Bladder capacity as a benchmark for patient stratification in interstitial cystitis/bladder pain syndrome.

OBJECTIVES

In a previous study we reported that molecular profiling of bladder mucosal tissue from a modest number of IC/BPS patients resulted in a clear separation based on anesthetic bladder capacity (BC), with 400 cc representing the apparent breakpoint between and BC. The purpose of the current study was to revisit this earlier stratification finding, using a combination of molecular and clinical data, from a large and heterogeneous patient cohort.

MATERIALS AND METHODS

To provide an updated assessment of IC/BPS patient stratification based on anesthetic BC, whole genome gene expression data from 48 mucosal biopsy samples (41 IC/BPS patients; 7 controls) were analyzed with unsupervised clustering and principal component analysis (PCA) to identify primary clusters of patients. This identified three primary individual clusters: (1) IC/BPS patients with a BC between 200-500 cc (n=19), (2) IC/BPS patients with a BC of 501-1500 cc (n=22), and (3) controls. Next, complete demographic, clinical, and questionnaire data prospectively collected from an additional 450 patients from our patient registry were used to conduct a combined analysis to verify this relationship. Characteristics of all 491 IC/BPS patients were compared between those having the current low BC cutoff (≤ 400 cc) and the proposed new cutoff (500 cc) by utilizing independent samples t-test (continuous variables) and chi square tests (categorical variables; p ≤ 0.05 was considered significant).

RESULTS

A statistical comparison of the demographic and clinical characteristics of the entire 491 IC/BPS patient cohort showed that those with a bladder capacity ≤ 500 cc were older, were more likely to have Hunner lesions, and had higher symptom scores. This group also had a lower average number of non-urologic associated symptoms, pelvic pain syndromes, and neurologic, immune, or systemic pain syndromes.

CONCLUSION

By combining newly acquired molecular data with clinical and demographic characteristics in a large cohort of IC/BPS patients, we conclude that anesthetic BC ≤ 500 cc provides a clinically meaningful biomarker for the bladder centric IC/BPS phenotypic subgroup.