CXCL10 and tropical spastic paraparesis: In this study, we were able to classify HAM/TSP patients into three groups based on the disease activity, which is assessed by “progression rate of motor dysfunction after the onset of motor symptoms” and “the concentrations of neopterin and CXCL10 in CSF.” Consequently, we propose a novel classification criteria in which HAM/TSP patients were divided into the three groups (High, Moderate, and Low) of the disease activity (Table 6).