Rare, Late Onset of Immune Checkpoint Inhibitor-Induced Type 1 Diabetes Mellitus in a Patient with Small-Cell Lung Cancer Treated with Serplulimab: a Case Report and Review of the Literature

Background As a newly approved immune checkpoint inhibitor in China, serplulimab has been widely used in the immunotherapy of tumors. However, the immune-related adverse events of immune checkpoint inhibitors should not be ignored. Although immune checkpoint inhibitor-induced type 1 diabetes mellitus is a rare complication, it may cause diabetic ketoacidosis and endanger the lives of patients. Case presentation This case report describes a 55-year-old male of Han nationality from China diagnosed with small-cell lung cancer with multiple metastases who experienced an adverse event of type 1 diabetes mellitus 68 weeks after receiving serplulimab therapy. The patient presented with typical symptoms of diabetic ketoacidosis, including severe thirst, nausea, vomiting, deep respirations, and stupor. Despite the absence of diabetes-related autoantibodies, the patient had extremely low levels of insulin and C-peptide release. Other potential causes of diabetes were ruled out, confirming the condition as serplulimab-induced immune checkpoint inhibitor-induced type 1 diabetes mellitus. After aggressive treatment to correct diabetic ketoacidosis, the patient’s blood glucose levels stabilized and symptoms of diabetes improved significantly, although long-term insulin maintenance therapy was necessary. Conclusion This case highlights a rare, late-onset adverse event of immune checkpoint inhibitor-induced type 1 diabetes mellitus that may be overlooked during treatment with serplulimab. The monitoring of blood glucose levels and early signs and symptoms of diabetes cannot be relaxed at the late stage of treatment, even if patients do not have elevated blood glucose levels before and during the middle stage of treatment.