MON-010 Immune Checkpoint Inhibitor-Associated Hypophysitis and Hormonal Deficiency

Abstract Disclosure: B. Cunningham: None. S. Mathew: None. M. Acharya: None. I. Gabriely: None. Hypophysitis is a rare but serious complication of immunotherapy, often leading to hypopituitarism due to disruption of anterior pituitary hormone production. Development of this condition may necessitate discontinuation of treatment; however, symptoms can persist despite cessation of therapy. Here, we present a case of an elderly woman who developed hypophysitis, secondary hypothyroidism, and adrenal insufficiency following immunotherapy. An 88-year-old female with a history of malignant melanoma, previously treated with resection and immunotherapy (nivolumab and ipilimumab), was admitted to the hospital after being found unresponsive by her family. She was confused, hypotensive, hypothermic, hyponatremic, and hypoglycemic. Laboratory results revealed a low TSH of 0.25 µIU/mL and a low free T4 of 0.28 ng/dL. Given clinical suspicion for adrenal insufficiency, the patient was empirically treated with intravenous hydrocortisone. Brain MRI supported the diagnosis of hypophysitis, showing characteristic pituitary enhancing and swelling. The patient showed clinical improvement with continued stress-dose steroids and initiation of levothyroxine. She was subsequently transitioned to oral hydrocortisone and levothyroxine. Review of her previous laboratory results indicated normal thyroid function a few months before admission and no prior history of adrenal insufficiency. Her most recent dose of immunotherapy had been administered two weeks prior to presentation, marking her fourth treatment session.Immune checkpoint inhibitors, particularly ipilimumab, are associated with a risk of hypophysitis, with reported incidence rates of up to 3.2%. When combined with nivolumab, this risk increases to 6.4%. Hypophysitis is typically diagnosed based on laboratory findings of secondary hypothyroidism and adrenal insufficiency, with MRI providing supportive evidence of pituitary enlargement or an adenoma-like appearance.Recognition of hypopituitarism secondary to immunotherapy is critical, as patients can present with life-threatening complications such as myxedema coma or adrenal crisis, as demonstrated in this case. Lifelong hormone replacement therapy is often required, and patients should undergo regular monitoring to adjust medications and prevent further complications. References: Barroso-Sousa R, Barry WT, Garrido-Castro AC, et al. Incidence of Endocrine Dysfunction Following the Use of Different Immune Checkpoint Inhibitor Regimens: A Systematic Review and Meta-analysis. JAMA Oncol. 2018;4(2):173-182. doi:10.1001/jamaoncol.2017.3064 Presentation: Monday, July 14, 2025