Factors predicting cure at one year after administration of radioactive iodine to patients with Graves' disease

To investigate the determinants of cure after radioactive iodine (RAI), a treatment frequently used to treat Graves' thyrotoxicosis.

We conducted a retrospective analysis of data from 160 consecutive patients with Graves' thyrotoxicosis who received 370MBq of iodine-131 (¹³¹I) at one centre between 2009 and 2018. Data included gender, age, cause of thyrotoxicosis, and number of RAI doses administered. Free thyroxine (fT4) and triiodothyronine (fT3) level at diagnosis, thyroid stimulating hormone (TSH), fT4 and fT3 levels on the day of RAI, and TSH, fT4 and fT3 at 3, 6, and 12-months post RAI treatment were reviewed. Cure was defined as achieving a euthyroid or hypothyroid state within one year of RAI administration.

Eighty one percent of the total cohort achieved cure at one year. Sixty one point eight percent of patients developed hypothyroidism within one year necessitating lifelong thyroxine replacement. fT4 at diagnosis (P=0.02), fT3:fT4 ratio at diagnosis (P=0.05) and the ratio of fT4 at diagnosis to fT4 pre-RAI ratio (P=0.05) and fT4 pre-RAI (P=0.002) were independent variables associated with cure after one year.

Radioactive iodine is a highly effective treatment for Graves' thyrotoxicosis. It is more likely to be successful in patients with lower fT4 at diagnosis and pre-RAI.