To identify differences in urodynamic parameters between female outpatients with interstitial cystitis (IC) and/or bladder pain syndrome (BPS) and severe overactive bladder (OAB).

This cross-sectional study included 24 and 28 consecutive IC/BPS and severe OAB female patients, respectively. IC/BPS was defined based on the American Urological Association guideline, and severe OAB was defined based on baseline symptoms recorded in a voiding diary. Before treatment, symptom assessment using questionnaires and a 3-day voiding diary, as well as laboratory tests, were performed at the initial visit. The patients' baseline characteristics and urodynamic parameters were compared between the IC/BPS and severe OAB groups.

The IC/BPS group showed fewer episodes of urge incontinence and shorter duration of symptoms than the severe OAB group (P = .019, P = .017, respectively). Volumes at first sense, normal desire, strong desire, and maximal capacity during filling cystometry (MBC) were significantly higher in the severe OAB group than in the IC/BPS group (P < .001, P < .001, P = .006, P < .001, respectively). The IC/BPS and severe OAB groups showed significant differences in urodynamic parameters in terms of MBC and the volume discrepancy between MBC and maximal voided volume (P < .001, both). The receiver operating characteristic curve also showed an area under the curve of 0.760 and 0.783 for MBC and volume discrepancy, respectively (both P < .001).

Data from our study suggest that combined with other clinical findings, urodynamic studies could provide useful information to differentiate between a diagnosis of IC/BPS or severe OAB.