Board Review Neuromuscular

Board Review Neuromuscular
Laura Donovan

Question 1 Which of the following is incorrect regarding electrophysiologic studies of the peripheral nervous system? SNAP amplitude is a measure of the number of axons that conduct between the stimulation and recording sites Sensory distal latency is the time it takes for the action potential to travel between the nerve stimulation site and the recording site. Action loss lesions result in reduced conduction velocities CMAP amplitude depends on the status of the motor axons, NMJ, and muscle fibers The F-wave and H-reflex are late responses

Answer 1 SNAP amplitude is a measure of the number of axons that conduct between the stimulation and recording sites Sensory distal latency is the time it takes for the action potential to travel between the nerve stimulation site and the recording site. Action loss lesions result in reduced conduction velocities CMAP amplitude depends on the status of the motor axons, NMJ, and muscle fibers The F-wave and H-reflex are late responses

Question 2 Which of the following is incorrect regarding electrophysiologic studies of the peripheral nervous system? CMAP amplitudes may be reduced in axon loss lesions Prolonged distal latency is seen in demyelinating lesions The H-reflex is the electrophysiologic equivalent of the ankle reflex The H-reflex is obtained by stimulating the tibial nerve The F-wave is obtained after submaximal stimulation of a motor nerve

Answer 2 Which of the following is incorrect regarding electrophysiologic studies of the peripheral nervous system? CMAP amplitudes may be reduced in axon loss lesions Prolonged distal latency is seen in demyelinating lesions The H-reflex is the electrophysiologic equivalent of the ankle reflex The H-reflex is obtained by stimulating the tibial nerve The F-wave is obtained after submaximal stimulation of a motor nerve

Sensory Nerve Conduction studies
SNAP – sensory nerve action potential Stimulate sensor nerve Record at a site along the nerve Amplitude Size of response – corresponds to number of axons between the stimulating and recording site Duration Distal Latency – time for AP to travel from stimulating to recording site Conduction velocity -

Motor Nerve conduction studies
CMAP – combined motor action potential Stimulate motor nerve Record at a muscle innervated by that nerve Amplitude Depends on axons, NMJ, and muscle fibers Duration Distal Latency Conduction velocity

Axonal vs. Demyelinating lesions
Amplitudes Decreased Normal Distal latency Prolonged Conduction velocity Slow

Question 3 Regarding needle EMG, which of the following is incorrect?
Insertional activity is increased in denervated muscles Fibrillation and fasciculation potentials are examples of spontaneous activity Short-duration motor unit potentials (MUPs) are seen more frequently in myopathic processes Long, polyphasic MUPs are seen in acute neuropathic lesions Reduced recruitment is seen in axon loss lesions.

Answer 3 Regarding needle EMG, which of the following is incorrect?
Insertional activity is increased in denervated muscles Fibrillation and fasciculation potentials are examples of spontaneous activity Short-duration motor unit potentials (MUPs) are seen more frequently in myopathic processes Long, polyphasic MUPs are seen in acute neuropathic lesions Reduced recruitment is seen in axon loss lesions.

Question 4 Which of the following is incorrect regarding the evaluation of a radiculopathy associated with an axon loss intraspinal canal lesion? Fibrillation potentials can be seen in a segmental myotome 3 weeks after the onset There are abnormal sensory SNAPs in a segmental dermatome Reinnervation or collateral innervation occurs in a proximal to distal gradient The H-reflex tests the S1 reflex arc and is helpful in the diagnosis of an S1 radiculopathy Large polyphasic motor unit potentials can be detected in chronic radiculopathies

Answer 4 Which of the following is incorrect regarding the evaluation of a radiculopathy associated with an axon loss intraspinal canal lesion? Fibrillation potentials can be seen in a segmental myotome 3 weeks after the onset There are abnormal sensory SNAPs in a segmental dermatome Reinnervation or collateral innervation occurs in a proximal to distal gradient The H-reflex tests the S1 reflex arc and is helpful in the diagnosis of an S1 radiculopathy Large polyphasic motor unit potentials can be detected in chronic radiculopathies

EMG Motor unit potentials (MUPs)
Obtained during voluntary contraction of the muscle Conformation: Polyphasic indicates RENERVATION Amplitude Duration Spontaneous activity – ALWAYS ABNORMAL Fibrillations – regular potentials of chronically denervated muscle fibers Fasiculations – irregular, represent irritation of the motor nerve at any point Myokymia, myotonic discharges, complex repetitive discharges Recruitment – number of muscle fibers firing during maximal voluntary contraction

EMG Myopathic vs. Neuropathic changes
Neuropathic – acute Neuropathic – Chronic MUP Amplitude Decreased Normal Increased Rate of firing (duration) Reduced Insertional activity Absent/increased Spontaneous activity Present Absent Present – fibs, PSWs Recruitment Occurs early, excessive **Polyphasic morphology can be seen with either – Small polyphasic MUPs in myopathic processes; large polyphasic MUPs in neuropathic processes

Question 5 A patient presents for evaluation of several months of weakness in the upper extremities. NCS and EMG were unremarkable. With rapid repetitive stimulation and evaluation after exercise, there was no increase in CMAP amplitude. Slow rep stim was obtained and is shown below. What is the most likely diagnosis? A myopathy A demyelinating neuropathy An axon loss neuropathy Myasthenia gravis Botulism

Answer 5 A patient presents for evaluation of several months of weakness in the upper extremities. NCS and EMG were unremarkable. With rapid repetitive stimulation and evaluation after exercise, there was no increase in CMAP amplitude. Slow rep stim was obtained and is shown below. What is the most likely diagnosis? A myopathy A demyelinating neuropathy An axon loss neuropathy Myasthenia gravis Botulism

Question 6 A patient is referred for an EMG/NCS for a possible diagnosis of a NMJ disorder. Which of the following is correct? CMAP increment after rapid repetitive stimulation is a feature of myasthenia gravis CMAP increment after a brief exercise is a feature of myasthenia gravis A decrement in the CMAP after 2-3Hz rep stim is consistent with myasthenia gravis Abnormal jitter on a single-fiber EMG is a very specific finding for the diagnosis of myasthenia Sensory NCS are typically abnormal in MG

Answer 6 A patient is referred for an EMG/NCS for a possible diagnosis of a NMJ disorder. Which of the following is correct? CMAP increment after rapid repetitive stimulation is a feature of myasthenia gravis CMAP increment after a brief exercise is a feature of myasthenia gravis A decrement in the CMAP after 2-3Hz rep stim is consistent with myasthenia gravis Abnormal jitter on a single-fiber EMG is a very specific finding for the diagnosis of myasthenia Sensory NCS are typically abnormal in MG

Question 7 A patient with lung cancer is being referred for evaluation of Lamber Eaton Myasthenic Syndrome (LEMS). Which of the following is incorrect? Needle EMG is usually normal in LEMS Low to borderline-low CMAP amplitudes at rest are common in LEMS Slow rep stim (2-3Hz) results in a decremental response of the CMAP amplitudes Fast rep stim (20-50Hz) results in an incremental response of the CMAP amplitudes Voluntary single fiber jitter analysis helps to distinguish MG from LEMS

Answer 7 A patient with lung cancer is being referred for evaluation of Lamber Eaton Myasthenic Syndrome (LEMS). Which of the following is incorrect? Needle EMG is usually normal in LEMS Low to borderline-low CMAP amplitudes at rest are common in LEMS Slow rep stim (2-3Hz) results in a decremental response of the CMAP amplitudes Fast rep stim (20-50Hz) results in an incremental response of the CMAP amplitudes Voluntary single fiber jitter analysis helps to distinguish MG from LEMS

NMJ disorders Decrement Facilitation Jitter on SF-EMG
Decrement with slow rep stim Yes NMJ disorder Increment with fast rep stim (20-50Hz) Yes: Presynaptic disorder No: Post-synaptic disorder Decrement Facilitation Jitter on SF-EMG

Myasthenia LEMS Location Post-synaptic Pre-synaptic Antibody Acetylcholine receptor** VG Calcium channels Paraneoplastic Thymoma SCLC NCS Normal CMAP Normal/low normal Slow rep stim Decrement Fast rep stim No change Increment Jitter on sfEMG Present

Question 8 Which of the following is incorrect regarding an axon loss peripheral nerve injury? Fibrillation potentials appear by the 3rd week of the injury Conduction block 10 days after the injury suggests segmental demyelination The presence of conduction block can help localize the site of segmental demyelination NCS 3 weeks after the injury are useful to localize a focal axon loss lesion Axon loss leads to Wallerian degeneration

Answer 8 Which of the following is incorrect regarding an axon loss peripheral nerve injury? Fibrillation potentials appear by the 3rd week of the injury Conduction block 10 days after the injury suggests segmental demyelination The presence of conduction block can help localize the site of segmental demyelination NCS 3 weeks after the injury are useful to localize a focal axon loss lesion Axon loss leads to Wallerian degeneration

Question 9 A 62 year old retired secretary presents to the clinic complaining of a painful tingling sensation and numbness in her left thumb, index, and middle finger that wake her up at night. On exam, motor power of her left arm, forearm and hand is normal. There is subtle loss of pinprick and LT on the distal first to third digits at the finger tips. Biceps and brachioradialis DTRs are normal. A tracing from her median nerve sensory NCS is shown below (normal SNAP latency is 4.0 ms); motor NCS and EMG are normal. What is the most likely diagnosis? C6 Radiculopathy C7 radiculopathy Carpal tunnel syndrome Median neuropathy at the elbow Brachial plexopathy

Answer 9 A 62 year old retired secretary presents to the clinic complaining of a painful tingling sensation and numbness in her left thumb, index, and middle finger that wake her up at night. On exam, motor power of her left arm, forearm and hand is normal. There is subtle loss of pinprick and LT on the distal first to third digits at the finger tips. Biceps and brachioradialis DTRs are normal. A tracing from her median nerve sensory NCS is shown below (normal SNAP latency is 4.0 ms); motor NCS and EMG are normal. What is the most likely diagnosis? C6 Radiculopathy C7 radiculopathy Carpal tunnel syndrome Median neuropathy at the elbow Brachial plexopathy

Pearl: IN RADICULOPATHY, THERE ARE NORMAL SNAPS

Brachial plexus! 5 roots (C5-T1) 3 trunks (upper, middle, lower)
C5 – Dorsal scapular nerve C5-7 - Long thoracic T1 - Sympathetic chain 3 trunks (upper, middle, lower) Upper trunk (C5-6): Suprascapular nerve, Subclavius 6 divisions (ant/posterior) 3 Cords (Lateral, posterior, medial) Lateral (C5, 6, 7) – Lateral pectoral nerve Posterior (C5, 6, 7, 8, T1) – Lower subscapular nerve, Upper subscapular nerve, thoracodorsal nerve Medial (C8, T1) – Medial antebrachial cutaneous, medial brachial cutaneous 5 nerves

Learn the Brachial Plexus in Five Minutes or Less
By Daniel S. Romm, M.D. Chief, Physical Medicine and Rehabilitation Department of Veterans Affairs, Biloxi, Mississippi and Dennis A. Chu, M.D. This material is the result of work supported with resources and the use of facilities at the VA Gulf Coast Veterans Health Care System.This material reflects the authors’ personal views and in no way represents the official view of the Department of Veterans Affairs of the U.S. Government.

Draw two headless arrows to the right.

Add a headless arrow to the left.

Add a “W”.

Add an “X”.

Add a “Y”. (Just a branch of the “Y” is added.)

Label C5 to T1.

Label the major branches:
MC = musculocutaneous, M = median U = ulnar R = radial AX = auxiliary

This diagram includes the main branches and main nerve roots with the proper connections.
Trunks Divisions Cords Nerves

More complex diagramming of the brachial plexus includes the four “3s
Neurosurgeons, neurologists, and physiatrists will use this diagram system.

The first “3” is the branches to C5, 6, and 7 which form LTN = long thoracic nerve.

Next, each of the headless arrows has three nerves attached to it
Next, each of the headless arrows has three nerves attached to it. To the top headless arrow, add its “3.”

Label these “3”: DSN = dorsoscapular nerve; SS = suprascapular nerve;
LP = lateral pectoral nerve.

Add the “3” to the middle headless arrow.

Label the second headless arrow “3”: SS = subscapular
TD = thoracodorsal nerve.

Add the final “3” on the bottom headless arrow.

Label the last “3.” MP = medial pectoral,
MBC = medial brachial cutaneous, and MABC = medial antebrachial cutaneous. Remember: the brachial cutaneous goes to the brachium or arm, and the MABC goes to the antebrachium or forearm. The nerve to the forearm starts distally.

Label roots, trunks, divisions, cords, terminal branches.

Radiologists, neurosurgeons and thoracic surgeons need to know the nerve to the subclavius (SUB).

The complete brachial plexus diagram:

Question 10 Regarding innervation of the upper extremity, which of the following is incorrect? The brachial plexus is formed from the anterior rami of the C5 to T1 nerve roots The middle trunk is formed from the C7 root The lower (inferior) trunk is formed from the C8 and T1 roots The Dorsal scapular nerve is the only nerve that branches directly off the nerve roots The cords of the brachial plexus are named according to their anatomic relationship to the axillary artery

Answer 10 Regarding innervation of the upper extremity, which of the following is incorrect? The brachial plexus is formed from the anterior rami of the C5 to T1 nerve roots The middle trunk is formed from the C7 root The lower (inferior) trunk is formed from the C8 and T1 roots The Dorsal scapular nerve is the only nerve that branches directly off the nerve roots The cords of the brachial plexus are named according to their anatomic relationship to the axillary artery

Question 11 Which of the following is correct regarding the median nerve? The median nerve arises solely as a continuation of the medial cord The median nerve carries C6-T1 fibers The median nerve innervates all forearm flexors The median nerve innervates all intrinsic hand muscles The median nerve innervates only forearm and hand muscles; it does not innervate any upper arm muscles

Answer 11 Which of the following is correct regarding the median nerve? The median nerve arises solely as a continuation of the medial cord The median nerve carries C6-T1 fibers The median nerve innervates all forearm flexors The median nerve innervates all intrinsic hand muscles The median nerve innervates only forearm and hand muscles; it does not innervate any upper arm muscles

Median Nerve Roots: C5-T1 Actions Branches
Forearm pronation Wrist flexion Branches AIN – 2nd/3rd finger flexion, thumb flexion, some pronation (pronator quadratus) Median sensory palmar cuntaneous Terminal motor: ABP, OP, 1st/2nd lumbricals Terminal sensory: Palmar survace of the thumb, 2nd/3rd finger and ½ of 4th finger Compression at Carpal Tunnel

Question 12 Regarding the ulnar nerve, which of the following is incorrect? It does not innervate any upper arm muscles It is a continuation of the lateral cord It is most susceptible to injury at the medial epicondyle It passes through Guyon’s canal to reach the hand It predominantly carries C8 and T1 fibers

Answer 12 Regarding the ulnar nerve, which of the following is incorrect? It does not innervate any upper arm muscles It is a continuation of the lateral cord It is most susceptible to injury at the medial epicondyle It passes through Guyon’s canal to reach the hand It predominantly carries C8 and T1 fibers

Ulnar nerve Roots: C7-T1 Actions: -wrist flexion and adduction
-Finger flexion 4th and 5th digits Branches Palmar cutaneous branch Pure motor after Gruyon’s canal Lumbricals (3rd/4th), Interossei, Thumb flexion (FPB) Compression: At elbow: weak wrist flexion, 4th/5th digit flexion At wrist: intrinsic hand muscles +/- sensory depending on location relative to canal

Question 13 A 40 year old man presents to the clinic complaining of left-hand weakness and significant loss of fine motor control in the left hand. On examination, he has atrophy of the intrinsic hand muscles, weakness of wrist flexion in an ulnar direction, flexion at the DIP of the fourth and fifth digits, and abduction and adduction of all the fingers. There is loss of sensation over the hypothenar eminence and the fourth and fifth digits, but not more proximally. Proximal arm muscle strength, forearm flexion and pronation, and flexion of the second and third digits at both the PIP and DIP joints are normal strength. Thumb abduction is mildly weak. On attempt to make a fist, there is hyperextension at the MCP joint of the 4th and 5th digits and flexion at the PIP, but not DIP joints. Ulnar nerve CMAPs are shown below. What is the most likely diagnosis?

Question 13 cont. C8 radiculopathy Ulnar neuropathy at the wrist
Medial cord lesion C7 radiculopathy Ulnar neuropathy at or above the elbow

Answer 13 C8 radiculopathy Ulnar neuropathy at the wrist
Medial cord lesion C7 radiculopathy Ulnar neuropathy at or above the elbow

Question 14 Which of the following is incorrect regarding the radial nerve? It is a continuation of the posterior cord It carries C5, C6, C7, and C8 fibers It innervates all three heads of the triceps muscle It provides sensory innervation to most of the posterolateral arm and forearm All of the forearm muscles innervated by the radial nerve are forearm extensors

Radial Nerve Roots: C6-C8 Actions: Branches
Forearm extension (triceps) Forearm flexion (brachioradialis) Wrist extension/abduction Supination Branches Above elbow: Posterior cutaneous nerve of the arm and forearm Lateral cutaneous nerve of the arm Below elbow: Superficial sensory nerve (dorsolateral hand, proximal 2/3 lateral thumb, proximal 2nd-3rd digits – distal is median nerve) Posterior interosseous nerve Wrist extension/adduction (ECU) Finger extension at MCP Thumb abduction in plane of palm (APL) Thumb extension (EPL) EIP – 2nd finger extension at MCP

Radial nerve compression
Above the spiral groove (Saturday night palsy) Triceps weakness At the spiral groove SPARES triceps Brachioradialis weakness, weakness in wrist/finger extension Sensory loss over dorsum of hand and thumb

Pearls Median and Ulnar nerves only innervate muscles in the forearm and hand Radial nerve innervates both upper arm, forearm, and hand

Question 15 A 52 year old truck driver since his teenage years presents with tingling in the 4th and 5th digits of his left hand. The tingling is mild, but annoying to him. On exam, there is reduced sensation to all modalities on the dorsal and palmer aspects of the 4th and 5th digits from the wrist crease to the finger tips with preserved strength in all muscle groups. Which of the following is correct? This man has carpal tunnel syndrome This man has an ulnar neuropathy at the elbow This man should be referred to a surgeon EMG is expected to show fibrillation potentials in the C6 and C7 myotomes Conservative management frequently fails in this disorder

Answer 15 A 52 year old truck driver since his teenage years presents with tingling in the 4th and 5th digits of his left hand. The tingling is mild, but annoying to him. On exam, there is reduced sensation to all modalities on the dorsal and palmer aspects of the 4th and 5th digits from the wrist crease to the finger tips with preserved strength in all muscle groups. Which of the following is correct? This man has carpal tunnel syndrome This man has an ulnar neuropathy at the elbow This man should be referred to a surgeon EMG is expected to show fibrillation potentials in the C6 and C7 myotomes Conservative management frequently fails in this disorder

Question 16 A 73 year old man with poorly controlled DM presents with complaints of painless weakness of extension of the fingers in the left hand. On exam, forearm extension and wrist extension and abduction are normal in strength, but wrist extension and adduction are weak. Forearm supination is weak, particularly when tested with the forearm extended, but there is no pain with active supination. Finger extension at the MCP joints is also weak, as is thumb abduction in the plane of the palm and thumb extension at the IP and MCP joints. Sensory exam is normal. On NCS, the superficial sensory radial nerve is normal. Triceps reflex is normal. What is the most likely diagnosis? Radial neuropathy at the spiral groove C7 radiculopathy Posterior interosseous nerve palsy Radial neuropathy at the elbow Supinator syndrome

Question 17 A 32 year old man is stabbed in the left antecubital fossa. He is stabilized in the ED. On follow up 8 weeks later, he denies any pain. His strength is 2/5 in forearm pronation, thumb opposition, flexion, and abduction, flexion at the DIP joint of the second digit and flexion at the PIP joint of the 2nd-5th digits. Wrist flexion is 4/5, but the hand deviates in an ulnar direction during flexion. Flexion at the DIP joint of the 4th and 5th digits is normal. Sensation is markedly reduced on the distal dorsal aspect of the first 3 digits and other lateral (radial) aspect of the palm and first three digits, as well as the lateral (radial aspect of the 4th digit. When asked to make a fist, the patient can barely flex the thumb, can partially flex the second digits, and has normal flexion of the 4-5th digits. What is the most likely diagnosis? Complete median nerve palsy at the level of the antecubital fossa Ischemic monomelia Anterior interosseous nerve syndrome A medial cord lesion A C7 radiculopathy

Answer 17 A 32 year old man is stabbed in the left antecubital fossa. He is stabilized in the ED. On follow up 8 weeks later, he denies any pain. His strength is 2/5 in forearm pronation, thumb opposition, flexion, and abduction, flexion at the DIP joint of the second digit and flexion at the PIP joint of the 2nd-5th digits. Wrist flexion is 4/5, but the hand deviates in an ulnar direction during flexion. Flexion at the DIP joint of the 4th and 5th digits is normal. Sensation is markedly reduced on the distal dorsal aspect of the first 3 digits and other lateral (radial) aspect of the palm and first three digits, as well as the lateral (radial aspect of the 4th digit. When asked to make a fist, the patient can barely flex the thumb, can partially flex the second digits, and has normal flexion of the 4-5th digits. What is the most likely diagnosis? Complete median nerve palsy at the level of the antecubital fossa Ischemic monomelia Anterior interosseous nerve syndrome A medial cord lesion A C7 radiculopathy

Question 18 A 52 year old woman presents to the clinic complaining of finger weakness in the right hand. She reports difficulty holding a teacup with the right hand using a pincer grasp. She denies any sensory symptoms. On exam of the right arm, there is weakness of flexion at the DIP joint of the 2-3rd digits, weakness of thumb flexion, and weakness of forearm pronation when forearm is fully flexed. Otherwise all other muscle groups are normal and there is no evidence of sensory loss. What is the most likely diagnosis? Complete median nerve palsy at the level of the antecubital fossa Ischemic monomelia Anterior interosseous nerve syndrome A medial cord lesion A C7 radiculopathy

Pearls Sounds like median nerve, but is MOTOR only
ANTERIOR INTEROSSEOUS NERVE Sounds like distal radial nerve, but is MOTOR only POSTERIOR INTEROSSEOUS NERVE

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