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 ≤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. Muscle Nerve, 2007