Clinical importance of anti-TG antibodies in patients with differentiated thyroid carcinoma

Abstract

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Objectives: The aim of this study is to investigate whether an elevated serum anti-thyroglobulin antibody(ATG) reflects recurrence in thyroglobulin(TG)-undetectable patients with differentiated thyroid carcinoma(DTC) after radioiodine ablation, and to assess the sensitivity of Tc 99m –MIBI whole body scans (WBS) in these patients, correlation of MIBI WBS results with high ATG levels.

Methods: In this retrospective study, we evaluated 14 patients with DTC, who underwent total or near total thyroidectomy followed by an ablative dose of I131 at various time intervals (13 women ,1 men; mean age 44 ± 19 years). 10 patients(%71,4) were diagnosed as having papillary and 4 patients(%28,6) as follicular cell carcinoma. All patients had a high serum ATG concentrations >40 IU/ml(62–2000 IU/ml), but low serum thyroglobulin concentrations (<1.6 ng/ml). They were examined with Tc 99m –MIBI WBS. Scans were visually evaluated for detecting metastases and/or local recurrence. The final evaluation for presence or absence of thyroid cancer was made with other diagnostic methodes including I131- WBS, postablative I131-WBS,bone scans, chest x-rays, computerized tomography (CT), ultrasonography, histopathologic evaluation and evolution of disease during follow-up.

Results: In 12 of these 14 patients (%86) with high serum ATG levels, recurrent and/or persistent disease were estimated. Recurrence and/or persistent disease was confirmed pathologically in 4 patients and clinically assessed using imaging methods in other 8 patients (bone scans, computerized tomography (CT), ultrasonography). The sensitivity of disease detection for MIBI WBS was %66.7, the specificity was %100, positive predictive value(PPV) was %100, and finally negative predictive value(NPV) was %14.3. For I-131 WBS, the sensitivity of disease detection was %55.6 and positive predictive value(PPV) was %90.9. Among 12 patients with recurrent and/or persistent disease, 10 showed responses to treatment:3 patients underwent surgery, 7 patients- radioiodine treatment, 2 patients surgery + radioiodine treatment. Eight of 10 patients (%80) resulted in in decreasing ATG levels, whilst 2 patients exhibited persistently elevated ATG levels despite treatment.

Conclusions: Persistently elevated ATG levels appears to serve as a useful marker for recurrent or persistent DTC in patients with undetectable serum TG results. Thus, the routine measurement of ATG antibody in such patient population is of great value. Tc 99m –MIBI can be used in case of elevated ATG levels, but undetectable serum TG levels for examination of recurence or metastases.