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MND Mimics — RACP Adult Medicine MCQ

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HardNeurologyMND MimicsRACP Adult Medicine

A 50-year-old man presents with a 3-week history of progressive bilateral hand weakness and wasting, fasciculations in the arms, and brisk lower limb reflexes. Sensation is intact. MRI cervical spine is normal. EMG shows widespread denervation in 3 body regions. What investigation is most important to exclude a treatable mimic?

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Correct answer: D — Anti-ganglioside antibodies (anti-GM1)

While the clinical picture suggests ALS/MND, multifocal motor neuropathy (MMN) is a critical treatable mimic that must be excluded. MMN presents with asymmetric LMN weakness, typically in the upper limbs, often with preserved reflexes in weak muscles. Anti-GM1 IgM antibodies are positive in ~50% of MMN cases. NCS showing conduction block is another key finding. MMN responds to IVIg therapy, making its distinction from ALS crucial. Other mimics include Kennedy's disease (X-linked bulbospinal muscular atrophy – androgen receptor CAG repeat expansion).

Reference: eTG – 2025 – Neurology; EAN/PNS – 2022 – MMN Guidelines