Long-term carbimazole intake does not affect success rate of radioactive 131Iodine in treatment of Graves' hyperthyroidism.
OBJECTIVE
The aim of this study is to assess the effect of long-term antithyroid drug intake on the success rate of iodine-131 (131I) treatment of Graves' hyperthyroidism, and to explore other clinical/laboratory factors that may predict/affect the treatment outcome.


METHODS
Fifty-eight patients with Graves' disease were referred for radioactive iodine therapy after failure of medical treatment, which was given for at least 6 months. Antithyroid drug (carbimazole) was stopped for at least 2 days before administration of a fixed dose of 370 MBq. Treatment outcome was determined at the end of 1-year follow-up after iodine administration. Treatment success was reported if the thyroid hormonal profile indicated euthyroid or hypothyroid state.


RESULTS
One year after 131I administration, 19% of our patients were still hyperthyroid (treatment failure), 15.5% became euthyroid and 65.5% were hypothyroid (treatment success, 81%). No statistically significant correlation was found between treatment outcome and patient's age at the time of I administration (P=0.20); duration of medical treatment before 131I administration (P=0.22) and duration of stoppage of medical treatment before 131I intake (P=0.15). In contrast, there was significant association between treatment outcome and pretreatment Tc99m-thyroid uptake (P=0.0001), thyroid size (P=0.001) and TSH level (P=0.04). Using receiver operator characteristic curve analysis, we generated a cut-off value for thyroid uptake (18%) and thyroid weight (70 g) to predict response to 370 MBq of 131I. The 18% thyroid uptake cut-off value predicted treatment outcome with 93.6% sensitivity, 100% specificity and 94.8% accuracy, whereas the 70 g thyroid weight predicted treatment outcome with sensitivity, specificity and accuracy of 80.9, 72.7 and 79.3%, respectively.


CONCLUSIONS
Long-term carbimazole treatment will not increase the failure rate of 131I treatment in patients with Graves' disease if the drug was discontinued for at least 2 days before iodine administration. A fixed dose of 370 MBq is efficient in patients with Tc99m-pertechnetate thyroid uptake less than 18% and gland weight less than 70 g. Patients with larger goitres and/or higher thyroid uptake level will probably need a higher dose of radioactive iodine.
Nuclear Medicine Unit, Cairo University Hospital, Cairo, Egypt. shrefaie@hotmail.com
Sherif Mohamed
SM
El Refaei
Wafaa
W
Shawkat
D013956:Antithyroid Agents / Q000008:administration & dosage; D002231:Carbimazole / Q000008:administration & dosage*; D004347:Drug Interactions; D005260:Female; D006111:Graves Disease / Q000188:drug therapy* / Q000532:radiotherapy*; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D019275:Radiopharmaceuticals / Q000008:administration & dosage; D017211:Treatment Failure
D013956:Antithyroid Agents; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D002231:Carbimazole