The spinal cord disorders that make up this category take the form of a leukomyelitis based on either demyelination or necrosis of portions of the spinal cord. The critical factor in their pathogenesis appears to be a disordered immune response, in some cases, as a response to an infection, and in others such as multiple sclerosis an idiopathic immune disorder. Varied clinical syndromes are produced, and the basic disease is classified in textbooks under headings such as acute transverse myelitis, postinfectious myelitis, postvaccinal myelitis, acute MS, neuromyelitis optica, and necrotizing myelitis. While each of these conditions may affect other parts of the nervous system (most often the optic nerves and brain), often the only manifestations are spinal. The aforementioned myelopathies are characterized by various degrees of inflammatory destruction, usually with lymphocytes congregating around venules in the cord, but they are sufficiently distinct to justify their separate classification. Nonetheless, transitional cases sharing the clinical and pathologic attributes of more than one disease are encountered in any large clinical practice and pathologic collection. The subjects of multiple sclerosis, neuromyelitis optica and other primarily inflammatory myelitidies are also discussed in Chap. 35. Some of the main points are recapitulated here.
Postinfectious and Postvaccinal Myelitides (See Also Chap. 35)
The characteristic features of these diseases are their temporal relationship following a viral infection or vaccination with the delayed development of neurologic signs over the period of a few days, and a monophasic course, that is, a single attack with variable degrees of recovery and no recurrence. These processes may involve the brain as well as the spinal cord, in which case the process is properly designated as acute disseminated encephalomyelitis (ADEM). On the basis of the clinical features of disseminated postinfectious encephalomyelitis and the animal model of experimental allergic encephalomyelitis (EAE), postinfectious myelitis is presumed to be immunologic in nature, reflecting an attack that is more or less confined to spinal cord myelin as described in more detail in Chap. 35.
The usual history in these cases is of weakness and numbness of the feet and legs (less often of the hands and arms), which typically develop over a few days, and for the sensory symptoms to ascend from the feet to the trunk. Paresthesias in the feet and legs, which simulate a polyneuropathy, are common early symptoms. Sphincteric disturbances and backache are also common in the first days but as often arise later. A slight asymmetry of the symptoms and signs, a sensory level on the trunk, or a Babinski sign clearly marks the disease as a myelopathy and serves to distinguish it from a rapidly progressive polyneuropathy such as the Guillain-Barré syndrome. Back pain of varying degree and headache and stiff neck may or may not be present. In about half of cases the patient can identify a recent infectious illness, usually a mundane upper respiratory syndrome, but the fever has usually abated when the neurologic symptoms begin. The illness evolves over several days, sometimes a single day or on the other extreme, over 1 or 2 weeks. Despite the term transverse myelitis, fewer than half of cases demonstrate a truly “transverse” involvement of the cord; more often there is an incomplete corticospinal and spinothalamic syndrome affecting one side more than the other. As discussed further on, it is usually not possible to distinguish an acute episode of postinfectious myelitis from the first attack of multiple sclerosis, but a well-defined preceding infection with certain organisms favors the former process. The latency between infection and myelitis is an uncertain matter but there are well-documented instances in which the febrile episode blends into the neurologic syndrome and others in which the latency has been 2 weeks; considerably longer intervals make the association suspect.