[Severe pancytopenia in an infant secondary to vitamin B12 deficiency].

Introduction: severe vitamin B12 deficiency presents a diagnostic challenge due to its various clinical manifestations. Case report: the case we present here, a 17-month-old infant who presented with asthenia, hyporexia, paleness and regression of maturational patterns of approximately 2 months of evolution, illustrates the unique characteristics of severe vitamin B12 deficiency, highlighting the key differentiators from other conditions, including decreased reticulocyte counts and elevated lactate dehydrogenase levels, indicative of suppressed erythropoiesis. Discussion: advanced cobalamin deficiency affects all cell lines and produces peripheral pancytopenia. Proposed mechanisms include fragile red blood cells prone to tearing, leading to schistocyte formation, and oxidative stress that exacerbates hemolysis. In conclusion, prompt recognition and treatment with vitamin B12 replacement is essential to prevent serious hematological complications.