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Myositis assessment — SCE Rheumatology MCQ

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EasyMusculoskeletal investigationsMyositis assessmentSCE Rheumatology

A 52-year-old man has a 6-week history of progressive symmetrical shoulder- and hip-girdle weakness. He has mechanic's hands, a dry cough and bibasal inspiratory crackles. Serum creatine kinase is 4800 IU/L. Pulmonary function tests and high-resolution CT of the chest have been arranged. Which additional serological investigation is most appropriate to define the inflammatory myopathy subtype and associated organ risks?

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Correct answer: A — Myositis antibody panel

The correct answer is A. Proximal weakness, markedly raised CK, mechanic's hands and probable interstitial lung disease strongly suggest an idiopathic inflammatory myopathy, particularly antisynthetase syndrome. A panel of myositis-specific and myositis-associated antibodies can identify anti-Jo-1 or less common antisynthetase antibodies and help define other clinically important subtypes. The antibody profile informs expected pulmonary, malignant and other extramuscular risks, although results must be interpreted alongside the clinical phenotype because commercial assays can produce false-positive or false-negative findings. ANA may support an autoimmune diagnosis but does not adequately subtype myositis. ANCA investigates small-vessel vasculitis, while anti-CCP antibodies and rheumatoid factor primarily support rheumatoid arthritis. Serology complements rather than replaces the already arranged HRCT and pulmonary function testing.

Reference: McMorrow FK, Anwyll N, Tansley SL. Autoantibody testing in myositis: an update. Current Opinion in Rheumatology. 2024;36(6):481-487. https://pubmed.ncbi.nlm.nih.gov/30826741/