Radioiodine treatment of hyperthyroidism. Success rate and influence of thyrostatic medication.

OBJECTIVE: The aim of this study is to evaluate the response rate of hyperthyroidism to radioactive iodine (RAI) treatment, optimum effective dose, effect of pretreatment with thyrostatic medications, etiology, ophthalmopathy, mortality and cancer incidence post RAI treatment.

METHODS: Retrospective study analysis of 360 patients records who received RAI treatment (dose 5-15 mCi) for hyperthyroidism in Hamad Medical Corporation, Qatar between 1984-1999, treated and analyzed. Follow-up data was available in 215 patients, with a follow-up range of 2-10 years, of these 84 were males and 131 were females, with an age range of 12-74 years. Eighty percent were toxic diffuse goiter, 13.5% were toxic multinodular goiter and 6.5% were toxic single nodule. Eighty-seven percent had been pre-treated with anti-thyroid medications. Free thyroxine4, and thyroid stimulating hormone were recorded at diagnosis; 6 months, one year and yearly post RAI treatment.

RESULTS: The incidence of hypothyroidism was 55.8% at 6 months and 67.9% at one year. There was no significant difference in the response rate to different doses of RAI treatment groups (50-59%, p=0.46). The response rate was significantly higher in the group without pre-treatment with anti-thyroid medications (95% versus 80.9%, p<0.0001) and 27.4% of our patients had ophthalmopathy. There was no significant worsening or new development of ophthalmopathy post RAI treatment. Three of our patients developed cancer: one with colonic, one with breast and one with acute leukemia. The mortality rate according to the age group was linear in the positive direction of age and the highest was 74-year-old (10.5 per 10,0000 population).

CONCLUSION: Radioactive iodine treatment is an effective modality for definitive treatment of hyperthyroidism with long-term cure approaching 80%. Response rate was not related to gender, etiology or RAI dosage. Pre-treatment with anti-thyroid medication reduces the response rate. Radioactive iodine treatment has no significant influence on ophthalmopathy, mortality or thyroid cancer.