Graves' disease with splenomegaly and pancytopenia, mimicking B-cell lymphoproliferative disease

A 48-year-old woman was referred to our hospital because of fever and general fatigue. Peripheral blood analysis showed a hemoglobin level of 82 g/l, a white blood cell count of 1.95 x 10(9)/l and a platelet count of 80 x 10(9)/l. There were 9% CD5-positive B-cells in peripheral blood and 35% CD10-positive B-cells in bone marrow. The patient had a high serum soluble interleukin-2 receptor (SIL-2R) level of 5,185 U/ml and splenomegaly. Lymphoproliferative disease was suspected, however monoclonal rearranged band of immunoglobulin heavy chain was not detected. She also showed hyperthyroidism, Graves' disease and then treatment with thiamazole started. However, the treatment was stopped because of agranulocytosis and she received subtotal thyroidectomy. After treatment for hyperthyroidism, serum SIL-2R level decreased to 504 U/ml and pancytopenia gradually improved. Fifteen months postoperatively, the percentage of CD5-positive B-cells in peripheral blood and CD10-positive B-cells in bone marrow decreased to 8% and 2%, respectively. This clinical course suggests that polyclonal B-cell proliferation was caused by hyperthyroidism.