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

Methods  A retrospective analysis was conducted on 102 patients with DTC who underwent re-treatment with ¹³¹I after surgery and had negative thyroid globulin antibody (TgAb) and sTg≥1.0 ng/ml at Jining First People′s Hospital from December 2021 to July 2024. Among them, 37 were male and 65 were female, with an average age of (45.5±11.7) years, ranging from 19 to 75 years. All patients had their serum sTg tested 1 day before treatment and underwent neck ultrasound examination. 72 to 96 hours after treatment, whole-body ¹³¹I scintigraphy (WBS) and neck and chest SPECT/CT imaging were performed. The tissue pathological examination results or clinical comprehensive diagnosis results were used as the "gold standard". The patients were divided into lymph node metastasis group and non-metastasis group based on whether they had lymph node metastasis. Statistical analysis was conducted using Mann-Whitney U test,and Delong test. The optimal critical values of sTg and the lesion of interest region (ROI) in SPECT/CT imaging and the ratio of radioactivity to muscle count (R/M) in the same layer of sternocleidomastoid muscle were determined using the receiver operating characteristic (ROC) curve. A comprehensive diagnostic model combining sTg, R/M, and neck ultrasound was constructed to evaluate the diagnostic efficacy of each indicator alone and in combination (the comprehensive diagnostic model) for cervical lymph node metastasis in patients with DTC who received re-¹³¹I treatment after surgery.

Results  (1) The serum sTg levels of patients in 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, and 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 diagnostic efficacies of sTg and R/M for diagnosing lymph node metastasis in patients with DTC who received re-¹³¹I treatment after surgery were 0.878 and 0.927 respectively, and the optimal cutoff values were 22.32 ng/ml and 1.89 respectively. (2) The AUC of sTg combined with neck ultrasound diagnosis was 0.926, and there was no statistically significant difference compared with the AUC of sTg alone diagnosis (Z=−1.417, P=0.156); the AUC of sTg combined with SPECT/CT diagnosis was 0.982, and the AUC of the comprehensive diagnostic model was 0.985, both significantly higher than the AUC of sTg alone diagnosis (Z=−2.379, -2.480, P=0.017, 0.013); the AUC of the comprehensive diagnostic model was significantly better than sTg combined with neck ultrasound (Z=−2.008, P=0.045).

Conclusion  The comprehensive diagnostic model of sTg combined with SPECT/CT and neck ultrasound can significantly improve the diagnostic efficacy of lymph node metastasis in patients with DTC who received re-¹³¹I treatment after surgery, providing a basis for clinical treatment decisions...