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Polymyositis – CD8+ T-Cell Invasion — SCE Neurology MCQ

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ModeratePeripheral Neuropathy & NeuromuscularPolymyositis – CD8+ T-Cell InvasionSCE Neurology

A 45-year-old man presents with a 3-year history of progressive symmetric proximal weakness affecting shoulders and hips. He has difficulty rising from chairs, climbing stairs, and lifting objects above his head. CK is 5,200 IU/L. He has no skin rash. EMG shows a myopathic pattern. Muscle biopsy shows endomysial inflammation with CD8+ T cells invading non-necrotic muscle fibres. What is the diagnosis?

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Correct answer: A — Polymyositis

Polymyositis presents with symmetric proximal weakness, elevated CK, myopathic EMG, and muscle biopsy showing endomysial inflammation with CD8+ T-cell invasion of non-necrotic muscle fibres (the pathological hallmark distinguishing PM from DM). No skin rash distinguishes it from DM. It responds to immunosuppression (prednisolone + steroid-sparing agent). Note: PM is now considered less common than previously thought — many cases are reclassified as IBM, IMNM, or anti-synthetase syndrome on further investigation. A: DM has skin features and perifascicular atrophy. C: IBM has rimmed vacuoles and different distribution. D: DMD is childhood-onset with dystrophin absence. E: Statin myopathy resolves on cessation.

Reference: ABN Inflammatory Myopathy Guidelines; ENMC Classification