Vitamin B(12) and methylmalonic acid levels in patients presenting with polyneuropathy.

This study was designed to determine the prevalence of definite vitamin B(12) deficiency (defined as < or =240 pg/ml) and possible vitamin B(12) deficiency (defined as >240 pg/ml and a methylmalonic acid [MMA] level >243 nmol/L) in patients with polyneuropathy and to determine whether patients in both groups respond to vitamin B(12) repletion. We performed a retrospective cohort study of 581 patients presenting with polyneuropathy over a 2-year period; 4% had definite vitamin B(12) deficiency and 32% had possible deficiency as the sole or contributing cause for their polyneuropathy. For those who received treatment with vitamin B(12), subjective improvement was seen in 87% with definite and in 43% with possible deficiency. Possible vitamin B(12) deficiency, defined as an elevated MMA level, is a common finding in patients with polyneuropathy and treatment of these patients with vitamin B(12) may lead to clinical improvement.