Endocrine Abstracts

Radioiodine (RAI) is widely used for the treatment of thyrotoxicosis. The efficacy and hypothyroidism rate following a single dose of RAI is variable and the optimum administered dose – sufficient to achieve remission but with an acceptable low hypothyroidism rate, is still debated.

Our audit sought to compare the results of local practice with published rates of success and hypothyroidism following RAI. We also examined the relationship between treatment success and hypothyroidism rate at one year, with parameters such as age, gender, fT₄ at diagnosis, pre-treatment with antithyroid drugs (ATD) and dose of RAI.

We randomly selected 105 patients over a two year period, undergoing RAI treatment for either Graves Disease (GD) or toxic nodular disease (TND) (Toxic Adenoma, and Toxic Multinodular Goitre). Patients with GD were younger than those with TND (GD 47.8±1.67 yrs vs TND 70.7±1.76 yrs; P<0.001). The median dose of RAI was 400 MBq (range: 180–800) for GD, and 600 MBq (range: 400–800) for TND. The success rate for GD was 73.8%, and for TND 77.5% – comparable to published success rates of 66–84%. The early hypothyroidism rate was 60% in patients with GD (20–76% in the published literature) and 22.5% in patients with TND (11.4–34% in the published literature).

Using multivariate regression analysis, fT₄ at diagnosis was the only factor related to a higher rate of treatment failure (P<0.001 for GD, P<0.014 for TND). Pre-treatment with ATD (P<0.001), dose of RAI (P=0.013), and gender (P=0.026), predicted a higher rate of hypothyroidism.

Our audit of RAI therapy showed similar success, but also high hypothyroidism rates at one year, compared to the published literature and confirms the efficacy of this treatment modality for both GD and TND. Our local experience suggests that patients with GD in particular need to be counselled about a risk of early hypothyroidism requiring lifelong thyroxine replacement.