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Immune-Mediated Necrotising Myopathy — RACP Adult Medicine MCQ

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HardRheumatologyImmune-Mediated Necrotising MyopathyRACP Adult Medicine

A 55-year-old man presents with symmetric proximal weakness (unable to rise from chair), dysphagia, and an elevated CK (8000 U/L). He has no rash. Anti-SRP antibody is positive. EMG shows myopathic features. Muscle biopsy shows necrotising myopathy with minimal inflammatory infiltrate. He has had a rapid onset over 3 weeks and is not on a statin. What is the most likely diagnosis?

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Correct answer: A — Immune-mediated necrotising myopathy

Rapidly progressive proximal weakness with very high CK, anti-SRP antibody, and biopsy showing necrotising myopathy with minimal inflammation is immune-mediated necrotising myopathy (IMNM). Anti-SRP and anti-HMGCR are the two specific IMNM antibodies. Anti-SRP IMNM is severe, often refractory to standard immunosuppression, and requires aggressive treatment (prednisolone + IVIG + rituximab or additional immunosuppressant).

Reference: ENMC – 2024 – IMNM Consensus; ACR/EULAR 2017 IIM