The acute effect of straining on pelvic floor neurological function.

Integrity of sensory and motor function is essential in the maintenance of continence. The pudendal nerve assumes a central role being a mixed sensory and motor nerve. Neuropathic changes may therefore lead to incontinence and stretch injury to the pudendal nerve has been implicated as an aetiological factor. However pudendal neuropathy, altered anal sensation and perineal descent do not always correlate in the same patient. To investigate this further we evaluated the effect of a simulated defaecation strain on pelvic floor neurological function in a group of patients with constipation and incontinence. Pudendal nerve terminal motor latency (PNTML) and anal electrosensitivity (AS) were measured at rest and after a simulated defaecation strain of 1 minute. At rest PNTML correlated with AS (r = 0.461, P = 0.003). Twenty-five patients had perineal descent of more than 1 cm on straining, and 13 had descent below the ischial tuberosities. After 1 minute of straining AS was significantly (P < 0.001) blunted and PNTML was significantly (P < 0.001) prolonged both changes returning to normal after 3 minutes. AS was significantly (P = 0.01) more blunted in patients with perineal descent of more than 1 cm. PNTML was significantly (P = 0.01) more prolonged in patients with perineal descent of more than 2 cm. Age was significantly correlated with AS (r = 0.45, P = 0.004) and PNTML (r = 0.49, P = 0.002). Anal sensation and PNTML are acutely affected by defaecation straining, and changes may occur in patients without perineal descent. Functional changes occur equally in constipated and incontinent patients.