Vitamin B12 deficiency mimicking acute leukemia

Vitamin B12 deficiency can cause extensive hematologic alterations such as pancytopenia, macrocytosis, hypersegmentation of neutrophils, and hypercellular bone marrow with blastic differentiation. These dysplastic changes can sometimes be so profound that they mimic myelodysplastic syndromes or even acute leukemia, leading to extensive workup and aggressive treatment measures. We present a patient who was referred to our tertiary care medical center for treatment of suspected acute myeloid leukemia on the basis of peripheral smear and bone marrow biopsy findings, and induction chemotherapy was considered. However, the patient was found to have vitamin B12 deficiency, with improvement in pancytopenia and blastic changes with parenteral vitamin B12 supplementation. This highlights the importance of recognizing that dysplastic changes in patients with vitamin B12 deficiency could be misleading.