In every large center, examples of this disorder are found among the many patients who present with a subacute paraplegia or quadriplegia, sensory loss, and sphincter paralysis. The neurologic signs may erupt so precipitously that a vascular lesion is assumed. In most other cases, the disease evolves at a slower and usually stepwise pace, over several months or years. Necrotizing myelopathy is distinguished from the more common types of transverse myelitis by a persistent and profound flaccidity of the legs (or arms if the lesion is cervical), areflexia, and atonicity of the bladder—all reflecting a widespread necrosis that involves both the gray and white matter of the spinal cord over a considerable vertical extent. This clinical picture is unexpected for a spinal cord lesion and, therefore, is often mistakenly attributed to spinal shock or to a completely different process such as Guillain-Barré syndrome.
This combination of spinal cord necrosis and optic neuritis corresponds to the syndrome described by Devic in 1894 and named by him neuromyelitis optica (Devic disease). Nearly all neurologists agree that a similar clinical syndrome involving the optic nerve and spinal cord (usually without necrosis) may also be caused by postinfectious encephalomyelitis or by MS, however, the finding by Lennon and colleagues of a specific serum IgG antibody in half of cases of Devic disease was a notable advance. The antibody is directed against the aquaporin channel in capillaries of the cord, brainstem and cerebellum and its role in the pathogenesis of the disease partially resolves the decades old uncertainty regarding a distinction between Devic disease and forms of multiple sclerosis, in which the antibody is not present.
In both the isolated necrotic myelopathy and in Devic disease, a few or up to several hundred mononuclear cells per cubic millimeter and increased protein may be found in the CSF but oligoclonal banding is usually absent. Some cases show only an elevated protein concentration. More so than with postinfectious transverse myelitis, the MRI reveals extensive signal changes and gadolinium enhancement, usually occupying several contiguous spinal segments; called a longitudinally extensive lesion (Fig. 42-5). Imaging studies performed weeks or more after the onset of symptoms show atrophy of the involved segments of cord. Persistent swelling of the affected region is more suggestive of spinal cord tumor or another type of inflammation, but the permissible duration of cord swelling may extend for weeks. The electromyogram (EMG) often shows denervation of several contiguous myotomes, reflecting damage to the gray matter of those segments.
In cases coming to postmortem examination at variable times after the onset of symptoms, the lesion has proved to be a necrotizing myelitis with widespread loss of spinal cord tissue. The pattern of tissue destruction appears, at least in part, infarctive, that is, not respecting the borders of gray and white matter. However, areas of residual inflammation and demyelination are often detected at the edges of the destructive lesions. Older lesions leave the spinal cord cavitated or collapsed over a vertical extent of 5 to 20 cm, with conical extensions of necrosis into the gray matter above and below the area of transverse damage. Probably many of these cases would now be categorized as part of the neuromyelitis family with aquaporin autoantibodies.