Objective To explore the diagnostic value of stimulated thyroglobulin (sTg) combined with therapeutic dose ¹³¹I SPECT/CT imaging and neck ultrasound for detecting cervical lymph node metastasis in patients with differentiated thyroid cancer (DTC) who underwent ¹³¹I treatment again after surgery.

Methods A retrospective analysis was conducted on 102 patients with DTC who underwent ¹³¹I treatment again after surgery at Jining First People′s Hospital from December 2021 to July 2024 and who had negative thyroglobulin antibody and serum sTg≥1.0 ng/ml. The patients included 37 males and 65 females, with an average age of (45.5±11.7) years, ranging from 19 to 75 years. All patients had their sTg levels measured and underwent neck ultrasound one day before ¹³¹I treatment. At 72 to 96 hours after treatment, ¹³¹I whole-body scan (WBS) and neck-chest ¹³¹I SPECT/CT imaging were performed. The results of histopathological examination or clinical comprehensive diagnosis were taken as the "gold standard". The patients were divided into the lymph node metastasis group and the non-metastasis group based on the presence or absence of cervical lymph node metastasis. The Mann-Whitney U test was used to compare measurement data between groups. Receiver operating characteristic curve was used to evaluate the diagnostic efficacy of sTg and the ratio of the maximum standardized uptake value of the cervical lesion region of interest (ROI) to the mean standardized uptake value of the sternocleidomastoid muscle ROI (R/M) in ¹³¹I SPECT/CT imaging for cervical lymph node metastasis in DTC patients who underwent ¹³¹I treatment again after surgery. Area under curve (AUC) was calculated. The optimal cut-off values of sTg and R/M were determined based on the maximum Youden index. Binary Logistic regression analysis was performed using sTg, R/M, and neck ultrasound examination data. A comprehensive diagnostic model was constructed to evaluate the diagnostic efficacy of sTg alone and its combination with multimodal imaging for cervical lymph node metastasis in DTC patients who underwent ¹³¹I treatment again after surgery. The Delong test was used to evaluate differences in AUC among different methods (sTg alone, sTg combined with ultrasound, sTg combined with ¹³¹I SPECT/CT, and the comprehensive diagnostic model).

Results (1) The serum sTg levels of the lymph node metastasis group (47 cases) and the non-metastasis group (55 cases) were 27.05 (10.75, 53.79) ng/ml and 4.41 (1.71, 4.66) ng/ml respectively. The R/M values were 2.15 (1.97, 2.36) and 1.55±0.20 respectively. The differences were statistically significant (Z=−6.175, −5.719, both P<0.001). The AUC values of sTg and R/M for diagnosing cervical lymph node metastasis in DTC patients who underwent ¹³¹I treatment again after surgery were 0.878 (95%CI: 0.788–0.968) and 0.927 (95%CI: 0.862–0.991) respectively, and the optimal cut-off values were 22.32 ng/ml and 1.89. (2) The AUC of sTg combined with cervical ultrasound diagnosis was 0.926 (95%CI: 0.863–0.988) and was not significantly different from that of sTg alone (Z=−1.417, P=0.156). The AUC of sTg combined with ¹³¹I SPECT/CT diagnosis was 0.982 (95%CI: 0.952–1.000), and that of the comprehensive diagnostic model was 0.985 (95%CI: 0.962–1.000). Both values were significantly higher than the AUC of sTg alone (Z=−2.379, −2.480, P=0.017, 0.013). The AUC of the comprehensive diagnostic model was significantly higher than that of sTg combined with cervical ultrasound (Z=−2.008, P=0.045).

Conclusion The comprehensive diagnostic model combining sTg with ¹³¹I SPECT/CT and cervical ultrasound can significantly improve the diagnostic efficiency of cervical lymph node metastasis in patients with DTC who underwent ¹³¹I treatment again after surgery, this work provides a basis for clinical treatment decisions.