Endocrine Abstracts

Background: RAI is used as definitive treatment for hyperthyroidism, but administered activities vary between institutions. We used a fixed activity of RAI therapy for Grave’s disease (GD) and toxic multinodular goitre (TMNG), and calculated activity for toxic adenoma (TA). We reviewed treatment outcomes at one year.

Methods: Thyroid function tests 1 year post RAI were reviewed retrospectively to asess outcome for 79 hyperthyroid patients divided into 3 etiological groups: those with GD treated with 200 MBq, TMNG treated with 400 MBq and TA treated with calculated activity (50–434 MBq), between January 2012 and June 2017. 24 hour isotope uptake results were examined retrospectively to assess relationship to clinical outcome.

Results: 48/79 patients had GD (60.8%%), 16/79 TMNG (20.2%) and 15/79 TA (19%). Patients with GD were younger (median 46 years) compared to those with TMNG and TA (median 62 and 59 years respectively). There were more females in both groups (85.5% female in GD, 93.7% in TMNG and 83.3% in TA). At one year post-RAI, more patients with GD were rendered hypothyroid 28/48 compared to TMNG and TA (62.5% vs. 18.75% vs. 53.33%) and fewer patients with GD were rendered euthyroid (25% vs. 46.6% vs. 53.3%) or had persistent hyperthyroidism compared to those with TMNG/TA (12.5% vs. 0% vs. 0%). 12/28 patients with GD who developed hypothyroidism had 24 hour uptake >60% and all patients with 24 hour uptake >60% became hypothyroid in GD and TMNG groups.

Conclusion: We used low activity RAI (200 MBq) as treatment for GD, an activity below international recommendations, with comparable outcomes and cure rate 87.5%. All patients with 24 hour uptake >60% in GD and TMNG group developed hypothyroidism post RAI indicating that lower activity RAI should be considered to reduce risk of hypothyroidism.