An ultrastructural study of subacute combined degeneration of the spinal cord in vitamin B12-deficient rhesus monkeys.

Prolonged deprivation of vitamin B12 in rhesus monkeys produced changes in the central nervous system that were indistinguishable topographically and histologically from those of human subacute combined degeneration. Ultrastructural studies of early lesions of the spinal cord disclosed a degeneration of myelin characterized by separation of myelin lamellae and formation of intramyelinic vacuoles, leading eventually to complete destruction of myelin sheaths. At a later stage, there was degeneration and loss of axons, and marked gliosis. The theories of pathogenesis of subacute combined degeneration are reviewed in the light of these observations.