Endocrine Abstracts

Aim: Retrospective survey on outcomes of ¹³¹I therapy in subjects with hyperthyroidism.

Methods: We analysed the outcomes at 1 year, of 55 episodes of ¹³¹I therapy in 52 patients (36 males, 15 females) who were treated between January 2007 and January 2009.

Results: At 1 year post ¹³¹I therapy, 31 (56.3%) subjects were hypothyroid (median age 54 years), 14 (25.5%) were euthyroid (median age 69 years) and 10 (18.2%) remained hyperthyroid (median age 73 years). 31 subjects (56.3%) had Graves’ disease, 20 (36.4%) had mutlinodular goitre (MNG) and 4 (7.3%) were not classified.

In 39 female subjects treated with ¹³¹I, 22 (56.4%) became hypothyroid, 10 (25.7%) remained euthyroid and 7 (17.9%) became hyperthyroid. Amongst the 16 male subjects, 9 (56.2%) became hypothyroid, 4 (25%) remained euthyroid, and 3 (18.8%) became hyperthyroid.

Out of 31 subjects who became hypothyroid, 21 (67.8%) had received 350 MBq, 9 (29%) had received 550 MBq and 1 (3.2%) had 650 MBq. Out of 14 subjects who were rendered euthyroid, 5 (35.7%) had 350 MBq, 8 (57.1%) had 550 MBq and 1 (7.1%) had 620 MBq. In the 10 subjects who remained hyperthyroid after ¹³¹I therapy, 5 (50%) had received 350 MBq and 5 (50%) had 550 MBq.

Thirteen subjects became profoundly hypothyroid (TSH>50) within one year. Of these, 10 (77%) had Graves’, 2 had MNG (15%) and 1 (8%) was not classified. 7 subjects (54%) had received 350 MBq whereas 6 (46%) had received 550 MBq of ¹³¹I therapy.

Conclusions: Despite the relatively small sample size, age, sex, aetiology and dose of ¹³¹I did not seem to influence the outcome of ¹³¹I therapy. Although larger studies are needed to confirm our observations, our series suggests an increased risk of profound hypothyroidism following ¹³¹I in subjects with Graves’ disease when compared to subjects with MNG.