Endocrine Abstracts

Introduction: Immune checkpoint inhibitors (ICPis) are increasingly used in the management of advanced malignancies but may cause immune-related endocrine adverse events, including thyroiditis. Differentiating ICPi-induced thyroiditis from other causes of thyrotoxicosis, such as amiodarone-induced thyroiditis or Graves’ disease, can be diagnostically challenging.

Case Presentation: We report a 73-year-old male with stage IV melanoma on ipilimumab and nivolumab who developed thyrotoxicosis one month after initiating ICPi therapy. He presented with malaise, fatigue, confusion, and poor oral intake. Laboratory findings revealed suppressed TSH (<0.02 mU/l) and markedly elevated free T4 (>150 pmol/l). Thyroid antibodies were negative, and examination showed a diffusely enlarged, non-tender thyroid gland. The patient was also on long-term amiodarone, raising the possibility of amiodarone-induced thyroiditis. He was managed with corticosteroids, propranolol, carbimazole, intravenous fluids, and antibiotics. His thyroid function gradually improved, and carbimazole was discontinued. At follow-up, thyroid function normalized, and clinical symptoms resolved. In this case, diagnostic complexity arose due to concomitant amiodarone therapy, which itself can precipitate thyrotoxicosis through destructive thyroiditis or excess iodine exposure. Key features supporting ICPi-induced thyroiditis in this patient included: temporal relationship with initiation of ICPi therapy, rapid onset and progression of symptoms, negative thyroid autoantibodies, absence of classical amiodarone-related biochemical or clinical features, improvement with steroids and supportive treatment

Conclusion: This case highlights ICPi-induced thyroiditis as an important differential in oncology patients presenting with thyrotoxicosis. Despite concurrent amiodarone therapy, the timing of onset, clinical course, negative antibody profile, and response to treatment supported ICPi-induced thyroiditis as the final diagnosis. Clinicians should maintain a high index of suspicion to enable prompt recognition and management of endocrine complications in patients receiving immunotherapy