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ABPN Neuromuscular Medicine study materials
ABPN Neuromuscular Medicine study resources

ABPN Neuromuscular Medicine practice questions

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Question 1Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 28-year-old woman has fluctuating ptosis and diplopia worse in the evening. Which finding on repetitive nerve stimulation best supports a postsynaptic neuromuscular junction disorder?

  1. Normal compound muscle action potential amplitude with no decrement
  2. Increment of more than 100% after 10 seconds of exercise
  3. Decrement of more than 10% at 3 Hz stimulation Correct answer.
  4. Prolonged distal latency with normal decrement

Explanation

A decrement greater than 10% on low-frequency (2-3 Hz) repetitive stimulation reflects loss of postsynaptic acetylcholine receptors, as seen in myasthenia gravis. Low-frequency decrement is the classic electrophysiologic signature of postsynaptic junctional failure.

Question 2Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which clinical feature most strongly distinguishes Lambert-Eaton myasthenic syndrome from myasthenia gravis?

  1. Ptosis that worsens through the day
  2. Improvement in strength after sustained voluntary contraction Correct answer.
  3. Presence of diplopia on sustained gaze
  4. Bulbar weakness with dysarthria

Explanation

In Lambert-Eaton syndrome, presynaptic calcium channel antibodies impair acetylcholine release, but sustained contraction augments release, producing post-exercise facilitation. Myasthenia gravis characteristically worsens with activity rather than improving.

Question 3Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient develops ascending symmetric flaccid weakness with areflexia two weeks after a diarrheal illness. Which electrodiagnostic finding is most consistent with Guillain-Barre syndrome?

  1. Normal motor conduction with isolated myopathic units
  2. Fibrillation potentials in paraspinal muscles with normal conduction
  3. Sensory nerve action potentials larger than normal
  4. Conduction block with prolonged distal latencies and absent F waves Correct answer.

Explanation

Guillain-Barre syndrome is an acute demyelinating polyradiculoneuropathy, so nerve conduction studies show slowing, conduction block, prolonged distal latencies, and prolonged or absent F waves. These demyelinating features reflect the underlying autoimmune attack on myelin and Schwann cells.

Question 4Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which cerebrospinal fluid pattern is most typical of Guillain-Barre syndrome one to two weeks after symptom onset?

  1. Elevated protein with normal cell count Correct answer.
  2. Normal protein with elevated cell count
  3. Low protein with elevated glucose
  4. Marked pleocytosis with low glucose

Explanation

Guillain-Barre syndrome classically produces albuminocytologic dissociation, meaning elevated CSF protein without a significant increase in white cells. This reflects breakdown of the blood-nerve barrier at the nerve roots.

Question 5Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 62-year-old man has asymmetric distal arm weakness, muscle atrophy, and fasciculations with hyperreflexia. Which diagnosis is most likely?

  1. Polymyositis
  2. Myasthenia gravis
  3. Chronic inflammatory demyelinating polyneuropathy
  4. Amyotrophic lateral sclerosis Correct answer.

Explanation

Combined upper and lower motor neuron signs in multiple regions, including hyperreflexia with atrophy and fasciculations, indicate amyotrophic lateral sclerosis. The presence of both upper and lower motor neuron findings in the same limb is characteristic.

Question 6Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which antibody is most specifically associated with myasthenia gravis in patients who have no thymoma and no detectable anti-acetylcholine receptor antibodies?

  1. Anti-Hu antibody
  2. Anti-muscle-specific kinase antibody Correct answer.
  3. Anti-voltage-gated calcium channel antibody
  4. Anti-ganglioside GQ1b antibody

Explanation

Anti-muscle-specific kinase (MuSK) antibodies define a subset of myasthenia gravis that is often acetylcholine receptor antibody negative and typically involves prominent bulbar and facial weakness. Anti-MuSK testing is indicated in seronegative generalized myasthenia gravis.

Question 7Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient has a painful, asymmetric, patchy sensory neuropathy with elevated blood glucose. Which nerve biopsy finding is most characteristic of diabetic lumbosacral radiculoplexus neuropathy?

  1. Onion bulb formations without inflammation
  2. Perivascular inflammation with microvasculitis Correct answer.
  3. Amyloid deposition in vessel walls
  4. Diffuse loss of large myelinated fibers only

Explanation

Diabetic radiculoplexus neuropathy is an ischemic injury from microvasculitis, and biopsy shows perivascular inflammatory infiltrates with axonal loss. This distinguishes it from the more indolent symmetric diabetic polyneuropathy.

Question 8Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which clinical finding is most characteristic of a myotonic disorder on examination?

  1. Delayed relaxation of grip after sustained contraction Correct answer.
  2. Loss of vibration sense in the feet
  3. Action tremor that resolves with rest
  4. Proximal weakness that improves with repeated effort

Explanation

Myotonia is defined by delayed relaxation of muscle after contraction, classically seen as grip myotonia that slowly releases. It results from repetitive muscle fiber action potentials due to ion channel dysfunction.

Question 9Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 45-year-old woman has proximal muscle weakness, a heliotrope rash, and Gottron papules. Which antibody is most strongly associated with this presentation?

  1. Anti-Mi-2 Correct answer.
  2. Anti-Jo-1
  3. Anti-signal recognition particle
  4. Anti-SRP with anti-Ro52

Explanation

Anti-Mi-2 antibodies are strongly associated with classic dermatomyositis, including the characteristic heliotrope rash and Gottron papules. Anti-Jo-1 is more associated with antisynthetase syndrome and interstitial lung disease.

Question 10Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with dermatomyositis has severe proximal weakness and a markedly elevated creatine kinase. Which additional evaluation is most important to perform?

  1. Screening for underlying malignancy Correct answer.
  2. Routine electroencephalography
  3. Lumbar puncture for oligoclonal bands
  4. Genetic testing for dystrophin mutations

Explanation

Adult dermatomyositis carries an increased risk of underlying malignancy, so age-appropriate cancer screening is recommended at diagnosis. This association is strongest in older adults and in those with certain antibody profiles.

Question 11Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 70-year-old man has symmetric proximal leg weakness, areflexia, and a monoclonal IgM protein. Which antibody should be tested?

  1. Anti-voltage-gated potassium channel antibody
  2. Anti-NMDA receptor antibody
  3. Anti-acetylcholine receptor antibody
  4. Anti-myelin-associated glycoprotein antibody Correct answer.

Explanation

Monoclonal IgM gammopathy with a symmetric sensory or sensorimotor demyelinating neuropathy suggests anti-myelin-associated glycoprotein antibody neuropathy. This entity is important to recognize because it responds differently from typical CIDP.

Question 12Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which finding on nerve conduction studies best supports a diagnosis of chronic inflammatory demyelinating polyneuropathy rather than axonal polyneuropathy?

  1. Multifocal conduction block and temporal dispersion Correct answer.
  2. Normal F waves with reduced sensory amplitudes
  3. Uniform symmetric axonal loss with reduced amplitudes
  4. Fibrillation potentials with normal conduction velocities

Explanation

CIDP is a demyelinating disorder, and nerve conduction studies show multifocal conduction block, temporal dispersion, and prolonged distal latencies. These features reflect patchy myelin damage rather than the length-dependent axonal loss of a typical axonal polyneuropathy.

Question 13Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 30-year-old man has episodic weakness triggered by carbohydrate meals and relieved by fasting, with normal strength between attacks. Which diagnosis is most likely?

  1. Hypokalemic periodic paralysis Correct answer.
  2. Hyperkalemic periodic paralysis
  3. Paramyotonia congenita
  4. McArdle disease

Explanation

Hypokalemic periodic paralysis produces episodic flaccid weakness often triggered by carbohydrate-rich meals or rest after exercise, with serum potassium low during attacks. Carbohydrate intake drives potassium intracellularly and precipitates weakness.

Question 14Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which clinical feature best distinguishes inclusion body myositis from polymyositis?

  1. Rapid response to corticosteroids
  2. Selective weakness of finger flexors and quadriceps with dysphagia Correct answer.
  3. Markedly elevated creatine kinase
  4. Prominent proximal shoulder weakness

Explanation

Inclusion body myositis characteristically causes asymmetric weakness of the deep finger flexors and quadriceps, often with dysphagia, and it responds poorly to immunosuppression. Polymyositis causes symmetric proximal weakness and usually responds to steroids.

Question 15Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient reports double vision that is worse in the evening and variable ptosis. Which bedside test is most useful to support a diagnosis of myasthenia gravis?

  1. Romberg testing
  2. Phalen maneuver
  3. Ice pack test on the ptotic eyelid Correct answer.
  4. Babinski sign testing

Explanation

Cooling the eyelid with an ice pack transiently improves ptosis in myasthenia gravis because lower temperature improves neuromuscular transmission. This bedside test supports a junctional cause of ptosis.

Question 16Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with a thymoma develops myasthenia gravis. Which management consideration is most appropriate?

  1. Observation of the thymoma with serial imaging alone
  2. Radiation therapy to the thymus only
  3. Surgical resection of the thymoma Correct answer.
  4. Corticosteroids without addressing the thymoma

Explanation

Thymoma in the setting of myasthenia gravis warrants surgical resection, since the tumor is locally invasive and removal may improve myasthenic symptoms. Thymectomy is standard for thymomatous myasthenia gravis.

Question 17Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which pattern of weakness is most typical of a distal symmetric polyneuropathy?

  1. Length-dependent sensory loss and weakness in the feet and hands Correct answer.
  2. Proximal weakness with fasciculations
  3. Proximal weakness with a heliotrope rash
  4. Asymmetric ptosis with fatigable weakness

Explanation

Distal symmetric polyneuropathy follows a length-dependent pattern, beginning in the feet and progressing proximally, so sensory loss and weakness are most prominent distally. This pattern reflects the vulnerability of the longest nerve fibers.

Question 18Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient develops acute flaccid paralysis with ophthalmoplegia, ataxia, and areflexia after a respiratory infection. Which antibody is most likely responsible?

  1. Anti-Hu antibody
  2. Anti-MAG antibody
  3. Anti-GQ1b antibody Correct answer.
  4. Anti-acetylcholine receptor antibody

Explanation

Miller Fisher syndrome is a variant of Guillain-Barre syndrome characterized by ophthalmoplegia, ataxia, and areflexia, and it is strongly associated with anti-GQ1b antibodies. These antibodies target gangliosides concentrated in the oculomotor nerves.

Question 19Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which finding on muscle biopsy is most characteristic of polymyositis?

  1. Endomysial inflammatory infiltrates with CD8-positive T cells Correct answer.
  2. Rimmed vacuoles with protein aggregates
  3. Perifascicular atrophy with complement deposition
  4. Grouped atrophy of both fiber types

Explanation

Polymyositis is characterized by endomysial inflammation with CD8-positive T cells invading non-necrotic muscle fibers. In contrast, dermatomyositis shows perifascicular atrophy and complement deposition on capillaries.

Question 20Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 55-year-old woman with long-standing myasthenia gravis on pyridostigmine develops recurrent weakness after a viral illness. Which factor most commonly precipitates myasthenic crisis?

  1. Dietary fiber intake
  2. Respiratory infection Correct answer.
  3. Excessive hydration
  4. Mild exercise

Explanation

Respiratory infections are among the most common triggers of myasthenic crisis because they increase metabolic demand and can worsen neuromuscular junction transmission. Identifying and treating the precipitant is essential in crisis management.

Question 21Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient has a severe, rapidly progressive demyelinating polyneuropathy with autonomic instability and prominent bulbar weakness. Which treatment is most appropriate?

  1. Intravenous immunoglobulin or plasma exchange Correct answer.
  2. Long-term azathioprine monotherapy
  3. Oral pyridostigmine
  4. High-dose corticosteroids alone

Explanation

Guillain-Barre syndrome is treated with intravenous immunoglobulin or plasma exchange, which hasten recovery in severe disease. Corticosteroids alone are not effective and may worsen outcomes.

Question 22Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient has a 12-year history of progressive asymmetric weakness, myotonia, and cataracts. Which diagnosis is most likely?

  1. Myotonic dystrophy type 1 Correct answer.
  2. Duchenne muscular dystrophy
  3. Lambert-Eaton myasthenic syndrome
  4. Facioscapulohumeral muscular dystrophy

Explanation

Myotonic dystrophy type 1 is an autosomal dominant disorder caused by a CTG repeat expansion, producing myotonia, progressive distal and facial weakness, cataracts, and cardiac conduction abnormalities. Multisystem features such as cataracts are a hallmark.

Question 23Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient taking a statin develops proximal muscle weakness and markedly elevated creatine kinase that persists after the statin is stopped. Which diagnosis should be considered?

  1. Hypothyroid myopathy
  2. Statin-induced immune-mediated necrotizing myopathy Correct answer.
  3. Statin-induced myalgia
  4. Polymyalgia rheumatica

Explanation

Immune-mediated necrotizing myopathy can be triggered by statins and characteristically persists after the drug is withdrawn, often requiring immunosuppression. Anti-HMG-CoA reductase antibodies support the diagnosis.

Question 24Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient has a chronic demyelinating polyneuropathy that is refractory to intravenous immunoglobulin and corticosteroids. Which finding would most strongly suggest that the diagnosis should be reconsidered?

  1. Marked conduction block in multiple nerves
  2. Symmetric areflexia with elevated CSF protein
  3. Uniformly prolonged distal latencies without conduction block Correct answer.
  4. Presence of anti-MAG antibodies

Explanation

CIDP typically shows nonuniform, multifocal demyelinating features such as conduction block and temporal dispersion. Uniformly prolonged distal latencies without conduction block raise concern for a hereditary demyelinating neuropathy such as Charcot-Marie-Tooth disease type 1.

Question 25Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with amyotrophic lateral sclerosis develops worsening respiratory symptoms. Which test is most useful for monitoring respiratory function?

  1. Forced vital capacity by spirometry Correct answer.
  2. Arterial blood gas at rest
  3. Serum creatine kinase
  4. Needle electromyography of the diaphragm

Explanation

Forced vital capacity, especially when measured upright and supine, is the standard test for monitoring respiratory muscle strength in amyotrophic lateral sclerosis. A declining vital capacity helps guide timing of noninvasive ventilation.

Question 26Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 24-year-old man has slowly progressive distal leg weakness and wasting, pes cavus, and absent ankle reflexes; his father has similar foot deformities. Which inheritance pattern is most consistent with this presentation?

  1. Mitochondrial
  2. X-linked recessive
  3. Autosomal dominant Correct answer.
  4. Autosomal recessive

Explanation

Charcot-Marie-Tooth disease type 1A, the most common hereditary neuropathy, is autosomal dominant and typically produces distal weakness, pes cavus, and areflexia with a positive family history across generations. Male-to-male transmission and multigenerational involvement exclude X-linked and mitochondrial patterns.

Question 27Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which electrodiagnostic finding is the defining feature of a myopathic disorder on needle electromyography?

  1. Long-duration, large-amplitude motor unit potentials with reduced recruitment
  2. Short-duration, small-amplitude motor unit potentials with early recruitment Correct answer.
  3. Fibrillation potentials with reduced recruitment
  4. Normal motor unit potentials with decrement on repetitive stimulation

Explanation

Myopathy produces loss of muscle fibers within motor units, so individual motor unit potentials become short and small, and more units must fire to generate force, giving early recruitment. Long large units indicate neurogenic reinnervation, and decrement indicates a neuromuscular junction disorder.

Question 28Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 60-year-old woman has painless proximal arm and leg weakness, difficulty rising from a chair, and a markedly elevated creatine kinase. Which diagnosis is most likely?

  1. Myasthenia gravis
  2. Amyotrophic lateral sclerosis
  3. Polymyositis Correct answer.
  4. Chronic inflammatory demyelinating polyneuropathy

Explanation

Subacute symmetric proximal weakness with markedly elevated creatine kinase and no sensory loss points to an inflammatory myopathy such as polymyositis. ALS causes upper and lower motor neuron signs with normal or mildly elevated CK, and myasthenia produces fatigable weakness with normal CK.

Question 29Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with a suspected neuromuscular junction disorder undergoes repetitive nerve stimulation. Which finding supports the diagnosis?

  1. Decrement of the compound muscle action potential with low-frequency stimulation Correct answer.
  2. Increment of the compound muscle action potential with low-frequency stimulation
  3. Conduction block with temporal dispersion
  4. Prolonged distal latency with normal amplitude

Explanation

In myasthenia gravis, repetitive low-frequency stimulation depletes available acetylcholine vesicles at the postsynaptic membrane, producing a decremental response of more than 10%. Increment after exercise suggests a presynaptic disorder such as Lambert-Eaton, and conduction block indicates demyelinating neuropathy.

Question 30Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which clinical feature most strongly suggests a myotonic dystrophy type 1 diagnosis in an adult with distal weakness and grip myotonia?

  1. Sensory loss in a stocking-glove distribution
  2. Fasciculations with hyperreflexia
  3. Cataracts with frontal balding and cardiac conduction abnormalities Correct answer.
  4. Proximal weakness with a heliotrope rash

Explanation

Myotonic dystrophy type 1 is a multisystem CTG repeat disorder with cataracts, frontal balding, cardiac conduction disease, and distal weakness with myotonia. Sensory loss and fasciculations indicate neuropathy or motor neuron disease, and a heliotrope rash suggests dermatomyositis.

Question 31Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 35-year-old man has acute ascending symmetric weakness, areflexia, and a recent diarrheal illness. Which finding on cerebrospinal fluid analysis is most typical?

  1. Albuminocytologic dissociation with elevated protein and normal cell count Correct answer.
  2. Marked pleocytosis with low glucose
  3. Xanthochromia with elevated opening pressure
  4. Elevated oligoclonal bands with normal protein

Explanation

Guillain-Barre syndrome classically shows elevated CSF protein with a normal white cell count, known as albuminocytologic dissociation, often appearing after the first week. Pleocytosis with low glucose suggests infection, and oligoclonal bands suggest demyelinating CNS disease.

Question 32Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which muscle group is most commonly affected earliest in amyotrophic lateral sclerosis?

  1. Sphincter muscles
  2. Pelvic floor muscles
  3. Bulbar and distal limb muscles Correct answer.
  4. Extraocular muscles

Explanation

ALS typically begins with distal limb weakness or bulbar symptoms such as dysarthria and dysphagia, reflecting involvement of upper and lower motor neurons. Extraocular muscles and sphincters are characteristically spared until very late.

Question 33Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which medication is used for symptomatic treatment of the fatigable weakness of myasthenia gravis by inhibiting acetylcholinesterase?

  1. Rituximab
  2. Azathioprine
  3. Prednisone
  4. Pyridostigmine Correct answer.

Explanation

Pyridostigmine is an acetylcholinesterase inhibitor that prolongs acetylcholine at the neuromuscular junction and provides symptomatic benefit in myasthenia gravis. Prednisone, azathioprine, and rituximab are immunomodulatory treatments that alter disease course rather than providing rapid symptomatic acetylcholinesterase inhibition.

Question 34Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 68-year-old man has progressive weakness and atrophy of the intrinsic hand muscles with fasciculations but no sensory loss. Which diagnosis is most likely?

  1. Amyotrophic lateral sclerosis Correct answer.
  2. Myasthenia gravis
  3. Diabetic polyneuropathy
  4. Polymyositis

Explanation

Painless progressive weakness with atrophy and fasciculations without sensory loss suggests a motor neuron disease such as ALS. Sensory involvement would point to neuropathy, and myasthenia produces fatigable weakness without atrophy or fasciculations.

Question 35Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient has a chronic demyelinating neuropathy with symmetric proximal and distal weakness, areflexia, and elevated CSF protein. Which treatment has the strongest evidence as initial therapy?

  1. Plasmapheresis as the only effective option
  2. Cyclophosphamide
  3. Intravenous immunoglobulin Correct answer.
  4. High-dose methotrexate

Explanation

Intravenous immunoglobulin, corticosteroids, and plasmapheresis are all evidence-based first-line therapies for CIDP, and IVIG is widely used. Methotrexate and cyclophosphamide are not standard first-line agents, and plasmapheresis is effective but not the sole option.

Question 36Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 45-year-old woman has fatigable ptosis and diplopia, and her weakness worsens with sustained upgaze. Which mechanism best explains her symptoms?

  1. Demyelination of the optic nerve
  2. Loss of anterior horn cells
  3. Antibodies against postsynaptic acetylcholine receptors at the neuromuscular junction Correct answer.
  4. Defective glycogenolysis in muscle

Explanation

Myasthenia gravis is caused by autoantibodies against postsynaptic acetylcholine receptors, producing fatigable weakness that worsens with sustained effort. Optic nerve demyelination causes visual loss rather than fatigable ptosis, and anterior horn cell loss causes lower motor neuron weakness.

Question 37Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with Lambert-Eaton myasthenic syndrome has proximal weakness that transiently improves after brief exercise. Which mechanism explains this facilitation?

  1. Defective acetylcholinesterase at the motor endplate
  2. Antibodies against presynaptic voltage-gated calcium channels with increased calcium influx after repetitive firing Correct answer.
  3. Loss of myelinated fibers in the peripheral nerve
  4. Antibodies against postsynaptic acetylcholine receptors

Explanation

In Lambert-Eaton syndrome, antibodies against presynaptic P/Q-type voltage-gated calcium channels reduce calcium entry and acetylcholine release. With brief exercise, calcium accumulates in the presynaptic terminal, transiently increasing release and producing facilitation.

Question 38Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which clinical finding most suggests a diagnosis of inclusion body myositis rather than polymyositis?

  1. Fatigable weakness of the extraocular muscles
  2. Proximal weakness with a heliotrope rash
  3. Symmetric proximal weakness with markedly elevated CK
  4. Weakness and atrophy of the quadriceps and finger flexors Correct answer.

Explanation

Inclusion body myositis characteristically produces asymmetric weakness and atrophy of the quadriceps and deep finger flexors, often with dysphagia. Polymyositis causes symmetric proximal weakness, and dermatomyositis features a heliotrope rash.

Question 39Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 30-year-old woman has recurrent episodes of severe weakness after emotional stress and after eating carbohydrate-rich meals; between attacks strength is normal. Which finding on electromyography during an attack is most likely?

  1. Repetitive discharges with myotonic potentials
  2. Compound muscle action potentials that decline after prolonged exercise Correct answer.
  3. Fibrillation potentials with reduced recruitment
  4. Conduction block with temporal dispersion

Explanation

Hypokalemic periodic paralysis produces attacks of flaccid weakness triggered by carbohydrate loads and stress, with reduced compound muscle action potential amplitude during attacks that declines further with prolonged exercise. Myotonic potentials and conduction block reflect other disorders.

Question 40Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient has a painful, burning neuropathy with distal sensory loss and autonomic symptoms after a recent viral illness. Which diagnosis is most likely?

  1. Myasthenia gravis
  2. Polymyositis
  3. Essential tremor
  4. Acute sensory neuropathy Correct answer.

Explanation

Acute painful sensory neuropathy with autonomic features after a viral illness suggests an acute sensory neuronopathy or small-fiber neuropathy, often immune-mediated. Myasthenia and polymyositis are motor disorders without prominent pain or autonomic features.

Question 41Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with long-standing diabetes develops a painless foot ulcer and loss of protective sensation. Which mechanism best explains the loss of sensation?

  1. Loss of anterior horn cells
  2. Antibodies against the neuromuscular junction
  3. Demyelination of the dorsal columns
  4. Length-dependent axonal degeneration of distal sensory fibers Correct answer.

Explanation

Diabetic distal symmetric polyneuropathy is a length-dependent axonopathy affecting the longest sensory fibers first, producing a stocking-glove pattern and loss of protective sensation. Dorsal column demyelination, anterior horn cell loss, and junctional antibodies produce different patterns.

Question 42Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

Which finding on nerve conduction studies distinguishes a demyelinating neuropathy from an axonal neuropathy?

  1. Fibrillation potentials on needle electromyography
  2. Markedly slowed conduction velocity with prolonged distal latencies Correct answer.
  3. Normal sensory responses with normal motor responses
  4. Reduced compound muscle action potential amplitude with normal velocity

Explanation

Demyelination slows conduction and prolongs distal latencies, often with conduction block or temporal dispersion. Axonal loss primarily reduces response amplitudes while conduction velocity remains relatively normal.

Question 43Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A 50-year-old man has progressive weakness and muscle wasting of the arms with upper motor neuron signs in the legs and no sensory loss. Which diagnosis is most consistent?

  1. Guillain-Barre syndrome
  2. Myasthenia gravis
  3. Dermatomyositis
  4. Amyotrophic lateral sclerosis Correct answer.

Explanation

Combined upper and lower motor neuron signs without sensory loss is the hallmark of ALS. Guillain-Barre is an acute demyelinating neuropathy with sensory features, and myasthenia and dermatomyositis do not produce upper motor neuron signs.

Question 44Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with myasthenia gravis develops respiratory distress and a weak cough. Which test best assesses ventilatory muscle strength?

  1. Chest radiograph
  2. Forced vital capacity Correct answer.
  3. Spirometry with bronchodilator response
  4. Arterial blood gas analysis

Explanation

Forced vital capacity directly measures ventilatory muscle strength and is used to monitor impending respiratory failure in neuromuscular disease. Arterial blood gases may remain normal until failure is imminent, and chest radiography does not assess muscle strength.

Question 45Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with a suspected myopathy has proximal weakness and normal creatine kinase. Which additional finding most favors a chronic myopathy rather than an acute inflammatory one?

  1. Fever with elevated inflammatory markers
  2. Long-standing stable weakness with fatty replacement on muscle imaging Correct answer.
  3. Marked CK elevation with myoglobinuria
  4. Recent onset of muscle pain and swelling

Explanation

Chronic myopathies such as muscular dystrophies show stable, long-standing weakness with fatty replacement on imaging and often normal CK. Acute inflammatory myopathies typically present with recent onset, pain, and marked CK elevation.

Question 46Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with a hereditary neuropathy has a duplication of the PMP22 gene. Which diagnosis is most likely?

  1. Myotonic dystrophy type 1
  2. Charcot-Marie-Tooth disease type 1A Correct answer.
  3. Facioscapulohumeral dystrophy
  4. Duchenne muscular dystrophy

Explanation

Charcot-Marie-Tooth disease type 1A is most often caused by a 1.5-Mb duplication of the PMP22 gene on chromosome 17p11.2, producing a demyelinating neuropathy. Myotonic dystrophy and the muscular dystrophies are caused by other genetic mechanisms.

Question 47Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient has a severe demyelinating neuropathy with ophthalmoplegia and ataxia, and nerve conduction shows absent sensory responses with normal motor responses. Which pattern of neuropathy is most likely?

  1. Distal symmetric polyneuropathy
  2. Mononeuropathy multiplex
  3. Radiculopathy
  4. Sensory neuronopathy Correct answer.

Explanation

Sensory neuronopathy causes absent or markedly reduced sensory responses with preserved motor responses because the dorsal root ganglia are affected. Distal symmetric polyneuropathy and mononeuropathy multiplex usually affect motor responses as well.

Question 48Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with a chronic inflammatory myopathy has persistent weakness despite corticosteroids and develops progressive dysphagia. Which diagnosis should be reconsidered?

  1. Inclusion body myositis Correct answer.
  2. Lambert-Eaton myasthenic syndrome
  3. Myasthenia gravis
  4. Guillain-Barre syndrome

Explanation

Inclusion body myositis is often misdiagnosed as polymyositis and is characteristically refractory to corticosteroids, with distal weakness and dysphagia. Myasthenia, GBS, and Lambert-Eaton have different clinical patterns and treatment responses.

Question 49Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with a suspected mitochondrial myopathy has exercise intolerance and lactic acidosis. Which finding on muscle biopsy would support the diagnosis?

  1. Ragged red fibers on Gomori trichrome stain Correct answer.
  2. Perifascicular atrophy
  3. Endomysial inflammatory infiltrates
  4. Rimmed vacuoles

Explanation

Mitochondrial myopathies show ragged red fibers on modified Gomori trichrome stain due to subsarcolemmal mitochondrial accumulation. Perifascicular atrophy indicates dermatomyositis, rimmed vacuoles indicate inclusion body myositis, and endomysial infiltrates indicate polymyositis.

Question 50Neuromuscular Medicine (broad content area; official domain breakdown not available in source)

A patient with a demyelinating neuropathy develops a new asymmetric weakness of the wrist extensors and foot dorsiflexors after a respiratory infection. Which diagnosis is most likely?

  1. Distal symmetric polyneuropathy
  2. Polymyositis
  3. Myasthenia gravis
  4. Multifocal motor neuropathy Correct answer.

Explanation

Multifocal motor neuropathy produces asymmetric distal weakness, often in the wrist extensors and foot dorsiflexors, with conduction block and little sensory involvement. Distal symmetric polyneuropathy is symmetric, and myasthenia and polymyositis have different patterns.