Neuro-immunological complications of retroviruses other than the HIV

Abstract

The aim of this review is to introduce and adjust the recent results of clinical and basic studies of neurological diseases associated with human T-lymphotropic virus type I (HTLV-I) and type 11. HTLV-I and II are type C retroviruses, members of the subfamily Oncoviridae. HTLV-I has been implicated as the causative agent of adult T-cell leukemia/lymphoma (ATL), first proposed as a clinical entity by Takatsuki and colleagues in Japan. This RNA virus was independently isolated from a patient with cutaneous T-cell lymphoma in the United States by Poiesz et al. in 1980 and from a patient with ATL in Japan by Hinuma et al. in 1981. The common causes of neurological complications of ATL were direct tumor cell invasion and hypercalcemia and the manifestations of ATL, including neurological signs and symptoms were variable. Another neurological disease associated with the same HTLV-I has been independently demonstrated in Martinique and Japan. The disease is now known under the combined acronym HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). A nationwide survey in Japan found about 700 cases of HAM/TSP. Approximately 450 persons with HAM/TSP have been reported from other countries, including those in the Caribbean basin, South America and Africa. In the Japanese nationwide survey, the mean age at onset of symptoms was 43 years and the male-to-female ratio of occurrence was 1:2.9. The main neurologic features of HAM/TSP are spasticity and/or hyper-reflexia of lower extremities, urinary bladder disturbance, lower extremity muscle weakness and sensory disturbances (mostly with poorly defined thoracic sensory levels). Histopathologic features consisted of chronic inflammatory changes which were most conspicuous in the lower thoracic cord. There is no convincing proof of virus infection in neural cells and immune pathogenesis for HAM/TSP may play a part. Currently, however, it would be too hasty to draw the conclusion that HTLV-1 infection in neural cells is not related to pathogenic mechanisms for the disease. Oral prednisone may have a beneficial effect in some cases, but effects may be transient. In contrast to HTLV-I, HTLV-II has not been associated conclusively with any specific disease.