Antithyroid drug-induced pancytopenia followed by acute lymphoblastic leukemia: A rare case

Antithyroid drugs (ATDs) have been used for the management of hyperthyroidism and rarely may cause life-threatening side effects such as agranulocytosis and pancytopenia. Lymphocytes of patients who develop agranulocytosis while on ATD may undergo blast transformation when exposed in vitro to ATD. A 26-year-old man with Graves' disease was found to have pancytopenia after treatment with carbimazole for 2 months, which was improved with supportive treatment. The patient restarted carbimazole and presented 4 months later with a diagnosis of acute lymphoblastic leukemia (ALL). This case of ALL was likely attributed by re-exposure to carbimazole, though the association of ALL with autoimmune thyroid disease cannot be denied.