Response of thyroglobulin to radioiodine therapy in thyroglobulin-elevated negative iodine scintigraphy (TENIS) syndrome.

Background: While radioiodine (131-I) is widely used in the treatment of differentiated thyroid cancer, its role remains less certain when abnormal 131-I uptake cannot be demonstrated in a pre-therapy diagnostic scan. Documentation of abnormal 131-I uptake in a post-therapy scan in such cases helps to justify the radioiodine therapy, but the post-therapy scan can remain persistently negative.

Aim: To evaluate (i) whether 131-I therapy had any measurable effect on thyroglobulin (Tg) levels in patients who were scan negative prior to radioiodine therapy and remained scan negative after therapy, and (ii) whether the magnitude of the effect on Tg depended on the pre-therapy Tg level.

Patients And Methods: Retrospective analysis of 78 patients. All patients had pre-therapy and post-therapy Tg levels measured under stimulation with thyroid stimulating hormone. Hospital data until date of last contact were analyzed to assess for recurrent disease.

Results: Tg levels decreased by 55% in those having Tg 10 μg/l or higher; and by 41% in those with less than 10 μg/l. In patients with detectable Tg antibodies, there were no statistically significant decreases demonstrated for either Tg or Tg antibody levels.

Conclusion: Radioiodine therapy can reduce Tg levels, independently of the pre-therapy level, even when the pre-therapy level is low and the pre-therapy, as well as the post-therapy, radioiodine scan remains negative.