Abstract
Neutropenia is a common side-effect in hyperthyroid patients with long-term use of antithyroid drugs. This may be caused by drug-induced immune dysfunction or increased thyroxine hematologic toxicity, which usually returns to normal after medication is discontinued or the hyperthyroidism becomes well controlled. However, hyperthyroidism with pancytopenia is extremely rare. The current case report presents a hyperthyroid patient complicated with pancytopenia who had taken antithyroid drugs for 14 years. Bone marrow analysis revealed primary leuokocytes, indicating M3 acute leukemia. Genetic analysis revealed promyelocytic leukemia-retinoic acid receptor α fusion and FMS-like tyrosine kinase 3-internal tandem duplication. The genetic abnormality was also associated with thyroid hormonal functions. After a standard anti-M3 regimen was administed, the patient achieved complete remission and maintained stable thyroid functions. To the best of our knowledge, this is the first reported case of a patient with hyperthyroidism acquiring M3 leukemia harboring the FMS-like tyrosine kinase 3-internal tandem duplication.