Immune Checkpoint Inhibitor–Induced Myocarditis with Myositis/Myasthenia Gravis Overlap Syndrome: A Systematic Review of Cases

BACKGROUND: The development of immune checkpoint inhibitors (ICIs) represents a paradigm shift in the treatment of cancers. Despite showing remarkable efficacy, these agents can be associated with life-threatening immune-related adverse events. In recent years, several cases of myocarditis with myositis and/or myasthenia gravis overlap syndrome (IM3OS) have been reported. However, given the rarity, the clinical features and outcomes of these cases remain poorly understood. We, therefore, attempted to systematically review and summarize all cases of IM3OS reported in the literature. MATERIALS AND METHODS: Studies reporting IM3OS were identified in Embase and MEDLINE. Only case reports and case series published in journals or presented at conferences were included. We conducted a systematic review according to the PRISMA Harms guidelines. RESULTS: A total of 60 cases were eligible. The patients' median age was 71 years, and the majority (67%) were males; melanoma was the most common indication for ICIs (38%). The most-reported symptoms were fatigue (80%) and muscle weakness (78%). The median number of doses to the development of IM3OS was one. The average creatine kinase level was 9,645 IU/L. Cardiac arrhythmias occurred in 67% of patients, and 18% had depressed ejection fraction. Initial treatment consisted of immunosuppression with high-dose steroids and supportive therapies. Sixty percent of the patients died in hospital because of acute complications. CONCLUSION: IM3OS can be associated with significant mortality and morbidity. Prospective studies are needed to understand the optimal approach to diagnose and manage these patients and to develop biomarkers to predict the occurrence and severity of this rare but serious condition. IMPLICATIONS FOR PRACTICE: Clinicians should suspect coexisting myositis and/or myasthenia gravis in all patients with immune checkpoint inhibitor-induced myocarditis, given their propensity to occur together. Early recognition and prompt treatment with the help of a multidisciplinary team might help improve the outcomes of this life-threatening condition.