Endocrine Abstracts

Radioiodine therapy (RAI) is widely used as definitive treatment for hyperthyroidism. Of the several regimes in use, we have used a standard 555 MBq dose of RAI to treat all patients with hyperthyroidism. Treatment is considered to have failed if patients remain hyperthyroid at 12 months and a repeat 555 MBq dose is administered. We have studied 584 consecutive patients for failure rate of RAI when it is used according to this regime (mean follow-up 3 years (range 1-10)). We have also studied the influence of age, gender, use of pre-RAI antithyroid medication, aetiology and free thyroxine (FT4) levels at diagnosis, upon the failure rate following the first dose of RAI. Mean age was 56 years (range 20-90) with female preponderance (496 (85%)). 356 (61%) patients had Graves' disease, 140 (24%) had toxic nodular disease while in the remaining 88 patients (15%) aetiology could not be ascertained by the criteria used. After one year 545 (93%) patients were either hypothyroid (411, 70%) or euthyroid (134, 23%) and considered to be cured, while 39 (7%) patients remained hyperthyroid and required repeat dosing. On multivariate analysis, FT4 level at diagnosis was the only factor which independently influenced the outcome with higher FT4 level predicting a lower cure rate. This is in contrast to other studies, which have shown that several pre-treatment factors have an independent influence on the outcomes when smaller RAI doses are used. In conclusion, a standard 555 MBq RAI dose is effective for the treatment of hyperthyroidism and has a low failure rate. High FT4 level at diagnosis predicted a higher failure rate of the first RAI dose.