Effect of radical prostatectomy on sensory threshold and pressure transmission

Purpose: The mechanisms involved in post-radical prostatectomy incontinence remain unclear despite previous anatomical and functional studies. In addi tion, the factors responsible for the restoration of continence are not wel l studied. To improve our understanding of the alterations in continence me chanisms, we prospectively investigated the temporal changes in urodynamic parameters after radical prostatectomy. Materials and Methods: Cystometry, urethral pressure profilometry and poste rior urethral sensory threshold measurements were performed in patients und ergoing radical prostatectomy. Preoperative pressure transmission was deter mined by the maximal urethral pressure divided by the maximal abdominal pre ssure during cough maneuvers at a bladder volume of 200 mi. Postoperative s ensory threshold, pressure transmission (% of pressure transmission), maxim al urethral closure pressure and functional sphincter length were measured 6 weeks and 6 months after prostatectomy. These parameters were compared be tween continent and incontinent patients. Results: Preoperative and postoperative urodynamic studies were completed i n 34 patients. The continence rate after 6 weeks was 18% (6 patients) and i mproved to 82% (28) after 6 months. Preoperatively sensory threshold was 16 +/- 11 mA. After 6 weeks and 6 months, respectively, sensory threshold was significantly higher in incontinent (84 +/- 11 mA., 70 +/- 8 mA,) compared to continent (65 +/- 8 mA., 41 +/- 12 mA.) patients. Preoperative proximal urethral sensory threshold was not correlated with degree of postoperative incontinence determined by pad tests. Pressure transmission was not differ ent in continent and incontinent patients postoperatively. After 6 weeks an d 6 months, respectively, pressure transmission was 77% and 91% in continen t, and 37% and 58% in incontinent patients (p = 0.04, p = 0.03), Maximal ur ethral closure pressure was significantly higher in continent patients (35 +/- 6 cm. H2O) compared to incontinent patients (11 +/- 9 cm. H2O). Sphinct er length decreased from 50 mm. preoperatively to 24 mm. after 6 weeks and 25 mm. after 6 months. There was no difference in sphincter length between continent and incontinent patients. Conclusions: Posterior urethral sensitivity and pressure transmission are i mpaired immediately after prostatectomy. An improvement in these parameters after 6 months is associated with the restoration of continence. These obs ervations suggest that urinary continence after radical prostatectomy depen ds on the integrity of posterior urethral sensation and the efficiency of p ressure transmission.