RESUMEN
Hematological disorders, especially single lineage abnormalities, have been described in hyperthyroidism. Pancytopenia has been reported, without myelodysplastic syndrome or megaloblastic anemia. We studied the peripheral blood smear and the bone marrow aspiration and biopsy of a 65-year-old lady, who presented with pancytopenia and thyrotoxicosis due to multinodular goiter. She denied ingesting any toxic medication. At diagnosis: WBC: 2500/ul, platelets count: 58,000/ul, hemoglobin level: 6.5 g/dl. The bone marrow was moderately hyper cellular with moderate myelofibrosis and arrested hematopoiesis. The TSH level was: 0.02 mIU/l (N: 0.25-4), the fT3: 18 pmol/l (N: 4-10), the routine serum immunologic tests were negative. After treatment with single agent neomercazole (carbimazole), complete recovery of the blood cell counts was obtained within one month. The bone marrow aspiration, performed three months after starting therapy, showed normal hematopoiesis. The thyroid function tests returned to normal and no autoimmune reaction was detected on routine serum testing. Persistent response was observed six months later under medical treatment. The patient has refused surgical treatment. Reversible myelodysplastic syndrome may also be part of the changes in blood picture of patients with hyperthyroidism, probably due to direct toxic mechanism.