Introduction: The objective was to determine the prevalence of, and factors that predict, detrusor underactivity (DU) in patients presenting with incontinence or lower urinary tract symptoms (LUTS) following radical prostatectomy (RP). We also determined the prevalence of bladder outlet obstruction (BOO) and detrusor overactivity (DO) in this population. Methods: Patients who underwent urodynamics post-RP were identified. Detrusor underactivity was defined as a maximum flow rate (Qmax) of ≤15 mL/s and detrusor pressure (Pdet) Qmax <20 cmH20 or maximum Pdet <20 cmH20 during attempted voiding. Abdominal voiding (AV) was defined as sustained increase in abdominal pressure during voiding. Bladder outlet obstruction and DO were identified using the Abrams-Griffiths nomogram and the International Continence Society criteria. Univariate logistic regression was used to determine factors predicting DU. The following factors were analyzed: age, year of RP, procedure type (minimally-invasive surgery [MIS] or open), postoperative radiation, nerve-sparing, clinical stage, biopsy Gleason grade and interval between RP and evaluation. Results: Between 2005 and 2008, 264 patients underwent urodynamics post-RP. Detrusor underactivity was observed in 108 patients (41%; 95% CI 35%, 47%), of whom 48% demonstrated AV. Overall, BOO and DO were present in 17% (95% CI 12%, 22%) and 27% (95% CI 22%, 33%), respectively. On univariate analysis, only MIS RP was predictive of DU (univariate odds ratio 2.05 for MIS vs. open; p = 0.009). Conclusions: Detrusor underactivity and AV are common in patients presenting for evaluation of incontinence or LUTS following RP. The etiology of DU in this setting is likely related to the surgical approach. Because DU may affect the success of male incontinence treatment with the male sling or artificial urinary sphincter, it is useful to document its presence prior to treatment. More studies are needed to elucidate the influence of DU on treatment success for male urinary incontinence following RP.
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