Removing Small Asymptomatic Kidney Stones Significantly Reduces Recurrence

Removing small, asymptomatic kidney stones during endoscopic removal of ureteral or contralateral stones significantly prolonged the time to relapse as compared with leaving the asymptomatic stones behind, a randomized trial showed.

The time to relapse averaged about 4.5 years with removal of asymptomatic stones versus about 2.5 years without (P<0.001). The difference represented an 82% reduction in the hazard ratio for relapse. In absolute terms, relapse occurred in 16% of patients with treated asymptomatic stones as compared with 63% of patients in the control arm.

When stone growth rate was excluded in sensitivity analysis, the relapse rate remained significantly higher in the control group. Surgery-related emergency department (ED) visits were similar between the two groups, reported Michael R. Bailey, PhD, of the University of Washington in Seattle, and co-authors, in the New England Journal of Medicine.

“Results of our prospective, randomized trial support removal of small, asymptomatic renal stones at the time of surgery to remove a symptomatic stone,” the authors said of their findings. “Whether to remove small asymptomatic kidney stones is a common surgical decision that currently lacks specific guidelines and may involve hundreds of thousands of surgeries annually in the U.S. alone. The additional 25 minutes needed to remove small, asymptomatic renal stones at the time of surgery for a primary stone … should be weighed against the potential need for repeat surgery in the 63% of patients who had a relapse.”

One financial comparison showed that 25 additional minutes of surgery at $36/minute would add $90,000 to the cost of 100 surgeries, the authors noted. On the other hand, 63 emergency department visits would have an estimated cost of $217,000.

The results are not surprising but the trial was nonetheless worthwhile, according to the author of an accompanying editorial. Modern endourologic technology and techniques in the hands of experienced endourologists facilitated the trial’s success, said David S. Goldfarb, MD, of the New York Harbor Veterans Affairs Healthcare System and NYU Langone Health in New York City.

The trial results left several questions unanswered. Can the preventive strategy be applied equitably to most patients with asymptomatic stones? Can general urologists also perform the procedure with the same results? Would the number of asymptomatic stones affect the results? Would increased use of preventive medication (only 25% in this study) have changed the results?

“Finally, and most provocatively, when should asymptomatic stones be removed endoscopically — only when a primary obstructing ureteral stone or a large, asymptomatic stone in the kidney is present, as this protocol dictated?” Goldfarb asked. “Asymptomatic stones are identified frequently and, most often, surgery is not recommended.”

“One can imagine that elective removal may allow these patients to avoid pain and trauma, inefficient and costly emergency department visits, infections, receipt of pain medications, and additional imaging studies,” he added. “An alternative to preemptive surgical intervention would be to finally figure out how to make those small stones detach and pass spontaneously.”

The prospective, multicenter study addressed the longstanding question of whether endoscopic removal of small asymptomatic kidney stones at the time of surgery for a symptomatic stone would is beneficial. Relevant U.S. and European clinical guidelines equivocate on the issue, Bailey and co-authors stated.

Multiple studies have shown that patients with asymptomatic stones have a 50% chance of recurrence within 5 years of surgery for a symptomatic stone. However, the only prospective study cited by guideline authors evaluated shock-wave lithotripsy for treating asymptomatic stones and favored observation at 1 year.

In an effort to provide prospective data to inform decision-making, investigators enrolled 75 adult patients scheduled to undergo endoscopic surgery (ureteroscopy or percutaneous nephrolithotomy) for a primary stone. The patients randomized to removal of secondary (asymptomatic) stones by ureteroscopy or observation (control group). Postoperative CT was performed 90 days and 1 year after intervention.

Patients were followed at 3-month intervals for up to 5 years. Median follow-up duration was 4.2 years. The primary outcome was the composite of ED visits related to stones on the same side as the original surgery, subsequent surgery to remove stones on the trial side, or growth of a new secondary stone. Secondary outcomes included surgical time to remove asymptomatic stones, ED visits within 2 weeks of surgery, and patient-reported stone passage or new stone growth.

All but two patients were included in the analysis of primary and secondary outcomes. The data showed that relapse occurred in six of 38 patients in the treatment arm versus 22 of 35 patients in the control group. The absolute difference of 47 percentage points exceeded the 35 percentage points used for statistical power calculations.

After excluding stone growth as a marker of relapse, the median time to relapse remained significantly prolonged in the treatment arm (1,717.1 vs 1,262.8 days). Four patients (11%) in the treatment group and 15 (43%) in the control arm had ED visits or additional surgery.

The 25.6 minutes of additional surgical time required for asymptomatic stone removal accounted for 27% of total surgery time (93.6 vs 59.8 minutes in the control group). Additional time with ureteroscopy averaged 25.0 minutes and 30 minutes with percutaneous nephrolithotomy.

Eight patients in the treatment arm and 10 in the control arm reported stone passage. Seven in the treatment group and six in the control arm reported passages of asymptomatic stones or fragments. New stone formation occurred in 14 patients in the treatment arm (average time 1,338 days to treatment) versus 13 in the control arm (1,381 days).