Immune checkpoint inhibitors (ICIs) have emerged in recent years as a promising treatment option for several malignant tumors. However, ICI therapy has also been associated with various immune-related adverse events (irAEs), especially with pre-existing autoimmune status, which sometimes can be life-threatening. A 68-year-old woman diagnosed with metastatic thymoma was treated with camrelizumab as her initial anti-tumor protocol at a nearby hospital. On 11 days after the first dose of camrelizumab, the patient was admitted to our hospital with symptoms of dyspnea, fatigue, and poor appetite. Workup on admission indicated dramatically elevated transaminase, troponin I, creatine kinase, and creatine kinase MB and a new-onset conduction abnormality on electrocardiography. She had no other underlying disease prior to ICI treatment; therefore, ICI-related myocarditis, myositis and hepatitis were diagnosed, and intravenous methylprednisolone (80mg/day) and other supporting treatments were administered sequentially. Coronary angiography was performed on day 3 of hospitalization, but no abnormality was detected. On the same day, she lapsed into a coma with respiratory muscle failure, which was highly suspected of myasthenic crisis. Therefore, mechanical ventilation and higher dose of methylprednisolone (1 g/day) plus intravenous immunoglobulin (20g/day) were applied immediately. The third artrioventricular block occurred abruptly and an urgent temporary pacemaker was placed. Repeated ventricular tachycardia (VT) occurred, and even multiple antiarrhythmic drugs used in combination failed to alleviate the VT storm. On day 5 of hospitalization, she suffered from ventricular fibrillation and die of cardiac arrest. In conclusion, close follow-up should be conducted after ICI treatment, especially for patients already with or at high risk for autoimmune disorders. Once diagnosed with severe irAEs, prompt high dose of glucocorticoid alone or in combination with other immunomodulators if necessary should be administered. A multidisciplinary team approach is of importance for better management of patients with multiple organs involvement.