Increased thyroid blood flow in the hypoechoic lesions in patients with recurrent, painful Hashimoto's thyroiditis at the time of acute exacerbation.

We report two cases with painful Hashimoto's thyroiditis, who developed recurrent fever and painful thyroid. Glucocorticoid treatment was transiently successful but tenderness in the thyroid gland and fever developed when glucocorticoid was tapered. One patient underwent total thyroidectomy uneventfully. As is well known, it is frequently difficult to make differential diagnosis between painful Hashimoto's thyroiditis and subacute thyroiditis particularly at the initial phase. Interestingly, color flow doppler sonography of patient 1 revealed an increased thyroid blood flow in the hypoechoic lesions at the time of acute exacerbation although the serum level of TSH was suppressed. In the other patient, thyroid blood flow was also increased mainly in the hypoechoic lesions when the serum level of TSH was moderately increased, and it disappeared completely after supplementation of prednisolone and L-T4. Since thyroid blood flow in subacute thyroiditis is always decreased, such an increased blood flow in the hypoechoic lesion may be one of clinical characteristics of painful Hashimoto's thyroiditis, and useful for differential diagnosis from subacute thyroiditis.