Immune checkpoint-mediated myositis and myasthenia gravis: A case report and review of evaluation and management.

Background: We present a case of myositis and possible overlapping neuromuscular junction disorder following treatment with nivolumab for recurrent/metastatic head and neck squamous cell carcinoma (HNSCC).

Methods: We report a 75-year-old man with recurrent stage IVA, T1N2cM0 oral cavity HNSCC treated with weight-dosed nivolumab who presented three weeks later with severe fatigue, generalized weakness, and bilateral ptosis. Evaluation demonstrated elevated creatine kinase and myopathic motor units on electromyography, supporting a diagnosis of an underlying muscle disease. Elevated serum acetylcholine receptor binding antibodies raised the possibility of concurrent myasthenia gravis.

Results: He received corticosteroids and plasmapheresis without improvement in muscle weakness. His course was complicated by bacteremia, cardiac arrest, and concerns for recurrent malignancy. Following a two-month hospital stay, he was made comfort care and died.

Conclusions: With increasing usage of checkpoint inhibitors in HNSCC, clinicians must be aware of and vigilant for associated rare but serious adverse events.