Neurological expression of vitamin B12 deficiency in children

The neurological presentation of vitamin B12 deficiency, although rare, can be the initial manifestation of the clinical picture, making diagnosis difficult. Inborn errors of vitamin B12 metabolism are exceptional, and vitamin B12 deficiencies in infants under one year of age are primarily linked to maternal deficiency or low vitamin B12 content in breast milk in the absence of dietary diversification. Its inclusion among treatable metabolic diseases justifies the need for neonatal screening, enabling early treatment and prevention of long-term neurocognitive sequelae. We report three cases of infants, two boys and one girl, aged 5, 11, and 15 months, respectively. The modes of presentation included encephalitis and/or meningitis in two cases. The neurological manifestations observed were a stroke revealed by a focal clonic seizure and the presence of an ischemic focus on brain MRI in one case, and psychomotor regression in the other two cases. The diagnosis was suggested by the association of extraneurological signs, particularly hematological involvement with bicytopenia and megaloblastosis, as well as digestive symptoms in two cases. A low plasma vitamin B12 level and an elevation of urinary methylmalonic acid in two cases, along with hyperhomocysteinemia in one case, confirmed it. Maternal deficiency with exclusive breastfeeding was implicated in all three cases. A cellular metabolic abnormality of vitamin B12, either lysosomal or mitochondrial, was suspected in two cases, in addition to nutritional deficiency. Neonatal screening remains the only effective measure to prevent neurocognitive sequelae related to vitamin B12 deficiency.