Graves disease complicated by agranulocytosis and thrombocytopenia in a 12-year-old girl.

Graves disease is the most common cause of hyperthyroidism in children. Although neutropenia and thrombocytopenia have been reported in adults with untreated Graves disease, these complications are rare in children. Here, we report a pediatric case of Graves disease complicated by agranulocytosis and thrombocytopenia at diagnosis. A 12-year-old girl presented with increased appetite, irritability, fever, and petechiae. Laboratory examination revealed thyrotoxicosis, and this was associated with agranulocytosis and thrombocytopenia. There was no history of antithyroid drug use. The diagnosis of Graves disease was established based on positive thyroid-stimulating hormone receptor antibodies and thyroid scintigraphy findings. After initiation of a β-blocker and potassium iodide, neutrophil and platelet counts gradually improved in association with the resolution of thyrotoxicosis, which allowed the subsequent introduction of methimazole. The β-blocker and potassium iodide were sequentially discontinued. Blood cell counts remained within the normal range thereafter, and thyroid function has remained well controlled with methimazole monotherapy. This case suggests that thyrotoxicosis itself is associated with cytopenia and provides valuable insight for clinicians when selecting a therapeutic strategy for Graves disease complicated by cytopenia.