Definition:

Human T lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic progressive myelopathy characterized by bilateral pyramidal tract involvement with sphincteric disturbances. HTLV-1 is the etiologic agent of HAM/TSP. Although the majority of HTLV-1-infected individuals remain asymptomatic during their lifetime, approximately one percent of this population develops a myelopathy consisting of a chronic inflammation of the white and gray matter of the spinal cord. Early in the disease process the leptomeninges, blood vessels and parenchyma are infiltrated with CD4+, CD8+, B lymphocytes and foamy macrophages, whereas later in the disease CD8+ lymphocytes predominate with subsequent progression to a relatively acellular, atrophic pattern with axonal and myelin degeneration.