Background: Thyrotoxicosis is associated with significant morbidity, therefore adequate control of the disease is paramount. The outcome of treatment of thyrotoxicosis using radioiodine shows variable failure rates depending, amongst other things, on the administered activity of radioiodine and the use of anti-thyroid drugs. Thus, management should follow an evidence based protocol, which has a low failure rate.
Method: We prospectively analysed the outcome of treatment using our Gateshead protocol of a fixed administered activity of radioiodine therapy (400 MBq) given to 201 patients (including 140 with Graves' disease, 48 with toxic multinodular goitre (TMNG) and 13 with toxic nodule) followed up for a median period of 12 months (range, 6-77 months). Carbimazole was discontinued in patients rendered euthyroid 16 days prior to radioiodine. No routine anti-thyroid drugs or thyroxine were given following radioiodine unless hypothyroidism or thyrotoxicosis occurred.
Results: Following the Gateshead protocol led to a failure rate of 6.5% (eight females with Graves' disease, four females with TMNG and one female with toxic nodule), 29% euthyroidism and 64% hypothyroidism. The rates of hypothyroidism for women and for men were: in Graves' disease 77% and 79%, in TMNG 29% and 75%, in toxic nodule 42% and 0%, respectively.
Conclusions: Our observations show that withholding an antithyroid drug in excess of just over 2 weeks prior to administering a fixed administered activity of radioiodine in patients with thyrotoxicosis leads to the lowest reported failure rate, irrespective of the underlying cause. One possible mechanism for this could be the avoidance of drug induced radio-resistance.