Severe agranulocytosis in patient with Graves' disease on second exposure to carbimazole.

Summary: For half a century, antithyroid drugs (ATDs) have been the first-line treatment for Graves' disease. ATDs, e.g. carbimazole, are associated with minor and serious adverse effects. These include rash, urticaria, arthralgia, hepatotoxicity, vasculitis, and agranulocytosis. Agranulocytosis is a potentially serious adverse effect characterised by a neutrophil count <0.5 × 109 cells/L, which may deteriorate further into sepsis and death. This is a case report of a 47-year-old female who had a 17-year history of Graves' disease. She received carbimazole for 2 years, which was stopped after remission. She presented with relapsed thyrotoxicosis in 2025 when carbimazole (40 mg) was reinstituted. Three weeks later, the patient self-presented to the hospital with sore throat, painful swallowing, and sweating. Examination found oral ulceration, pharyngeal erythema, and tender cervical lymphadenopathy. She was admitted to the hospital and treated under the endocrinology team as agranulocytosis, carbimazole was stopped, and she was treated per local guidelines of neutropenic sepsis. After agranulocytosis was resolved, the patient underwent total thyroidectomy. Despite being well-tolerated, doctors and patients should be well aware of this potentially serious adverse effect of carbimazole. Learning points: Antithyroid drugs (ATDs) are rarely associated with agranulocytosis. ATD-induced agranulocytosis is regarded as a serious life-threatening emergency. The only option for the management of patients with Graves' disease-developed agranulocytosis is surgery. Educating the patients regarding the symptoms of agranulocytosis is vital for saving their life. ATD-induced agranulocytosis can happen long time after exposure or even after second exposure to these drugs.