Real-world study finds higher risk of second procedure after SWL

May 20, 2008

Patients undergoing shock wave lithotripsy are significantly more likely to undergo a subsequent surgical procedure than are patients undergoing ureteroscopy, according to results of a study designed to investigate real-world practice patterns in surgical therapy for urinary lithiasis. Researchers from Duke University, Durham, NC, reported the finding at the AUA annual meeting yesterday.

Patients undergoing shock wave lithotripsy are significantly more likely to undergo a subsequent surgical procedure than are patients undergoing ureteroscopy, according to results of a study designed to investigate real-world practice patterns in surgical therapy for urinary lithiasis. Researchers from Duke University, Durham, NC, reported the finding at the AUA annual meeting yesterday.

The analysis, based on a nationwide dataset of privately insured beneficiaries, included 17,669 subjects who underwent a fragmentation procedure in 2004 and had at least 1 year of continuous follow-up. SWL accounted for 56% of initial procedures, URS with lithotripsy laser and URS alone (URS+L and URS-L) each accounted for about 20%, and about 3% of patients underwent percutaneous nephrolithotomy.

Second fragmentation procedure was analyzed as the primary outcome measurement. Kaplan-Meier curves showed the cumulative event-free rate was highest for the URS procedures and lowest for SWL. At 90 days after the first procedure, the second procedure rate was 27% for SWL versus 14% for URS+L.

In a Cox proportional hazards model analysis in which patients who underwent URS+L represented the reference group, the risk of a second treatment was almost 2.4 times greater in patients who had SWL as the first procedure and about 1.2-fold higher in those undergoing PNL initially.

"We know from clinical trials that SWL is a good treatment for certain stones, but our study in a community-based cohort shows it has a high second procedure rate," said first author Charles D. Scales, Jr, MD, who worked on the study with Glenn Preminger, MD, and colleagues. "These results need to be interpreted with caution, given the limitations of our claims-based analysis. However, we believe our findings are robust, and we need to understand the cause with the goal in mind of optimizing quality care for our patients.

"We would recommend that future investigations be conducted in a separate dataset and aim to correlate SWL and URS use with clinical data that would include stone size, stone location, and shock rate."