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PMA vs MMN – Differential Diagnosis — SCE Neurology MCQ

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ModeratePeripheral Neuropathy & NeuromuscularPMA vs MMN – Differential DiagnosisSCE Neurology

A 48-year-old man presents with a 2-year history of progressive bilateral hand weakness and wasting. He has fasciculations in both arms. Tendon reflexes are absent in the upper limbs and normal in the lower limbs. Sensation is intact. There are no upper motor neurone signs. EMG shows widespread chronic denervation in the upper limbs. Lower limb EMG is normal. What is the most important differential diagnosis to exclude?

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Correct answer: A — Multifocal motor neuropathy

In a patient presenting with progressive lower motor neurone weakness in the upper limbs without sensory or UMN signs, the key differential between MND (progressive muscular atrophy variant) and multifocal motor neuropathy (MMN) must be resolved. MMN is treatable with IVIg and should be actively excluded in all patients with progressive asymmetric LMN weakness. NCS with conduction block studies and anti-GM1 antibody testing are essential. B: Myelopathy would cause UMN signs. C: MG causes fatigable weakness without wasting. D: Polymyositis causes proximal weakness without fasciculations. E: CTS has a median nerve distribution.

Reference: NICE NG42 MND (2016); EAN/PNS MMN Guidelines (2010)