Authors: Deepinder Kaur Maini , Varun Rehani , Rajiv Anand

Abstract

Background: Immune checkpoint inhibitor-induced (ICI) myasthenia gravis (MG) is rare but may present as a fulminant overlap syndrome with myositis and myocarditis.

Case Presentation: A 63-year-old man with carcinoma of the oral cavity receiving Toripalimab presented with fluctuating ptosis, dysarthria, dysphagia, generalized weakness, and breathlessness. He developed type 2 respiratory failure requiring non-invasive ventilatory (NIV) support. Anti-AChR and anti-MuSK antibodies were negative, and RNST was non-decremental. Creatinine Kinase (CK), Serum Glutamic Pyruvic Transaminase (SGPT), and Serum Glutamic-Oxaloacetic Transaminase (SGOT) were elevated, supporting myositis. High-sensitivity troponin I, CPK-MB, and NT-proBNP were raised, supporting myocarditis overlap. Imaging excluded major alternate central and thromboembolic causes. He was treated with immunomodulatory therapies (intravenous methylprednisolone and immunoglobulin-IVIG).

Conclusion: ICI-induced seronegative MG with myositis-myocarditis (MMM syndrome) overlap should be suspected in patients receiving PD-1 inhibitors who develop acute ocular-bulbar weakness and respiratory decline, even when antibody and electrophysiologic studies are negative. Early recognition is critical because cardiac and respiratory involvement may be life-threatening.

Keywords: Immune checkpoint inhibitor, toripalimab, seronegative myasthenia gravis, myositis, myocarditis, MMM syndrome, respiratory failure; case report.