Anti-SRP Necrotising Myopathy — SCE Neurology MCQ

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HardPeripheral Neuropathy & NeuromuscularAnti-SRP Necrotising MyopathySCE Neurology

A 60-year-old woman presents with progressive dysphagia, nasal regurgitation, and limb weakness over 6 months. She is found to have elevated CK (3,200 IU/L), anti-SRP (signal recognition particle) antibodies, and a necrotising myopathy on biopsy with minimal inflammation. What is the diagnosis?

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Correct answer: C — Immune-mediated necrotising myopathy (IMNM)

Anti-SRP antibodies are associated with immune-mediated necrotising myopathy (IMNM), a severe form of inflammatory myopathy characterised by rapidly progressive proximal weakness, very high CK (often >5,000), and muscle biopsy showing necrosis and regeneration with minimal inflammatory infiltrate. Anti-SRP IMNM tends to be more severe and treatment-resistant than other inflammatory myopathies. Anti-HMGCR antibodies are another cause of IMNM (often statin-triggered). A: Dermatomyositis has skin features and perifascicular atrophy. B: Polymyositis has endomysial inflammation with CD8+ T-cell invasion. D: IBM has rimmed vacuoles and is steroid-resistant. E: Statin myopathy resolves on statin cessation (unless anti-HMGCR IMNM).

Reference: ENMC IMNM Classification (2017); ABN Inflammatory Myopathy Guidelines