COMPARISON OF SCORES FROM THE VALIDATED PPLA RENAL PAPILLARY GRADING SYSTEM TO STONE ANALYSIS PROVIDES INSIGHTS TO STONE PATHOGENESIS
Prior research using the PPLA Grading System (PPLA) demonstrated the strong relationship between Randall&[prime]s plaque and pitting. The aim of this study is to compare PPLA scores to stone analysis to determine if endoscopic findings can predict stone type and if any insights to stone pathogenesis can be established.
From an IRB-approved single institution prospective database, 56 kidneys had undergone renal papillary endoscopic mapping and PPLA grading from 2015-2016 at time of percutaneous nephrolithotomy. Interobserver and intraobserver reliability have been previously shown to be substantial for PPLA. Demographics and baseline characteristics were collected. Stone analysis was performed by micro CT. Infection and uric acid stones were excluded. All possible pairwise correlations of per papillae per kidney mean scores for the four components of the PPLA were determined. Mean PPLA scores for kidneys whose stones were majority (40-60% or more) apatite (group CaP) were compared to pure calcium oxalate stones and mixed calcium oxalate and apatite stones with less than 40% apatite (group CaOx). Statistical tests performed included Pearson correlation, Fisher&[prime]s exact, and ANOVA.
There were no differences in baseline characteristics between groups. From PPLA correlation analysis, pitting was positively related to Randall&[prime]s plaque (r=0.39, p =0.004) while plugging was negatively correlated to Randall&[prime]s plaque (r=-0.5, p=0.0002). Plugging positively correlated with loss of contour (r=0.5, p=0.0003). In total, 15 out of 56 (27%) kidneys were majority apatite stones. CaP had higher mean plugging scores compared to CaOx (1.35 vs. 0.78, p=0.009). CaOx had higher mean plaque scores compared to CaP (0.77 vs. 0.39, p=0.04). There were no differences in mean kidney pitting or loss of contour scores between groups.
There appears to be two distinct stone formation pathways that are endoscopically identifiable given the positive and negative correlations of pitting and plugging to Randall&[prime]s plaque, respectively. Further supporting this are the different stone types associated with plugging (CaP) and Randall&[prime]s plaque (CaOx). Further studies are needed to determine if the association of plugging to loss of contour has clinical implications on renal function or other clinical parameters.
Funding: NIH PO1 DK-56788