Methimazole-induced Agranulocytosis Complicated by Thyrotoxic Crisis: A Case Report

Abstract

Methimazole is one of the most commonly used drugs in the management of hyperthyroidism but rarely leads to potentially life-threatening agranulocytosis, which can significantly complicate clinical management. We report the case of a 49-year-old male with a known history of hyperthyroidism for ten years who presented with high-grade fever, profuse sweating, cough with expectoration, reeling sensation, shortness of breath, and generalized weakness following methimazole therapy. Laboratory investigations revealed profound agranulocytosis with an absolute neutrophil count below 500/µL, along with marked thyrotoxicosis, raising suspicion of an evolving thyrotoxic crisis. Methimazole was immediately discontinued, and treatment with broad-spectrum intravenous antibiotics, granulocyte-colony stimulating factor, beta-blockers, corticosteroids, and supportive care was initiated. The patient showed significant clinical and hematological improvement with recovery of neutrophil counts and stabilization of thyroid function and was discharged in a stable condition. This case emphasizes the need for early recognition of methimazole-induced agranulocytosis, which may progress to severe and life-threatening complications. Timely withdrawal of the offending drug along with early multidisciplinary intervention is crucial in reducing morbidity and preventing fatal outcomes.