Isolated Adrenocorticotropic Hormone Deficiency Associated with Severe Hyperkalemia During Pembrolizumab Therapy in a Patient with Ureteral Cancer and an Ileal Conduit: A Case Report and Literature Review

BACKGROUND Immune checkpoint inhibitors (ICIs) are anticancer medications that enhance the antitumor immune response. The clinical benefit afforded by ICIs, however, can be accompanied by immune-related adverse events (IRAEs). One of the common endocrine IRAEs is hypophysitis, which often causes hypopituitarism with secondary adrenal insufficiency (AI). Secondary AI, including isolated adrenocorticotropic hormone (ACTH) deficiency (IAD), is often associated with hyponatremia. Here, we report an unusual case of ICI-related IAD associated with severe hyperkalemia. CASE REPORT A 78-year-old woman who had an ileal conduit, chronic kidney disease, type 2 diabetes mellitus, and hypertension and was taking an angiotensin II receptor blocker began treatment for advanced ureteral cancer with the anti-programmed cell death protein 1 inhibitor pembrolizumab. The therapy effectively controlled the cancer, but 4 1/2 months after starting it, the patient developed anorexia, general weakness, and muscle pain and was diagnosed with IAD associated with severe hyperkalemia and hyperchloremic metabolic acidosis. She recovered after prompt administration of corticosteroids and treatment with sodium bicarbonate, glucose/insulin, and cation exchange resins. CONCLUSIONS Hyperkalemia is a common symptom of primary AI but is less common in patients with central AI because a lack of ACTH does not cause aldosterone deficiency and mineralocorticoid action is preserved. The present case demonstrates the need for physicians to be aware of severe hyperkalemia as a life-threatening complication of secondary AI induced by ICIs, particularly in patients with predisposing factors, such as kidney dysfunction, diabetes mellitus, an ileal conduit, and renin-angiotensin-aldosterone system inhibitor use.