Association of the Ultrasonographic Findings of Subacute Thyroiditis with Thyroid Pain and Laboratory Findings

We aimed to determine whether ultrasonography is a useful diagnostic tool by correlating its findings with biological data of patients with subacute thyroiditis (SAT). Thirty-two SAT patients were evaluated in a retrospective study. Thirty-one patients (96.9%) had tenderness, 14 (43.8%) had localized pain, and 11 patients (34.4%) had radiating pain during a state of SAT. With ultrasonography, we found 51 hypoechoic areas in 32 patients. The hypoechoic volume per unilateral thyroid gland (%) was significantly larger in areas accompanied with pain (P<0.001). Out of 27 patients measured, 18 (67%) were positive for thyroglobulin antibodies (TgAb), of whom all were females. TgAb levels ranged from 0.3 to 13.8 U/ml. During therapy, TgAb levels gradually increased in 2 of the 7 patients who were measured several times. Both thyroglobulin antigen (TgAg) and free thyroxine (FT4) correlated well with total hypoechoic volume (cm 3 ), and the TgAg level showed a strong correlation with the FT4 level (r = 0.7; P<0.0001). The area (%) that the hypoechoic volume occupied in the total thyroid gland, even if the area was over half, was not related to the need of L-T4 replacement therapy. Also, none of the other variables (age, days from onset until diagnosis, serum levels of FT4, TgAg, CRP, autoantibodies, therapies, treatment) differed between the patients with and without replacement therapy. In summary, we found that the hypoechoic area in patients with SAT reflected the degree of inflammation and thyroid hormone levels, though it was difficult to predict continuous hypothyroidism.