Purpose: We determined the natural history and clinical significance of small, asymptomatic, noninfection related stone fragments after extracorporeal shock wave lithotripsy (ESWL).
Materials and methods: We prospectively followed 160 patients with 4 mm. or less asymptomatic calcium oxalate/phosphate stone fragments after ESWL for 1.6 to 88.8 months (mean 23) to stone-free status, censorship or intervention. Kaplan-Meier estimates of probability to anatomical stone-free, decreased or stable status were determined as well as the probability of symptomatic episodes or required urological intervention.
Results: Stone-free status or a decreased, stable or increased amount of residual stone occurred in 38 (23.8%), 26 (16.3%), 67 (41.9%) and 29 (18.1%) of the 160 patients, respectively. At 5 years after ESWL the probability of a stone-free, stone-free or decreased status, or stone-free, decreased or stable status was 0.36, 0.53, and 0.80, respectively. A total of 91 patients (56.9%) remained asymptomatic while 69 (43.1%) had a symptomatic episode or required intervention 1.6 to 85.4 months (mean 26) after ESWL (probability estimated at 0.71 at 5 years).
Conclusions: While patients with small noninfection related stone fragments after ESWL may be followed expectantly, a significantly number will require intervention or have symptomatic episodes within 2 years. The term clinically insignificant applied to any residual stone after ESWL is likely a misnomer.