ETA2023 Poster Presentations Hyperthyroidism (9 abstracts)
1University Medical Centre Ljubljana, Department of Nuclear Medicine, Department of Nuclear Medicine, University Medical Centre Ljubljana, Department of Nuclear Medicine, University Medical Centre Ljubljana, Ljubljana, Slovenia; 2School of Clinical Medicine, University of Cambridge, Cambridge, United Kingdom; 3University Medical Centre Ljubljana, Department of Nuclear Medicine, Ljubljana, Slovenia; 4Faculty of Medicine, University of Ljubljana, University Medical Centre Ljubljana, Department of Nuclear Medicine, Ljubljana, Slovenia; 5University Medical Centre Ljubljana, University of Ljubljana, Faculty of Medicine, Department of Nuclear Medicine, Ljubljana, Slovenia
Aim: In Graves disease (GD) the goal of radioiodine (I-131) application is the elimination of hyperthyroidism. The reported success rate 1 year after treatment is up to 90%. The aim of this retrospective study was to assess the factors influencing the early outcome 3 months after I-131 treatment of GD patients in an iodine sufficient area.
Materials and Methods: We reviewed medical records of GD patients who received I-131 therapy between January 2013 and December 2017. In all patients antithyroid drugs were discontinued at least 3 days before I-131 application. Prior I-131 therapy, uptake of iodine-123 (I-123) at 20-hours or technetium-99m-pertechnetate (Tc-99m) was measured. During follow-up, thyroid function was evaluated up to 3 months after I-131 application and time to occurrence of hypothyroidism was established. Patients characteristics influencing the early outcome of I-131 treatment were estimated, p value of <0.05 was considered statistically significant.
Results: We evaluated 849 GD patients (660 females and 189 males) aged between 16 and 91 years (mean age, 50.4±17.0 years). The median I-123 uptake, measured in 37.8% (321/849) patients, was 69.0%, and the median Tc-99m uptake, measured in 62.2% (528/849) patients, was 3.18%. The median treatment I-131 activity was 623 MBq I-131 (range, 436-1123 MBq). Follow-up data were available for 91.6% (778/349) patients. At 3 months after I-131 application we confirmed hypothyroidism in 81.6% (635/778) patients, hyperthyroidism in 14.1% (110/778) and euthyroidism in 4.3% (33/778) patients. Hypothyroid patients were younger than hyperthyroid and euthyroid patients (49.1± 16.7 years, 55.7±17.4 years and 57.8±17.0 years, respectively, P < 0.001), with a higher proportion of females (chi-square=6.6, P = 0.04). Their median I-123 uptake was higher (72.2%, 62.5% and 33.0%, respectively, P = 0.02), but their Tc-99m uptake did not differ (3.20% and 2.78% and 2.98%, respectively, P = 0.38). In hypothyroid patients applied I-131 activity was lower (587 MBq, 737 MBq and 728 MBq, respectively, P < 0.001). Mean time to hypothyroidism was 2.3±0.9 months. There was a significant correlation between time to hypothyroidism and younger age (r =-0.087, P = 0.03), but no correlation was confirmed with I-123 uptake (r =-0.004, P = 0.95), Tc-99m uptake (r =-0.017, P = 0.73) or applied I-131 activity (r =-0.007, P = 0.86).
Conclusion: More than 80% of GD patients develop hypothyroidism already within 3 months after I-131 therapy. This outcome is more frequently associated with younger age, female sex and higher uptake of I-123. Careful monitoring of patients following I-131 application is necessary to identify and treat the early outcome in a timely manner.
References: none