There are other rare forms of poliomyelitic reactions of unknown, possibly viral etiology. One such condition presents as an acute febrile or afebrile meningomyelitis and leaves all the limbs paralyzed and flaccid, sparing the brainstem and affecting the diaphragm to a variable extent. Several such patients have harbored a cancer or Hodgkin disease, and the pathology was more typical of a poliomyelitic viral infection rather than of the usual paraneoplastic syndromes (Chap. 30). Involvement of the white matter with sensory and motor paralysis below the level of a lesion has also been reported in so-called “dumb” rabies (in contrast to the usual form of “mad” or “furious” rabies encephalitis), and in an infection transmitted by the bite of a monkey, called the B virus. These are decidedly rare. More common are the viral myelopathy of HIV-AIDS and of HTLV-I infection. With these exceptions, one may say that myelitis that expresses itself mainly by dysfunction of motor and sensory tracts will usually prove not to be viral in origin but rather to one of the disease processes in category III (noninfectious, inflammatory) of the preceding classification, for example, multiple sclerosis. The unique myelopathies of HIV and of human HTLV infections are described below.
Vacuolar Myelopathy With HIV (See Also “HIV Myelopathy” in Chap. 32)
As the neurology of AIDS has been elucidated, the clinical and pathologic characteristics of a viral myelopathy have been studied in detail. The frequency of this condition is impressive—it was present in 20 of 89 successive cases of AIDS on whom a postmortem examination was performed by Petito and colleagues. Often, the clinical symptoms and signs of spinal cord disease are obscured by a neuropathy or one or more of the cerebral disorders that complicate AIDS either because of HIV or due to an opportunistic infection (CMV, toxoplasmosis, progressive multifocal leukoencephalopathy [PML]). In 5 cases of severe vacuolar myelopathy in the aforementioned series, there was leg or leg and arm weakness, often asymmetrical and developing over a period of weeks, to which the signs of sensory tract involvement and sphincteric disorder were added. A sensory ataxia has also been a common early feature in our experience. The CSF shows a small number of lymphocytes, a slight elevation of protein, and, occasionally, bizarre giant cells.
The white matter of the spinal cord is vacuolated, by which is meant a ballooning within myelin sheaths of the long tracts. The changes are most severe in thoracic segments with the posterior and lateral columns are affected diffusely. Axons are involved to a lesser degree, and lipid-laden macrophages are present in abundance. Similar vacuolar lesions may be seen in the brain in some cases. The lesions in the spinal cord resemble those of subacute combined degeneration but levels of vitamin B12 and folic acid are normal. (A similar lesion was found in one of our patients with myelopathy from chronic lupus erythematosus.)
The antiretroviral drugs that slow the progress of AIDS, with the exception of a few cases, seem to have little effect on the myelopathy and one can only resort to symptomatic treatment of spasticity.
This disease was brought to the attention of neurologists 50 years ago through the observations and writings of Cruickshank. However, it is only more recently that a chronic infective-inflammatory disease of the spinal cord caused by the retrovirus HTLV-I has been discovered and its connection to what had been called tropical myelitis, appreciated. The implications of this discovery are potentially broad and extend even to the demyelinative and possibly the degenerative diseases.