A clinical nomogram for predicting bladder outlet obstruction in non-neurogenic male patients with overactive bladder

Purpose: Bladder outlet obstruction (BOO) is a common cause of overactive bladder (OAB) symptoms in men, but not all men with OAB symptoms have BOO. The strategies for treatment of OAB symptoms are different in men with BOO and those without BOO. Pressure-flow studies are considered the reference standard to diagnose BOO. However, the procedure is invasive, expensive and time-consuming. A non-invasive diagnostic method for BOO in men with OAB symptoms is warranted. The nomogram creates a simple graphical representation of a statistically predictive model which generates a numerical probability of a clinical event. In this study, we want to develop a nomogram for detection of BOO in male patients with OAB symptoms.

Materials and Methods: We prospectively recruited male patients presenting with OAB symptoms from our urology outpatient clinic between August 2008 and July 2015. Patients with overt neurological disorders were excluded. All patients received the prostate specific antigen (PSA) test and transabdominal ultrasound which provided the information of intravesical prostatic protrusion (IPP), prostate volume (PV) and detrusor wall thickness (DWT). Symptom severity was evaluated with International Prostate Symptoms Score (IPSS), Overactive Bladder Symptom Score (OABSS). All patients underwent catheter-free uroflowmetry, post-void residual urine measurement and urodynamic pressure-flow studies. BOO was defined based on a provisional ICS method for the definition of obstruction, which defined BOO as (PdetQmax-2Qmax) > 40. Multivariable regression analysis was performed to assist in choosing candidate predictors to build up a nomogram. Internal validation of the nomogram was performed.

Results: A total of 211 patients were enrolled. The mean age of the patients was 73.6 years (range 52–91). BOO was diagnosed in 118 patients. Among univariate analysis, patients with BOO had a higher prevalence of PSA>2 (p=0.001), PV>30 (p=0.003), longer IPP (p<0.001), and larger Qmax (p<0.001), Qmean (p<0.001) on uroflowmetry. Among multivariate analysis, only IPP (p=0.014) is statistically important, with odds ratio 3.119 (95% CI: 1.259–7.722). A nomogram, demonstrating a predictive accuracy of 70%, was constructed from PSA, IPP and catheter-free Qmax.

Conclusion: This nomogram is a predictive tool, upon external validation, that can be used to counsel male patients with OAB symptoms in predicting the presence of BOO.