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

Sensory Neuronopathy Revealing Severe Vitamin B12 Deficiency in a Patient with Anorexia Nervosa: An Often-Forgotten Reversible Cause

Vitamin B12 (B12) deficiency is known to be associated with various neurological manifestations. Although central manifestations such as dementia or subacute combined degeneration are the most classic, neurological manifestations also include sensory neuropathies. However, B12 deficiency is still rarely integrated as a potential cause of sensory neuronopathy. Moreover, as many medical conditions can falsely normalize serum B12 levels even in the context of a real B12 deficiency, some cases may easily remain underdiagnosed. We report the illustrating case of an anorexic patient with sensory neuronopathy and consistently normal serum B12 levels. After all classical causes of sensory neuronopathy were ruled out, her clinical and electrophysiological conditions first worsened after folate administration, but finally improved dramatically after B12 administration. B12 deficiency should be systematically part of the etiologic workup of sensory neuronopathy, especially in a high risk context such as anorexia nervosa.

[Metabolic and nutritional neuropathies: update in diabetes, vitamin B12 and copper deficiency]

Metabolic and deficiency neuropathies retain a growing interest because of their important prevalence. The dismemberment of diabetic neuropathies is proceeded, letting distinct pathophysiological mechanisms appear. So, even if glycaemic control remains determining for preventing the neuropathy associated with type 1 diabetes, it seems to have a restricted role with type 2 diabetes in which other metabolic factors are involved. The diagnosis of neuropathy due to B12 vitamin deficiency remains a real challenge for the clinician. Indeed, positive and negative predictive values of serum B12 and metabolites assay are weak, only a good therapeutic response allows a reliable diagnostic. It is so recommended to know the clinical and contextual particularities of this etiology in order to not delay the vitamin substitution, determining for the functional outcome. Finally, copper deficiency remains an unknown cause of neuropathy which is suitable to raise in case of malabsorption but also and especially in case of abuse of dental adhesive rich in zinc.