The differential diagnosis of myelopathies poses a clinical dilemma. Over a dozen different infectious agents have been associated with acute or chronic myelitis 1121, yet these agents are conclusively related to only a small number of the total cases; multiple sclerosis is often suspected, but long-term follow-up studies show that this disease accounts for less than 10% of cases 1301. In a majority, the cause remains unknown. High rates of subacute or chronic spastic paraparesis in certain geographic foci, particularly in the tropics, have suggested local toxic or infectious agents 1291.
Over the last year, a flurry of notes and letters in Lancet have incriminated human lymphotropic virus type I (HTLV-I) in some of these geographic foci of spastic paraparesis. HTLV-I is a human retrovirus originally associated with acute adult T-cell leukemia in southern Japan, and subsequently associated with this leukemia and non-Hodgkin's lymphoma in the Caribbean islands, parts of South America, southern Italy, Africa, and southeastern United States 1391. Antibodies to HTLV-I and HTLV-I1 are now being found with increasing frequency in intravenous drug users in the northeastern United States 1261. The first report of myelopathy from the Caribbean island of Martinique described antibodies to HTLV-I in 60% of patients with tropical spastic paraparesis compared to a 4%