Endocrine Abstracts

Radioiodine is the treatment of choice for relapsed hyperthyroidism although the optimum protocol is uncertain. We assessed the outcome of therapy with ¹³¹I in relapsed hyperthyroidism using a fixed dose regimen.

We retrospectively studied 449 patients (M: F 82: 367; age range 13–89 y, median 42 y) treated between 2003 and 2007 with a fixed dose of 550 MBq ¹³¹I for relapsed hyperthyroidism. Patients were classified as either Graves’ disease, toxic multinodular goitre or indeterminate aetiology. Where patients were on antithyroid drugs these were stopped at least 1 week prior to radioiodine.

One year following radioiodine 334 patients (74%) were hypothyroid, 85 (19%) were euthyroid and 30 (7%) had required a further dose of ¹³¹I. Patients with Graves’ disease were more likely to become hypothyroid than those with toxic multinodular goitre (78 vs 37%, P<0.001) whereas the latter were more likely to become euthyroid (55 vs 11%, P<0.001). Free T₄ >80 pmol/l at presentation was associated with an increased failure rate (17% compared with 5 and 3% for 40–79 pmol/l and <40 pmol/l respectively; P=0.01). Patients with a small/no goitre were more likely to be successfully treated by a single dose of radioiodine (96%) than those with a medium/large goitre (85%, P<0.001). Anti-thyroid medication was taken by 345 patients (77%) (carbimazole n=319) and was associated with an increased failure rate (8 vs 2%, P=0.027).

In conclusion, a single fixed dose of 550 MBq ¹³¹I is highly effective in treating relapsed hyperthyroidism. The aetiology, severity of hyperthyroidism, goitre size and prior anti-thyroid medication have a significant effect on outcome.