A high prevalence of human T-lymphotropic virus type I carriers in patients with antithyroid antibodies.

Human T-lymphotropic virus type I (HTLV-I) is a causative retrovirus of adult T-cell leukemia lymphoma and HTLV-I associated myelopathy/tropical spastic paraparesis. HTLV-I is also associated with some forms of pulmonary alveolitis, chronic arthropathy, polymyositis, and uveitis. In this study, the possible role of HTLV-I infection in the pathogenesis of autoimmune thyroid diseases with positive antithyroid antibody (ATA) to microsomal antigen or thyroglobulin was evaluated. In Fukuoka Prefecture or the northern part of Kyushu Island located in the southwestern part of Japan, the prevalence of patients with HTLV-I antibody was screened using the particle agglutination test and then was further confirmed either by the indirect immunofluorescence method or the western blot method. The observed prevalence in patients with thyroid disorders and the estimated prevalence calculated considering the sex- and age-specific prevalence among healthy blood donors (n = 16,008) were as follows: 19 (7.4%) vs 7.8 (3.0%) (p < 0.001) for ATA-positive chronic thyroiditis (n = 257), 21 (7.0%) vs 6.6 (2.2%) (p < 0.001) for ATA-positive Graves' disease (n = 298), 4 (4.3%) vs 2.1 (2.2%) (ns) for ATA-negative Graves' disease (n = 94), 1 (2.9%) vs 1.1 (3.1%) (ns) in ATA-negative hypothyroidism (n = 35), and 3 (1.8%) vs 5.0 (2.9%) (ns) for ATA-negative nodular goiter (n = 170). These findings thus suggest that HTLV-I infection may have some relationship to ATA-positive thyroid disorders.