The neurophysiological significance of perineal descent.

The establishment of a linear relationship between perineal descent (PD) and pudendal nerve motor terminal latency (PNMTL) is important in understanding the pathophysiology of pudendal neuropathy. The amount of stretching of the pudendal nerve resulting from the extent of PD, should correlate with the amount of injury sustained (PNMTL). The two key previous studies which used different techniques to measure PD, have differed on this vital issue. A prospective study was undertaken in 141 consecutive patients with PD (M:F = 57:84; mean age 46.3 SEM 1.6 years) to clarify this discrepancy. The patients had chronic constipation (81), neurogenic faecal incontinence (31), rectal mucosal prolapse (17) or female urinary stress incontinence (9). All underwent measurements of PD (by perineometry), anal sphincter pressures, single fibre anal sphincter electromyography and PNMTL. These variables, as well as age were analyzed for a linear relationship with PD by multiple regression analysis. Age was the only independent variable predicting PD at rest (T = -3.2; p < 0.005). PNMTL was the only independent variable predicting PD on straining (T = -3.0; p < 0.005). In conclusion, a linear relationship between PD on straining and PNMTL was confirmed, supporting the previous study which also measured PD by perineometry. The other study which refuted such a relationship measured PD radiologically, and it is likely that the difference was in the measurement technique.