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IBM – Distinguishing from OPMD — SCE Neurology MCQ

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HardPeripheral Neuropathy & NeuromuscularIBM – Distinguishing from OPMDSCE Neurology

A 60-year-old man presents with a 4-month history of bilateral ptosis, dysphagia, and neck flexion weakness. He has wasting of the sternocleidomastoid muscles. Serum CK is 700 IU/L. AChR antibodies are negative. EMG shows both myopathic and neuropathic changes. Muscle biopsy shows rimmed vacuoles with 15-18 nm tubulofilamentous inclusions. He does not respond to steroids. What is the diagnosis?

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Correct answer: A — Inclusion body myositis

IBM can present with ptosis and dysphagia (mimicking OPMD) in addition to its characteristic distal weakness (finger flexors, quadriceps). The combination of mixed myopathic and neuropathic EMG changes, rimmed vacuoles with tubulofilamentous inclusions on biopsy, lack of response to steroids, and negative AChR antibodies is characteristic of IBM. The filamentous inclusions in IBM are 15–18 nm (vs 8.5 nm intranuclear filaments in OPMD). A: AChR antibodies are negative and biopsy shows myopathy. C: OPMD has GCG repeat expansion in PABPN1 and 8.5 nm intranuclear filaments. D: Polymyositis responds to steroids and has different biopsy findings. E: MND would have different biopsy.

Reference: ABN Inflammatory Myopathy Guidelines; Griggs IBM Criteria