Outcomes of long-term follow-up of asymptomatic renal stones and prediction of stone-related events

Objectives To evaluate the long-term outcomes of patients undergoing observation of asymptomatic renal calculi and identify factors associated with stone-related events. Patients and Methods Patients with asymptomatic renal calculi electing active surveillance of their stones were retrospectively reviewed. Patients underwent annual ultrasonography and clinical visits with standardised questions regarding the development of symptoms or complications from calculi. Spontaneous stone passage, stone growth, development of stone-related symptoms, and requirement for intervention during follow-up were deemed as stone-related events. Results Between 2007 and 2017, 293 patients were reviewed to evaluate the natural history of asymptomatic renal calculi. The mean follow-up was 4.2 years. Overall incidences of spontaneous passage, stone growth, development of stone-related symptoms, and requirement of intervention were 32.1%, 16.7%, 28.3% and 12.3%, respectively. Stones >5 mm and lower pole stones were significantly less likely to pass spontaneously. Patients with diabetes mellitus (DM), hyperuricaemia or non-lower calyceal stone were more likely to experience stone growth. Stones >5 mm or non-lower pole stones were more likely to become symptomatic. Significant predictors of surgical intervention were stone size (>5 mm) and patients' age (>60 years). Primary therapy was extracorporeal shockwave lithotripsy in 33 patients and flexible ureteroscopy in three. Conclusion The natural history of asymptomatic renal stones rarely requires intervention, although they do have a slightly higher rate of symptomatic events and growth over the intermediate term. In particular, patients with stones >5 mm, DM, hyperuricaemia, or non-lower calyceal stones are at higher risk of developing stone-related events, and should therefore be recommended for regular follow-up.