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Inflammatory myopathy — SCE Rheumatology MCQ

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ModerateConnective tissue diseasesInflammatory myopathySCE Rheumatology

A 44-year-old man has an 8-week history of progressive symmetrical proximal muscle weakness. Hip flexion and shoulder abduction are weak, but reflexes and sensation are preserved. He has no rash, dysphagia or exposure to a recognised myotoxic drug. Serum creatine kinase is 4,800 IU/L; thyroid function and electrolytes are normal. A comprehensive myositis-specific and myositis-associated antibody panel, including anti-HMGCR and anti-SRP antibodies, is negative. MRI of the thighs shows patchy muscle oedema without fatty replacement. Which investigation is most appropriate to establish the diagnosis and classify the myopathy?

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Correct answer: C — Muscle biopsy

Muscle biopsy is the most appropriate investigation. He has objective proximal myopathy with markedly raised CK and MRI evidence of active muscle disease, but no diagnostic rash, drug exposure or myositis autoantibody. Histopathology can classify seronegative inflammatory myopathy and distinguish immune-mediated necrotising myopathy, dermatomyositis-spectrum pathology, inclusion-body myositis and non-inflammatory mimics. MRI helps select an affected but non-end-stage muscle. Electromyography may confirm myopathic physiology but does not reliably establish subtype. Broad genetic testing may subsequently be appropriate if biopsy suggests an inherited myopathy. CT or FDG PET-CT may be used for malignancy assessment according to the eventual phenotype and risk profile, but neither establishes the cause of the muscle weakness.

Reference: Kleinveld VEA et al. Diagnostic Value of Muscle Biopsy for the Evaluation of Adult Myopathy in Daily Clinical Practice. Diagnostics. 2025;15:3102. https://pubmed.ncbi.nlm.nih.gov/41464103/