Epithelial hyperplasia and decreased colloid content of the thyroid gland in triiodothyronine-predominant Graves' disease.

Patients with T3-predominant Graves' disease have an increased serum T3 level despite a normal or even lower level of serum T4 caused by antithyroid drug treatment. This study investigated the morphological characteristics of the thyroid gland in this type of hyperthyroidism. Ultrasound showed a similar thyroid echogenicity in both T3-predominant and ordinary Graves' disease, but thyroid weight was significantly greater in T3-predominant Graves' disease than in the controls [91 +/- 37 g vs. 48 +/- 17 g (mean +/- SD); P < 0.01]. The height of thyroid follicular epithelial cells were significantly greater in T3-predominant Graves' disease than in the controls (9.6 +/- 1.0 vs. 6.4 +/- 1.1 microns), but the epithelial height did not correlate significantly with the serum TSH receptor antibody titers. Epithelial cells occupied 26.4 +/- 10.9% of the total thyroid tissue in T3-predominant Graves' disease, while they occupied only 14.5 +/- 6.8% in the controls. Intracolloidal vacuoles also occupied a significantly greater area in the T3-predominant group (6.6 +/- 3.9% vs. 1.9 +/- 1.0% for controls). These findings suggest that the thyroid gland is more active in T3-predominant Graves' disease and has a more rapid turnover of intrathyroidal iodine than in the ordinary type of Graves' disease.