The Diagnostic Value Of US And ¹⁸F-FDG PET/CT In The DTC Patients With Positive Serum TgAb But Negative Serum Tg And ¹³¹I-Dx-WBS

At present,the incidence of thyroid cancer in the population increased year by year,and the incidence of women was significantly higher than men,including papillary thyroid cancer?PTC?,follicular thyroid cancer?FTC?,medullary thyroid cancer?MTC?and undifferentiated thyroid cancer.The PTC and FTC are classified as differentiated thyroid cancer?DTC?because of the characteristics of high degree of differentiation and low degree of malignancy.The main treatments of DTC patients are surgical resection,postoperative selective ¹³¹ I ablation and TSH inhibition therapy,and the main contents of follow-up after treatment are serum Tg levels,cervical ultrasonography and ¹³¹ I diagnostic whole body scan(¹³¹I-Dx-WBS).The serum Tg levels in TSH-stimulated state was the most sensitive tumor marker to predict the recurrence or metastasis of DTC.Since Tg can be produced by normal thyroid tissue and DTC lesions,when the DTC patients underwent surgery and postoperative ¹³¹ I ablation treatment,the serum Tg levels will be in a very low level or even undetectable,so the elevated serum Tg indicates a recurrence or metastases in the presence of better differentiation tumor cells.However,the determination of serum Tg may be affected by the presence of TgAb.During the follow-up of DTC patients,elevated TgAb may indicate the presence of recurrence or metastasis.TgAb may be used as a tumor marker for follow-up after DTC treatment the same as Tg.However,the clinical application of TgAb in clinical follow-up and prognosis does not form a unified view,especially for the DTC patients with positive serum TgAb but negative serum Tg and ¹³¹I-Dx-WBS,it is a major problem in the clinical work.Cervical ultrasonography has been routinely used in the follow-up of DTC patients,but its application value was usually easy to ignore.The application value of ¹⁸F-FDG PET / CT scan in the follow-up of DTC patients has been paid attention in recent years.Therefore,it is important to research the value of cervical ultrasonography and ¹⁸F-FDG PET / CT in clinical diagnosis and subsequent treatment of the DTC patients who have elevated serum level of TgAb but negative findings in serum Tg measurement and ¹³¹I-Dx-WBS.ObjectiveTo evaluate the diagnostic value of neck US and ¹⁸F-FDG PET / CT imaging in the follow-up of DTC patients who underwent thyroidectomy and subsequent ¹³¹ I ablation therapy with elevated serum level of TgAb but negative findings in serum Tg measurement and ¹³¹I-Dx-WBS.Materials and Methods53 patients with differentiated thyroid carcinoma were enrolled in our hospital from September 2014 to February 2017,including 7 males and 46 females.Serum Tg,TgAb,cervical ultrasonography and ¹³¹I-Dx-WBS were reviewed in TSH-stimulated state after 4-6 months of treatment.All of them content serum TgAb positive?> 115 kU / L?but serum Tg and ¹³¹I-Dx-WBS are negative,and underwent ¹⁸F-FDG PET / CT examination.Ultrasound or CT-guided fine needle aspiration biopsy or surgical resection was performed on all suspected lesions which were found by the cervical ultrasonography and ¹⁸F-FDG PET / CT.The recurrence or metastasis was diagnosed according to the histopathological findings.All patients were divided into two groups according to the results of the cervical ultrasonography: neck US positive and negative group,then the recurrence or metastasis rate were compared between the two groups.To evaluate the diagnostic value of cervical ultrasonography and ¹⁸F-FDG PET / CT imaging in the recurrence or metastasis of these patients,and to compare the difference in the diagnostic value of cervical recurrence or metastases between the cervical ultrasonography and ¹⁸F-FDG PET / CT imaging.The data was analyzed by the ?2 test.Finally,the role of neck ultrasound and ¹⁸F-FDG PET / CT imaging in the subsequent treatment of these patients were analyzed.Results1.Among the 53 patients with elevated serum level of TgAb but negative findings in serum Tg measurement and ¹³¹I-Dx-WBS,¹⁸ patients were confirmed with recurrence and metastasis by the pathologic,the recurrence or metastasis rate was 33.96%..2.The sensitivity,specificity,positive predictive value,negative predictive value of cervical ultrasonography in the diagnosis of these patients were 66.67%,68.57%,52.17% and 80.00% respectively,and the sensitivity,specificity,positive predictive value,negative predictive value of ¹⁸F-FDG PET / CT imaging in the diagnosis of these patients were 94.44%,71.43%,62.96% and 96.15% respectively when the threshold of SUVmax was 2.50.The sensitivity and specificity of ¹⁸F-FDG PET / CT imaging were 66.7% and 100% respectively when the threshold of SUVmax was 6.30.3.Among the 53 patients,14 of them were confirmed with lymph node metastasis by pathology,the cervical ultrasonography have found 12,and ¹⁸F-FDG PET / CT have detected all of them.The sensitivity of them are 85.71% and 100%,the specificity of them are 71.79% and 74.36%,and the veracity of them are 75.47% and 81.13%,the difference was all in no statistically significant?P=0.48,0.799 and 0.480?.4.There were 17 patients changed the treatment regimen because of undergoing US and ¹⁸F-FDG PET / CT examination,11 of them underwent surgical treatment and 6 patients underwent high-dose ¹³¹ I treatment.Conclusion1.In clinical follow-up,when the serum TgAb showed positive in patients with DTC,which indicated that there may be recurrence or metastases.2.In the follow-up of DTC when the patients with elevated serum level of TgAb but negative findings in serum Tg measurement and ¹³¹I-Dx-WBS,for the suspicious lesions of neck,the US should be the first choice,and puncture biopsy of suspicious tissue should be done to identify the nature of the lesion.3.¹⁸F-FDG PET / CT imaging is important for the diagnosis of recurrence or metastasis of the DTC patients with elevated serum level of TgAb but negative findings in serum Tg measurement and ¹³¹I-Dx-WBS,and can compensate for the lack of cervical ultrasound.4.The cervical ultrasound and ¹⁸F-FDG PET / CT imaging have important significance in subsequent treatment of the DTC patients who have elevated serum level of TgAb but negative findings in serum Tg measurement and ¹³¹I-Dx-WBS.