Ureteric stents compromise stone clearance after shockwave lithotripsy for ureteric stones: results of a matched-pair analysis

To identify the effect of the presence of a ureteric stent on the outcome of extracorporeal shockwave lithotripsy (ESWL), by comparing patients with ureteric stones with matched-pair analysis. Patients undergoing ESWL with the Sonolith Vision lithotripter (Technomed Medical Systems, Vaulx-en-Velin, France) were identified from our prospectively maintained database. Only adult patients with a solitary, radio-opaque, previously untreated ureteric stone were considered for further analysis. A follow-up of >= 3 months with a plain abdominal film was used to identify residual fragments. Patients were exactly matched for gender, side, location in the ureter and size (in two dimensions, within +/- 2 mm). If both diameters could not be matched exactly, the size was extended to +/- 1 mm and then to +/- 2 mm of both diameters. An effort was finally made to match patients by age. The treatment outcome in terms of stone-free rates was assessed and compared using McNemar's test. In all, 45 patients with a ureteric stent in place during ESWL were identified. The only patient who could not be adequately matched was a 40-year-old man with an 8 x 3 mm stone in the upper ureter. The best/closest match for age was selected. Most stones were in the upper ureter (77%); the mean stone size was 8.5 and 8.6 mm, respectively, with no statistical differences between the groups for age and size of stones (P = 0.41 and 0.86, Student's t-test). In 12 pairs, only patients with no stent were stone-free, compared to two pairs where the patient with a stent was stone-free. Using McNemar's test, the odds ratio was 6.0 (95% confidence interval 1.3-55.2) and the difference between the groups was statistically significant (P = 0.016). These results show that the presence of a stent is associated with a worse outcome after ESWL for ureteric stones. Ureteric stents should still be used in cases of obstruction, when there is a risk of sepsis, and in patients with intolerable pain or deteriorating renal function. However, their use in patients offered ESWL for ureteric stones should be considered with caution.