Objective: To assess the effect of antithyroid drug pretreatment on radioiodine (I-131) treatment outcomes for benign thyroid disease.
Method: Retrospective analysis of all patient records on the clinical database that underwent I-131 treatment for benign thyroid disease between 1989 and 2007.
Results: About 544 patients were identified, 98 males (18%) and 446 females (82%). The mean age was 54 years (11-88). 464 patients (85.3%) were of White ethnicity, 69 (12.6%) South Asian and 13 (2%) other. The underlying diagnosis was autoimmune thyroid disease in 31% of cases, 22% non-autoimmune and 47% not specified. The median I-131 dose used was 555mBq (296598mBq). Twenty-six cases required second dose of I-131, and the median duration between first and second I-131 was 496 days (2613505 days).
About 67.1% of the total became hypothyroid by the time of the audit (median follow-up 4.4 years (0.318.1) after I-131). The median time from I-131 to hypothyroidism was 110 days (155103, mode 89). 27% were rendered euthyroid (median follow-up 3.1 years (018.1)). 5.9% of the total remained hyperthyroid at median 1.8 years (016.4) follow-up. Outcomes were similar in all ethnic groups. Of the 26 cases receiving a second dose of I-131, 65.5% developed hypothyroidism, 23% euthyroidism and 11.5% had recurrence of hyperthyroidism.
Among the 60 patients treated with propylthiouracil prior to I-131, 70% developed hypothyroidism, 25% became euthyroid and 5% had persistent hyperthyroidism. From the 430 patients treated with carbimazole prior to I-131, 70% developed hypothyroidism, 23% euthyroidism and 7% hyperthyroidism. Thyroid opthalmopathy was reported in 92 cases, 79 (85.9%) before and 13 (14.1%) after I-131.
Conclusion: There was no difference in treatment failure rates or hypothyroidism between patients treated with propylthiouracil or carbimazole before I-131. The findings may be influenced by the local policy of stopping all antithyroid medication two weeks before I-131 treatment.