PANCYTOPENIA SECONDARY TO AUTOIMMUNE VITAMIN B₁₂ DEFICIENCY IN GRAVES DISEASE

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.

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.

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 <0.01 mIU/L (RR is 0.50 to 4.30 mIU/L), free thyroxine was 3.7 ng/dL (RR is 1.0 to 1.6 ng/dL), and total triiodothyronine was 221 ng/dL (RR is 91 to 218 ng/dL). Due to suspicion for drug-induced pancytopenia, methimazole was discontinued. Three days later, she was hospitalized for a syncopal episode with a further decline in hemoglobin to 6.7 g/dL, neutrophils to 0.68 × 10⁹ cells/L, and platelets to 69 × 10⁹ cells/L. Bone marrow biopsy findings showing marrow hypercellularity and hypersegmented neutrophils suggested vitamin B₁₂ deficiency. Vitamin B₁₂ was <70 ng/L (RR is 180 to 914 ng/L). Intramuscular vitamin B₁₂ injections were initiated, and pancytopenia resolved within 1 month.

Although rarely described in the literature, autoimmune vitamin B₁₂ deficiency can be missed as an underlying etiology for pancytopenia in patients with GD. The clinical picture can be further confounded when these patients are treated with antithyroid drugs known to cause bone marrow suppression.