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 μg) 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.