Compound muscle action potential conduction block in at least 3 nerves (c) Prolonged distal motor latencies in at least 4 nerves (d) Prolonged F-wave latency or absent F wave

88 Answer: D Commentary: The criteria require conduction velocity to be reduced in 2 or more nerves, compound muscle action potential conduction block or abnormal temporal dispersion in 1 or more nerves, prolonged distal motor latencies in 2 or more nerves, and prolonged F wave or absent F wave. Three of these four criteria must be present. Ref: Amato AA, Dumitru D. Acquired neuropathies. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 940.

88. Regarding the electrodia gnos tic t est ing of a patient with definite myasthenia gravis, which statement is TRUE?(a) An increment on repetiti ve s timul ati on at 1Hz of up to 25% is expected. (b) A stimulation rate of 2- 3Hz is mo st useful in demonstrating a decrement. (c) An initial low amplitude com pound mo tor ac tion potential after a supramaximal stimulus is expected. (d) Motor unit variability i s re flect ed by dec reased jitter during single fiber EMG.

88. (b) A 2 to 3Hz stimulation is optimal for demonstrating a decremental response. At this rate there is no build up of Ca++ concentration within the nerve terminal and the amount of acetylcholine in the readily available stores diminishes, making failure of some of the neuromuscular junctions possible in those patients with an already small safety factor. A decrement of up to 10% on 2 to 3Hz repetitive stimulation is considered normal. Small CMAPs initially are more suggestive of myasthenic (Lambert-Eaton) syndrome than of myasthenia gravis. Single fiber EMG reveals increased jitter and may reveal blocking.

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88. Which filter setting is usually considered appropriate for rou tine sens ory nerve cond uct ion studies? LOW-FREQUENCY FILTER HIGH-FREQUENCY FILTER (a) 2-10Hz 10,000Hz (b) 2-10Hz 2,000Hz (c) 20-30Hz 10,000Hz (d) 20-30Hz 2,000Hz" 88 (b) There is no universally accepted guideline for filter settings. However, based on clinical experience, certain ranges have been determined and are recommended. Each procedure has particular filter settings based on the optimum frequency content of the mean waveforms that are routinely observed. The recommended filter setting for routine sensory nerve conduction studies is 2-10Hz for the low-frequency filter and 2,000Hz for the high-frequency filter.

98. Which statement regarding myotonic discharges is TRUE? (a) They are variable in frequency. (b) They have a constant amplitude. (c) They arise from the anterior horn cell. (d) They are rarely seen without clinical myotonia.

98 (a) Myotonic discharges consist of repetitive waveforms of similar configuration which wax and wane in their frequency and amplitude.

98. The potentials shown in this grap h a re(a) fibrillations. (b) myopathic motor units. (c) end plate spikes. (d) complex repetitive disch arge s.

98. (c) The duration of these potentials is approximately 5ms, too short for a motor unit. The initial deflection is negative, distinguishing this potential as an end plate spike rather than a fibrillation.

"41.

A 26-year-old mail handler is sent to you for management of her severe sen sorimoto r carpal tunn el sy ndrom e co nfirm ed by e le ctrod iagno st ic eva lu ation. Sh e w as gi ven a splint for her presumed carpal tunnel syndrome 3 months ago, which she has worn 24 hours a day since that time without relief. She notes severe tingling in her fingers that is worse at night, and she also notes difficulty with gripping the mail, because of subjective weakness. She is now having severe pain, which radiates up her hand into her forearm. You consider that a corticosteroid injection might benefit this patient. Which statement is most correct regarding this injection? (a) The risk of intraneural injection is too high, and the patient should not be injected be injec ted. (b) So that intraneural injection can clearly be recognized, do not dilute the cortico steroid with anesthetics. cortico steroid with ane st hetic s. (c) Persisting or worsening pain and numbness or swelling normally last for more than 48 hours post injectin. re than 48 hours post inj ec tion. (d) Local tenderness and superficial hematomas are rare after this injection." 41 (b) The risk of intraneural injection is real, but in experience d hands this injection is safe. Anesthetics mixed with the corticosteroid can mask the pain associate d with needle placement into the nerve and should not be used. Numbness is a nticip ated with this i njec tion w ith out use of anesthetics, an d h el ps to conf ir m proper plac emen t. Lo ca l tend ern ess an d hem at omas a re com mon wi th th is in jec tion and do not r epresent a complication. Persistent or worsening pain or swelling lasting more than 48 hours are signs of nerve injection or neurotoxic injury.

"128.

A 33-year-old woman who had a prolonged labor 6 weeks ago, reports pain in the groin radiating along the medial aspect of the thigh. Needle electromyographic exam shows evidence of denervation in the gracilis and adductor muscles. Most likely she has a lesion in the (a) femoral nerve. (b) obturator nerve. (c) sciatic nerve. (d) genitofemoral nerve. " 128 Answer: (b) Commentary: The nerve common to the affected muscles is the obturator nerve. There is some innervation of the adductor magnus by a branch off the sciatic nerve, but the gracilis, adductor brevis, and adductor longus are supplied by the obturator nerve. Injuries of the obturator nerve are uncommon, but one cause in such cases is compression of the nerve between the fetal head and the pelvic wall during prolonged labor. Reference: (1) Dumitru D, Zwarts MJ. Lumbosacral plexopathies and proximal mononeuropathies. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 844, 847, 870-1. (2) Stewart JD. Chapter 20: Obturator nerve. In: Stewart JD. Focal Peripheral Neuropathies. 3rd ed. Montreal, Canada: Lippincott Williams & Wilkins; 2000. p 483-7.

"28.

Electrophysiologic findings of compound muscle action potential conduction block a nd tempo ral d isp er sion, pro longe d minim um F-wa ve la te ncy , a nd reduc ed con duc ti on velocity would most likely be seen in (a) Charcot-Marie-Tooth disease. (b) myasthenic syndrome. (c) Guillain-Barré syndrome. (d) amyloidosis." 28 (c) All the findings mentioned are features associated with an a cquired demyelinating condition such as Guillain-Barré syndrome or acute inflammatory demye linating p olyradi culoneuropathy (AIDP). Hereditary motor sensory neuropathies do not u sually have tem poral d ispe rsion of compoun d muscle action pot ent ia ls. My asth en ic syndro me i s a ne uro mu sc ular ju nct ion diso rd er a nd a mylo ido sis is a sso ci ate d wit h a form of axonal peripheral neuropathy.

"38.

Which description best localizes the extensor indic is propri us m uscle (with the forearm fully pronated) for needle electrode examination? (a) Junction of the upper and middle third of the forear m between the radius and ulna (b) Four fingerbreadths proximal to the wrist and direct ly over t he u lnar side of the radius (c) Two fingerbreadths proximal to the ulnar styloid and just rad ial to the ulna (d) Mid-forearm along the radial border of the ulna" 38. (c) Answer (a) describes the location of the extensor digitorum communis muscle; answer (b) describes the location of the extensor pollicis brevis muscle; and answer (d) describes the location of the extensor pollicis longus.

"178. The potential above is (a) a fibrillation. (b) an end plate spike. (c) a voluntary motor unit. (d)

a fasciculation." 178 (d) The potential is of a duration consistent with a motor unit and fires only once over a 500-ms period. The firing rate would be inconsistent with a volu ntary moto r unit but is typical of a fasciculation. The amplitude and duration of th e potent ial would also p recl ude an en d plate spike or fibril lat ion p ote nti al. Fu rt hermore , a fibr il lat io n pote nti al wou ld ha ve an in it ial pos iti ve de fle ct ion .

"38. In patients with steroid myopathy, the needle electromyographic study usually reveals (a) small motor unit action potentials (MUAPs) with early recruitment. (b) small MUAPs with reduced recruitment. (c) positive waves and fibrillation potentials in proximal muscles. (d)

normal MUAPs and normal recruitment. " 38 Answer: (d) Commentary: Needle examination in patients with steroid myopathy usually reveals normal insertional activity and no abnormal spontaneous activity. Motor unit potential morphology and recruitment do not reveal any abnormalities. This combination occurs because in steroid myopathy the type 2 muscle fibers are preferentially affected, in contrast to the first-recruited type 1 fibers. Reference: Dumitru D, Amato AA. Acquired myopathies. In: Dumitru D, Amato AA, Zwarts MJ, editors. Electrodiagnostic medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2002. p 1397-8.