Severe Hyponatremia Triggered by Immune Checkpoint Inhibitor Therapy in a Patient With Mulvihill-Smith Syndrome.

Background/objective: Immune checkpoint inhibitors (ICI), including Programmed Cell Death 1, Programmed Cell Death Ligand 1, and Cytotoxic T-lymphocyte Associated Antigen 4 inhibitors, upregulate T-cell responses against tumor cells and are becoming a cornerstone in the treatment of various advanced solid and hematological cancers. Mulvihill-Smith Syndrome (MSS) is a rare genetic syndrome that has been associated with metabolic abnormalities and early-onset tumors, including malignancies. We report the first known case of ICI-induced hyponatremia attributable to syndrome of inappropriate antidiuretic hormone ADH release (SIADH) in a patient with MSS.