Endocrine Abstracts

Controversy about the optimal dose of ¹³¹I in thyrotoxicosis is ongoing. High doses result in higher cure rates, but are associated with elevated risk of hypothyroidism and irradiation exposure. There is no consensus as to the optimum period of thionamide discontinuation prior to treatment, nor to its impact on the success of RAI.

We retrospectively analysed 151 clinical records of patients with thyrotoxicosis due to Grave’s disease or toxic nodular goitre, treated with ¹³¹I between 2001 and 2005 and followed up for minimum 2 years.

Carbimazole, when received, was stopped 14 days before RAI and patients were given β-blockers alone, prior to,and post RAI. 79 subjects (group A) were prescribed high dose ¹³¹I, >230 MBq (mean 372 MBq), whilst 72 (group B) were prescribed low dose ¹³¹I (<230 MBq, mean 195 MBq). Cure was defined as detectable TSH at 2 years or need for thyroxine replacement.

In group B 56% were cured. Of these 60% received no carbimazole. In the treatment failure group 50% had been pre-treated with carbimazole (P=NS). In group A, 72% were cured, 56% of these received no carbimazole. In the non responders, only 41% had received carbimazole. In group B the cure rate was significantly less at 56% (P<0.05), prior therapy with carbimazole had a prevalence of 50% in the treatment failure arm. Hypothyroidism rate was 79% in group A and 70% in group B (P=NS), occurring earlier at 6 months post therapy in the former and 9 months post therapy in the latter. Factors favouring cure were lower FT4 levels pretherapy in group A only (mean 67.2 pmol/l, failure high dose versus 47.3 successful high dose) P<0.05 and a higher dose of RAI. Carbimazole pre-treatment had no effect on cure rate for either dose. Larger goitre size was associated with treatment failure, as previously described.