Therapeutic Approaches for HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis: From the Past to the Forefront, and the Future

Human T-cell leukemia virus-1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic inflammatory disease of the spinal cord induced by immunological activation due to high HTLV-1 proviral load in the peripheral blood. HAM/TSP is representative of HTLV-1-related inflammatory diseases and its main neurological symptoms—namely, motor dysfunction of the lower extremities through spastic paraparesis with urinary disturbance—are progressive and lead to deterioration in the quality of life of patients once these dysfunctions develop. Therefore, novel and safe therapeutic regimens are needed, enabling patients to commence treatment as soon as possible after the diagnosis of HAM/TSP. To date, various treatments have been developed for correction of the associated immunological or virological abnormalities, which have produced some good results. However, there are still many problems, such as insufficient treatment effects and side effects. In addition, most of these treatments are still in the open trial phase, and it remains unclear whether or not they are suitable for the long-term treatment of HAM/TSP induced by a chronic inflammatory status. Thus, we need safe therapeutic regimens for long-term or even lifelong courses of treatment. As treatments for HAM/TSP have not yet been established as therapeutic strategies, in this review, we summarize the clinical trials conducted to date, including representative regimens against HAM/TSP as existing therapeutic approaches, and discuss new regimens showing potential for further investigation as part of new therapeutic strategies in future research.