Papillary calcifications: a new prognostic factor in idiopathic calcium oxalate urolithiasis

Metabolic evaluation is not suitable to forecast the course of the disease in idiopathic calcium oxalate stone formation (iCaOxU). An important pathway in CaOx stone formation is the overgrowth on interstitial apatite papillary plaques. Therefore, we studied whether the extent of such plaques may be used as a prognostic factor in CaOxU. Prospectively, we studied n = 100 patients with iCaOxU. For stone analysis, X-ray diffraction/polarizing microscopy was used. During flexible ureteroscopy and flexible percutaneous nephrolithotomy, all the renal papillae were inspected, counted and the severity of calcifications assessed. A calcification index (CI) was calculated: sum of the No. of papillae × calcification grade (1–3) × No. of calcified/total No. of papillae. Furthermore, the following parameters were examined in all patients: age, sex, BMI, arterial blood pressure, stone episodes, DM; blood: creatinine, glucose, uric acid, calcium, sodium and potassium; urine: pH, volume, calcium, uric acid, citrate, ammonia and urea. Using the statistic programme Prism 5 (GraphPad), summary statistics and non-parametric correlations (Spearman) and their significance were calculated. The CI correlated significantly (r = 0.37; p = 0.012) with the No. of stone episodes. Apart from citrate (r = 0.51; p = 0.002), none of the conventional metabolic parameters correlated significantly with the No. of stone episodes. Paradoxically, the citrate excretion—although citrate being an inhibitor of CaOx stone formation—positively correlated to the recurrence rate. The endoscopic assessment of papillary plaques/calcifications and the calculation of the CI are a more suitable prognostic factor in CaOx than conventional metabolic evaluation.