#00061082

An 8-month-old female, exclusively breastfed, presented with pallor and a two-month history of vomiting, diarrhea, and failure to thrive.  CBC showed absolute neutropenia in the setting of normal white blood cell count (WBC 5.3x103/µL; ANC 0.42x103/µL, ALC 4.67 x103/µL), marked macrocytic anemia (Hgb 6.5 g/dl, MCV 96.2 fl, MCH 34.4 pg, MCHC 35.8 g/dL), mild thrombocytopenia (147x103/µL). The peripheral blood was remarkable for presence of macroovalocytes, microcytes, basophilic stippling, and rare hypersegmented neutrophils (panel A).  The differential diagnosis included nutritional deficiency, congenital bone marrow failure syndrome, infection- or drug-induced bone marrow suppression, and acute leukemia.  The marrow was hypercellular with absolute erythroid hyperplasia, megaloblastic erythroid and myeloid maturation, dyserythropoiesis and dysgranulopoiesis (panels B-D). There was no morphologic or immunophenotypic evidence of acute leukemia, and normal cytogenetics. Additional studies: vitamin B12< 30 pg/mL, LDH 2274 IU/L and normal iron studies and folate. The diagnosis of B12 deficiency was made and the patient was treated with B12 injection with subsequent marked increase in reticulocytes (from 3.18% to 9.88%) and clinical improvement.

While rare, vitamin B12 deficiency is seen in young children and should be included in the differential diagnosis of macrocytic anemia with pancytopenia, gastrointestinal symptoms, failure to thrive, and neurologic dysfunction.