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ABPMR Neuromuscular Medicine study materials
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ABPMR Neuromuscular Medicine practice questions

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Question 1Disorders of the Anterior Horn Cell and Spinal Cord

A 58-year-old man has 8 months of progressive painless weakness in both hands and one leg. Which electrodiagnostic finding most strongly supports ALS?

  1. Denervation and reinnervation across multiple myotomes Correct answer.
  2. Repetitive nerve stimulation showing a 20% decrement
  3. Sural sensory amplitude loss with normal motor studies
  4. Uniform demyelinating conduction block across multiple nerves

Explanation

ALS causes both upper and lower motor neuron degeneration, so needle EMG shows active denervation with chronic reinnervation in multiple limbs and myotomes. Sensory conduction studies are typically normal because sensory neurons are spared. The widespread neurogenic pattern helps distinguish ALS from radiculopathy or demyelinating neuropathy.

Question 2Disorders of the Anterior Horn Cell and Spinal Cord

Which genetic abnormality causes spinal muscular atrophy?

  1. C9orf72 repeat expansion
  2. DMD deletion
  3. Homozygous SMN1 deletion Correct answer.
  4. SMN2 duplication

Explanation

Spinal muscular atrophy is autosomal recessive and results from biallelic loss of SMN1. SMN2 copy number modifies disease severity but does not cause the disorder. This explains why SMN2-targeted therapies can improve the phenotype.

Question 3Disorders of the Anterior Horn Cell and Spinal Cord

Which pattern is typical of paralytic poliomyelitis?

  1. Symmetric distal sensory loss
  2. Asymmetric flaccid weakness with normal sensation Correct answer.
  3. Ascending symmetric weakness with a sensory level
  4. Spasticity from the onset

Explanation

Poliovirus destroys anterior horn cells, producing lower motor neuron weakness that is often asymmetric and proximally prominent. Sensation remains normal because sensory pathways are not affected. Spasticity is not an early feature of the acute paralytic illness.

Question 4Disorders of the Anterior Horn Cell and Spinal Cord

Kennedy disease is caused by which repeat expansion?

  1. X-linked CAG repeat in androgen receptor Correct answer.
  2. Autosomal dominant CAG repeat in HTT
  3. Autosomal recessive GAA repeat in FXN
  4. X-linked CGG repeat in FMR1

Explanation

Kennedy disease, or spinal and bulbar muscular atrophy, is an X-linked disorder caused by a CAG repeat expansion in the androgen receptor gene. Affected men develop bulbar and limb lower motor neuron weakness, gynecomastia, and reduced fertility. Cognition is usually preserved.

Question 5Disorders of the Anterior Horn Cell and Spinal Cord

Which history best fits post-polio syndrome?

  1. New sensory level 2 weeks after polio
  2. Upper motor neuron signs only
  3. New weakness after decades of stability following polio Correct answer.
  4. Family history of similar weakness

Explanation

Post-polio syndrome is characterized by new weakness, fatigue, or atrophy after a long stable period, usually at least 15 years after acute polio. The examination shows lower motor neuron findings in previously affected and sometimes newly affected muscles. Sensory levels and purely upper motor neuron signs are not part of the syndrome.

Question 6Disorders of the Anterior Horn Cell and Spinal Cord

Sudden paraplegia with bilateral pain and temperature loss below T8 and preserved vibration sense points to which lesion?

  1. Anterior spinal artery infarction Correct answer.
  2. Spinal dural arteriovenous fistula
  3. Posterior column demyelination
  4. Unilateral cord hemisection

Explanation

The anterior spinal artery supplies the anterior two-thirds of the cord, including the corticospinal tracts and spinothalamic fibers. Infarction therefore causes paraplegia and pain/temperature loss while sparing dorsal column vibration and proprioception. This pattern is sometimes called anterior spinal artery syndrome.

Question 7Disorders of the Anterior Horn Cell and Spinal Cord

Cape-like loss of pain and temperature over the shoulders and arms with preserved proprioception suggests which lesion?

  1. Lateral corticospinal tract lesion
  2. Dorsal root ganglion lesion
  3. Cauda equina lesion
  4. Central cord syrinx Correct answer.

Explanation

A syrinx in the central cervical cord first interrupts decussating spinothalamic fibers, producing suspended cape-like pain and temperature loss. Dorsal columns and corticospinal tracts are affected later as the cavity expands. This explains the characteristic dissociated sensory loss.

Question 8Disorders of the Anterior Horn Cell and Spinal Cord

Which presentation is most consistent with a spinal dural arteriovenous fistula?

  1. Progressive myelopathy with T2 cord signal and flow voids Correct answer.
  2. Acute hemorrhagic myelitis
  3. Isolated dorsal column loss
  4. Sensory level with a normal MRI

Explanation

Spinal dural arteriovenous fistulas cause venous congestion and progressive myelopathy, often in older men. MRI shows T2 hyperintensity and enlarged perimedullary flow voids, sometimes with contrast enhancement. Symptoms may worsen with activity or upright posture.

Question 9Disorders of the Anterior Horn Cell and Spinal Cord

Vitamin B12 deficiency typically produces which spinal cord pattern?

  1. Dorsal and lateral column degeneration Correct answer.
  2. Isolated spinothalamic loss
  3. Anterior horn cell loss
  4. Cauda equina compression

Explanation

Vitamin B12 deficiency causes subacute combined degeneration, affecting the dorsal columns and corticospinal tracts. Patients develop impaired vibration and proprioception, sensory ataxia, and spastic weakness. Peripheral neuropathy and cognitive changes may coexist.

Question 10Disorders of the Anterior Horn Cell and Spinal Cord

Which finding is characteristic of tabes dorsalis?

  1. Spastic paraparesis with a sensory level
  2. Asymmetric flaccid weakness
  3. Cape-like pain and temperature loss
  4. Impaired vibration sense with ataxia and Argyll Robertson pupils Correct answer.

Explanation

Tabes dorsalis is a late manifestation of neurosyphilis that damages the dorsal columns and dorsal roots. It produces impaired vibration and proprioception, sensory ataxia, lancinating pain, and Argyll Robertson pupils. Strength is often preserved until late.

Question 11Disorders of the Anterior Horn Cell and Spinal Cord

Right-sided spastic weakness and loss of vibration below T6, with left-sided pain and temperature loss below T6, localizes to which lesion?

  1. Right hemicord Correct answer.
  2. Central cord
  3. Bilateral anterior horns
  4. Left dorsal columns

Explanation

This is a Brown-Séquard syndrome. A right hemicord lesion affects the right corticospinal tract and dorsal columns, causing ipsilateral spastic weakness and vibration loss. It also interrupts right-sided spinothalamic fibers that have already crossed, causing contralateral pain and temperature loss.

Question 12Disorders of the Anterior Horn Cell and Spinal Cord

Which clinical picture best supports cervical spondylotic myelopathy?

  1. Lower motor neuron signs at one level only
  2. Spastic gait, clumsy hands, and hyperreflexia Correct answer.
  3. Sensory level with absent reflexes
  4. Radicular pain with a normal examination

Explanation

Cervical spondylotic myelopathy compresses the cord and produces upper motor neuron signs below the level, often with spastic gait and clumsy hands. Lower motor neuron signs may appear at the compressed level. Radicular pain alone without examination findings does not establish myelopathy.

Question 13Disorders of the Anterior Horn Cell and Spinal Cord

Which virus causes tropical spastic paraparesis?

  1. Varicella-zoster virus
  2. Poliovirus
  3. HTLV-1 Correct answer.
  4. HIV

Explanation

HTLV-1 causes tropical spastic paraparesis, a slowly progressive myelopathy with spastic weakness, bladder urgency, and mild sensory signs. It is endemic in parts of the Caribbean, Japan, and South America. MRI may show thoracic cord atrophy without prominent inflammation.

Question 14Disorders of the Anterior Horn Cell and Spinal Cord

Which gene is the most common cause of familial ALS and also causes frontotemporal dementia?

  1. C9orf72 Correct answer.
  2. SMN1
  3. SOD1
  4. PMP22

Explanation

C9orf72 hexanucleotide repeat expansion is the most common genetic cause of familial ALS and can produce frontotemporal dementia. It may cause ALS, FTD, or both in the same family. SOD1 is another ALS gene but is not typically associated with FTD.

Question 15Disorders of the Anterior Horn Cell and Spinal Cord

A 20-year-old man has unilateral distal upper limb atrophy and weakness without sensory loss. Cervical flexion MRI shows forward displacement of the cord. What is the diagnosis?

  1. Cervical spondylosis
  2. Hirayama disease Correct answer.
  3. Syringomyelia
  4. Amyotrophic lateral sclerosis

Explanation

Hirayama disease causes juvenile muscular atrophy of the distal upper limb, usually in young men. Neck flexion produces anterior displacement of the cord and compression against the vertebral body, with venous congestion. Sensory loss is typically absent.

Question 16Disorders of the Anterior Horn Cell and Spinal Cord

Which feature favors a conus medullaris lesion over a cauda equina lesion?

  1. Asymmetric radicular pain with areflexia
  2. Early bladder dysfunction with symmetric saddle anesthesia Correct answer.
  3. Sensory loss in a single dermatome
  4. Pure unilateral foot drop

Explanation

The conus medullaris contains sacral cord segments, so lesions cause early bowel and bladder dysfunction with symmetric saddle anesthesia. Ankle reflexes may be preserved because lumbar roots are spared. Cauda equina lesions tend to be asymmetric with radicular pain and areflexia.

Question 17Disorders of the Anterior Horn Cell and Spinal Cord

Which finding is typical of bulbar-onset ALS?

  1. Mixed flaccid-spastic dysarthria with tongue fasciculations Correct answer.
  2. Isolated tongue sensory loss
  3. Fatigable ptosis
  4. Dysphonia with a normal examination

Explanation

Bulbar ALS affects both lower and upper motor neurons supplying the tongue and pharynx. This produces mixed flaccid-spastic dysarthria, tongue wasting and fasciculations, and exaggerated jaw or gag reflexes. Isolated sensory loss or fatigable ptosis suggests another diagnosis.

Question 18Disorders of the Anterior Horn Cell and Spinal Cord

An infant has severe hypotonia, tongue fasciculations, and weakness before 6 months of age. Which diagnosis is most likely?

  1. SMA type 1 Correct answer.
  2. SMA type 4
  3. SMA type 3
  4. Kennedy disease

Explanation

SMA type 1 presents before 6 months with severe hypotonia, bulbar weakness, and tongue fasciculations. It is caused by homozygous SMN1 deletion with usually two SMN2 copies. SMA type 4 begins in adulthood, and Kennedy disease affects adult men.

Question 19Disorders of the Anterior Horn Cell and Spinal Cord

Under the Awaji criteria, which EMG finding can serve as evidence of lower motor neuron involvement in a clinically affected region?

  1. Prolonged F-wave latency alone
  2. Fasciculation potentials with chronic neurogenic changes Correct answer.
  3. Motor conduction block
  4. Reduced sensory nerve action potential amplitude

Explanation

The Awaji criteria allow fasciculation potentials to count as active denervation when they occur in a muscle showing chronic neurogenic motor unit changes. This increases diagnostic sensitivity while maintaining specificity for ALS. Reduced sensory amplitudes and conduction block point toward other neuromuscular disorders.

Question 20Disorders of the Anterior Horn Cell and Spinal Cord

Which MRI finding is most characteristic of acute spinal cord infarction?

  1. Pencil-like T2 hyperintensity with restricted diffusion Correct answer.
  2. Dorsal flow voids
  3. Ring-enhancing intramedullary lesion
  4. Cord expansion with a syrinx

Explanation

Acute spinal cord infarction often produces pencil-like T2 hyperintensity on sagittal images and restricted diffusion on axial imaging, sometimes called the owl-eye appearance. Conventional T2 changes may be absent very early, so diffusion-weighted imaging can be helpful. Enhancement may appear later.

Question 21Disorders of the Anterior Horn Cell and Spinal Cord

Which feature is associated with shorter survival in ALS?

  1. Young age at onset
  2. Bulbar onset with early respiratory involvement Correct answer.
  3. Male sex alone
  4. Limb onset with preserved weight

Explanation

Bulbar onset and early respiratory muscle weakness are poor prognostic features in ALS. Older age at onset, rapid functional decline, and weight loss also predict shorter survival. Limb onset and younger age generally carry a more favorable prognosis.

Question 22Disorders of the Anterior Horn Cell and Spinal Cord

Which disorder causes infantile distal weakness and diaphragmatic palsy due to IGHMBP2 mutation?

  1. SMA type 1
  2. Congenital myasthenic syndrome
  3. SMARD1 Correct answer.
  4. Pompe disease

Explanation

SMARD1 is spinal muscular atrophy with respiratory distress type 1, caused by IGHMBP2 mutations. It presents in infancy with distal-predominant weakness and diaphragmatic palsy, often before severe proximal weakness. This distinguishes it from classic SMA type 1.

Question 23Disorders of the Anterior Horn Cell and Spinal Cord

Which MRI finding supports tethered cord syndrome?

  1. Cervical syrinx
  2. Conus below L2-L3 with a thickened filum Correct answer.
  3. Dorsal flow voids
  4. Conus at T10

Explanation

The normal conus terminates at about T12 to L1-L2. A low-lying conus below L2-L3 with a thickened filum suggests tethered cord, which can cause progressive lower limb weakness, sensory loss, and bladder dysfunction. MRI of the whole spine is needed because other dysraphic features may coexist.

Question 24Disorders of the Anterior Horn Cell and Spinal Cord

A patient has longitudinally extensive transverse myelitis. Which antibody is most specific for neuromyelitis optica spectrum disorder?

  1. MOG
  2. NMDA receptor
  3. Hu
  4. Aquaporin-4 Correct answer.

Explanation

Aquaporin-4 IgG targets astrocytic water channels and is highly specific for neuromyelitis optica spectrum disorder. It is associated with longitudinally extensive transverse myelitis and optic neuritis. MOG antibodies define a separate demyelinating syndrome.

Question 25Disorders of the Anterior Horn Cell and Spinal Cord

What is the mechanism of riluzole in ALS?

  1. Chelates copper
  2. Blocks nicotinic acetylcholine receptors
  3. Reduces glutamate release and antagonizes NMDA receptors Correct answer.
  4. Increases SOD1 activity

Explanation

Riluzole reduces presynaptic glutamate release and has NMDA receptor antagonist effects, limiting excitotoxic injury. It modestly prolongs survival or time to ventilation in ALS. It does not restore lost motor neurons or reverse weakness.

Question 26Disorders of the Anterior Horn Cell and Spinal Cord

A 55-year-old man had paralytic poliomyelitis at age 4. After 30 stable years, he develops new asymmetric weakness and fatigue in previously affected limbs without sensory loss. Which process best explains this presentation?

  1. Degeneration of surviving enlarged motor units Correct answer.
  2. Compression of lumbar nerve roots
  3. Reinfection with a wild-type poliovirus
  4. Inflammatory demyelination of peripheral nerves

Explanation

Post-polio syndrome typically appears after decades of stability and is attributed to distal degeneration of motor units that enlarged during reinnervation. Sensory loss and a clear root level are not expected. There is no active poliovirus infection.

Question 27Disorders of the Anterior Horn Cell and Spinal Cord

A 60-year-old man has progressive bulbar and proximal limb weakness, gynecomastia, and reduced fertility. Which genetic abnormality is most likely?

  1. GAA repeat expansion in FXN
  2. CTG repeat expansion in DMPK
  3. CAG repeat expansion in the androgen receptor Correct answer.
  4. Hexanucleotide repeat expansion in C9orf72

Explanation

This is spinal and bulbar muscular atrophy (Kennedy disease), an X-linked disorder caused by a CAG repeat expansion in the androgen receptor. Androgen insensitivity produces gynecomastia and impaired fertility. FXN expansions cause Friedreich ataxia, DMPK expansions cause myotonic dystrophy, and C9orf72 expansions cause ALS or frontotemporal dementia.

Question 28Disorders of the Anterior Horn Cell and Spinal Cord

Which cognitive-behavioral syndrome is most closely associated with amyotrophic lateral sclerosis?

  1. Frontotemporal dementia Correct answer.
  2. Amnestic mild cognitive impairment
  3. Isolated visuospatial neglect
  4. Acute confusional state

Explanation

ALS shares pathologic TDP-43 inclusions with frontotemporal lobar degeneration, and many patients have executive or behavioral change. A minority meet criteria for frontotemporal dementia. Amnestic syndromes and delirium are not characteristic.

Question 29Disorders of the Anterior Horn Cell and Spinal Cord

In spinal muscular atrophy caused by biallelic SMN1 loss, which factor best predicts a milder clinical phenotype?

  1. Serum creatine kinase level
  2. Higher SMN2 gene copy number Correct answer.
  3. Size of the SMN1 deletion
  4. Age at first symptom onset alone

Explanation

SMN2 produces a small amount of functional SMN protein, so higher copy number generally correlates with later onset and milder disease. SMN1 deletion size does not determine phenotype because the gene is absent. Creatine kinase is nonspecific, and age at onset is a consequence rather than an independent predictor.

Question 30Disorders of the Anterior Horn Cell and Spinal Cord

A child develops acute asymmetric flaccid weakness after a febrile respiratory illness. Spinal MRI shows T2 hyperintensity restricted to the central gray matter of the cervical cord over several segments. Which diagnosis is most likely?

  1. Acute flaccid myelitis Correct answer.
  2. Spinal epidural abscess
  3. Guillain-Barré syndrome
  4. Aquaporin-4 neuromyelitis optica

Explanation

Acute flaccid myelitis produces poliomyelitis-like anterior horn injury, often after enterovirus D68, with gray-matter-restricted cord signal change. Guillain-Barré syndrome is a peripheral nerve disorder without cord signal abnormality. Neuromyelitis optica usually causes central white and gray matter lesions with sensory involvement, and epidural abscess is extramedullary.

Question 31Disorders of the Anterior Horn Cell and Spinal Cord

A 35-year-old has 8 years of progressive spastic paraparesis, brisk reflexes, extensor plantar responses, and urinary urgency, with no sensory loss or arm involvement. Family history is autosomal dominant. Which gene is most commonly implicated?

  1. SMN1
  2. PLP1
  3. SPAST Correct answer.
  4. ABCD1

Explanation

This is pure hereditary spastic paraplegia, and SPAST (SPG4) is the most common autosomal dominant cause. PLP1 causes Pelizaeus-Merzbacher disease, ABCD1 causes adrenoleukodystrophy, and SMN1 loss causes spinal muscular atrophy. Those disorders have different inheritance patterns or additional features.

Question 32Disorders of the Anterior Horn Cell and Spinal Cord

Which clinical pattern most suggests an intramedullary spinal cord tumor rather than an extramedullary one?

  1. Radicular pain that awakens the patient from sleep
  2. Ipsilateral spastic weakness followed by contralateral pain and temperature loss
  3. Pure flaccid areflexic weakness without a sensory level
  4. Sacral sensory sparing with early urinary urgency Correct answer.

Explanation

Intramedullary lesions expand from the center outward and often spare the sacral dermatomes while disturbing bladder function early. Extramedullary lesions commonly cause radicular pain and a Brown-Séquard syndrome. Pure flaccid areflexic weakness suggests a peripheral or anterior horn process rather than a cord tumor.

Question 33Disorders of the Anterior Horn Cell and Spinal Cord

A 50-year-old man with amyotrophic lateral sclerosis has a confirmed pathogenic SOD1 variant. Which medication is most specifically directed at this cause?

  1. Tofersen Correct answer.
  2. Nusinersen
  3. Riluzole
  4. Edaravone

Explanation

Tofersen is an antisense oligonucleotide that reduces SOD1 protein production and is approved for SOD1-associated ALS. Riluzole and edaravone have general disease-modifying effects unrelated to SOD1, and nusinersen is used in spinal muscular atrophy. Genetic confirmation is required before tofersen is considered.

Question 34Disorders of the Anterior Horn Cell and Spinal Cord

A 55-year-old has 5 years of progressive spastic tetraparesis, dysarthria, and pseudobulbar affect, with no muscle atrophy or fasciculations. Electromyography shows no active denervation. Which diagnosis is most likely?

  1. Primary lateral sclerosis Correct answer.
  2. Amyotrophic lateral sclerosis
  3. Cervical spondylotic myelopathy
  4. Kennedy disease

Explanation

Primary lateral sclerosis is a pure upper motor neuron disorder with at least 4 years of progression and no electromyographic denervation. ALS requires lower motor neuron involvement, Kennedy disease causes bulbar and limb denervation with androgen insensitivity, and cervical spondylotic myelopathy usually has sensory findings and neck-related symptoms.

Question 35Disorders of Nerve Roots and Plexus

Which cervical nerve root is most frequently implicated in cervical radiculopathy?

  1. C5
  2. C7 Correct answer.
  3. C6
  4. C8

Explanation

C7 is the most commonly affected cervical root, usually from a C6-C7 disc herniation or spondylotic foraminal narrowing, with C6 a close second. C7 compression typically produces triceps weakness and a diminished triceps reflex.

Question 36Disorders of Nerve Roots and Plexus

Which lumbar nerve root is most commonly affected in symptomatic lumbar disc herniation?

  1. L5 Correct answer.
  2. L3
  3. S1
  4. L4

Explanation

L5 is the most frequently affected lumbar root, most often from a paracentral L4-L5 disc herniation, with S1 from L5-S1 a close second. L5 compression causes weakness of ankle dorsiflexion and great toe extension with sensory loss over the dorsum of the foot.

Question 37Disorders of Nerve Roots and Plexus

The classic 'waiter's tip' posture after an obstetric traction injury reflects damage to which roots?

  1. C3-C4
  2. C8-T1
  3. C7-T1
  4. C5-C6 Correct answer.

Explanation

Erb's palsy is an upper trunk lesion of C5-C6, weakening the deltoid, biceps, and brachioradialis while leaving finger flexors relatively preserved. The arm hangs adducted, internally rotated, extended, and pronated.

Question 38Disorders of Nerve Roots and Plexus

Klumpke's palsy from a birth injury involves which nerve roots?

  1. C8-T1 Correct answer.
  2. C5-C6
  3. C6-C7
  4. C4-C5

Explanation

Klumpke's palsy is a lower trunk lesion of C8-T1 causing intrinsic hand weakness, a claw hand deformity, and sensory loss over the medial forearm and hand. T1 sympathetic fiber involvement may produce an ipsilateral Horner syndrome.

Question 39Disorders of Nerve Roots and Plexus

Which finding in a patient with acute low back pain mandates emergent lumbosacral MRI?

  1. Urinary retention with saddle anesthesia Correct answer.
  2. Chronic mechanical low back pain
  3. Unilateral L5 distribution foot drop
  4. Positive straight-leg raise at 40 degrees

Explanation

Bowel or bladder dysfunction combined with saddle anesthesia indicates cauda equina syndrome, a surgical emergency requiring urgent imaging of the entire lumbosacral spine. Delay risks permanent sphincter and sensory deficit.

Question 40Disorders of Nerve Roots and Plexus

The long thoracic nerve innervates which muscle?

  1. Trapezius
  2. Rhomboid major
  3. Supraspinatus
  4. Serratus anterior Correct answer.

Explanation

The long thoracic nerve (C5-C7) runs along the chest wall to supply the serratus anterior, which protracts and fixes the scapula. Injury produces medial scapular winging that worsens with forward flexion or wall push-ups.

Question 41Disorders of Nerve Roots and Plexus

Which muscles are supplied by the suprascapular nerve?

  1. Deltoid and teres minor
  2. Levator scapulae
  3. Supraspinatus and infraspinatus Correct answer.
  4. Biceps and brachialis

Explanation

The suprascapular nerve arises from the upper trunk and supplies the supraspinatus and infraspinatus. It can be compressed at the suprascapular notch, causing both weakness and pain, or at the spinoglenoid notch, causing isolated infraspinatus weakness.

Question 42Disorders of Nerve Roots and Plexus

Loss of the ankle jerk reflex localizes most specifically to which nerve root?

  1. S1 Correct answer.
  2. L4
  3. L3
  4. L5

Explanation

The ankle reflex is mediated by the S1 root through the tibial nerve and is the most reliable reflex marker for S1. The knee jerk corresponds to L4 and the medial hamstring reflex to L5.

Question 43Disorders of Nerve Roots and Plexus

A patient has C6 distribution weakness, and needle EMG shows fibrillation potentials in the cervical paraspinal muscles at two levels. This finding best supports which localization?

  1. Radiculopathy rather than plexopathy Correct answer.
  2. Myopathy rather than neuropathy
  3. Anterior horn cell disease rather than radiculopathy
  4. Plexopathy rather than radiculopathy

Explanation

The paraspinal muscles are innervated by the posterior primary ramus, which branches proximal to the plexus. Fibrillation potentials in paraspinal muscles therefore place the lesion at the root or anterior horn cell, and multilevel paraspinal involvement with limb findings in a matching myotome favors radiculopathy.

Question 44Disorders of Nerve Roots and Plexus

A patient reports numbness of the lateral foot. The soleus H reflex is prolonged while the sural sensory response is normal. These findings most suggest which diagnosis?

  1. S1 radiculopathy Correct answer.
  2. Common peroneal neuropathy at the fibular head
  3. L4 radiculopathy
  4. Tibial neuropathy at the tarsal tunnel

Explanation

The H reflex assesses the S1 afferent and efferent loop through the tibial nerve. A normal sural sensory response places the lesion proximal to the dorsal root ganglion, so a prolonged H reflex with preserved sural SNAP points to an S1 root lesion.

Question 45Disorders of Nerve Roots and Plexus

Which feature most strongly supports neuralgic amyotrophy over cervical radiculopathy?

  1. Painless, slowly progressive proximal arm weakness over months
  2. Severe unilateral shoulder pain followed by patchy weakness Correct answer.
  3. Sensory loss restricted to a single dermatome with normal strength
  4. Fibrillation potentials confined to cervical paraspinal muscles on EMG

Explanation

Neuralgic amyotrophy classically begins with abrupt, severe shoulder or arm pain that subsides over days to weeks and is followed by multifocal, patchy weakness, often with scapular winging. Symptoms commonly extend beyond a single root or trunk distribution.

Question 46Disorders of Nerve Roots and Plexus

Which electrodiagnostic pattern is most consistent with neurogenic thoracic outlet syndrome?

  1. Isolated mild slowing of median F waves
  2. Prolonged median distal motor latency with thenar wasting
  3. Reduced ulnar sensory amplitude with hypothenar denervation Correct answer.
  4. Absent sural sensory response with distal leg numbness

Explanation

Neurogenic thoracic outlet syndrome typically affects the lower trunk (C8-T1), producing ulnar sensory loss and denervation in hypothenar and medial thenar muscles. Routine nerve conduction studies are often normal because only the most severely affected fibers show abnormality.

Question 47Disorders of Nerve Roots and Plexus

Which finding on needle EMG favors radiation-induced brachial plexopathy over tumor infiltration of the plexus?

  1. Severe pain requiring escalating opioids
  2. Myokymic discharges on needle EMG Correct answer.
  3. Ipsilateral Horner syndrome
  4. Rapid progression over a few weeks

Explanation

Myokymic discharges are a characteristic sign of radiation-induced nerve injury, although they can also appear in chronic compressive lesions. Tumor infiltration more often causes severe pain, rapid progression, Horner syndrome from sympathetic involvement, and a visible mass on imaging.

Question 48Disorders of Nerve Roots and Plexus

Which feature is most characteristic of diabetic lumbosacral radiculoplexus neuropathy?

  1. Asymmetric thigh pain with weight loss Correct answer.
  2. Symmetric distal small-fiber sensory loss
  3. Isolated foot drop without pain
  4. Painless proximal weakness over years

Explanation

Diabetic lumbosacral radiculoplexus neuropathy is an asymmetric, painful, subacute syndrome with prominent weight loss and weakness, thought to reflect microvasculitic injury. It often begins focally and then spreads, and recovery is usually partial and slow.

Question 49Disorders of Nerve Roots and Plexus

After an acute nerve root compression, fibrillation potentials in paraspinal muscles typically first appear after how long?

  1. 6 to 8 days
  2. 2 to 3 weeks Correct answer.
  3. 24 to 48 hours
  4. 3 to 5 days

Explanation

Wallerian degeneration and the resulting membrane instability require roughly two to three weeks to produce spontaneous fibrillations. An EMG performed earlier may show only reduced recruitment and neurogenic motor unit changes, so a normal early study does not exclude a root lesion.

Question 50Disorders of Nerve Roots and Plexus

Which presentation most suggests a Pancoast tumor?

  1. Neck pain with C5-C6 weakness and a reduced biceps reflex
  2. Buttock pain with L5 weakness and a dropped foot
  3. Arm pain worsened by overhead work with ulnar paresthesias
  4. C8-T1 weakness with shoulder pain and Horner syndrome Correct answer.

Explanation

An apical lung tumor can invade the lower brachial plexus and the cervical sympathetic chain, producing hand weakness, medial arm pain, and an ipsilateral Horner syndrome. Smoking history and shoulder pain radiating down the medial arm are common.