Role and Outcome of RA131 I Therapy in Patients with Autonomous Toxic Adenoma

Abstract

Radioactive iodine (RAI) therapy is preferred in the treatment of toxic autonomous adenomas because of its effectiveness, noninvasiveness, and low costs(1 ). Among patients with toxic adenomas, radioiodine therapy not only ameliorates hyperthyroidism but also reduces the size of the adenomas(2).Objective: The aim of this retrospective study is to detect the long term effects of this therapy on the thyroid function of patients with toxic adenoma treated in our department. Patients and methods: The study population included 60 cases with autonomous toxic adenoma seen at Nuclear Medicine Unit, Cairo University during the period of January 2004 till December 2010 for RAI-131 therapy. All patients were followed for 4 to 6 years (mean 5, 61 ± 0.53, median 5) following RAI- 131 therapy till December 2014. Clinical examination was done for all patients together with laboratory investigations including TSH level, FT3, FT4 measured by a radioimmunoassay (RIA).Thyroid imaging using 99m-Tc pertechnetate was done and thyroid uptake was estimated for all cases with normal reference range (0.5-4%). Neck U/S for detection of nodule size was also done. RAI dose were given us infixed dose according to nodule size (20-29 mCi).Follow up was done through clinical and laboratory evaluation guided by FT3, FT4, and TSH levels 3, 6 months after treatment then every year to exclude any possible complications. Results:131I therapeutic dose was given to all patients. The studied population was divided into two groups: Group (1): 12 patients (20%) with moderate sized nodule received 20 mCi of I- 131. Group (2): 48 patients (80%) with large sized nodule received 25-29 (mCi). No differences were observed between patients who became hypothyroid and those who became euthyroid after 131I treatment of toxic adenoma, as regards age at the time of treatment, pre 131I medical treatment, 99m-Tc pertechnetate thyroid uptake, size of the adenoma (smaller or larger than 3 cm) or pre 131I TSH levels.. Normal level of TSH is seen in 52 patients (86.7%) in their 1 st follow up visit 6 months after treatment with euthyroid state, while 8 patients (13.3%) had hypothyroidism with TSH level (>5 mIu/L) within 7.82 ±0.58 months. Among the 40 patients (66.6%) had nodules with complete suppression to the rest of thyroid tissue, no patients turned hypothyroid, whereas in the 20 patients (33.6%) who had partial suppression to the rest of thyroid tissue, 8 patients turned hypothyroid, 5 of them received 20 mCi, while the other 3 patients received 25-29 (mCi).Persistence or recurrence thyrotoxicosis was not observed in the studied population.Conclusion, Treatment of toxic adenoma with 131I in the dose of 20-29 mCi is a welltolerated therapy, leading to rapid relief of hyperthyroid symptoms. Hypothyroidism is a late side effect of RAI that needs life-long treatment and regular follow-up once or twice a year; it developed within the first year after 131I administration in 13.3% of the patients, specially those patients with partial suppression.