Triple M Overlap Syndrome: A Rare Complication of Immune Checkpoint Inhibitors

Immune checkpoint inhibitors are a major part of many cancer treatment protocols. Most side effects are generally minor, including fatigue, rashes, flu-like symptoms, headaches, or cough. However, some potential side effects may require prompt treatment to ensure optimal outcomes, so it is essential for clinicians to be knowledgeable about these rare but possible complications. We report a case of an 88-year-old woman who presented with the triple M overlap syndrome (TMOS) of myasthenia gravis, myositis, and myocarditis after receiving four rounds of atezolizumab treatment. This diagnosis was confirmed based on the elevated acetylcholine level of 0.89 nmol/L, elevated C-reactive protein level of 1.0 mg/dL, and peak troponin level of 1011 pg/mL. She was treated with high-dose steroids as well as intravenous immunoglobulins and showed clinical improvement. She was eventually transferred to a rehab facility.