Increase in pudendal nerve terminal motor latency with defaecation straining.

The relationship between perineal descent and pudendal nerve damage was tested in 57 consecutive patients by measuring the left and right pudendal nerve terminal motor latency (PNTML) before and after a maximal defaecation straining effort. In 13 patients the PNTML was also measured 1 and 4 min later. The difference between the mean PNTML before and after straining (delta PNTML) was correlated with the amount of descent (r = 0.40, P less than 0.005), and with the perineal position during straining (r = -0.46, P less than 0.001). Four minutes after the straining effort the PNTML again approached the resting value in each subject. These findings support the concept that perineal descent causes pudendal nerve damage.