STUDIES ON THYROTROPHIN RECEPTOR ANTIBODIES IN PATIENTS WITH EUTHYROID GRAVES' DISEASE

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Abstract
SUMMARY: Thyroid stimulating antibodies (TSAb) and TSH‐binding inhibitor immunoglobulins (TBII) were assessed in 30 patients with euthyroid Graves' disease. TSAb were detected in 24 cases (80.0%), the incidence being not significantly different from that in hyperthyroid Graves' disease (29/30,97.6%). On the other hand, the incidence of TBII in patients with euthyroid Graves' disease (12/30, 40.0%) was significantly lower than that in patients with hyperthyroid Graves' disease (30/30, 100.0%). The mean TSAb and TBII activities in the euthyroid patients were significantly lower than in the hyperthyroid patients (P < 0.f005 and P < 0.001, respectively). Both TBII and, more closely, TSAb activities correlated with T3‐nonsuppressibility and inhibition of serum TSH response to TRH stimulation. The findings supported the stimulation in vivo of the thyroid by these antibodies.Both antithyroglobulin and antimicrosomal antibody titres in euthyroid Graves' disease were significantly lower than in hyperthyroid Graves' disease (P < 0.05, P < 0.01, respectively). Goitre size was significantly smaller (P < 0.001), and 99mTc thyroid uptake was significantly lower (P < 0.001) in the euthyroid than in the hyperthyroid group. Thus, the reduced mass of thyroid tissues responding to the stimulators was considered to be one of the factors responsible for the euthyroidism despite the presence of TSAb.The high incidence of TSAb and relatively low incidence of TBII in euthyroid Graves' disease indicate that the presence of TSAb does not necessarily lead to hyperthyroidism and that the development of overt thyrotoxicosis may require augmentation of both TSAb and TBII.