This study will use three different magnetic resonance imaging (MRI) techniques to study HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/STP)-a disease of slowly progressive weakness in the legs. It is not known how the HTLV-1 virus causes this disease, but it is thought that as the body's immune system tries to destroy the virus, parts of the nervous system-primarily the spinal cord-are damaged.