Pancytopenia due to vitamin B12 deficiency associated with Graves' disease.

Pancytopenia has a broad differential diagnosis, which can be narrowed depending on the cellularity of the bone marrow. The authors describe a complex patient with a history of Graves' disease who presented with pancytopenia, initially suspected of being due to aplastic anemia. He was later diagnosed with Vitamin B12 deficiency as a result of pernicious anemia. The potentially striking hematologic effects of cobalamin deficiency and the autoimmune basis for concurrent Graves' disease and pernicious anemia are reviewed.