Thyroidal response to an increase or decrease of endogenous TSH in patients with hyperthyroidism and its correlation with TSH binding inhibiting immunoglobulin.

One hundred and twenty-one patients with hyperthyroidism of Graves' disease were treated with antithyroid drugs for 3 years and thyroidal response to an increase or decrease of TSH and the serum thyroid stimulating immunoglobulin (TSI) activity were studied in relation to the presence or absence of TSH binding inhibiting immunoglobulin (TBII). TBII activity was positive in 83% of untreated patients but decreased gradually with time during antithyroid drug therapy. Thyroidal radioactive iodine uptake (RAIU) was suppressed by T3 in 86 of 121 treated patients but 16% of suppressible patients had TBII activity. Thyroidal RAIU was not suppressed by T3 in 35 treated patients, and 19 of 35 unsuppressible patients had TBII activity but other 16 patients did not. When suppressible and unsuppressible patients were combined, suppression of serum T4 and thyroidal RAIU by T3 tended to be less in the presence of TBII activity. TSI activity was detected in the sera of untreated patients but did not correlate with TBII activity. TSI activity was undetectable after treatment for 3 years irrespective of presence or absence of TBII activity and T3-suppressibility. TSH, T4 and T3 elevation in response to 500 micrograms thyrotropin releasing hormone (TRH) was normal in all treated patients irrespective of presence or absence of TBII activity and T3-suppressibility. It is suggested that in vivo thyroidal responsiveness to an increase or decrease of endogenous TSH did not correlate with the presence or absence of TBII activity after long-term therapy with antithyroid drugs.