The Terrible Triad of Checkpoint Inhibition: A Case Report of Myasthenia Gravis, Myocarditis, and Myositis Induced byCemiplimab in a Patient with Metastatic Cutaneous SquamousCell Carcinoma

We report a case of a patient with squamous cell carcinoma (SCC) who developed myasthenia gravis (MG), myositis,and myocarditis after receiving cemiplimab, an anti-PD-1 immune checkpoint inhibitor (ICI).Case Presentation.An 86-year-oldman with metastatic periocular SCC presented with decreased vision in the left eye, severe fatigue, and lower back and bilateral hippain 3 weeks after receiving cemiplimab. Within hours, he developed dysphonia, pharyngeal secretions, and dysphagia, ne-cessitating intubation. Endomyocardial biopsy revealed active lymphocyte-mediated necrosis consistent with ICI-inducedmyocarditis. Anti-striated muscle and anti-acetylcholine receptor antibodies were elevated, consistent with myositis and my-asthenia gravis. Despite plasma exchange therapy, steroids, and intravenous immunoglobulin, he died from cardiac arrest.Conclusions. 'e presence of myasthenia gravis, myocarditis, or myositis should prompt evaluation for all three toxicities as theymay represent an overlap syndrome. 'e severity of these immunotoxicities highlights the need for clinicians to suspect multiplesimultaneous adverse effects of ICIs.