Interleukin-6: a marker of thyroid-destructive processes?

Increased serum interleukin-6 (IL-6) concentrations have recently been reported in patients with subacute thyroiditis and in some patients with amiodarone-induced thyrotoxicosis, possibly because of cytokine release from damaged thyroid cells. In this study, serum IL-6 levels were determined by an enzyme-linked immunosorbent assay method in 18 patients given percutaneous intranodular ethanol injection (PIEI) for autonomously functioning thyroid nodule, 12 patients treated with radioactive iodine (RAI) for Graves' disease or toxic adenoma, and 23 patients submitted to fine needle aspiration (FNA) for nonfunctioning thyroid nodules. Baseline serum IL-6 levels did not differ in the 3 groups. PIEI was followed by a dramatic increase in median IL-6 values from 42 fmol/L (range, < 25 to 84) to 381 fmol/L (range, 61-9870; P < 0.0001); the peak value was attained as little as 10 min after injection. RAI was also followed by a significant (P < 0.0001) increase in IL-6 from 52 fmol/L (range, < 25 to 84) to 189 fmol/L (range, 119-1417 fmol/L); the increase after RAI was lower than that after PIEI (P < 0.05), and the peak value was attained later (after 24 h). FNA was also followed by a slight, but significant, increase in the serum IL-6 concentration from 21 fmol/L (range, < 25 to 103) to 109 fmol/L (range, < 25 to 360; P < 0.0001 vs. baseline). The increase in IL-6 was correlated with the size of nodule or goiter (P < 0.0001), but not with the amount of injected ethanol or the dose of radioiodine delivered to the thyroid. Serum thyroglobulin also increased after PIEI, RAI, or FNA, but no significant correlation could be demonstrated with the increase in IL-6. The results of this study support the concept that in the absence of nonthyroidal illnesses, which are often associated with increased serum concentrations of the cytokine, IL-6 can be regarded as a useful marker of thyroid-destructive processes.