AUA 2024: Paradigm-Shifting, Practice-changing Clinical Trials in Urology: Office-Based Removal of Small Urinary Stones

(UroToday.com) Dr. Matthew Sorensen (University of Washington) comprehensively reviewed the evolving approach to managing small stones and fragments. This is essential, especially since all currently available minimally invasive therapies have an increased likelihood of leaving residual stone fragments in place. Although previously referred to as “clinically insignificant”, these urolith fragments serve as a nidus for growth and require retreatment in up to 20% of patients with long-term follow-up data.

The focus on the initial outcomes of the ultrasonic propulsion clinical trial is particularly intriguing. Utilizing non-invasive and non-surgical methods like ultrasonic propulsion to reposition small, asymptomatic residual fragments for easier clearance represents a promising approach. An ultrasound probe, placed on the patient’s skin can be used to sweep fragments towards the ureter from, for example, the lower pole calyx.

The multicenter, randomized controlled trial involving 84 adults with residual stone fragments up to 5 mm in size provides robust data to assess the efficacy of ultrasonic propulsion compared to observation alone. By measuring nephrolithiasis relapse through symptomatic episodes, medical visits, surgeries, or stone growth observed on CT scans, the study addresses important clinical endpoints. Fragment passage and any adverse events were monitored for 21 days or 90 days following the intervention, respectively. Stone growth outcomes were assessed by CT scans at least 90 days after the procedure and continued annually up to a 5-year follow-up period (Figure 1).
Figure 1. Inclusion criteria for the ultrasonic propulsion randomized clinical trial

Demographic and clinical characteristics were similar (Table 1). After a mean follow-up period of 2.6 years, the risk of relapse was 70% lower in the ultrasonic propulsion group compared to the control group (HR: 0.30; 95% CI: 0.13-0.68). This corresponded to an absolute difference in relapse of 20% vs. 50%, respectively. Moreover, the treatment group had 52% longer time-to-relapse than controls (4.2 vs. 2.8 years, p<0.003, log-rank test) (Figure 2).
The shaded area represents the 95% confidence interval. Small circles represent censored data. Participant relapse data was censored when participants did not have a relapse before being lost to follow-up or by the end of the follow-up.
Overall, propulsion-mediated fragment repositioning reduced stone relapse and was well-tolerated in an office-based setting. No medications were needed during any of the procedures. Not surprisingly, the spontaneous stone passage rates within the 3 weeks following ultrasonic propulsion were 12-fold higher in the treatment group (63%) compared to the control (5%). Most of the adverse events were mild and transient: 63% in the treatment group and 40% in the control group.

But what if the same device could help you break down uroliths into smaller fragments as well as facilitate fragment relocation to maximize one’s chances of spontaneous stone passage? This dual functionality could offer a comprehensive solution to both fragment disintegration and repositioning, maximizing the likelihood of spontaneous stone passage while minimizing the need for invasive procedures. Well, the future is way closer than we think with Sonomotion’s ultrasound machine, which facilitates burst wave lithotripsy and ultrasound-promoted fragment relocation (Figure 3). Whether these novel technologies will cause a paradigm shift in small renal stones has yet to be determined, yet the perspective of a novel way of approaching nephrolithiasis, as noted by Dr. Sorensen, is extremely exciting (Figure 4).
Figure 3. Ultrasound-based urolith fragment relocation and burst-wave lithotripsy.
Figure 4. Future Directions

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