Steroid Myopathy in MG Patient — SCE Neurology MCQ

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ModeratePeripheral Neuropathy & NeuromuscularSteroid Myopathy in MG PatientSCE Neurology

A 55-year-old man with known AChR-positive generalised MG presents with progressive difficulty climbing stairs and rising from a chair over 6 months. His CK is normal. He is on prednisolone 5 mg daily and azathioprine 150 mg daily. His MG symptoms (ptosis, diplopia, bulbar) are well controlled. What additional diagnosis should be considered?

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Correct answer: E — Steroid myopathy

Chronic corticosteroid use can cause steroid myopathy — a painless proximal myopathy with normal CK. Even low-dose prednisolone (5 mg) can contribute over prolonged periods, though it is more common at higher doses. In an MG patient with well-controlled myasthenic symptoms but new proximal weakness, steroid myopathy should be distinguished from MG worsening. EMG may show myopathic changes without MG-related decrement. Trial dose reduction of prednisolone (if clinically safe) may help differentiate. B: Azathioprine does not typically cause myopathy. C: MG crisis would affect bulbar and respiratory muscles. D: LEMS has different antibodies and NCS findings. E: IBM is possible but steroid myopathy is more likely in context.

Reference: ABN MG Guidelines (2025); BNF – Corticosteroid Side Effects