HTLV-I infection in patients with autoimmune thyroiditis (Hashimoto's thyroiditis).

To investigate the possible relationship of HTLV-I virus infection to autoimmune thyroid disease, we examined, firstly, the frequency of HTLV-I seropositivity among patients with Hashimoto's thyroiditis and, secondly, the frequency of Hashimoto's thyroiditis in patients with HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP). Of 144 patients with Hashimoto's thyroiditis in the Tokushima and Kochi Prefectures, Japan, 9 (6.3%) were positive for serum HTLV-I virus antibody 2 of whom were confirmed histologically to have Hashimoto's thyroiditis. This percentage is significantly higher (P < 0.01) than the estimated prevalence (2.2%) of HTLV-I carriers among the general population in this region. Of 9 patients with HAM/TSP, 3 (33.3%), including 2 biopsy-proven cases, had evidence of Hashimoto's thyroiditis. This proportion is apparently much higher than the prevalence (1.7%) of Hashimoto's thyroiditis in the general population. These findings suggest that HTLV-I virus may be related to the development of Hashimoto's thyroiditis.