Treatment of diffuse hyperthyroid goiter with radioiodine. Influence of propylthiouracil pretreatment

Background: To stabilize Graves disease and deplete the preformed hormone, the use of antithyroid drugs prior I-131 therapy has been suggested, specia lly in those patients with severe thyrotoxicosis and in the elderly. Howeve r, PTU may reduce the effectiveness of I-131. Aim: To study the effects of PTU pretreatment before I-131 administration. Subjects and methods: A retro spective analysis of the medical records of patients with Graves disease tr eated wit I-131 from 1989 to 1997 was made. Of 244 patients wit adequate fo llow-up for at least 12 months after I-131 treatment, 142 had not been pret reated and 102 had received PTU prior to I-131 therapy. Pretreated patients were distributed according to the number of das that PTU was discontinued before reciving I-131, forming four groups (a=5d, b=6-14 d, c=15-30 d and d =31-60 d). Radioiodine was delivered according to our protocol of 120 mu ci per gram of thyroid tissue, as estimated by clinical examination. Therapy was considered successful when laboratory evidence of euthyroidism or hypot hyroidism after one year of treatment was obtained and as a failure when un detectable TSH values persisted after 12 months of treatment with I-131. Re sults: All groups were comparable as to age, gender, goiter size, and 24 h radioiodine uptake. Control of hyperthyroidism was achieved in 76% of the n on pretreated group. A similar percentage was observed in groups (b), (c) a nd (d). However, the disease was controlled in only 50% of group (a) patien ts (p<0.003). Conclusions: the therapeutic efficacy of I-131 is significant ly reduced when the PTU is stopped for only a few days prior to the use of radioiodine. We postulate that PTU has to be discontinued for at least 10 d ays before radioiodine administration.