External validation of the medical expulsive therapy stone score (METSS) for predicting spontaneous passage in proximal and mid-ureteral stones

Purpose: The medical expulsive therapy stone score (METSS) was developed to assess the success of MET in distal ureteral stones. In this study, we aimed to perform an external validation of the METSS to estimate spontaneous passage in patients with proximal and mid-ureteral stones. Materials and methods: We retrospectively analyzed 62 adult patients with 4-10 mm proximal or mid-ureteral stones treated with medical expulsive therapy (MET) between September 2022 and June 2024. MET consisted of silodosin (4 mg) once daily. Patients were followed weekly for up to four weeks to assess stone passage. METSS scores were calculated, and treatment outcomes were compared. Results: Spontaneous stone passage occurred in 53.7% of the 54 patients who completed the study. Stone size, stone burden, and the METSS score were significantly associated with treatment outcomes. Patients with lower METSSs had higher stone passage rates. The area under the ROC curve (AUROC) for the METSS was 0.674 (p=0.029). The METSS score demonstrated a sensitivity of 76% and specificity of 56%, indicating moderate predictive performance. Conclusion: The METSS scoring system has a moderate ability to predict the spontaneous passage of proximal and mid-ureteral stones. Nevertheless, it may assist clinicians in making informed decisions between conservative and interventional treatment strategies.