MCQs on Peripheral Nerves

Written by Dr. James Whitfield (MBBS, FRACGP) – General Practitioner

Question 1

A 45-year-old man, Alan, presents to your clinic for the first time with complaints of frequent tripping of his right foot over the past few months, which has worsened in the past month. On examination, there is noticeable wasting of the interosseous muscles of the right foot and foot drop on the same side. The plantar reflex is equivocal on the right but extensor on the left. Deep tendon reflexes in the lower limbs are normal.

Which one of the following investigations is most likely to establish the diagnosis?

A) MRI of the head and cervical spine
B) Acetylcholine receptor antibodies
C) CT scan of the head and cervical spine
D) Lumbar puncture
E) Electromyography (EMG)

Correct Answer: E) Electromyography (EMG)

Alan has clinical signs suggestive of both upper and lower motor neuron involvement. The right-sided foot drop and interosseous muscle wasting are consistent with a lower motor neuron lesion, while the left-sided extensor plantar response indicates an upper motor neuron lesion.

The combination of UMN and LMN signs at different anatomical sites raises strong suspicion for a motor neuron disease (MND), such as amyotrophic lateral sclerosis (ALS). Electromyography (EMG) is the most appropriate investigation in this context, as it can detect evidence of widespread denervation and reinnervation, supporting the diagnosis of MND.

Spinal canal stenosis, although a potential differential, is less likely here due to the absence of chronic pain (a typical early feature) and because the neurological pattern observed does not align with segmental UMN and LMN signs seen in stenosis. Other listed investigations are not first-line in diagnosing this mixed-pattern motor neuron disorder.

Question 2

A 52-year-old man presents to your clinic with progressive spasticity and weakness in his left lower limb over the past three months. He reports increasing difficulty with walking. On examination, fasciculations are noted in the left deltoid and small muscles of the hand, but muscle power, reflexes, and sensation in the upper limbs are normal. In the lower limbs, bilateral extensor plantar reflexes are present. He has left-sided foot drop, weakness, and spasticity. Lower limb sensation is intact.

Which one of the following investigations is the most appropriate to reach a diagnosis?

A) CT scan of the brain
B) MRI of the cervical spine
C) Electromyography
D) Lumbar puncture (LP)
E) MRI of the brain

Correct Answer: C) Electromyography

This patient presents with a combination of upper motor neuron (UMN) signs—such as spasticity and extensor plantar reflexes—and lower motor neuron (LMN) signs, such as fasciculations and foot drop. The presence of both UMN and LMN features in different regions, with intact sensation, is highly suggestive of a motor neuron disorder, most likely amyotrophic lateral sclerosis (ALS).

ALS is the most common adult-onset motor neuron disease. It is characterized by progressive degeneration of both upper and lower motor neurons, leading to muscle weakness, wasting, fasciculations, spasticity, and eventually respiratory failure. Sensory pathways are typically spared, helping differentiate ALS from other neurological disorders.

Electromyography (EMG), often combined with nerve conduction studies (NCS), is the most useful investigation in confirming a diagnosis of ALS. EMG helps identify widespread denervation and reinnervation in clinically affected and unaffected muscles, supporting a diagnosis of motor neuron disease.

While imaging such as CT or MRI may help exclude other differential diagnoses (e.g. multiple sclerosis, cervical myelopathy), they are typically normal in ALS and not diagnostic. Lumbar puncture is only useful in atypical presentations to rule out infections, inflammation, or malignancy. In this case, the combination of clinical features makes EMG the most appropriate next step.

Question 3

An 11-year-old boy is brought to your practice with progressive difficulty climbing stairs, walking, and running over the past few days. On examination, bilateral lower limb weakness is noted. All lower limb deep tendon reflexes are absent, but sensation is intact.

Which one of the following tests is most likely to confirm the diagnosis?

A) CSF analysis
B) Forced vital capacity
C) MRI
D) Nerve conduction studies
E) X-ray

Correct Answer: D) Nerve conduction studies

This child presents with acute bilateral lower limb weakness, areflexia, and preserved sensation—features highly suggestive of Guillain-Barré syndrome (GBS), an acute inflammatory demyelinating polyneuropathy.

GBS commonly begins with distal weakness that progresses proximally and is often preceded by a recent infection, such as gastroenteritis. The hallmark clinical features are rapidly progressive symmetric muscle weakness and loss of reflexes, with relatively preserved sensation.

The diagnosis of GBS is clinical but supported and confirmed by investigations. Nerve conduction studies (NCS) are the most accurate and sensitive test for confirming GBS. NCS typically show a demyelinating pattern and provide essential information for diagnosis and prognosis.

Although cerebrospinal fluid (CSF) analysis may show albuminocytologic dissociation, this finding may not be present early in the disease. Forced vital capacity (FVC) is used to monitor respiratory function and determine the need for intensive care, but it is not diagnostic. Imaging studies like MRI and X-ray have no role in diagnosing GBS.

Thus, nerve conduction studies are the investigation of choice for confirming the diagnosis in this patient.

Previous Next

1. Neurology Module

1.1 Cerebrovascular Disorders

1.2 Cranial Nerves

1.3 Spinal Cord

1.4 Peripheral Nerves

1.5 Headaches

1.6 Seizure Disorders

1.7 Movement Disorders

1.8 Neuroimaging

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