A prospective study of the changes in thyrotropin binding inhibitory immunoglobulins in Graves' disease treated by subtotal thyroidectomy or radioactive iodine.

The effects of subtotal thyroidectomy and radioactive iodine on thyroid-stimulating immunoglobulins, as measured by a receptor assay, more appropriately termed TSH binding inhibitory immunoglobulins (TBII), were studied in 74 patients with Graves' disease. Fourty-four patients received radioactive iodine therapy, while 30 were subjected to subtotal thyroidectomy. After radioactive iodine, more patients were TBII-positive (90.5% vs. 81.8%) than before treatment, and the mean TBII index decreased dramatically, the maximum decrease being at 3 months. The mean TBII index subsequently returned gradually to the pretreatment level. Subtotal thyroidectomy had a different effect on TBII activity. TBII indices were positive in 89.3% of these patients before any treatment but were positive in only 40% (12 patients) after antithyroid drugs had been given before surgery. After surgery, TBII indices remained positive in 7 patients, while the remaining 5 patients became TBII negative. Seventeen patients (56.7%) were TBII negative before operation and remained so after surgery. One patient who was TBII negative before operation became TBII positive 2 months after operation. Interestingly, postoperative relapse of hyperthyroidism occurred in 3 patients who were TBII positive, while hypothyroidism occurred in 7 patients who were TBII negative. Thus, the TBII activity after subtotal thyroidectomy might be an important factor in determining the outcome of surgery.