A study of antithyroid drug (ATD) therapy with a mean follow-up period of 10 years (range 2-25) in 434 patients with Graves' disease has been made by linking hospital records with those of a central follow-up register. The majority (89%) were treated with carbimazole and 87% received combined therapy with triiodothyronine (T3) (73%) or thyroxine (T4) (14%). Sixty-one per cent were assessed for T3 suppression tests on completion of treatment, of whom 61% (95% CL, 55-67%) suppressed. The overall 5-year cumulative proportion developing recurrent hyperthyroidism was 54-62% with rates of 26-44% in suppressed patients and 65-79% in those not suppressed. In unsuppressed patients, most (72%) of the recurrences occurred within 1 year with only an additional 10% predicted up to 10 years. In suppressed patients 30% of recurrences occurred in the first year, 60% between 1 and 5 years and a further 10% between 5 and 10 years. Suppression with T3 is probably the best and cheapest predictor of outcome but has an accuracy of only 70% for both positive and negative tests which limits its usefulness in planning long-term follow-up and surveillance. A standard format should be adopted for the analysis and reporting of follow-up studies, based on actuarial methods of estimating the cumulative proportion with recurrences or other events, to facilitate comparisons between different centres.

Thyroidal secretion of 3,3',5'-triiodothyronine (reverse T3, rT3) and its control by TSH was assessed by measuring (1) arterio-venous hormone gradients in patients undergoing surgery, (2) changes of hormone concentrations after induction of anaesthesia, and (3) changes induced by TRH administration. In ten patients in whom thyroid activity was under TSH control (parathyroidectomy and non-toxic goitre) increased thyroid vein/carotid artery ratios (TV/CA) for rT3 (mean TV/CA ratio 2.53) were found when compared to six patients with non-toxic goitre on suppressive doses of T4 (mean TV/CA ratio, 1.27) (P less than 0.05). The mean calculated operative secretion rate of rT3 was 12.5 microgram/day but only 2.4 microgram/day in patients receiving T4. In thirteen patients undergoing elective surgery induction of anaesthesia significantly increased rT3 levels. In nine euthyroid adults intravenous TRH (200 microgram) increased peripheral venous rT3 levels between 3 h (P less than 0.005) and 8 h (P less than 0.05) after the injection. It is concluded that significant amounts of rT3 are secreted by the thyroid gland at operation and this is, in part, under TSH control.

Abstract. The kinetics of [123I]iodide uptake were studied when organification of iodine by the thyroid gland was normal and when this binding function was diminished by drugs or disease. Each study was terminated by a sodium perchlorate discharge test (300–600 mg iv) at 60 min or, in some cases, 10–30 min. The results confirmed that binding takes place rapidly in the uninhibited gland with the binding rate constant being at least 0.150 min−1. Discharge from the uninhibited gland is less than 3.5% of the gland uptake when perchlorate is given 60 min after the radioiodide. Subjects with an intrinsic binding defect manifested discharges of 11% or greater of the 60 min uptake and the estimated binding rate constants ranged from 0.003–0.057 min−1. Thyrotoxic subjects receiving 5 mg carbimazole twice daily manifested discharges ranging from 5.4–64.2%, and in those receiving 20 mg twice daily the observed discharges were 67.6–94.6% of the 60 min uptake. The study shows that a correctly performed perchlorate discharge test will detect minimal inhibition of iodine binding. An important factor is the duration of the follow-up period after perchlorate is given. In some of the cases studied discharge was not complete until 60 min after the perchlorate.

The initial prescriptions and later adjustments of thyroxine (T4) replacement have been analysed in 2246 hypothyroid patients who have been monitored by a thyroid follow-up register for a mean period of 6 years (range 1-13 years). In 465 (21%) patients of 65 years or over, initial T4 doses were on average only 20 micrograms lower than in younger patients. However, only 40% of the elderly were taking 200 micrograms of T4/day or more, compared with 60% of the younger patients. Over 10 years, the predicted proportion of patients who have a downward adjustment of their T4 prescription is 3%, but there is no difference in recognized overtreatment between older and younger patients. The findings suggest that the majority of the elderly may receive larger doses of T4 than are required for optimal replacement. There are strong reasons for the standardization of thyroxine prescribing in the elderly and for the provision of routine surveillance of thyroxine replacement through the type of follow-up system used in this study.

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