Objectives: To determine the frequency of serum cobalamin (Cbl) deficiency and to clarify the biologic importance of low screening Cbl levels in patients with multiple sclerosis (MS) and idiopathic myelopathy (MYL).
Background: A significant association between Cbl metabolism and MS has been postulated based on the observations that patients with MS have lower serum Cbl levels, higher unsaturated Cbl binding capacities, and a higher prevalence of macrocytosis than do normal controls. Whether such observations have biologic importance as documented by abnormal accumulation of metabolites that would result from Cbl deficiency has not yet been determined.
Methods: Serum Cbl and folate levels were determined in 208 consecutively evaluated patients seen in an outpatient MS clinic setting during a 7-month period. Necessary blood samples were obtained for 165 of these patients. One hundred twenty-five patients had clinically definite MS, 31 had clinically probable MS, and nine had MYL. Serum methylmalonic acid (MMA) and homocysteine (HCY) concentrations, which rise in biologically severe Cbl deficiency, were subsequently determined in all patients whose Cbl levels were lower than 301 pg/mL.
Results: A Cbl level lower than 301 was found in 32 of 156 patients with either clinically definite MS or clinically probable MS but in none of the patients with MYL. Elevated MMA or HCY levels were found in seven of 32 patients with either clinically definite MS or clinically probable MS, six of whom had an elevated HCY level and one of whom had elevated HCY and MMA levels.
Conclusions: Despite the observation that 32 (19.4%) of 165 of these patients with MS and MYL had screening Cbl levels less than 301 pg/mL, only seven (4.2%) of 165 had elevated MMA or HCY levels. The frequency of biologically severe Cbl deficiency in these patients with MS and MYL was very low.