January - March 2007, Volume 3, Issue 1

Ursu HI, Trifanescu R, Belgun M, Tatu-Chitoiu G, Podia-Igna C, Serban T, Hortopan D, Gudovan E, Goldstein A

The outcome of radioiodine treatment in amiodarone-induced hyperthyroidism

Acta Endo (Buc) 2007, 3 (1): 55-68
doi: 10.4183/aeb.2007.55

Background. In most type 1 and mixed forms of amiodarone-induced thyrotoxicosis (AIT), after restoration of euthyroidism and whether amiodarone can be withdrawn, an ablative therapy (thyroidectomy or radioiodine) is required. Radioiodine ablation of the thyroid was reported to prevent recurrence of AIT after amiodarone reintroduction.\r\nAims. To assess the efficacy and safety of radioiodine treatment in type 1 and mixed forms of AIT.\r\nPatients and methods. 9 patients (6M/3F) with type 1 and mixed form of AIT, mean age 62.2 ? 13.3 years (range: 50-85 years), pretreated with methimazole, received radioiodine treatment. The underlying thyroid disease was Graves disease (n= 5), toxic multinodular goiter (n= 3) and toxic adenoma (n=1). TSH, total T3, total T4, free T4, TPOAb were measured by radioimmunoassay; radioiodine uptake, thyroid ultrasonography, color flow Doppler ultrasonography were performed.\r\nResults. Multiple radioiodine doses were required in 4 out of 9 patients. Pretreatment 24 hours radioiodine uptake exceeded 10% in 12 out of 16 doses. Mean cumulative dose was 23.17 ? 17.48 mCi 131I (range 6-50 mCi). The period between amiodarone withdrawal and 131I administration was 11.72 ? 12.45 months (range: 2-41 months). Mean cumulative 131I dose was higher in AIT due to toxic multinodular goiter and toxic adenoma (30.25 ? 20.09, range: 11-50 mCi) versus Graves disease (17.5 ? 14.76, range: 6.5-40 mCi). In one patient with toxic adenoma, thyroidectomy was contraindicated due to a comorbidity-central core disease - a non-progressive congenital myopathy, associated with an increased risk for malignant hyperthermia. Hypothyroidism occurred in all patients but one (euthyroid), within 14 ? 3 months (range: 5-27) after the first radioiodine dose. Sinus rhythm was restored in 3 out of 5 patients. One case of radiation thyroiditis occurred after a single 6.5 mCi 131I dose.\r\nConclusion. Radioiodine ablation therapy is an effective and safe alternative in patients with type 1 and mixed forms of amiodarone-induced thyrotoxicosis. Since amiodarone should need sometimes to be restarted, post radioiodine hypothyroidism should be viewed as a goal rather than a complication.

Keywords: amiodarone, thyrotoxicosis, radioiodine therapy, atrial fibrillation

Correspondence: Horea Ursu, Institute of Endocrinology, 34 - 36 Bd Aviatorilor, Bucharest, Romania, e-mail: hursu@opensys.ro