Int J Colorect Dis (1988) 3:158-160 Col6 'ec/al Disease 9 Springer-Verlag 1988 Asymmetrical pudendal nerve damage in pelvic floor disorders D. Z. Lubowski, P. N. Jones, M. Swash and M. M. Henry Sir Alan Parks Anorectal Physiology Unit, St. Mark's Hospital, London, UK Abstract. Differences in the left and right puden- dal nerve terminal motor latencies have been ob- served in patients with pelvic floor disorders. Until now the mean value of the left and right pudendal latencies has been used as the index of pudendal neuropathy. In 22 patients of a group of 156 patients studied the pudendal nerve terminal motor latency was abnormally raised on one side only. These patients are thought to have pudendal neuropathy whether or not the mean value of the left and right pudendal latencies is also raised. This observation may have therapeutic implications. Tests of motor conduction in the pudendal nerves are now well established in the diagnosis of pelvic floor disorders [1-6]. Transrectal measurement of the pudendal nerve terminal motor latency (PNTML) has proved particularly useful in assess- ing patients with faecal incontinence [1, 2, 7, 8], rectal prolapse [8] and the solitary rectal ulcer syn- drome [9]. Similarly measurement of the motor latency in the perineal branches of the pudendal nerve has been used in patients with stress urinary incontinence [6]. Evidence of pudendal neuropathy has been obtained by recording the PNTML in the left and right pudendal nerves and calculating the mean value from these two recordings [1-5]. A raised mean PNTML has been shown to indicate pudendal nerve damage. It has been our clinical impression both in the preoperative assessment of patients and at opera- tion that pelvic floor muscle damage in patients with pudendal neuropathy is not always symmet- rical. In addition we have sometimes observed a considerable difference between the left and right PNTML, particularly in patients with idiopathic faecal incontinence. We have therefore examined the clinical importance of the separate left and right PNTMLs compared with the mean PNTML, as measures of pudendal nerve damage. Patients and methods One hundred and fifty-six patients referred to the Anorectal Physiology unit at St Mark's Hospital, but otherwise unselected, were included in the study. There were 46 men and 110 women, mean age 54 years (range 23-80 years). Fifty-eight were referred with idiopathic faecal incontinence and 24 with severe constipa- tion. Other diagnoses included rectal prolapse [8], anterior mucosal prolapse [10], solitary rectal ulcer syndrome [6], exter- nal anal sphincter injuries [14], idiopathic perineal pain [13], and a miscellaneous group [13]. The patients were carefully assessed clinically and under- went anorectal physiology studies, including anorectal manome- try, measurement of pudendal nerve terminal latency and, in some cases, single fibre EMG studies (fibre density measure- ment) in the external anal sphincter muscle [10]. Pudendal nerve terminal motor latency The PNTML was measured using the St Mark's pudendal nerve stimulator [1]. This consists of an electrode complex mounted on a rubber finger stall, with stimulating electrodes at the tip and surface recording electrodes at the base. The lubricated device is mounted on the gloved index finger and inserted into the rec- tum. The left and right pudendal nerves were stimulated at the level of the ischial spines and the evoked compound muscle action potentials were recorded from the external anal sphincter muscle. Supramaximal stimuli were delivered to each nerve at a rate of 1/s until a reproducible latency was observed. During each test the position of the stimulating electrode was varied until the point of maximal nerve stimulation was found so that in each case the shortest reproducible latency was recorded. Each recording was displayed and stored on the oscilloscope screen and recorded on the paper print-out The mean value of the left and right pudendal latencies is called the "mean PNTML". In our laboratory the mean PNTML in normal subjects is 2.0 _+ 0.2 ms (SD) [l, 4, 9]. Individual recordings were considered abnormal if they exceeded the mean value by more than two SD, that is greater than 2.4 ms.