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Thyroid Cancer with High TG Response to TSH but Negative Scan

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Question

He is a 37 yo man that I first saw in 2003 following excision of a thyroglossal duct cyst (he presented with a neck mass), which showed a 1cm papillary carcinoma focus within it. He then underwent a total thyroidectomy which showed papillary cancer in a right thyroid nodule. There was no neck dissection done. Pathology showed an 0.8cm papillary carcinoma, confined to the thyroid, no angiolymphatic invasion, surgical margins were free of tumor.

He was treated in June 2003 with 109 mCi I131 for remnant ablation; post ablation scan showed no distant mets. Thyroglobulin levels on adequate replacement were 1.0 – 1.2. Six months later a whole body scan showed uptake in the neck and his thyroglobulin was 102 (TSH 91.5). He was treated in April 2004 with 203 mCi of I131. Post ablation scan showed no distant mets.

6 months after the 2nd I131 treatment (Oct 2004), his withdrawal whole body scan was negative, but his TG was 166 (TSH 99). A CXR was unremarkable. CT of the neck showed a questionable 5mm focus of tissue in the right paratracheal region. A whole body PET scan was negative. Thyroglobulin on suppression was 0.7. There was no clinical evidence of recurrence.

In January 2006 he had another negative withdrawal scan. His TG had been 0.6 – 1.0 on suppression, but increased to 146 on withdrawal of levothyroxine. An US of the neck was negative in July 2006. A repeat whole body PET scan was negative in Sept 2006. TG remains suppressed on levothyroxine but increases in response to thyrogen to over 100.

He developed Horner’s Syndrome in April 2007, with negative MRI’s of the neck and brain. It was felt to be related to a sinus infection.

I’m at a loss as to the next step. He was not given further I131 ablation after the second treatment, as it had not resulted in a change in this thyroglobulin level. Should I continue to search for remaining thyroid tissue? The tissue obviously does not take up I131. Perhaps a CT of the chest and abdomen? Bone Scan? Another PET scan? Would you treat him again with I131 simply based on the thyroglobulin level. I wouldn’t know where to use external irradiation as the location of tissue is not defined.Thanks for any help you can give with this case.

Vanessa Richardson, MD, FACP ,Pittsburgh, PA

Response

Your case is unusual for sure. I assume the TG antibodies are negative. Is it possible the patient was somehow contaminated with iodine when scanned in 2004? I think I would do a scan using a T4 half-dose protocol, or rTSH, and checking his urinary iodine before starting and at the time of the scan. Such a TG response, starting from such a low suppressed level, is unusual, but the remarkable response also suggests it is a valid test and not some strange lab abnormality. While searching for a neck focus is logical, I do not believe that a node (or nodes) would react this way unless massive, which you would have found on neck US. Assuming all of these tests are negative, certainly CAT of chest and abdomen without contrast, MRI of neck, bone scan, PET scan are logical, searching for a focus of significant size that is poorly differentiated. The Horners and the finding in the R paratracheal area on CAT makes one wonder about a neck metastasis. Failing any positive sign, I believe it would be usual to try another treatment with RAI hoping that the post therapy scan would be informative. Maybe some of our readers will have a better idea??

Leslie J De Groot, MD