[Diagnosis of vitamin B12 deficiency: a case illustrating diagnostic pitfalls]

Vitamin B12 deficiency is a longstanding public health problem which affects more than 20% of the elderly population. Among multiple causes of vitamin B12 deficiency, Biermer's disease is currently mentioned in about 25% of the cases.

We report the case of a 71-year-old woman, taking folate substitution therapy who, over 2 years, progressively developed spinal combined sclerosis, subacute dementia and severe neuropathy leading to a bedridden state. The initial assessment revealed normocytic anemia, without vitamin B12 deficiency and without increased plasma level of biological markers. The plasma folate level was high. Vitamin B12 assay was repeated leading to the diagnosis of deficiency associated with the presence of intrinsic factor antibodies.

This observation illustrates the broad spectrum of clinical presentations of vitamin B12 deficiency. In the present case, the lack of sensitivity of biological markers delayed diagnosis and had a dramatic impact on outcome. This case highlights the importance of promoting factors such as isolated folate substitution in B12 deficient patients.