By far the largest number of cases of diffuse nonsystemic disease of the cord, excluding multiple sclerosis, are the so-called "myelopathies" or "myeloses." In these, the histopathologic changes, although essentially similar, may show some variations, largely owing to differences in the causative agents and the duration of the disease.
Myelopathic processes in diffuse nonsystemic disease of the cord, excluding multiple sclerosis, may be produced by (1) toxins or (2) circulatory interference. Toxins may produce myelopathy by affecting the ectodermal or the mesodermal elements of the cord, or both. Our cases belonged to the ectodermal group, and the pathologic process resembled that produced experimentally by introducing various toxins into the circulation or into the subarachnoid space. In the absence of other demonstrable etiologic factors we designate these cases as toxic myelopathies. When the mesodermal elements (blood vessels) alone are involved, the pathologic process is one of secondary softening due to circulatory