Association of HTLV-I with autoimmune thyroiditis in patients with adult T-cell leukaemia (ATL) and in HTLV-I carriers

OBJECTIVE Human T-lymphotrophic virus type I (HTLV-I) is a retrovirus that causes adult T-cell leukaemia (ATL). This virus is associated with a variety of autoimmune disorders. The possible association between HTLV-I infection and autoimmune thyroiditis has not been fully studied. We therefore evaluated anti-thyroid peroxidase antibodies (TPOAb) and anti-thyroglobulin antibodies (TGAb) in the sera of patients with ATL, carriers of HTLV-I, and in healthy control subjects to investigate the possible association between such infection and autoimmune thyroiditis. PATIENTS AND METHODS Fifty-two ATL patients (21 males, 31 females; mean age 56.4 years) and 50 HTLV-I carriers (18 males, 32 females; mean age 56.7 years) were studied. The control subjects were 877 healthy adults (271 males, 606 females; mean age 54.8 years) who were negative for HTLV-I antibody. TPOAb, TGAb, thyroxine (T4) and thyrotrophin (TSH) were measured in serum using a radioimmunoassay kit. RESULTS Positivity for thyroid autoantibodies (TPOAb and/or TGAb) was found in 21 of 52 ATL patients (40.4%), 15 of 50 HTLV-I carriers (30.0%), and 120 of 877 control subjects (13.7%). The difference between the HTLV-I-infected and the control subjects was statistically significant (P < 0.005). Female control subjects had a significantly higher prevalence of positivity for thyroid autoantibodies than the males (17.3 vs 5.5%, P < 0.001). Carriers of HTLV-I and patients with ATL of each sex showed an equally high prevalence of positivity for thyroid autoantibodies. Of the subjects who were positive for thyroid autoantibody, 7.5% of control subjects, 19.0% of ATL patients, and 40.0% of HTLV-I carriers had hypothyroidism. A significant difference in this respect was noted between the HTLV-I infected subjects and the control subjects (P < 0.005). CONCLUSIONS This study demonstrates a high prevalence of positivity for thyroid autoantibodies (TPOAb and/or TGAb) in the adult T-cell leukaemia patients and the HTLV-I carriers. The adult T-cell leukaemia patients and the HTLV-I carriers each had a high prevalence of hypothyroidism. There was an association between HTLV-I infection and autoimmune thyroiditis.