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IBM Treatment Resistance — SCE Rheumatology MCQ

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ModerateMyositisIBM Treatment ResistanceSCE Rheumatology

A 65-year-old man has biopsy-confirmed sporadic inclusion body myositis. Over 5 years he has developed slowly progressive, asymmetric weakness of the deep finger flexors and knee extensors. Which statement best describes the expected treatment response compared with correctly classified polymyositis?

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Correct answer: C — IBM usually shows no sustained response to immunotherapy, whereas polymyositis generally improves with immunosuppression.

Explanation lettering: E = shown as A · D = shown as B · B = shown as C · C = shown as D · A = shown as E

IBM is characteristically refractory to conventional immunotherapy, including glucocorticoids and IVIg, with no convincing sustained improvement in limb weakness or disease progression. By contrast, correctly classified polymyositis is an immune-mediated inflammatory myopathy that generally improves with glucocorticoids and additional immunosuppression. IVIg may occasionally provide transient benefit for IBM-associated dysphagia, but it is not an effective disease-modifying treatment. Options A and E reverse the expected relationship; C incorrectly describes polymyositis as generally untreatable; and D ignores the marked difference in treatment responsiveness. In an older patient with slowly progressive asymmetric finger-flexor and quadriceps weakness, an apparent diagnosis of treatment-resistant polymyositis should prompt reconsideration of IBM or another myopathy.

Reference: Santos EJF et al. Efficacy and safety of pharmacological treatments in inclusion body myositis: a systematic review. RMD Open. 2025;11:e005176. https://pubmed.ncbi.nlm.nih.gov/30890877/