Vitamin B12 levels of cerebrospinal fluid in patients with a variety of neurological disorders.

The vitamin B12 levels of cerebrospinal fluid were assayed microbiologically (Lactobacillus leichmannii method) using samples from 44 patients with various neurological disorders, 4 patients with megaloblastic anemia and 34 controls. Twenty-seven controls that did not receive vitamin B12 showed a mean cerebrospinal fluid vitamin B12 level of 21.5 pg/ml (range: 0-60). No decrease in cerebrospinal fluid vitamin B12 level was seen in patients with subacute myelo-optico-neuropathy (SMON). High levels of cerebrospinal fluid vitamin B12 were observed only in the patients receiving long term administration of the vitamin. Intrathecal administration of vitamin B12 caused only a slight increase in serum vitamin B12 level after four hours. The existence of blood brain barrier for vitamin B12 was suggested.