Use of antithyroid drugs after radioactive iodine treatment for hyperthyroidism

Graves disease (GD), toxic multinodular goiter (TMNG) and toxic adenoma (TA) are frequent causes of hyperthyroidism. Antithyroid drugs (ATD), radioiodine (RAI) therapy and surgery are therapeutic options of hyperthyroidism. There is still no consensus about the use of ATD after RAI treatment in the American Thyroid Association (ATA) 2011 guidelines. This study aimed to constitute a database about the management attitudes on the use of ATD after RAI treatment of hyperthyroidism, and to investigate its effects on provision of euthyroidism. The study was approved by the Başkent University Medical and Health Sciences Research Committee. 138 patients, who received RAI treatment for hyperthyroidism in the Department of Endocrinology and Metabolism, Başkent University Faculty of Medicine between 2011 and 2016, constituted the study population. The patients were grouped as two diagnostic categories, namely GD and toxic nodular group (which composed of TMNG and TA). Both groups were separately evaluated in terms of RAI treatment schedules, ATD use, thyroid morphology characteristics and the course of thyroid function tests. Thirty-nine of 41 GD patients used ATD median 12 (1-60) months before RAI treatment. ATD was stopped median 5 (3-360) days before RAI treatment. For those who used ATD post-RAI, it was restarted median 5 (3-90) days after RAI treatment. Median time to provision of euthyroidism was 3 (1-21) months in this group of patients. Fifty-eight of 97 TA/TMNG group of patients used ATD median 6 (1-48) months before RAI treatment. ATD was stopped median 5 (3-360) days before RAI treatment. For those who used ATD post-RAI, it was restarted median 7 (3-60) days after RAI treatment. Median time to provision of euthyroidism was 3 (1-12) months in this group of patients. A negative, moderate degree correlation was determined between time to provision of euthyroidism after RAI treatment and age and pre-RAI TSH levels in GD patients (r= -0.35; r= -0.32, respectively; p<0.05). A positive, moderate degree correlation was determined between time to provision of euthyroidism after RAI treatment and pre-RAI ATD doses (r= 0.40; p<0.05). A positive, strong correlation was determined between time to provision of euthyroidism after RAI treatment and duration of ATD used post-RAI in GD group (r= 0.75; p<0.05). A negative, weak correlation was determined between time to provision of euthyroidism after RAI treatment and pre-RAI TSH levels in TA/TMNG patients (r= -0.23; p<0.05). A positive, moderate degree correlation was determined between time to provision of euthyroidism after RAI treatment and pre-RAI total thyroid volume and time to restart of ATD post-RAI (r= 0.27; r= 0.34, respectively; p<0.05). A positive, strong correlation was determined between time to provision of euthyroidism after RAI treatment and duration of ATD used post-RAI in TA/TMNG group (r= 0.68; p<0.05). This study has exhibited that, ATD given early after RAI treatment may not affect time to euthyroidism negatively, and may even shorten in some circumstances. Prospective, long term research with increased number of cases on the subject should be designed; the results may affect clinical practice.