A 56-year-old woman was hospitalized for the investigation of progressive weight loss, palpitation and dyspnea. Hormonal studies revealed hyperthyroidism associated with positive anti-TSH receptor and anti-microsomal antibodies. Mild enlargement of thyroid gland with increased vascularity found from ultrasound examination. Laboratory data showed pancytopenia, with a WBC count of 2050/μl, hemoglobin of 5.7 g/dl (MCV: 84.6 fl), platelet count of 59 x 103/μl and reticulocyte of 5.8%. Bone marrow cytology was hypercellularity with adequate megakaryocyte. Patient is a vegan for 13 years, with mild decreased iron reserve (ferritin: 48.2 ng/ml), normal folic acid level (13.4 ng/ml) but low vitamin B12 of 149 pg/ml.
Under the impression of Graves’ disease with vitamin B12 deficiency and pancytopenia, antithyroid drug with methimazole 15mg/day was used. 4 units of pack RBC were transfused during hospitalization for severe anemia and heart failure. Hydroxocobalamin 1mg IM daily was given for 5 days. Patient discarded her vegetarian life and started to eat meat after discharge. Patient became euthyroid and pancytopenia disappeared after 6 months of treatment with methimazole. Vitamin B12 level was also normal at that time. Pancytopenia is a rare complication of hyperthyroidism. Several cases had been reported before in the literature, the pathogenesis is poorly understood. It is theorized that there exists a cross antigenicity between human TSH receptors and polynuclear neutrophils. Others have suggested that the granulocytes have a decreased circulating time. Thyroid hormones may have a direct effect on hematopoiesis at a stage earlier than erythropoietic stem cell differentiation, disturbing maturation and differentiation of the pluripotent stem cells. Our case was complicated with the concomitant of vitamin B12 deficiency. It makes the true etiology of pancytopenia unknown, since vitamin B12 deficiency may cause pancytopenia too. From here, we suggest that hematologic evaluation of all patients with thyrotoxicosis should be performed before administering antithyroid drugs. |
