Teriflunomide in HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis

Background: HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a rare, progressive disease. It occurs in some people infected with the HTLV-1 virus. It leads to weakness in the lower limbs and other serious problems. It has no treatment. Teriflunomide is a drug used to treat multiple sclerosis. It reduces immune cells that make the disease worse. Researchers want to learn if this drug can help people with HAM/TSP. Objective: To learn the effects, immune response, safety, and tolerability of teriflunomide in people with HAM/TSP. Eligibility: Adults ages 18 and older with HAM/TSP. Design: Participants will be screened under protocol 98-N-0047. Participants will have a medical history. They will have physical and neurological exams. They will have blood and urine tests. Participants will take 1 tablet of the study drug once a day for 9 months. They will keep a drug diary. Participants will have lymphapheresis. For this, blood is drawn from a needle in one arm. A machine divides the blood into red cells, plasma, and white cells. The white cells are removed. The plasma and red cells are returned to the participant through a needle in the other arm. Participants will have lumbar punctures ( spinal taps ). For this, a thin needle is inserted into the spinal canal in the lower back. Spinal fluid is removed. Participants will have magnetic resonance imaging (MRI) of the brain and spine. The MRI scanner is a metal cylinder surrounded by a strong magnetic field. During the MRI, participants will lie on a table that can slide in and out of the scanner. Participation will last for 15 months.