Acute Myeloid Leukaemia Presenting as B12 Vitamin Deficiency When Multiple Horses Become a Zebra

Vitamin B12 deficiency is a common finding in medical practice. It is easily treated with supplementation and typically has a favourable prognosis. In rare circumstances, it can hide a severe disease that should be promptly addressed. We report the case of an acute myeloid leukaemia presenting as an initially predictable B12 deficiency in a vegetarian patient with chronic gastritis. The supplementation rapidly corrected the deficit and the accompanying cytopenias. However, in the following month the cell counts fell once again, leading to the suspicion that other aetiology could be lying beneath the surface. Maintaining a normal peripheral blood smear, the bone marrow biopsy showed myeloblasts and extensive fibrosis compatible with the diagnosis of acute myeloid leukaemia. The neoplasm justified the vitamin deficit by excessive cellular turnover, a vicious cycle only uncovered after supplementation and that ultimately led to the patient’s death.