Endocrine Abstracts

Background: Radioiodine(RAI) has been used to treat hyperthyroidism for more than seven decades. Effects of RAI treatment on thyroid function tests(TFT), risk of hypothyroidism, gland and autonomous nodule volumes and on ultrasonographic features in toxic adenoma (TA) and toxic multinodular goitre TMNG patients, have been previously studied by ourselves and other. However, studies evaluating ultrasonographic changes in thyroid and toxic nodule volumes usually have a follow-up period less than 36 months. Thus we aimed to study the long-term effects of RAI treatment on thyroid functions, ultrasonographic morphology and volume changes in patients with TA and TMNG.

Methods: Thyroid function tests and ultrasonography (US) reports of patients diagnosed with TA or TMNG between the years 2000 and 2021 were retrospectively analysed.

Results: We included 100 patients (n=65 TA, n=35 TMNG) whom thyroid function and US reports were obtained before and at least 36 months post-RAI. At the end of the median follow-up of 7.3 ± 0.3 years (TA, 6.6 ± 0.5 years; TMNG, 8.5 ± 0.7 years), the mean thyroid volume (TV) reduction in patients with TA and TMNG was mean±sd, 56.6±3.1% and 51.1±6.7%, respectively. Mean volume decrease of all toxic nodules was 80.5±1.9%. When the TA patients were divided into age groups as <50 and ≥50 years, the TV reduction was significantly higher in younger patients(64.5±4.7% vs 53.1±3.8%, P<0.05). One year after RAI treatment, the maximal volume reduction of the toxic nodules (TN) was 66.5%. The volume of the thyroid and TN was significantly reduced up to 12 years (P<0.01) after RAI treatment. Between 3 and 10 years after RAI therapy, the annual incidence of hypothyroidism was 2.0% and 1.5% in the TA and TMNG groups, respectively. Patients who developed hypothyroidism in both TA and TMNG groups had significantly smaller pre-treatment TV when compared to euthyroid patients [i.e. 51.1 ± 4.7 mL and 21.4±1.8 mL (P<0.05)]. Compared with pretreatment sonography findings, TN were more frequently solid, hypoechoic and macrocalcified in post-RAI ultrasounds (P<0.01).

Conclusions: The volume of thyroid gland and toxic nodules continuously decreases, as the risk of hypothyroidism increases up to 10 years after RAI treatment. Thus, follow up to check thyroid functions should continue. In post-RAI examinations, toxic nodules may show ultrasonographic features suspicious for malignancy. Hence history should include previous RAI treatment and old scintigraphy scans should be evaluated to avoid unnecessary procedures and non-diagnostic biopsy results.