Poor response to prednisolone of idiopathic thrombocytopenia with human T-lymphotropic virus type I infection.

We describe the unique clinical characteristics of patients with idiopathic thrombocytopenic purpura (ITP) who are infected by human T-lymphotropic virus type I (HTLV-I). Thirty-seven patients with ITP were examined in the present study: 10 patients had HTLV-I infection, and the remaining 27 did not. The mean age of the group with HTLV-I infection was significantly older than that of the group without infection (57.8 +/- 14.0 and 42.4 +/- 20.1, P = 0.022). The difference in mean platelet counts at diagnosis between the two groups was not significant, 29 x 10(9)/L and 21 x 10(9)/L, respectively. The levels of platelet associated IgG, red blood cell count, white blood cell count, bone marrow cell count, and megakaryocyte count did not show any significant difference. Nine patients in the group with HTLV-I infection were treated with prednisolone (1 mg/kg, daily oral). Only 3 of them responded to the therapy (one complete response [CR] and two partial responses [PR]). However, 17 of 22 patients not infected with HTLV-I were treated with prednisolone successfully: 14 patients achieved CR, and 3 patients achieved PR. There was a significant difference in response to prednisolone between the two groups (P = 0.034). Two patients with the infection and one patient without the infection achieved CR with splenectomy. These results suggest that HTLV-I infection may cause immune thrombocytopenia by a different mechanism than classical ITP; HTLV-I may modify the clinical features of ITP through an unknown immune pathway.