Urodynamic assessment of urethral sphincter function in post-prostatectomy incontinence

Direct measurement of maximum urethral pressure by urethral profilometry has been used widely to assess urethral sphincter function. We attempted to determine if there was any relationship between maximum urethral pressure, which is measured at the level of the membranous urethra, or extrinsic urethral sphincter function, and the amount of abdominal pressure needed to cause leakage (abdominal leak point pressure) in men with post-prostatectomy incontinence. We also examined the relationship between external sphincter function and continence or incontinence.

We retrospectively evaluated fluoro-urodynamics performed in 37 men with post-prostatectomy incontinence. Urodynamic study consisted of measurement of maximum urethral and abdominal leak point pressures, and assessment of extrinsic sphincter function by pressure measurements and radiographically.

Data were analyzed on 27 patients for whom abdominal leak point and maximum urethral pressures were available. Mean maximum urethral pressure was 52.5 cm. water (range 20 to 165) and mean abdominal leak point pressure was 77.8 cm. water (range 27 to 132). Regression analysis was performed between maximum urethral and abdominal leak point pressures. A Pearson correlation coefficient of 0.13834 was calculated (p = 0.4914) indicating virtually no correlation between the 2 measurements in our sample. Extrinsic urethral sphincter was normal in all patients. Only 1 of 37 patients had no evidence of intrinsic sphincter deficiency, that is there was no urine leakage with increases in abdominal pressure and the patient was incontinent solely based on bladder dysfunction (detrusor instability).

Our study indicates that incontinence after prostatectomy due to an increase in abdominal pressure (stress incontinence) does not depend on extrinsic sphincter function and is not related to maximal urethral pressure. We conclude that post-prostatectomy incontinence due to sphincter dysfunction results from intrinsic sphincter deficiency. In our experience bladder dysfunction is rarely the sole cause of post-prostatectomy incontinence.