Defining Voiding Dysfunction in Women: Bladder Outflow Obstruction Versus Detrusor Underactivity

Abstract

Purpose: We aimed to develop urodynamic criteria to improve the accuracy of the diagnosis of bladder outlet obstruction (BOO) and detrusor underactivity (DU) in women with lower urinary tract symptoms (LUTS).

Methods: Initially, in a group of 68 consecutive women with LUTS and increased postvoid residual (PVR) who had undergone urodynamic investigations, we examined the level of agreement between the operating physician's diagnosis of BOO or DU and the diagnosis according to urodynamic nomograms/indices, including the Blaivas-Groutz (B-G) nomogram, urethral resistance factor (URA), bladder outlet obstruction index (BOOI), and bladder contractility index (BCI). Based on the initial results, we categorized 160 women into 4 groups using the B-G nomogram and URA (group 1, severe-moderate BOO; group 2, mild BOO and URA≥20; group 3, mild BOO and URA<20; group 4, nonobstructed) and compared the urodynamic parameters. Finally, we redefined women as obstructed (groups 1+2) and nonobstructed (groups 3+4) for subanalysis.

Results: The agreement between the B-G nomogram and physician's diagnosis was poor in the mild obstruction zone (κ=0.308, P=0.01). By adding URA (cutoff value=20), excellent agreement was reached (κ=0.856, P<0.001). Statistically significant differences were found among the 4 groups (analysis of variance) in maximum flow rate (Qmax) (P<0.0001), voided volume (VV) (P=0.042), PVR (P=0.032), BOOI (P<0.0001), and BCI (P<0.0001), with a positive linear trend for Qmax and VV and a negative linear trend for PVR and BOOI moving from groups 1 to 4. In the subanalysis, all parameters showed statistically significant differences between obstructed and nonobstructed women, except BCI (Qmax, P=0.0001; VV, P=0.0091; PVR, P=0.0005; BOOI, P=0.0001).

Conclusion: The combination of the B-G nomogram with URA increased the accuracy of diagnosing BOO among women with LUTS. Based on this combination, most women in the mild obstruction zone of the B-G nomogram would be considered underactive rather than obstructed.

Keywords: Lower urinary tract symptoms; Underactive; Urinary bladder; Urinary bladder neck obstruction.

Fig. 1.

Agreement between the final physician’s diagnosis and urodynamic parameters under evaluation. The use of URA ≥20 as a cutoff value provided the highest level of agreement with the physician’s diagnosis of obstruction. BOOI, bladder outlet obstruction index; URA, urethral resistance factor.

Fig. 2.

Estimated probabilities of non-BOO versus URA values, based on the logistic regression model. The optimal cutoff point for URA was calculated to be 20. BOO, bladder outlet obstruction; URA, urethral resistance factor.

Fig. 3.

Canonical discriminant analysis graph of patients’ group categorization. Group 2 (red) is closer to the definitive obstruction group 1 (blue) than group 3 (green) is to the definitive nonobstruction group 4. Group 1, severe-moderate BOO; group 2, mild BOO and URA≥20; group 3, mild BOO and URA<20; group 4, nonobstructed. BOO, bladder outlet obstruction; URA, urethral resistance factor.

Fig. 4.

Receiver operating characteristic (ROC) curve of the binary logistic regression model for the 2 merged groups.

Fig. 5.

Incomplete bladder emptying during free urinary flow, distributed across the 4 groups of patients. In almost half of the patients, the primary cause seemed to be detrusor underactivity rather than obstruction. Group 1, severe-moderate BOO; group 2, mild BOO and URA≥20; group 3, mild BOO and URA<20; group 4, nonobstructed. BOO, bladder outlet obstruction; URA, urethral resistance factor; BVE, bladder voiding efficiency