Influence of l-thyroxine Administration in Patients with Euthyroid Hashimoto's Thyroiditis

Background: The present study aimed to evaluate the immune suppressive effect of l-thyroxine (LT4) on euthyroid Hashimoto's thyroiditis (HT). HT is the most common form of autoimmune thyroid disease and is characterized by lymphocytic infiltration of the thyroid gland, gradual destruction of the organ, and the production of thyroglobulin antibody (Tg-Ab) and thyroid peroxidase antibody (TPO-Ab). Methods: We examined the effect of 6-month LT4 administration in euthyroid HT patients. Twenty patients with euthyroid HT were enrolled. Ten patients were treated with 100 μg/day LT4 for 6 months. The other 10 were not treated with LT4. Thyroid function tests, thyroid volume, and autoantibody titers were measured before and after the 6-month study period. Results: There was significantly decreased serum TPO-Ab, Tg-Ab, thyroid-stimulating hormone, and increased free T4 levels in the LT4-treated group (860±220 vs. 415±182 mIU/ L, 168±61 vs. 71±43 mIU/L, 2.5±0.3 vs. 0.5±0.1 U/L, and 14.1±0.2 vs. 22.2±0.3 pmol/L, p ＜ 0.05, respectively). In contrast, TPO-Ab and Tg-Ab levels did not change significantly; they were slightly increased in the LT4-untreated patients. Thyroid volume did not differ before and after therapy in both groups. Conclusions: Thus, early prophylactic LT4 treatment might be useful for ameliorating the progression of euthyroid HT autoimmunity. The long-term clinical benefit of LT4 therapy in euthyroid HT is yet to be clarified.