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ICI-Related MG with Myositis — SCE Neurology MCQ

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HardPeripheral Neuropathy & NeuromuscularICI-Related MG with MyositisSCE Neurology

A 62-year-old man on nivolumab for NSCLC develops diplopia, ptosis, dysphagia, and proximal weakness over 10 days. AChR antibodies positive. RNS shows decrement. CK is 2,500 IU/L. What is the diagnosis?

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Correct answer: A — ICI-related MG with concurrent myositis

ICIs can trigger de novo MG often with concurrent myositis (elevated CK) and sometimes myocarditis. The combination of fatigable weakness, AChR antibodies, decremental RNS, AND elevated CK suggests overlapping MG and myositis. A: Elevated CK suggests concurrent myositis. C: LEMS has incremental response. D: Pure polymyositis lacks decremental response. E: Botulism has different features.

Reference: MGFA ICI-Related MG Consensus (2020)