A study of thyroid function after subtotal thyroidectomy for Graves' disease: particularly on TRH tests, T3 suppression tests and antithyroid antibodies in euthyroid patients.

Of 305 patients who underwent subtotal thyroidectomy for Graves' disease between 1969 and 1975, recurrent hyperthyroidism was found in 31 (10.2%) and hypothyroidism in 18 (5.9%). The remaining 256 patients were clinically euthyroid, but an elevated serum TSH level was found in 104 (34.1%) and an elevated serum T3 level in 19 (6.28%). In 57 of 133 clinically and biochemically euthyroid patients, a TRH test, T3 suppression test and measurement of antithyroid antibodies were performed. Twenty-nine of the 57 patients (50.9%) showed an abnormal response to TRH. Eight of these (14.0%) showed an impaired or absent response. The T3 suppression test showed that 15 of the 57 patients (26.3%) were non-suppressible. Positive antithyroid antibodies, especially antimicrosomal antibodies, were more frequent in non-suppressible and TRH-non-responsive patients than in suppressible and TRH-responsive patients. It is suggested that after operation for Graves' disease: 1) only half of the clinically euthyroid patients were biochemically euthyroid, 2) of the clinically and biochemically euthyroid patients, there were many with abnormalities in TRH responsiveness and T3 suppressibility, and 3) thyroid functional status is unstable and long careful follow-up is important after operation for Graves' disease.