I am a board certified pediatric endocrinologist in private practice in Tampa, FL.I would like to ask your expert opinion on a 18 years old young lady I am following for Papillary thyroid carcinoma diagnosed when she was 13 years of age. She also has type 1 DM and hypothyroidism due to autoimmue thyroid disorder. The lymph nodes were negative. She had total excision of the thyroid glands and received60 mci of I-131 therapy. Neck ultrasound has been negative as of 03/2006. She is receiving synthroid 175 mcg daily with T4 16.4 (5.1-10), Free T4 1.7 (0.8-1.5), TSH 0.153 ( 0.4-5.8), Anti-TPO 23 (0-20), Anti-Thyroglobulin 14 (0-100), Thyroglobulin (TG-RIA) 9.4 ng/ml ( performed at Esoterix lab). The Thyroglobulin level from the same labwas 4-5 ng/ml in 2005 on 2-3 occasions, 8-9 in 2005.
My question is whether I should do a thyroid I-123 scan at this time? Also, should I push the synthroid dosage more to suppress the TSH to 0.001? The last time she had a thyroid scan was about 3 years ago. Do you have other suggestions? Thank you very much for your help.
Tsu-Hui Lin, M.D.
I can offer one answer, but probably there are several different approaches. First, your patient has autoimmune thyroid disease, so the antibodies may be playing a role despite the "negative" values. Also, the antibodies are supposed to disappear if the patient is thyroid-tissue free. So we must interpret the TG with caution, even if it has gone up slightly.. Also, at her age, with her treatment, and her presumed TG level, and negative US, she is clearly in a very low risk category.
One approach would be to watch, do at least annual surveys with exam and US and rTSHimulated TGs, and not do more unless TG begins to elevate. I suppose the most likely source of TG (if actually present) would be residual thyroid, or a small node which has yet to be discovered. A second approach would be to do a withdrawal or rTSH stimulated TG and whole body scan, and consider treatment depending on the results of the scan. Another approach would be to do a withdrawal or rTSH stimulated TG, and if the value becomes significantly higher (15-20?) assume that she has disease somewhere. This could lead on to body scan, neck MRI, chest CAT, and even PET scan in an attempt to find treatable disease. I believe many thyroidologists would follow the first approach. At this time, my personal approach would be the second. I would not further suppres the TG unless more significant evidence of disease was discovered.
L De Groot, MD