Deleu et al report on the potential role of folic acid deficiency in nitrous oxide–induced myelopathy; however, in our case, as we pointed out in our article, the serum folic acid level was normal (30 nmol/L [normal range, 5-30 nmol/L]). Subclinical folic acid deficiency, which Deleu et al estimate has a prevalence of around 10%, has to be considered; however, cobalamin deficiency in the elderly population is not uncommon—Pennypacker et al1 found a prevalence of cobalamin deficiency of 14.5% and Yao et al2 reported a prevalence of 21% of serum cobalamin levels less than 300 µg/mL accompanied by elevated levels of metabolites. Neurological complications of folate deficiency exist, but they are usually considered to be rare.3
Marié R. In reply. Arch Neurol. 2001;58(1):134–135. doi:
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