Thyroid Function in Patients Treated with Radioactive Iodine for Thyrotoxicosis

A series of 105 patients treated at least two years earlier with radioactive iodine for thyrotoxicosis have been surveyed. Eighty-five patients (81%) were euthyroid clinically and on the basis of routine thyroid function tests. Of the euthyroid patients 46 (54%) had normal thyroid-stimulating hormone (TSH) levels and 39 (46%) had raised TSH levels. There was no difference in serum triiodothyronine levels between these two groups but the serum protein bound iodine and serum thyroxine, though still well within the normal range, were significantly lower in the group with raised TSH levels. The serum cholesterol was also significantly higher in this latter group.Most of the euthyroid patients were seen again a year later. None had become hypothyroid and neither those with normal nor those with raised TSH levels showed any evidence of a decline in the level of serum thyroxine.It is concluded that raised serum TSH levels in patients treated with iodine-131 are not necessarily indicative of hypothyroidism. There is no indication that patients who have this abnormality become overtly hypothyroid over a 12-month follow up.     

Effect of Pretreatment with Carbimazole in Patients with Thyrotoxicosis Subsequently Treated with Radioactive Iodine

Preliminary treatment with carbimazole in a series of 181 patients with thyrotoxicosis selected for treatment with radioactive iodine did not make any significant difference to the subsequent response to ¹³¹I therapy.     

Remission of Thyrotoxicosis during Treatment with Propranolol

Twenty-eight thyrotoxic patients were treated with propranolol. In seven patients the drug had to be discontinued after one or two months, but in the remaining 21 clinical improvement was observed. Serial clinical studies and tests of thyroid function performed at monthly intervals showed that in four patients thyrotoxicosis remitted and all indices of thyroid function returned to normal. A fifth patient shows distinct evidence of remission with the 20-minute ¹³²I uptake falling to normal, although the free-thyroxine index remains slightly raised. It is likely that these remissions reflect the natural tendency of the disease to remit since propranolol is not considered to have any direct in-vivo effect on thyroid function.However, because of failure to gain adequate control of symptoms in all patients treated, and the fact that circulating thyroid hormone levels were often not restored to normal, propranolol is considered an unsatisfactory alternative to conventional antithyroid drugs for routine treatment.