Introduction: Radioiodine (RAI) is safe and effective but further information to predict outcomes, specifically treatment failure and residual symptoms following treatment of hypothyroidism, may help improve outcomes.
Methods: Retrospective, observational, single-centre study. Electronic medical record review (n= 664) and patient questionnaire (n= 174).
Results: Complete cohort: Analysis of outcomes limited to 555 patients receiving first dose of 400 MBq. 77.1% hypothyroid, 5.6% euthyroid, 16.8% hyperthyroid and 3 deceased at 1 year. Treatment failure was associated with higher TRAb (OR 1.8, P=0.01 for TRAb above median); the only significant predictor in a model including gender, age, pre-treatment fT4 and TSH. Pre-treatment with thionamides (51.8% of cases) was associated with a 2.9-fold increased risk of treatment failure (P<0.001). Thionamide after RAI (28.0%) carried a 2.3-fold increased risk of failure (P<0.001).
Questionnaire: 31% were current smokers at the time of RAI. Thyroid eye disease was present in 10.9% prior to treatment and in 19.0% after. Median weight change was +6.0 kg (IQR 3.67.4), with multiple regression identifying only higher pre-treatment fT4 as a predictor of weight gain (P=0.03). 59.6% reported weight gain (A), 51.8% required more sleep since RAI (B), 44.4% felt less energetic (C), 41.8% felt slower mentally (D) and 42.4% reported more difficulties with memory (E). Logistic regression identified female gender (A,B,C); higher levothyroxine dose (A,B); and lower fT4 (A,D,E) as independent predictors of greater symptoms following RAI. 79.4% would recommend RAI to a friend.
Conclusions: TRAbs may be a useful tool in stratifying radioiodine dose.
Thionamide therapy may increase treatment failure risk, independently of disease activity.
Patients are largely satisfied with RAI despite high prevalence of symptoms.
Greater symptoms in those with lower fT4 despite larger dose of levothyroxine raise questions regarding optimal replacement therapy.