Studies on replacement and suppressive dosages of 1-thyroxine

The effect of suppressive therapy of nontoxic diffuse goiter on serum levels of thyroxine, 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine

We studied the effect of suppressive therapy with graded doses of thyroxine (T4) on serum levels of T4, 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine [rT3] in patients with diffuse, nontoxic goiter. For comparison and in order to elucidate the degree of suppression of the pituitary thyroid axis by T3 the effect of suppressive therapy with T3 was studied in the same type of patients. We found that T4 in serum rose significantly to a constant level during T4 treatment (0.10, 0.15 and 0.20 mg/day). Dose-related rises in T4 were only seen after 3 months of treatment. T3 and rT3 only changed minimally. The T4/T3 ratio rose to a constant level during the initial 3 months of treatment. T3/rT3 ratio remained unchanged. No dose-related differences in T4/T3 and T3/rT3 ratio were observed. Treatment with T3 in doses of 0.06 mg per day caused a significant but slow fall in T4 and rT3 to hypothroid levels while T3 only rose slightly. The T4/T3 ratio dropped significantly during T3 therapy.

Thyroid function after surgical treatment of nontoxic goitre. A randomized study of postoperative thyroxine administration

Following thyroid resection for nontoxic goitre, 29 euthyroid patients were randomly allocated to no medication or to 0.2 mg levothyroxine daily (17 and 12 patients). The two groups were comparable in age, sex, extent of surgery and thyroid pathology. The patients were free from other endocrine disorders and had no other medication. Serum TSH, T4 and T3 were measured and T3-resin test performed preoperatively and 14 days and 3, 6, 12 and 18 months postoperatively. All values were within normal range. Only at the 3-month follow-up could statistically significant intergroup differences be observed, with T4 higher in the thyroxine-treated and TSH higher in the untreated group, but the outset values were thereafter regained. The T3 values in both groups were slightly reduced immediately after the operation. There was no recurrence of goitre in the 18-month observation period, and none of the findings suggested that routine thyroxine treatment is of value after resection of nontoxic goitre "in Denmark".

Preventive effect of levothyroxine in patients operated for non-toxic goitre: a randomized trial of one hundred patients with nine years follow-up

OBJECTIVE

Earlier reports have shown different effects of levothyroxine in the prevention of recurrence of non-toxic goitre after operation. These studies have been either retrospective or of short-term follow-up. This study was designed to evaluate the efficacy of long-term Eltroxin treatment (levothyroxine 0.1 mg daily) in the prevention of post-operative recurrence of non-toxic goitre.

DESIGN

Randomized prospective non-placebo controlled study with 9 years follow-up. Group A (n = 40) received levothyroxine and group B (n = 60) did not.

PATIENTS

One hundred patients consecutively operated for non-toxic goitre. All clinically and biochemically euthyroid and none taking any thyroid and/or antithyroid medication.

MEASUREMENTS

T3, T4, TSH, thyroid antibodies (microsomal/thyroglobulin), weight and neck circumference were measured and thyroid palpation were done preoperatively, 3 and 12 months after surgery and thereafter yearly up to 9 years.

RESULTS

Sixty-nine patients completed 9 years follow-up. Incidence of recurrence in group A vs group B was 14.5 vs 21.8% (P < 0.05) irrespective of type of operation, pathoanatomical diagnosis, removed amount or remnant size of the thyroid gland and level of TSH.

CONCLUSION

No preventive effect on incidence of recurrence of goitre by Eltroxin 0.1 mg daily in patients operated for non-toxic sporadic goitre was observed.

Hyperthyrotrophinaemia during thyroxine replacement therapy

During the follow-up of 224 cases of treated hypothyroidism, 14 clinically euthyroid patients were found to have elevated serum thyrotrophin and normal total thyroxine concentrations. Closer observation of these patients during the following 27 months resulted in the serum thyrotrophin levels returning to normal spontaneously in 8 patients (Group 1) whilst remaining elevated in 6 (Group 2), despite no significant differences in thyroid hormone levels between the two groups. Serum thyrotrophin in Group 2 patients remained high until an additional 50 micrograms/day thyroxine was prescribed although only 2 patients noted any benefit. Non-compliance or inadequate dosage of thyroxine are the probable causes of this sub-clinical hypothyroidism. Thyroid hormone estimations fail to differentiate the two conditions and we recommend a period of closer observation before making any thyroxine dosage adjustments in order to detect non-compliance.

Recurrence of nontoxic goitre with and without postoperative thyroxine medication

The incidence of postoperative recurrence of nontoxic goitre was evaluated in 175 patients. The average observation period was 8.8 years. Levothyroxine (Eltroxin) had been taken by 104 of these patients as long-term prophylaxis against goitre recurrence. Ten (9.5%) of the 104 had recurrence. The other 71 patients received no or only brief thyroxine medication postoperatively. In this group there were eight recurrences (11.3%). The difference was not significant, nor did the two groups differ significantly in regard to sex and age distribution, pathologic anatomy and observation time. Routine long-term administration of thyroxine after thyroid resection is not justified from the results of this study.

Familial inappropriate TSH secretion: evidence suggesting a dissociated pituitary resistance to T3 and T4

The study of pituitary thyroid relationships of a 40-year-old woman, suffering from recurrent goiter, is presented. The characteristics of this case were the following: i) constant hyperthyrotropinemia (range 8.2 to 29 micro u/ml) despite high thyroid hormone levels (mean total T4:13.4 microgram/dl; mean total T3:255 ng/dl) and clinical euthyroidism; ii) this TSH hypersecretion is not regulated by an excess of T4, while a suppressive effect is easily observed with T3. Together with the clinical effects observed with administration of T3 and T4, this suggests that thyroid hormone resistance predominates at the pituitary level, for T4 while not T3; iii) evidence is presented for the familial distribution of the trait and its mode of transmission. The clinical aspect and the pattern of resistance exhibited by the propositus and her progeny appear distinct from those of previous observations of thyroid hormone resistance.

Thyroxine replacement therapy: prescribing patterns and problems in 2710 patients. Scottish Automated Follow-up Register Group

The use of thyroxine replacement therapy was studied in 2710 patients with a previous diagnosis of either thyrotoxicosis or primary hypothyroidism. The patients, who were treated in five centres, were followed-up continuously using an automated register. Seventy per cent of patients had been prescribed daily doses of thyroxine of 200 microgram or more. The estimated 10-year cumulative incidence of detected undertreatment was 13 . 2% (95% confidence limits 10 . 9-15 .6%). The median cumulative incidence of recognised overtreatment was 6 . 2%. Improved patient education and the dissemination of guidelines to doctors on the use of thyroxine replacement may reduce the incidence of undertreatment or overtreatment.