Simultaneous immune checkpoint blockade-associated diabetes mellitus and thyrotoxicosis

Immune checkpoint inhibitors (ICIs) have become an increasingly prominent therapeutic option in the management of a variety of cancers. As their clinical use expands, so too should our understanding of immune-related adverse events (irAEs) associated with these agents. By enhancing immune activation, ICIs can cause off-target inflammation in various tissues, including endocrine. We present a case illustrating a rare but life-threatening manifestation of ICI toxicity: simultaneous severe diabetes mellitus and thyrotoxicosis after just a single dose of ICI. This case highlights the importance of prompt recognition and timely intervention of acute, life-threatening endocrine irAEs. We discuss the pathophysiology, management, and clinical course of ICI-induced diabetes mellitus and thyroid disease, with brief discussion of endocrine irAEs as a surrogate of therapeutic efficacy.