Megaloblastic anemia (MA) due to vitamin B12 deficiency is a reversible form of ineffective hematopoiesis. Myelodysplastic syndrome (MDS) is an acquired, irreversible disorder of ineffective hematopoiesis, characterized by stem cell dysfunction as a consequence of DNA damage manifested in part by karyotype anomalies. Importantly, MA and MDS are generally considered mutually exclusive diagnoses. We report the case of a 73-year-old woman with a profound macrocytic anemia, monocytosis and neurologic symptoms. Low cobalamin levels and the presence of anti-intrinsic-factor antibodies definitely established a diagnosis of pernicious anemia. Replacement therapy resulted in resolution of neurologic findings and macrocytosis; however, the anemia and monocytosis persisted. Bone marrow biopsy revealed trilineage myelodysplasia, which together with the peripheral monocytosis suggested a diagnosis of chronic myelomonocytic leukemia. Karyotype analysis revealed a clone with 45, XX, +der(1;7)(q10;p10)-7 . Eighteen months after documented vitamin B12 replenishment her MDS transformed to terminal acute myeloid leukemia with the same clonal abnormality. Reversible cytogenetic abnormalities have been observed with MA, occasionally including karyotypes typically associated with MDS or myeloid leukemias. These abnormalities, like the anemia, resolve with vitamin replacement. This case suggests that MA and MDS can occur simultaneously; clinicians should be aware that this phenomenon occurs. Whether acquired karyotype abnormalities from the MA were related to the MDS and subsequent myeloid leukemia in this woman is a speculative but intriguing consideration that is discussed.
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