CONTEXT

No previous study determined monocyte- and lymphocyte-suppressing effects of levothyroxine and selenomethionine and assessed whether their coadministration is superior to treatment with only one of these drugs.

OBJECTIVE

Our objective was to compare the effect of levothyroxine and selenomethionine on monocyte and lymphocyte cytokine release and systemic inflammation in patients with Hashimoto's thyroiditis.

DESIGN, SETTING, PARTICIPANTS, AND INTERVENTION: We conducted a randomized clinical trial involving a group of 170 ambulatory euthyroid women with recently diagnosed and previously untreated Hashimoto's thyroiditis and 41 matched healthy subjects. Participants were randomized in a double-blind fashion to receive a 6-month treatment with levothyroxine, selenomethionine, levothyroxine plus selenomethionine, or placebo. One hundred sixty-five patients completed the study.

MAIN OUTCOME MEASURES

Monocyte and lymphocyte release of proinflammatory cytokines and plasma levels of C-reactive protein (CRP) were assessed.

RESULTS

Compared with the control subjects, monocytes and lymphocytes of Hashimoto's thyroiditis patients released greater amounts of all cytokines studied. Levothyroxine reduced monocyte release of TNF-α, IL-1β, IL-6, and monocyte chemoattractant protein-1, whereas selenomethionine inhibited lymphocyte release of IL-2, interferon-γ, and TNF-α, which was accompanied by a reduction in plasma CRP levels. The decrease in cytokine release and in plasma CRP levels was strongest when both drugs were given together.

CONCLUSIONS

Despite affecting different types of inflammatory cells, levothyroxine and selenomethionine exhibit a similar systemic antiinflammatory effect in euthyroid females with Hashimoto's thyroiditis. This action, which correlates with a reduction in thyroid peroxidase antibody titers, may be associated with clinical benefits in the prevention and management of Hashimoto's thyroiditis, particularly in subjects receiving both agents.