[Vitamin B12 deficiency: a challenging diagnosis and treatment]

Vitamin B12 deficiency is usually evoked in presence of compatible hematologic or clinical (usually neurologic) signs. However, many cases of deficiency are little or not symptomatic. Pernicious anemia, caused by a deficiency in intrinsic factor, is a rare cause of vitamin B12 deficiency. The most frequent causes are gastric disorders, pancreatic insufficiency, or chronic drug treatment (proton pump inhibitors or metformin) that interfere with the digestion of vitamin B12 digestion, or disorders of the ileum mucosa reducing the absorption of vitamin B12. Oral treatment of vitamin B12 deficiency is possible whatever the etiology, but it has only been validated in small series. Parenteral treatment remains indicated for severe neurologic deficits or whenever patient adherence with treatment is doubtful.