Endocrine Abstracts

We have previously (Allehabadia et al., JCEM, 2001) reported better cure rates for patients treated with a single fixed dose of 370 MBq ¹³¹I compared with 185 MBq. We have since increased the standard dose of administered radioiodine to 600 MBq and re-audited our data in 1240 consecutive thyrotoxic patients. We aimed to compare the efficacy of the new dose regimen and to explore factors that might predict outcome. Patients were categorised in 3 diagnostic groups: Graves’ disease (GD, n=528), toxic nodular hyperthyroidism (TN, n=144) and hyperthyroidism of mixed/indeterminate aetiology (n=568). Cure after a single dose of ¹³¹I was defined as euthyroid off all treatment for 6 months or T₄ replacement for hypothyroidism. Patients given a single dose of 600 MBq (n=477) had a higher cure rate (84.5%) compared with those receiving 385 MBq (74.7%,P<0.001) and those given 185 MBq (62.8%, P<0.001), but an increased incidence of hypothyroidism at 1 year was evident in those receiving higher doses (600 MBq:60.8%, 400 MBq:51.4%, P=0.005, 200 MBq:38.3%, P<0.001). There was no difference in cure rate between GD patients (71%) and those with TN (70.4%), but GD patients had a higher rate of hypothyroidism (53.2% vs 15.3%, P<0.001). Overall female patients (77.1% vs 65.5%, P<0.001) and those aged >40 years (79.1% vs 66.9%, P<0.001) had higher cure rates. Those cured with a single dose of ¹³¹I had lower mean fT4 concentrations (44.3 pmol/L vs 52.3 pmol/L, P<0.001) and patients with medium/large goitres were less likely to be cured than those with absent/small goitres (60.7% vs 81%, P<0.001). Binary logistic regression analysis identified 600MBq dose (AOR 3.25, P<0.001), female gender (AOR 1.86, P<0.001), lower presenting fT4 concentration (AOR 1.2, P=0.01) and small goitre size (AOR 2.7, P<0.001) to be independent prognostic factors for cure.

Conclusion: A single fixed dose of 600 MBq of ¹³¹I is effective in curing hyperthyroidism and should be administered to males, those with severe thyrotoxicosis, younger patients and patients with large goitres.