Quiz Form

Question Date: 28/07/2023

Question: A 40 year old male presents with right grip weakness since 2 years. Examination reveals radial and ulnar weakness without sensory abnormalities. Nerve conduction studies show presence of motor conduction block with normal sensory responses. CSF and serum protein electrophoresis are normal. Which of these statements is true regarding the diagnosis of MMN (Multifocal motor neuropathy)?

Options:

• MMN may present with distal asymmetric upper extremity weakness with fasciculations
• IgM anti-GM 1 antibodies are diagnostic of this condition
• IVIG and plasma exchange are effective treatment options
• MRI of brachial/lumbo sacral plexus is normal

Correct Answer: MMN may present with distal asymmetric upper extremity weakness with fasciculations

Explaination: Multifocal motor neuropathy usually presents with distal, asymmetric, progressive upper extremity weakness (80%) in the distribution of a nerve. Cramps and fasciculations are seen, though it raises possibility of ALS also. It is diagnosed by presence of conduction blocks without temporal dispersion in two motor nerves in non compressible sites. CSF is usually normal, mild elevation of protein<100 mg/dl may be seen in a third. High titer of Ig M anti-GM 1 antibodies are seen in 50-60% of patients. But it is not necessary or sufficient for diagnosis as such antibodies are seen in AMAN variant of GBS and 10% of amyotrophic lateral sclerosis. MRI of brachial and lumbosacral plexus may show focal enlargement of affected nerve trunks. IVIG is the most effective treatment option followed by cyclophosphamide. Corticosteroids and plasma exchange are ineffective and may occasionally worsen the condition.

Reference: Allen J. Chronic Demyelinating Polyneuropathies. Continuum 2017;23(5):1310-1331.