Drug-induced liver injury due to potassium iodide during thyroid storm

Thyroid storm is a life-threatening condition causing multiorgan failure, including liver dysfunction. Potassium iodide (KI) is one of the key drugs used to control thyroid hormone levels. While thionamides sometimes cause drug-induced liver injury (DILI), KI has not been reported to cause DILI. Herein, we report a case of likely KI-induced DILI during treatment for thyroid storm due to Graves disease. A 30-year-old man presented with thyrotoxicosis due to Graves disease, with hyperbilirubinemia and elevated liver transaminases. The patient was diagnosed with thyroid storm, and treatment was initiated with methimazole, KI, corticosteroids, and beta-blockers. Although the thyroid hormone levels improved during the treatment, total bilirubin levels increased to 32.4 mg/dL (SI: 553 µmol/L) (reference range, <1.2 mg/dL [SI: <20.5 µmol/L]). DILI was suspected, and methimazole was discontinued; however, bilirubin levels remained elevated. Plasma exchange also failed to improve the liver injury. After KI was discontinued, the bilirubin levels rapidly decreased. Lymphocyte transformation tests for methimazole and KI were negative and positive, respectively, confirming the diagnosis of KI-induced DILI. This case highlights that KI should be recognized as a potential cause of DILI in patients with KI therapy who present with abnormal liver function.