Evaluation of the intrinsic innervation of the internal anal sphincter using electrical stimulation.

Abstract

SUMMARY Stimulation of the rectal mucosa with a bipolar electrode leads to relaxation of the internal anal sphincter. Intraoperative studies in two subjects showed that transmission of the impulse was independent of extrinsic nerves and was interrupted by circular myotomy. Characteristics of the reflex were studied in 11 healthy women and 19 women with severe idiopathic constipation. One control subject and two patients did not tolerate the test. In the remainder the stimulus caused a clearly defined fall in internal sphincter pressure. The mean resting maximum anal canal pressure before stimulation was the same in both groups (90 (10) v 104 (7) cm H20, p=0 3, controls v patients). The threshold stimulus for relaxation (12 (2) v 14 (1) mamps, p=0 5), the maximum percent fall in resting pressure (43 (7) v 46 (4)%, p=0.7) and the lowest absolute resting pressure produced by stimulation (48 (13) v 49 (6) cm H20, p=09) were the same in both groups. The stimulus required to achieve maximum relaxation was significantly higher in the patient group (23 (3) v 32 (2) mamps, p=0.012) suggesting abnormal intrinsic innervation of the sphincter in these patients. Electrical stimulation should not replace balloon distension for,routine testing of the rectoanal reflex but it may be useful in quantitative studies.In 1877 Gowers described relaxation of the anal canal in response to intrarectal balloon distension,' and this reflex was later confirmed by Denny-Brown.' Although the rectoanal reflex has traditionally been demonstrated using their methods, a recent report has shown that it can also be elicited by electrical stimulation of the rectal mucosa. We wished to confirm this report and define the characteristics of the electrically induced anal relaxation. Methods S U B J EC I SEleven healthy women (mean age 31 years, range 23-47) without gastrointestinal complaints were studied as controls. Nineteen women with severe idiopathic constipation (mean age 32 years, range 20-42, duration of constipation >three years) were also studied. All patients had infrequent bowel actions, with a spontaneous stated bowel frequency range of one to four weeks, and all suffered from difficulty Address for corresponldence: I)r M Kamm, St Mark's Hospital, (ity Road, I ondlon EC I V 2PS.

Sacral Neuromodulation in Patients With Fecal Incontinence: A Single-Center Study

“…44 Sphincter relaxation occurs early in the defecation process, which is thought to be mediated by the intrinsic nervous system, which consists of intracolonic and intrarectal nerves and a number of interconnecting plexuses. 45,46 In neurogenic incontinence, this intrinsic innervation of the internal anal sphincter is normal and the visceral sensory abnormality is more likely to involve the extrinsic nerve supply, which not only affects the sphincter mechanism but also the afferent pathways from the rectum. 41 It is known that in patients with bilateral loss of sacral nerves, there is a serious impairment of rectal filling sensations in contrast to patients with unilateral loss of the sacral nerves who have no significant impairment of rectal filling sensations.…”

Clinical features of idiopathic megarectum and idiopathic megacolon.

“…We could not elicit the reflex by electrostimulation despite patients feeling the stimulus, ensuring the electrodes' mucosal contact, and the known intact architecture of the intrinsic enteric innervation in this condition.27 This may reflect altered responsiveness of the intrinsic nerves, as is seen in idiopathic constipation.8 12 We could not confirm the value of electrical stimulation as a diagnostic test in patients with a dilated rectum.…”

“…Of these patients, 12 became symptomatic in infancy, nine at age 5-10 years and one at age 18 years. The six patients with idiopathic megacolon were significantly (p=00007) older (median 42 years, range 37-59) than the patients with megarectum.…”

Abnormal visceral autonomic innervation in neurogenic faecal incontinence.

“…Recent work from our laboratory suggests that sphincter relaxation occurs early during defaecation before peristalsis reaches the rectum,39 and that this sphincter relaxation is likely to be mediated via intrinsic intracolonic and intrarectal nerves. 24 The normal response of the internal anal sphincter to two distinct types of rectal stimulation, that is rectal electrical stimulation and distension, in patients with incontinence suggests that the intrinsic innervation is normal. In contrast, using balloon distension as a stimulus, Read et al found that the volume required to produce the rectoanal inhibitory reflex by balloon distension was lower in incontinent subjects.'…”