SAT-753 - Immunotherapy-Induced Hypoparathyroidism: A Rare Endocrine Adverse Event

Introduction:
Immune checkpoint inhibitors (ICIs) are increasingly used in the treatment of various cancers, and as their use expands, unusual side effects are recognized. The majority occur within the first three months of therapy, particularly with Durvalumab, the focus of this case report. The most commonly reported immune-related adverse events with Durvalumab include hypothyroidism, hyperthyroidism, pneumonitis, dermatitis, colitis, and hepatitis. In contrast, ICI-induced hypoparathyroidism remains an exceptionally rare immune-related adverse event, with limited cases reported in the literature.

Case report:
A 68-year-old man with a past medical history of hypertension, eczema, and metastatic hepatocellular carcinoma with underlying liver cirrhosis from chronic hepatitis C, receiving Durvalumab immunotherapy, presented three weeks after his third infusion with severe, diffuse body spasms and tetany, accompanied by profound weakness. Laboratory evaluation revealed a calcium level of 4.8 mg/dL and a magnesium level of 1.5 mg/dL, with a parathyroid hormone (PTH) level < 1.0 pg/mL and Vitamin D deficiency (13 ng/mL). He was admitted for hypocalcemic tetany secondary to immunotherapy. He was started on IV calcium gluconate, oral calcium carbonate, oral magnesium oxide, and calcitriol. Immunotherapy was temporarily withheld until the patient’s symptoms resolved and calcium levels were corrected. The patient was then discharged home following clinical improvement with resolution of neuromuscular symptoms, along with endocrinology and oncology outpatient follow-up.

Conclusion:
This case report highlights a rare adverse event of ICI therapy and emphasizes the importance of considering hypoparathyroidism in patients receiving immunotherapy and presenting with symptomatic hypocalcemia, with careful monitoring of calcium and magnesium levels, temporary withholding of immunotherapy until symptom resolution, and appropriate supplementation.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*