Immune Checkpoint Inhibitor-Induced Type 1 Diabetes Mellitus in a Patient With Melanoma: A Case Report

Pembrolizumab, an anti-programmed cell death protein 1 (anti-PD-1) monoclonal antibody, has been approved for use in patients with advanced melanoma and various other indications. Autoimmune diabetes mellitus is one of several immune-related adverse events (irAEs) that have been described with pembrolizumab and other immune checkpoint inhibitor (ICI) therapies. We report the case of a 72-year-old man with no history of diabetes mellitus who was treated with pembrolizumab for advanced melanoma. After six cycles of therapy, he presented to the emergency department with a three-day history of polydipsia, polyuria, and dry mouth. His blood glucose level was 42.9 mmol/L, with a high anion gap metabolic acidosis. A diagnosis of diabetic ketoacidosis (DKA) was made. Treatment with rehydration and intravenous insulin was initiated until recovery, followed by a subcutaneous basal-bolus insulin regimen. Pembrolizumab treatment was continued due to a favorable therapeutic response. ICI-induced type 1 diabetes mellitus is a potentially life-threatening irAE, making blood glucose monitoring imperative during ICI therapy.