Atezolizumab-Induced Hypothyroidism in a Patient With Pre-existing Triiodothyronine (T3) Thyrotoxicosis Due to Graves’ Disease: A Case Report and Literature Review

The use of immune checkpoint inhibitors has improved the management and prognosis of many solid tumors. Because of their mechanism of action, and as checks on the immune systems are reduced, immune-related adverse events are common, including the exacerbation of the pre-existing autoimmune disease. The literature is scanty regarding reports of the use of immune checkpoint inhibitors in patients with pre-existing Graves’ disease. We report a case of a woman with pre-existing triiodothyronine (T3) thyrotoxicosis (hyperthyroidism) secondary to Graves’ disease, who developed thyroiditis followed by severe hypothyroidism after receiving an immune checkpoint inhibitor (atezolizumab) for the treatment of small-cell lung cancer. She had been on an anti-thyroid drug for Graves’ disease for two and a half years and was on the waiting list for a total thyroidectomy. However, the discovery of the severe hypothyroidism following atezolizumab-induced thyroiditis resulted in the need for long-term thyroid replacement therapy, and the planned surgery was no longer required. This case is one of the very few published reports of the use of atezolizumab in a patient with pre-existing Graves’ disease, resulting in the conversion from pre-existing T3-thyrotoxicosis to overt hypothyroidism. A multidisciplinary team approach is required when using immune checkpoint inhibitors in patients with pre-existing Graves’ disease or any other autoimmune disease.