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Anti-HMGCR IMNM — SCE Neurology MCQ

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HardPeripheral Neuropathy & NeuromuscularAnti-HMGCR IMNMSCE Neurology

A patient develops progressive proximal weakness and CK 3,800 IU/L that persists for months after atorvastatin withdrawal. Anti-HMGCR antibodies are strongly positive. Which diagnosis best fits?

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Correct answer: A — Anti-HMGCR immune-mediated necrotising myopathy, given the imaging pattern, in this presentation

The best answer is “Anti-HMGCR immune-mediated necrotising myopathy, given the imaging pattern, in this presentation”. Persistent weakness, marked CK elevation and anti-HMGCR antibodies after statin cessation distinguish immune-mediated necrotising myopathy from self-limited statin toxicity. “Self-limited toxic statin myopathy resolving after drug withdrawal” remains a plausible alternative in a different presentation, but it does not fit the decisive finding or management threshold here. “Inclusion body myositis with predominant finger-flexor weakness” remains a plausible alternative in a different presentation, but it does not fit the decisive finding or management threshold here. “Lambert–Eaton myasthenic syndrome caused by a presynaptic channel antibody” remains a plausible alternative in a different presentation, but it does not fit the decisive finding or management threshold here. “Polymyalgia rheumatica without primary muscle-fibre injury” remains a plausible alternative in a different presentation, but it does not fit the decisive finding or management threshold here.

Reference: 2017 ENMC classification of immune-mediated necrotising myopathies: https://pubmed.ncbi.nlm.nih.gov/30329187/