EVALUATION OF GLUCOSE TOLERANCE IN HIGH DOSE RADIOACTIVE IODINE-131 TREATED THYROID CARCINOMA PATIENTS.
Radioactive iodine is an effective therapy for differentiated thyroid carcinoma (DTC). Radioactive iodine enters thyroid follicular cells via sodium iodide symporter (NIS) to destroy the residual normal thyroid tissue. NIS was also found on pancreatic tissue by immunohistochemistry and gene expression study. We make a hypothesis that high doses radioactive iodine may have harmful effect to beta cell function and result in impair insulin secretion.
Sixteen DTC patients (median age at evaluation was 46 years; range 26 – 69 years) treated with a single doses radioactive iodine (range 100-150 mCi ) were evaluated for glucose tolerance by 75 grams oral glucose tolerance test at before , 3 months and 6 months after radioactive iodine treatment. We measured plasma glucose, insulin level and C-peptide level every at 0, 30, 60, 90 and 120 minutes. At baseline we also measured lipid profile, HbA1C, free thyroxine (FT4), thyroid stimulation hormone (TSH), thyroglobulin (Tg) and anti-thyroglobulin (anti-Tg). Indices of beta cells function were calculated. Indices of insulin secretion were determined using 1) Insulinogenic index 2) homeostasis model assessment (HOMA) of beta cells function (HOMA-B). Indices of insulin sensitivity were determined using 1) HOMA of insulin resistance (HOMA-IR) 2) insulin sensitivity index or Matsuda Index 3) oral disposition index. Indices based on the areas under the concentration curves were computed as AUCinsulin (0-120)/AUCglucose(0-120).
Fasting plasma glucose level were increased significantly (84, 84 and 87 mg/dl at baseline, 3 months and 6 months; P=0.021). No significant difference were observed in metabolic parameters, indices of beta cells function and indices of insulin sensitivity. Interestingly, the indices of beta cells function, HOMA-B but not insulinogenic index, were declined following radioactive iodine treatment but not statistically significant (65.5, 62.9 and 61.1, at baseline, 3 months and 6 months after radioactive iodine treatment, respectively, P=0.368).
The results of this study could not prove the probable effect of high dose radioactive iodine on glucose tolerance at 6 months after receive high doses radioactive iodine. Whether higher dose of radioactive iodine or longer follow up time might have harmful effects to glucose tolerance are still needed to explore.