Propranolol versus carbimazole as the sole treatment for thyrotoxicosis. A consideration of circulating thyroid hormone levels and tissue thyroid function

Use of propranolol and potassium iodate in the presurgical management of hyperthyroid cats

A prospective study was carried out using a combination of propranolol and potassium iodate to assess whether there were beneficial effects in preparing hyperthyroid cats for surgical thyroidectomy. Group A (n = 11) received propranolol from days 1 to 10, followed by propranolol and potassium iodate from days 11 to 20; group B (n = 10) received the reverse regimen. Blood samples were taken daily for subsequent determination of serum total L-thyroxine (TT4), L-triiodothyronine (TT3) and reverse T3 (rT3) concentrations. The signs of hyperthyroidism improved in all cats over the treatment period. At surgery, 36 per cent of the cats in group A had reference range serum TT4 concentrations, while 89 per cent with initially elevated TT3 concentrations had reference range concentrations. In group B, 10 per cent of the cats had reference range TT4 concentrations, while 75 per cent with initially elevated TT3 concentrations had reference range concentrations. The drug regimen used in group A was better tolerated and more effective and offers an alternative before thyroidectomy in cats that cannot tolerate carbimazole.

Reappraisal of thyroxine treatment in primary hypothyroidism

The optimum daily dose of thyroxine was calculated for 13 children aged 3-16 years with primary hypothyroidism by titrating their doses at monthly intervals. The condition of the thyroid was assessed by sensitive assay of thyroid stimulating hormone concentrations, as well as measurement of total and free thyroid hormone concentrations and systolic time interval ratios. Serum thyroid stimulating hormone concentration was found to be the most responsive to small changes in thyroxine. The calculated optimum daily replacement dose of thyroxine (102 micrograms/m2 or 3.5 micrograms/kg) was fractionally lower than that previously recommended, and was more closely related to surface area (coefficient of variation 8.2%) than to body weight (coefficient of variation 16.2%). Our results suggest that though monthly may be the optimal time interval for increases in the dose of thyroxine, any reduction in the dose should be made more gradually.

Heart failure in sinus rhythm as the sole manifestation of Graves' disease

A middle-aged man with Graves' disease presented with heart failure in sinus rhythm which preceded the more typical manifestations of the disease by some months. Once suspected, the diagnosis was supported by measurement of systolic time intervals, enabling the instigation of treatment in advance of biochemical confirmation.

Reversible alteration of the visual evoked potential in hypothyroidism

The pattern-shift evoked potential was measured in 19 hypothyroid patients before treatment, and after short- (one week) and long-term (12 to 24 weeks) thyroid hormone replacement therapy. Before treatment, nine patients had an abnormally prolonged visual evoked potential latency, more than 115 msec. After one week of therapy with 50 micrograms per day of L-triiodothyronine, the mean visual evoked potential latency for the entire group was unchanged, 114 +/- 8 to 114 +/- 7 msec. However, long-term therapy with 100 to 200 micrograms per day of L-thyroxine significantly shortened the visual evoked potential latency to 105 +/- 1 msec (p less than 0.001). In eight of the nine patients with initially abnormal results, the visual evoked potential latency was completely restored to normal. The visual evoked potential amplitude was also significantly changed by long-term L-thyroxine, 4.8 +/- 0.7 to 9.0 +/- 1.0 microV (p less than 0.01). It is concluded that the visual evoked potential is reversibly altered in hypothyroidism. This neurophysiologic parameter permits quantitation of the effects of hypothyroidism on the central nervous system and the extent and rate of response to thyroid hormone replacement therapy.