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Sources of Funding: none

Introduction

The causes of renal papillary abnormalities observed endoscopically within a single kidney are incompletely known. One testable theory is that plugging, and perhaps Randall's plaque (RP), are random and independent events of crystallization whose risk is increased by local supersaturations. If so, their occurrence in the papillae of a kidney must follow the Gaussian distribution. Using scores from a previously introduced and validated papillary grading system, we sought to test if this is true.

Methods

We reduced papillary grading scores from patients who had undergone unilateral ureteroscopic stone treatment to &[Prime]present&[Prime] or &[Prime]absent&[Prime] for each variable in the grading system - pitting, plugging, loss of contour, and RP. From this we calculated the proportion of graded papillae in a given kidney involved. Probability density functions were generated and Shapiro-Wilks (SW) and Anderson-Darling AD) tests of normality were applied.

Results

Our cohort included 42 patients (42 kidneys), all of whom had calcium stones - 28 calcium oxalate and 14 calcium phosphate - on subsequent analysis. The mean number of papilla graded per kidney was 5.97 (95% CI 5.40-6.55). The mean proportion of papillae with plugging was 51.7% (±4.3), pitting was 20.1% (±3.0), loss of contour was 22.7% (±3.6), and RP was 33.7% (±4.0). Probability density functions are shown in Figure 1. Unlike pitting, loss of contour, and RP, plugging is uniquely normally distributed (SW and AD tests p>0.01).

Conclusions

Unlike pitting, loss of contour, and RP, plugging is uniquely normally distributed (SW and AD tests p>0.01), supporting that plugging is a random and independent process in individual papillae and plaque, pitting, and contour changes cannot be.

Funding

none