Pathogenesis

TROPICAL SPASTIC PARAPARESIS/HUMAN T CELL LEUKEMIA TYPE 1-ASSOCIATED MYELOPATHY (TSP/HAM) PATHOGENESIS.

The human T cells lymphotropic virus type 1 (HTLV-I) is a slow progression virus and with low virulence. However, a low number of individuals with tropical spastic paraparesis and associated myelopahy to the HTLV-I (TSP/HAM) show immunopathologic characteristics as T lymphocytes proliferation. This is related to the high production of interleukins, such as the IL-2, in some individuals infected by the HTLV-I. In fact, HTLV-I-infected individuals show activation capability, proliferation, and differentiation of the T cells. For that to take place, two mechanisms are explained: 1) the T cells are normal and 2) the T cells show genetic deficiency with possible neoplasic results. This would demonstrate the emergence of adult T cell leukemia (ATL), a highly pathogenic process that frequently leads to death within a few months, without considering the therapeutic effects (2).

The TSP/HAM, reported by Japanese researchers, is a neurological disease developed in 14 out of 1464 HTLV-I-infected individuals after a long period of incubation, with approximately in range of 43 years of age (3). The TSP/HAM main neurological characteristics consist in contractions and weakness in the lower limbs, urinary disturbances, and sensorial disturbances at the thoracic level (4,5). The main pathological findings consist in the inflammatory reaction and the demyelinization process located in the spinal column (6,7). A high concentration of T cells and monocytes is found in this region, but no evidence of malignity was described in these cells (8,10). Since the TSP/HAM histopathologic process is essentially inflammatory, the mechanism for which the HTLV-I causes this disease differs from the ATL.