Anorectal sensitivity in patients with obstructed defaecation.

Patients with obstructed defaecation (OD) perform major defaecatory efforts that lead progressively to pudendal motor neuropathy. Anorectal sensory function in these patients and its possible influence in the pathogenesis of the disease have been little studied. In the present paper we investigated anorectal sensitivity to electric and thermal stimuli in patients with OD, and studied the possible existence of pudendal sensory neuropathy associated to their known pudendal motor neuropathy. Forty subjects were divided into two groups: 21 healthy controls (11 females and 10 males; mean age 51.8 +/- 11 years, range 33-67) and 19 patients with OD (18 females and 1 male; mean age 48 +/- 15 years, range 20-71). The patients with OD suffered constipation and an obstruction sensation upon defaecating, even in the case of soft stools. Clinical perineometry, manometry, pudendal motor latency studies, external anal sphincter single fibre electromyography and the evaluation of sensitivity to electric and thermal stimuli were carried out in all cases. All pudendal motor function parameters showed statistically significant differences between the two groups. In the controls the electrical sensitivity threshold was minimal in the mid anal canal, where sensory receptor presence is greater. Sensitivity was significantly higher in the upper and lower anal canal regions (P < 0.05), and much higher in the rectum (P < 0.001). A similar sensory profile was recorded in the patients with OD, though with significantly higher thresholds at all points with respect to the controls. The thermal stimulus thresholds in the lower and middle anal canal were significantly smaller than in the upper canal region and rectum, and the thresholds were again higher among the patients with OD than among the controls. In all cases the thresholds for heat were lower than for cold stimuli. In both groups the motor function parameters were correlated with the sensory function variables, and the latter between themselves. Patients with OD presented sensory deterioration at all points studied in the anal canal and rectum. Sensory pudendal neuropathy was found to be associated with the pudental motor neuropathy.