Sonography of Hashimoto's thyroiditis.

Fifty-three untreated patients with histologically confirmed Hashimoto's thyroiditis were divided into two groups according to the echogenicity of the thyroid. In 25 cases, the echogenicity of the thyroid was almost the same as or less than that of the adjacent muscles. Such cases were classified as group A. The other 28 cases were classified as group B. Mean T4 levels in group A were significantly lower than those in group B. In addition, the cases in group A had abnormally low T4 and abnormally high TSH more frequently than those in group B. In all cases in group A, there was severe degeneration and disappearance of thyroid follicles, whereas in most of the cases in group B, follicles of normal size were generally seen. Hypoechogenicity of the thyroid is a sign suggesting hypothyroidism and severe follicular degeneration.