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Progressive Muscular Atrophy — SCE Neurology MCQ

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ModeratePeripheral Neuropathy & NeuromuscularProgressive Muscular AtrophySCE Neurology

A 55-year-old man presents with progressive bilateral upper and lower limb weakness, distal wasting, and areflexia. NCS show markedly reduced CMAP amplitudes with preserved SNAP amplitudes and normal conduction velocities. EMG shows widespread active denervation. There are no upper motor neurone signs. Anti-GM1 IgM antibodies are negative. He has no fasciculations. MRI brain and spine are normal. What is the most likely diagnosis?

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Correct answer: D — Progressive muscular atrophy

Progressive muscular atrophy (PMA) is a pure lower motor neurone variant of MND, characterised by progressive weakness and wasting without upper motor neurone signs. NCS show low CMAPs (motor axonal loss) with preserved SNAPs (distinguishing it from peripheral neuropathies). Some PMA patients develop UMN signs over time (converting to ALS). PMA has a slightly better prognosis than ALS (~5-year median survival vs ~3 years). A: ALS requires combined UMN and LMN signs. C: CIDP has demyelinating NCS and sensory involvement. D: MMN has conduction block and anti-GM1 antibodies. E: Adult SMA has proximal weakness and a genetic basis (SMN1).

Reference: NICE NG42 MND (2016); El Escorial Criteria