Normal vitamin B12 turnover in subacute combined degeneration of the spinal cord.

Vitamin B12 turnover studies were carried out in 2 patients with pernicious anemia and subacute combined degeneration of the spinal cord. The retention of a tracer dose (0.5 mug) of intravenously administered 58Co-labeled vitamin B12 in these 2 patients was measured by whole-body monitoring over periods of 94 and 134 days. Vitamin B12 turnover (per cent per day) was calculated and the results compared with normal subjects and with pernicious anemia patients having no neurologic dysfunction. The loss of radioactive-B12 from the body was described by a single exponential model, confirming that the loss of vitamin B12 takes place as though from a single pool. There was no difference in vitamin B12 turnover between the patients with subacute combined degeneration of the spinal cord and normal subjects or other pernicious anemia patients without neurologic involvement. These findings contradict the suggestion that the development of neuropathy in vitamin B12 deficiency might be related to an increased requirement for vitamin B12.