Pancytopenia Secondary To Autoimmune Vitamin B12 Deficiency In Graves Disease

Objective: To describe a case of Graves disease (GD) and coexistent pancytopenia associated with autoimmune vitamin B12 deficiency. While thyrotoxicosis and antithyroid drugs can cause pancytopenia, other autoimmune conditions such as vitamin B12 deficiency can occur, leading to severe anemia and pancytopenia. Methods: A 19-year-old female with GD treated with methimazole presented with thyrotoxicosis and evidence of pancytopenia. Diagnostic studies included a complete blood cell count, peripheral blood smears, thyroid function tests, and a bone marrow biopsy. Results: White blood cells were 2.4 × 109 cells/L (reference range [RR] is 3.4 to 9.6 × 109 cells/L), hemoglobin was 7.9 g/dL (RR is 11.6 to 15.0 g/dL), neutrophil count was 1.2 × 109 cells/L, and platelets were 84 × 109 cells/L (RR is 157 to 371 × 109 cells/L). Thyroid-stimulating hormone was