Immune checkpoint inhibitors (ICI) targeting cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 ligand (PDL1), such as Tremelimumab plus Durvalumab combination immunotherapy, known as STRIDE regimen, has become a novel treatment approach for patients with advanced unresectable hepatocellular carcinoma. However, it is associated with immune-related adverse events (irAE), including endocrinopathy.

We present a 73-year-old male diagnosed with hepatocellular carcinoma recently underwent immunotherapy with Tremelimumab plus Durvalumab.

Baseline thyroid function test was normal with the following results: TSH 1.4 uIU/mL, FT4 1.14 ng/dL, FT3 2.59 pg/mL. Few days after the 1st cycle, he presented with psychosis and neck swelling. Chemistry showed low TSH (0.01 uIU/mL), elevated FT4 (4.87 ng/dL), elevated FT3 (6.77 pg/mL), low FT3/FT4 ratio (0.166), and negative TSH receptor antibodies, indicating new-onset thyroiditis. Patient was started on Prednisone 20 mg/tablet once a day for 1 week, with notable improvement of symptoms and down trending of FT4 and FT3 levels over the course of weeks. Continuous monitoring of thyroid function test was done before clearing the patient for subsequent cycles of immunotherapy.

Thyroiditis is a recognized irAE of Tremelimumab and Durvalumab, both as monotherapy or as combination regimen. This case highlights a rare presentation of thyroiditis related to immunotherapy and underscores the critical need for proactive surveillance of thyroid function among patients receiving immune checkpoint inhibitors.