Login to Access Video or Poster Abstract: MP19-18
Sources of Funding: none

Introduction

An emerging hypothesis regarding calcium stones (CS) pathogenesis involves formation on Randall&[prime]s plaques (RP) with subsequent shedding of this complex into the urinary space leaving behind a pit. If RP are uniform in production, pitting creates disorder if stone complexes shed randomly. Pitting variability should exceed that of RP in kidneys with low RP variability (complex formed but not shed) but not when RP variability is higher (disordered by complex shedding). We aimed to test this hypothesis.

Methods

We identified a cohort of stone formers whose renal papillae were scored ureteroscopically using a previously described grading system that quantifies the degree of RP, pitting, plugging, and contour on each papillum. We included stone formers with at least three papillae graded. Standard deviations (SD) of pitting and RP scores were used as a measure of variability. A general linear model (GLM) with backward stepwise selection was created to identify factors associated with variability and then used to calculate adjusted variability, which was compared between RP and pitting.

Results

Of the 57 patients, stone composition was 57.9% calcium oxalate, 35.1% calcium phosphate, and 7.0% unknown. Mean number of papillae graded was 5.1 per kidney (±0.31). The GLM identified pitting mean and stone type as factors affecting the pitting variability, and stone type, RP mean, and gender as factors affecting RP variability. After adjusting for these factors, pitting and RP variability were compared by plotting these values and their regression line against a line of identity (Figure 1). Variability in pitting exceeds that of RP for almost all (10/12) patients in kidneys with low levels of RP variability (left of regression line), versus 6/14 for kidneys with high RP variability (X² = 4.473, p=0.034).

Conclusions

These findings support the hypothesis that RP formation is a uniform process that becomes disordered by stone shedding - a stochastic process. This further supports the thought that pathogenesis of CS involves formation on RP and subsequent shedding off the papillae into the urinary space, leaving behind a pitting defect in the papillum.

Funding

none