Long term follow-up of treated hyperthyroid and hypothyroid patients.

The objective was to assess the success rate in patients receiving surgery or radioactive iodine for primary hyperthyroidism and the incidence of subsequent hypothyroidism. A long term follow up of patients on L-thyroxine has also been performed from a cohort of patients on the Tayside Thyroid Register. The case series has been followed-up for up to 21 years. 2,038 patients were registered of whom 90.1% were female. 1,045 had had previous hyperthyroidism and 993 had hypothyroidism. Treatment for thyrotoxicosis varied with age, 80.4% of patients under the age of 40 being treated by thyroidectomy and 72.6% of patients over 50 being given the iodine. Overall 9% of patients required medical therapy alone (carbimazole), and this varied little with age. Compared to radioactive iodine, thyroidectomy was more successful (90.2% vs 82.9%, p < 0.01) and had a lower rate of subsequent hypothyroidism (22.0% vs 47.6% at 5 years, p < 0.001). Of patients treated with radioactive iodine, those who were unsuccessful had received a lower dose (mean 354MBq vs 489MBq, p < 0.001). Of patients receiving L-thyroxine (n = 1,180), 58.5% had a suppressed level of thyroid stimulating hormone, 38% had a detectable but not elevated level, and 3.5% had an elevated level (> 4.0 mU/l). Patients with a suppressed level were taking a higher dose of L-thyroxine than those with a detectable level (114.2 +/- 56.9 micrograms vs 100.4 +/- 45.9 micrograms, p < 0.01), but those with an elevated level were prescribed an even higher mean L-thyroxine dose (137.1 +/- 58.8 micrograms)); many were probably poorly compliant.(ABSTRACT TRUNCATED AT 250 WORDS)