In the study of 21 patients with euthyroid Hashimoto's Thyroiditis, who had normal range TSH, but elevated antibody levels, half of the patients were treated with levothyroxine for a year, the other half were not treated. After 1 year of therapy with levothyroxine, the antibody levels and lymphocytes (evidence of inflammation) decreased significantly only in the group receiving the medication. Among the untreated group, the antibody levels rose or remained the same.
The researchers concluded that preventative treatment of normal TSH range patients with Hashimoto's disease reduced the various markers of autoimmune thyroiditis, and speculated that that such treatment might even be able to stop the progression of Hashimoto's disease, or perhaps even prevent development of the hypothyroidism.
If you have thyroid symptoms, the TSH test alone might not be enough. Make sure your doctor tests for antibodies, and if you have evidence of Hashimoto's disease, even though TSH is "normal" -- consider finding a doctor willing to provide treatment.
For more information, read: Treatment Can Help Those Who Test Positive for Thyroid Antibodies.