Thyroid function after subtotal thyroidectomy for hyperthyroidism. A follow-up study with special reference to thyroid stimulating hormone (TSH) and the thyrotropin releasing hormone (TRH) stimulation test.

193 patients operated on for hyperthyroidism were examined at follow up a mean 4.5 years after operation (range 1-6 years). The patients were examined clinically and biochemically. It was found that 4.6% had a permanent paralysis of the recurrent nerve and 2.6% a permanent hypoparathyroidism. Recurrent hyperthyroidism was found in 2.6%. The patients were grouped according to the results of basal S-TSH and the TRH-stimulation test. Within the groups it was found that all patients with a normal basal TSH were clinically euthyroid. 35 patients had a raised basal TSH or a hypothyroid pattern in the TRH-test, or both. Among these, 14 clinically hypothyroid patients were found. The remaining 21 patients were euthyroid clinically and were classified as subclinically hypothyroid. The levels of basal TSH were significantly higher in subclinically hypothyroid patients than in euthyroid patients and still higher in clinically hypothyroid patients. The response to TRH stimulation was also higher in the hypothyroid patients than in the subclinically hypothyroid patients. It was also found that the proportion of clinically hypothyroid patients was significantly higher, after 5 years than after one year. Since it cannot be decided if the patients with a subclinical hypothyroidism are at risk for manifest disease a close follow up of these patients is recommended.