Central Diabetes Insipidus Following Steroid Replacement for Hypoadrenalism in Pembrolizumab-Induced Hypophysitis

Immune checkpoint inhibitors are increasingly associated with complex immune-related endocrine adverse events that may evolve dynamically over time. We report a rare case of pembrolizumab-induced hypophysitis complicated by central diabetes insipidus, which was unmasked following glucocorticoid replacement. A 68-year-old female patient receiving immunotherapy for lung adenocarcinoma presented with hyponatremia and secondary adrenal insufficiency, followed by abrupt severe hypernatremia after steroid initiation. Subsequent evaluation confirmed central diabetes insipidus, and treatment with desmopressin resulted in clinical and biochemical recovery. This case highlights the diagnostic challenges posed by overlapping pituitary dysfunction and emphasizes the importance of dynamic endocrine reassessment when electrolyte disturbances evolve during immunotherapy.