Transient hypothyroidism after iodine-131 therapy for Grave's disease

Abstract

We studied 355 patients with Grave's disease to characterize transient hypothyroidism and its prognostic value following 131I therapy. Methods: the patients received therapeutic 131I treatment as follows: 333 received a dose 10 mCi (12.8 +/- 2.9 mCi). Diagnosis of transient hypothyroidism was based on low T4, regardless of TSH within the first year after 131I followed by recovery of T4 and normal TSH. Results: after administration of 10 mCi) of 131I. Iodine-131 uptake > 70% at 2 hr before treatment was a risk factor for developing transient hypothyroidism (Odds ratio 2.8, 95% confidence interval 0.9-9.4). At diagnosis of transient hypothyroidism, basal TSH levels were high (51%), normal (35%) or low (14%); therefore, the transient hypothyroidism was not centralized. If hypothyroidism developed during the first 6 mo after basal TSH > 45 mU/liter ruled out transient hypothyroidism. Conclusion: the development of transient hypothyroidism and its hormonal pattern did not influence long-term thyroid function. Since no prognostic factors reliably predicted transient hypothyroidism before 131I or at the time of diagnosis, if hypothyroidism appears within the first months after 131I, the reevaluation of thyroid function later is warranted to avoid unnecessary chronic replacement therapy