Multisystem Immune-Related Adverse Events Following Pembrolizumab: A Critical Care Case of Myocarditis, Diabetic Ketoacidosis, and CNS Demyelination.

The advent of immune checkpoint inhibitors has significantly advanced cancer treatment. Pembrolizumab, an immune checkpoint inhibitor, has been shown to significantly improve both the progression-free interval and overall survival of patients with melanoma. However, the use of these medications is not without drawbacks and can lead to immune-related adverse events (irAEs), which, though rare, can have permanent sequelae. We present a case of a male in his fifties with a history of melanoma who developed severe multi-system dysfunction following pembrolizumab therapy. Five days following his third cycle of pembrolizumab, the patient presented in severe diabetic ketoacidosis, with hemodynamic instability and acute kidney injury. Subsequently, he developed myocarditis and central nervous system (CNS) demyelination. Management involved high-dose corticosteroids, empiric antimicrobial therapy, and supportive measures including invasive ventilation, hemodynamic support, and renal replacement therapy. This case illustrates the complex and evolving spectrum of pembrolizumab-related immune toxicity and contributes to the literature by documenting a rare combination of multisystem irAEs occurring in close succession. It reinforces the importance of early recognition and prompt, tailored management of irAEs in patients receiving immune checkpoint inhibitors.