Adult T cell leukemia following HTLV-I-associated myelopathy/tropical spastic paraparesis : case reports and implication to the natural course of ATL

Adult T cell leukemia (ATL) is the T cell malignancy caused by human T lymphotropic virus type I (HTLV-I), and HTLV-I is also the causative agent of HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Although HTLV-I causes both diseases, concomitant occurrence is reported to be rare. This paper describes two cases of HAM/TSP that developed into lymphoma-type ATL after the onset of HAM/TSP. In one case, the same HTLV-I infected clone could be detected by polymerase chain reaction in peripheral blood obtained when the patient was diagnosed as HAM/TSP. This finding showed that the HTLV-I clone already existed at the stage of HAM/TSP. Since frequent detection of clonal proliferation of HTLV-I infected cells has been reported previously in patients with HAM/TSP, careful follow-up is needed for patients with HAM/TSP.