SAT448 Effects Of Radioactive Iodine Therapy Of Compensated Autonomous Thyroid Nodule After Pharmacological Suppression Of Tsh Secretion

Disclosure: A. Skoczylas: None. W. Mularczyk: None. M. Zyla: None. E.C. Lubocka: None. A. Kluza: None. A. Partyka: None. A. Golebiowska: None. I. Linkert: None. J. Raniszewska: None. M. Skoczylas: None. P. Piwkowski: None. P. Wozniak: None. D. Jedrzejuk: None. Introduction An autonomous nodule with autonomous function on scintigraphy, usually (but not always) leading to hyperthyroidism are representing by around 5-10% of solitary thyroid nodules. Progressive development is observed from a compensated autonomous nodule (in which TSH is not yet completely suppressed, but accompanied by symptoms suggesting an excess of thyroid hormones - most often of cardiac origin) to overt hyperthyroidism in about 60% in 5 years. The method of choice used in the treatment of a solitary nodule with associated hyperthyroidism is radioactive iodine therapy (I-131). Due to the low TSH concentration, the iodine uptake of the remaining thyroid parenchyma is inhibited, which results in the low risk of an after-treatment hypothyroidism. Objective In patients with autonomous nodules without low TSH level but clinical symptoms, will radioactive iodine therapy be equally effective and the risk of hypothyroidism minimalized if suppression of TSH secretion has been achieved pharmacologically before treatment? Methods There were 20 patients (female, mean age of 61,1) with ultrasound-confirmed goiter and autonomous nodule with partial suppression of surrounding thyroid tissue on scintigraphy (mean iodine uptake 14.1%) and mean TSH concentration was 0.48 (0.1-0.83), who had related to the circulatory and nervous system symptoms. These patients were treated with radioiodine the mean activity 364 MBq (242-600MBq). Radioactive iodine therapy was preceded by a 4-week treatment period with 100 µg/d thyroxine and 20 µg triiodothyroxine for suppression of thyrotropin secretion and subsequent reduction of iodine uptake by the thyroid tissue outside the autonomous area and with 5mg/d bisoprolol to minimize thyrotoxicosis. As a result, suppression of thyrotropin secretion mean TSH 0.049 concentration on the day of treatment was achieved, accompanied with iodine uptake inhibition in the part of the thyroid gland outside the autonomous nodule. Radioactive iodine therapy was conducted under these conditions after one day discontinuation of thyroid hormones. Seven days after I-131treatmet each patient was issued to take thiamazole 5 mg/d for 4 weeks with bisoprolol. Results Clinical symptoms disappeared completely. One year after radioactive iodine therapy the mean TSH concentration was 1.46 (0.8-2.65) in all subjects. In 4 years of observation 85% of patients remained euthyreotic with main TSH of 3,0. The mean volume reduction of the autonomous nodules was 45,6% with a reduction of 21.5% of the remaining thyroid parenchyma. Conclusion Radioactive iodine therapy preceded by pharmacological TSH suppression can be used for radical treatment of patients with autonomous nodules with partial TSH reduction to remain the majority (85%) of these patients euthyreotic for 4 years of observation and to reduce radioiodine activity used for treatment. Presentation: Saturday, June 17, 2023