Steroid Myopathy vs Active Myositis — RACP Adult Medicine MCQ

Instant feedback + full explanation. One question, done properly.

ModerateRheumatologySteroid Myopathy vs Active MyositisRACP Adult Medicine

A 65-year-old woman with polymyositis on prednisolone 20 mg daily develops proximal weakness. Her CK has normalised. What is the most important clinical distinction to make?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — Active myositis vs steroid myopathy

When a patient on corticosteroids for inflammatory myopathy develops weakness with a normal CK, the critical distinction is between active myositis and glucocorticoid-induced (steroid) myopathy. Steroid myopathy causes type II fibre atrophy without inflammation – CK is normal, and EMG may show myopathic changes without spontaneous activity. In active myositis, CK is usually elevated and EMG shows fibrillation potentials. MRI (STIR sequences showing muscle oedema) helps distinguish active inflammation from steroid myopathy.

Reference: eTG – 2025 – Rheumatology; BSR – 2022 – Myositis Guidelines