Predictors of recurrent thyrotoxicosis in a cohort of Egyptian thyrotoxic patients treated with radioactive iodine

Background
The use of radioactive iodine (RAI) in the treatment of thyrotoxicosis is increasing either in recurrent cases or as first-line therapy. RAI has the advantages of being relatively inexpensive, reliable, safe, easy to administer, and highly effective.
Objective
The purpose of this retrospective study is to assess the efficacy of RAI in the treatment of hyperthyroidism and to determine the different prognostic factors that affect the outcome.
Patients and methods
Our cohort include 60 patients with hyperthyroidism who were treated with RAI in the Nuclear Medicine Unit, Mansoura University Hospital and Internal Medicine Hospital during the period from 2009 to 2015 inclusive. Patients’ records were reviewed for the following data: age, gender, history of antithyroid medications (antithyroid drugs), size of the gland, cause of hyperthyroidism (Graves’ disease, and multiple and single functioning nodules), level of fT4, and dose of RAI.
Results
There was female predominance of hyperthyroidism with a female to male ratio of 4.5 : 1. Sixty percent of patients were less than or equal to 50 years and 71.7% received antithyroid medications. Thyroid gland was moderately or markedly enlarged in 55% of patients. A high level of fT4 (>4 ng/ml) was recorded in 56.7%. Graves’ disease was the most common pathological diagnosis. Most patients (68.3%) received a higher dose of RAI (≥10 mCi). After 6 months of RAI therapy; hypothyroidism was observed in 29 patients (48.3%) while 12 were euthyroid (20%). Hypothyroidism was higher in Graves’ disease than other causes of thyrotoxicosis (=0.04), while patients who have previously received antithyroid medications were less likely to develop it (=0.04). Response to RAI was significantly higher in those with a low level of fT4 (=0.03), small size of the gland (=0.02), and higher dose of RAI (=0.02). Efficacy of RAI was not dependent on age (=1) and gender (=1).
Conclusion
Our results of this study of a cohort patient with thyrotoxicosis demonstrated that the size of the thyroid gland, the dose of RAI, use of antithyroid drugs, the cause of thyrotoxicosis, and the level of fT4 significantly affect the response to RAI, while the age and gender do not. So we should appreciate these factors when planning the treatment of such cases.