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SFEMG Sensitivity – Seronegative MG — SCE Neurology MCQ

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HardClinical NeurophysiologySFEMG Sensitivity – Seronegative MGSCE Neurology

A patient has fatigable ptosis and diplopia but acetylcholine-receptor and MuSK antibodies are negative. Repetitive stimulation is nondiagnostic; single-fibre EMG shows reproducible increased jitter and blocking. What does this establish?

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Correct answer: C — Impaired neuromuscular transmission supporting seronegative myasthenia in the appropriate clinical context

The best answer is “Impaired neuromuscular transmission supporting seronegative myasthenia in the appropriate clinical context”. Single-fibre EMG is highly sensitive for impaired transmission, although the result is not disease-specific and must match the phenotype. “A primary inflammatory myopathy” is plausible in a different neurological context, but the decisive findings here argue against it. “A length-dependent axonal neuropathy” is plausible in a different neurological context, but the decisive findings here argue against it. “Motor neurone disease” is plausible in a different neurological context, but the decisive findings here argue against it. “Normal neuromuscular-junction physiology” is plausible in a different neurological context, but the decisive findings here argue against it.

Reference: Association of British Neurologists guideline for myasthenia gravis: https://pn.bmj.com/content/15/3/199