Multiple sclerosis associated with vitamin B12 deficiency.

We describe 10 patients with a previously unreported, to our knowledge, association of multiple sclerosis and unusual vitamin B12 deficiency. The clinical features and the age at presentation were typical of multiple sclerosis, with eight cases occurring before age 40 years, which is a rare age for vitamin B12 deficiency. Nine patients had hematologic abnormalities, but only two were anemic. All six patients examined had low erythrocyte cobalamin levels. Only two patients had pernicious anemia; in the remaining patients the vitamin B12 deficiency was unexplained. A vitamin B12 binding and/or transport is suspected. The nature of the association of multiple sclerosis and vitamin B12 deficiency is unclear but is likely to be more than coincidental. Further studies of vitamin B12 metabolism, binding, and transport in multiple sclerosis are indicated, as these cases may offer a clue to the understanding of a still mysterious neurologic disorder.