SIGNIFICANCE OF THYROID-STIMULATING ANTIBODY AND LONG-TERM FOLLOW-UP IN PATIENTS WITH EUTHYROID GRAVES-DISEASE

We examined 13 patients with euthyroid Graves' disease suspected ophth almologically, by comparing them with 20 patients with untreated Grave s' disease and by following them up for 5 to 10 years. They had Graves ' ophthalmopathy (NOSPECS class II similar to IV) without other ocular diseases, normal levels of serum thyroid hormones, and no previous hi story of Graves' disease. Proptosis in euthyroid Graves' disease was n ot significantly different from that in untreated Graves' disease. In 3 patients with euthyroid Graves' disease, TSH was suppressed. There w as either no TSH response to TRH or it was low in 7 of 12 patients exa mined. The result of a TS-suppression test was abnormal in 8 of II pat ients examined. Titers of serum TGHA, MCHA, TSH-binding inhibitory imm unoglobulin (TBII), and thyroid stimulating antibody (TSAb) were signi ficantly lower in patients with euthyroid Graves' disease compared tha n in patients with untreated Graves' disease. TSAb, however, was posit ive in 12 of 13 (92%) patients. In spite of positive TSAb, 9 of 13 pat ients with euthyroid Graves' disease had normal radioactive iodine upt ake (RAIU). During the observation period, various abnormalities in th yroid function developed: persistent hyperthyroidism in 5 patients (38 %), transient thyrotoxicosis in 2 (15%) and transient hypothyroidism i n 1 (8%). We conclude that euthyroid Graves' disease is a subtype of G raves' disease that minimally develops thyrotoxicosis in spite of the existence of TSAb due to some mechanism inhibiting thyroid growth or s timulation, and that the measurement of TSAb provides a useful marker for the diagnosis of this disease.