INTRODUCTION: Amiodarone (AM) is frequently used in the therapy of patients with 
cardiac disorders. However, due to high iodine content, it has side effects on 
thyroid function. The use of radioiodine therapy (RIT) in amiodarone-induced 
thyrotoxicosis (AIT) with low radioactive iodine uptake (RAIU) is still 
controversial. In these patients therapeutic choices for refractory disease 
include surgery, antithyroid drugs, or glu ocorticosteriods.
AIM: The aim of the study was to evaluate the efficacy of RIT in patients 
presenting AIT and low RAIU in two-year follow-up.
PATIENTS AND METHODS: 40 patients (25 men and 15 women) aged from 63 to 83 years 
(x +/- SD: 66.2 +/- 5.0 years; median: 65 years) treated with RIT were included 
into the study. In these patients AM therapy was essential for the underlying 
heart disorder, while surgery, antithyroid drugs or glucocorticosteroids, were 
contraindicated. Forty seven patients with toxic multinodular goiter (TMNG) (39 
women and 8 men), matched for age (67 +/- 12 yr; range 54-89 yr), were enrolled 
into the study as a comparative group. The diagnostic procedures included 
baseline thyroid function tests (thyrothropin - TSH, free triiodothyronine - fT3 
and free thyroxine - fT4 levels), thyroid autoantibodies measurement 
(antithyroglobulin autoantibodies - TgAb, antithyroid peroxidase autoantibodies 
- TPOAb, anti-TSH receptor autoantibodies - TRAb), thyroid ultrasonography, 
thyroid scintiscan and RAIU assessment.
RESULTS: Serum values of TSH, TgAb, TPOAb and TRAb were undetectable in both 
groups. In patients with AIT fT4 level was 18.7 to 38.7 pmol/l (mean: 27.1 +/- 
5.8) and fT3 concentration was 3.9 to 5.6 pmo/l (mean: 5.7 +/- 1.4), while in 
TMNG patients level of fT4 was 31.5 to 22.2 pmol/l (mean: 25,3 +/- 5,8) and fT3 
concentration was 3.8 to 4,2 pmo/l (mean: 4,2 +/- 0,2). Mean RAIU values after 
5h and 24h in AIT patients were 2.3 +/- 0.5 and 3.1 +/- 0.9%, while in TMNG 
patients were 18,0 +/- 3,8 and 35,7 +/- 9,1%, respectively. A significant 
difference (p<0.001) between 5h and 24h RAIU in AIT compared to TMNG was noted. 
In all patients with AIT, a dose of 800 MBq of 131I was administered. During 
two-year-observation recurrence of hyperthyroidism was observed in two patients 
(5%) with TMNG. These patients received a second radioiodine dose 16.2 +/- 15 
months later (the mean re-treatment dose was 735.93 +/- 196.1 MBq). In 
comparison, none of the patients with AIT required a second 131I dose and only 
one patient (2.5%) 6 months after ablative 131I dose needed anti-thyroid 
medication. Transient hypothyroidism was observed in only two patients (5%) with 
AIH, though was not observed in TMNG. During follow-up time, no sudden deaths in 
AIT patients were observed; one patient was diagnosed with prostate cancer, and 
in one patient acute toxic hepatitis after AM occurred.
CONCLUSION: RIT may be a safe and useful method of AIT therapy in patients with 
low RAIU, in whom other treatment methods are contraindicated.