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Polymyositis — SCE Rheumatology MCQ

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HardMyositisPolymyositisSCE Rheumatology

A 64-year-old stopped atorvastatin eight weeks ago but has progressive proximal weakness and CK 11,000 IU/L. Muscle biopsy shows myofibre necrosis with little inflammation. Which serological result would most specifically support an exposure-associated immune-mediated necrotising myopathy?

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Correct answer: A — Anti-HMGCR antibody positivity

Persistent severe weakness and CK elevation after statin withdrawal, together with a necrotising biopsy, should prompt anti-HMGCR testing. Anti-cN1A is associated with inclusion-body myositis, anti-Mi-2 and anti-MDA5 with dermatomyositis phenotypes, and anti-Jo-1 with antisynthetase syndrome.

Reference: BSR guideline for idiopathic inflammatory myopathy in children and adults (Published April 2022): https://academic.oup.com/rheumatology/article/61/5/1760/6555980; Nature Reviews Rheumatology: immune-mediated necrotising myopathy (Published October 2020): https://www.nature.com/articles/s41584-020-00515-9