Goitrous hypothyroidism with blocking or stimulating thyrotropin binding inhibitor immunoglobulins

The significance of thyrotropin-binding inhibitor immunoglobulin (TBII) was evaluated in goitrous hypothyroidism associated with chronic thyroiditis (serum TSH greater than 10 mU/L, n = 148). TBII was measured by a RRA, and thyroid-stimulating antibody (TSab) and thyroid-stimulation-blocking antibody (TSBab) were determined using porcine thyroid cells. The prevalence of patients having TBII was 11% or 7.4% of 148 patients, which was not significantly different from that of 5% or 9.6% of 52 patients with atrophic thyroiditis. Although TBII was shown to be TSBab in 6, TSab was found in the other 5 patients despite hypothyroidism. There was little correlation between severity of hypothyroidism and TBII or TSBab activity. One patient continued to be latently hypothyroid despite apparently positive TSBab. Five other patients with TSBab and 2 patients with TSab suffered from overt, irreversible hypothyroidism, and 2 of the patients with TSBab continued to be hypothyroid even after the disappearance of TSBab. Biopsy of the thyroid gland performed in 4 patients revealed severely damaged thyroid follicles with mononuclear cell infiltration with or without fibrosis. Three of the patients with TSab had been taking excess iodine, and recovery of thyroid function was observed after iodine restriction. A perchlorate discharge test performed in two of these patients was positive, suggesting an iodide organification defect. These results indicate that, although TBII is not infrequently found in goitrous hypothyroidism, cellular or chemical damage of the thyroid gland plays an important role in the pathogenesis of thyroid hypofunction and TSBab may only have a precipitating role.