Steroid Myopathy — SCE Dermatology MCQ

Correct answer: B — Steroid myopathy (from prolonged Prednisolone causing proximal muscle weakness)

The correct answer is B, steroid myopathy (from prolonged prednisolone causing proximal muscle weakness). This patient has been on long-term prednisolone for six months and, despite biochemical and cutaneous remission of dermatomyositis (normalised CK, improved rash), still has proximal weakness. This dissociation between normal CK and persistent weakness is the classic discriminator for steroid-induced myopathy, which results from glucocorticoid-mediated catabolism of type II muscle fibres rather than inflammatory necrosis, so CK stays normal. Chronic corticosteroid use is a recognised cause of proximal myopathy, and this must be excluded before escalating immunosuppression for presumed refractory disease, since correct management (steroid dose reduction) is opposite to what active myositis would require. EMG lacks the fibrillation potentials seen in active DM, and weakness typically improves on steroid tapering. Why the other options are wrong: D. Deconditioning only: does not selectively track with steroid dose and duration, and is a diagnosis of exclusion rather than the specific complication expected in a patient on prolonged high-dose steroids. E. Drug-induced lupus: presents with arthralgia, serositis, rash and antihistone antibodies, not isolated proximal myopathy, and is not a recognised complication of methotrexate or prednisolone in DM. A. Vitamin D deficiency only: can cause proximal myopathy but is not the specific treatment-related complication being tested; it should be checked but is not the expected mechanism here. C. Neuropathy from methotrexate: methotrexate causes hepatotoxicity, pneumonitis and mucosal toxicity, not peripheral neuropathy, and neuropathy gives distal sensory signs, not proximal weakness. Key point: persistent proximal weakness with a normal CK on long-term corticosteroids points to steroid myopathy, not refractory dermatomyositis, and warrants a trial of steroid dose reduction rather than treatment escalation.

Reference: BNF (NICE), Prednisolone: Side-effects, musculoskeletal and connective tissue disorders (proximal myopathy with long-term corticosteroid use), https://bnf.nice.org.uk/drugs/prednisolone/