Radioiodine therapy in patients with type II amiodarone-induced thyrotoxicosis

The treatment of amiodarone-induced thyrotoxicosis (AIT) still remains a clinical challenge, requiring the cooperation of both endocrinologists and cardiologists. Unfortunately, even today AIT is related to significantly increased mortality.

The aim of this study was to compare the efficacy of radioidine therapy for type II AIT in 2 groups of patients: with high or normal radioiodine uptake and treated by amiodarone (AM) in the past (AM- group) and with low radioiodine uptake and currently treated with AM (AM+ group).

The AM- group included 57 patients and the AM+ group, 49. All patients received iodine-131 at a dose of 22mCi~800. Patient data were collected for over 2 years.

After radioiodine administration, serum thyroid-stimulating hormone levels in the AM- group and AM+ group were 0.0 ±0.0 and 0.0 ±0.0, respectively, at 1 month; 1.2 ±3.3 and 0.6 ±1.2, respectively, at 12 months; and 4.2 ±3.6 and 1.9 ±0.8, respectively, at 2 years. All differences between the groups were statistically significant (P <0.0001). Free triiodothyronine and thyroxine levels were significantly higher in the AM+ group compared with the AM- group. During follow-up, death occurred in 22 patients in the AM+ group and 6 patients in the AM- group.

Radioiodine treatment is a safe and effective therapeutic modality for patients with type II AIT despite low radioiodine uptake, especially for patients with contraindications to other types of treatment (eg, thyroidectomy). Moreover, since thyrotoxicosis in patients with AIT is a significant risk factor for increased mortality, and since there are no alternative antiarrythmic treatments, radioiodine administration seems to be the only effective therapeutic modality.