Association of autonomously functioning thyroid nodules with Hashimoto's thyroiditis: study on a large series of...

Autonomously functioning thyroid nodules (AFTNs) associated with Hashimoto's thyroiditis (HT) are rarely reported. This study evaluates the magnitude of such association, elaborating the clinical and biochemical characteristics of HT and AFTN.

We reviewed the records of our patients with thyroid nodules, including serum TSH, free T4 and T3, Tg-Ab, TPO-Ab, ultrasonography, Tc-99m Sodium Pertechnetate scintigraphy (performed in overt or subclinical hyperthyroid patients). HT patients with coexisting AFTN(s) (group A) were compared with patients with AFTNs alone (group B, n=267).

80 patients (65 women and 15 men; F:M ratio 4.3:1; age 57±15 years) had AFTN(s) and coexisting HT. Except 9 patients who were under methimazole, all had suppressed (<0.01 mU/L) or low (<0.4 mU/L) TSH; 17/71 (24%) had increased FT4 and/or FT3. Subclinical hyperthyroidism prevailed over frank hyperthyroidism in group A (76 vs. 24%), but not in group B (56 vs. 44%) ( P=0.005). Group A patients had lower serum FT3 (∼0.6 pmol/L or 9%) and FT4 (∼0.9 pmol/L or 4%) as compared to group B. The maximum diameter of the AFTN(s) was 8% smaller in group A as compared with group B, thus matching the said difference in FT3. A positive correlation between nodule size and age was found only in group B ( P=0.015).

Even if difference in the size of nodules between groups A and B does not reach statistical significance, the chronic intrathyroid lymphocytic infiltration of HT may decrease the tendency of the AFTNs to grow and diminish their degree of functioning.