Clinical importance of anti-thyroglobulin auto-antibodies in patients with differentiated thyroid carcinoma: comparison with 99mTc-MIBI scans.

Aims: (1) To investigate whether elevated serum anti-thyroglobulin antibody (ATG) reflects the recurrence of cancer in patients with differentiated thyroid carcinoma (DTC) in whom thyroglobulin was undetectable after radioiodine ablation. (2) To assess the sensitivity of disease detection for (99m)Tc-MIBI whole-body scans (WBSs) in these patients and investigate the correlation between MIBI WBS results and high serum ATG levels.

Materials And Methods: In this retrospective study, we evaluated 14 patients (13 women and 1 man; mean age 44 +/- 19 years) with DTC who underwent total or near-total thyroidectomy followed by an ablative dose of I at various time intervals. According to histopathological findings, 10 patients (71.4%) who were diagnosed as having papillary carcinoma and four patients (28.6%) as having follicular cell carcinoma, had high serum ATG concentrations (> 40 IU x ml(-1); range, 62-2000 IU x ml(-1)), but low serum thyroglobulin concentrations (< 1.6 ng x ml). Post-therapeutic and diagnostic (131)I WBSs and (99m)Tc-MIBI WBSs were performed. Scans were visually evaluated for detecting recurrence. If necessary, bone scans, chest X-rays, computerized tomography, ultrasonography and histopathological evaluation were performed.

Results: Recurrent and/or persistent disease was found in 12 of the patients. This was confirmed pathologically in four patients and by using other imaging methods in eight (bone scans, computerized tomography, ultrasonography). The sensitivity and specificity of disease detection for MIBI WBSs was 66.7% and 100%, respectively. For (131)I WBSs, the sensitivity of disease detection was 55.6%. Among these 12 patients, 10 responded to treatment (three underwent surgery, seven received radioiodine therapy, and two had surgery + radioiodine therapy). ATG levels decreased in eight of the 10 patients, but remained persistently elevated in two despite treatment.

Conclusions: (1) Persistently elevated ATG levels appear to serve as a useful marker for recurrent or persistent DTC in patients with undetectable serum tyroglobulin levels. Thus, the routine measurement of ATG antibody in such patients is of great value. (2) In these patients, (99m)Tc-MIBI has a relatively high sensitivity in the diagnosis of a recurrence of thyroid cancer or metastases. So, in patients with elevated ATG but undetectable serum thyroglobulin levels, (99m)Tc-MIBI can be used to determine whether there is a recurrence of DTC or metastases.