The importance of methylmalonic acid dosage on the assessment of patients with neurological manifestations following bariatric surgery.

Vitamin B12 or cyanocobalamin is an important substance that is included in several metabolic pathways. Its deficiency is a common event after bariatric surgery, decreasing the vitamin B12 absorption after almost all of the stomach and duodenum are eliminated from the digestion process. Neurological manifestations of cyanocobalamin deficiency are not uncommon. We report a case of a young woman who developed ataxia, weakness and peripheral neuropathy after bariatric surgery, but with normal value of vitamin B12 dosage. For the diagnosis, it was necessary to dose methylmalonic acid. We discuss the importance of methylmalonic acid dosage after bariatric surgery in patients who present suspect of cyanocobalamin deficiency with normal values of this vitamin and the role of proton pump inhibitor use and vitamin supplementation in patients with early neurological presentation.