Induction of the rectoanal reflex by electric stimulation. A diagnostic aid for Hirschsprung's disease

Functional outcome after Swenson's operation for Hirshsprung's disease

BACKGROUND/AIM

Hirschsprung's disease (HD) is one of the most common causes resulting in lower intestinal obstruction in children with atypical clinical symptoms and inconspicuous morphological findings by barium enema X-ray. Recently, this situation has been largely ameliorated by improvement of instrument for measurement of anorectal pressure. By now, anorectal manometry has been regarded as a routine means for functional assessment and diagnosis of HD. It is accurate in nearly all cases of HD with characteristic absence of rectoanal inhibitory reflex. Different surgical modalities of treatment are available and Swenson's operation is one of the surgical procedures done for HD. Anorectal manometric findings may change after Swenson's operation with improvement of rectoanal inhibitory reflex in some cases. We aimed to evaluate functional results after Swenson's operation for HD using anorectal manometry.

PATIENTS AND METHODS

Between 1996 and 2005, 52 patients were diagnosed with HD and operated upon by Swenson's operation in Gastroenterology Center, Mansoura University. There were 33 males (63.46%) and 19 females (36.54%) with a mean age of 3.29 +/- 1.6, (range 2-17 years). Anorectal manometry and rectal muscle biopsy were done preoperatively for diagnosis but after operation anorectal manometry was done after every six months and then yearly.

RESULTS

All of the 52 patients showed absent rectoanal inhibitory reflex on manometric study with relatively higher resting anal canal pressure and within normal squeeze pressure. Postoperatively, there were 35 continent patients (67.31%) with 11 patients (21.15%) showing minor incontinence and six (11.54%) with major incontinence. On the other side, there were five patients (9.62%) with persistent constipation after operation (three due to anal stricture and two due to residual aganglionosis). Postoperative manometric study showed some improvement in anal sensation with the rectoanal inhibitory reflex becoming intact in six patients (11.54%) four years after operation.

CONCLUSION

Anorectal manometry is a more reliable method for diagnosis of HD than barium enema X-ray but for final diagnosis, it is reasonable to combine anorectal manometry with tissue biopsy. Functional outcome after Swenson's operation for HD may improve in some patients complaining of incontinence or constipation. Anorectal manometry may show improvement of the parameters after Swenson's operation.

Intestinal sensitivity testing by transmucosal electrical nerve stimulation: stimulus parameters to induce conscious perception

Intestinal sensitivity can be tested using transmucosal electrical nerve stimulation. The aim of this study was to establish the stimulus characteristics that determine perception. In six healthy subjects constant current electrical stimuli were applied via an intrajejunal bipolar electrode while measuring perception. Intensity-response tests with stimuli trains of various frequencies (5 and 100 Hz) and pulse durations (50 and 1000 mus) were performed. All stimuli within the broad range tested induced similar-type abdominal sensations, but the intensity of the stimuli to produce perception differed depending on both pulse duration and frequency. A 20-fold increase in pulse duration decreased the intensity of perceived stimuli by a factor of 0.34 +/- 0.04 (P < 0.05); a similar increase in pulse frequency decreased the intensity by a 0.63 +/- 0.07 factor (P < 0.05). When the frequency and duration concomitantly increased, the stimulus intensity decreased by the product of both factors (0.22 +/- 0.04). Transmucosal electrical nerve stimulation of the intestine induces perception within a broad range of stimuli. However, the intensity of the stimuli required to activate sensory pathways is primarily weighted by the duration rather than by the frequency of the pulses.

Internal anal sphincter: advances and insights

The internal anal sphincter, the smooth muscle component of the anal sphincter complex, has an ambiguous role in maintaining anal continence. Despite its significant contribution to resting anal canal pressures, even total division of the internal anal sphincter in surgery for anal fistulas may fail to compromise continence in otherwise healthy subjects. However, recently reported abnormalities of the innervation and reflex response of the internal anal sphincter in patients with fecal incontinence indicate its significance in maintaining continence. The advent of sphincter-saving surgery and restorative proctocolectomy has re-emphasized the major contribution of the internal anal sphincter to resting pressure and its significance in preventing fecal leakage. The variable effect of rectal excision on rectoanal inhibitory reflex has led to a reappraisal of the significance of this reflex in discrimination of rectal contents and its impact on anal continence. Electromyographic, manometric, and ultrasonographic evaluation of the internal anal sphincter has provided new insights into its pathophysiology. This article reviews advances in our understanding of internal anal sphincter physiology in health and disease.

Abnormal visceral autonomic innervation in neurogenic faecal incontinence

Changes of denervation in the anal sphincter striated and smooth muscle in patients with neurogenic faecal incontinence are well established. This study aimed to determine if there is also a more proximal visceral autonomic abnormality. Thirty women with purely neurogenic faecal incontinence (prolonged pudendal nerve latencies and an intact sphincter ring) and 12 patients with neuropathic changes together with an anatomical disruption were studied. Two control groups consisted of 18 healthy volunteer women and 17 women with normal innervation but an anatomically disrupted sphincter. Rectal sensation was assessed using balloon distension and electrical mucosal stimulation, and anal sensation by electrical stimulation. Rectal compliance was studied to determine whether sensory changes were primary or caused by altered rectal wall viscoelastic properties. Anal canal pressure changes in response to both rectal distension and rectal electrical stimulation were measured to assess the intrinsic innervation of the internal anal sphincter. Patients with neurogenic incontinence alone had impaired rectal sensation to distension (53.1 v 31.5 ml, p < 0.05, neurogenic v controls) and to electrical stimulation (24.4 v 14.8 mA, p < 0.005). Patients with neurogenic incontinence and sphincter disruption also showed impaired sensation compared with healthy controls (55.8 ml v 31.5 ml, p < 0.05 and 22.9 mA v 14.8 mA, p < 0.05). Patients with only a disrupted sphincter had normal visceral sensation to both types of testing. Both rectal compliance and the response of the internal anal sphincter to rectal distension and electrical stimulation were normal in all patient groups. This study suggests that there is a visceral sensory abnormality in patients with neurogenic incontinence which is not caused by altered rectal compliance. As evaluated in this study the intrinsic innervation of the internal anal sphincter is not affected in this process.

The internal anal sphincter: mechanisms of control and its role in maintaining anal continence

The human IAS has particular structural and functional characteristics. This smooth muscle constantly generates rhythmic electrical slow waves, but no action potentials. The slow waves are linked to calcium fluxes and both are essential for mechanical activity, i.e. the ASPW. The IAS is pharmacologically characterized by the presence of alpha excitatory and beta inhibitory adrenergic receptors. Cholinergic drugs have an indirect effect through the release of an inhibitory neurotransmitter, very probably VIP, from NANC nerves. The myogenic activity of the IAS is enhanced by its extrinsic sympathetic innervation. Thus, at rest, the IAS is in a state of partial tetanus and contributes approximately 55% of the MABP. Because the IAS ring cannot be completely closed, the anal mucosa and the haemorrhoidal plexuses fill the gap. By compressing these tissues, the IAS perfectly closes the anal canal to retain not only solids but also fluid stool and gas. Acute rectal distension and rectal activity, mainly through intramural pathways, induce reflex IAS relaxation, permitting the rectal contents to be sampled by receptors in the upper anal canal while continence is temporarily maintained by EAS activity and by expansion of the haemorrhoidal cushions. There is a correlation between the volume of rectal distension and the parameters of IAS relaxation. At maximal IAS relaxation, ASPW are absent, indicating the completeness of the inhibition. Although this RAIR is not essential for defecation, insufficient relaxation may be implicated in constipation. Hyperactivity of the IAS resulting in a high MABP and AUSPW has been considered both as a cause and as an effect in haemorrhoids and anal fissure. Continence for fluids and gas is impaired if IAS activity is decreased (i.e. a low MABP), either by direct trauma or by damage of its sympathetic innervation. Severe faecal incontinence will develop when the contractility of both the IAS and the EAS is affected.

Rectoanal reflex induced by H2O thermal stimulation

To obtain clear evidence of the rectoanal reflex, cold water was injected into the rectum. All patients with a normal reflex had a rectoanal reflex when the water was either 4 degrees C or 17 degrees C. The same reflex was seen when a balloon was used for distention. No reflex was evident when the water was 37 degrees C. At 27 degrees C or 45 degrees C, the reflex was evident occasionally. In patients with Hirschsprung's disease, the rectoanal reflex was absent with balloon distention, and when water at any temperature was injected. As cold water will induce the rectoanal reflex safely and without rectal distention, measurement of the reflex using cold water is useful when the presence or absence of the reflex is doubtful. The authors' results suggest that the receptor related to the reflex is neuronal in origin and not muscular, and that the receptor locates near the mucosa.

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

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 H2O, 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 H2O, p = 0.9) 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.

Diagnosis of Hirschsprung's disease by anorectal manometry

Anorectal manometry was performed in 48 Japanese children with Hirschsprung's disease and 61 normal children. The resting pressure of the rectum and anal canal was not significantly different between these groups of subjects. The frequency of rhythmical contractions of the anal canal of patients was significantly lower than for the normal subjects, but the frequencies overlapped considerably. Therefore, the frequency is an inadequate indicator for identifying these patients. Conventional manometry elicited a distinct rectoanal relaxation reflex from 90% of the normal children, and the rate increased to 98% when indistinct reflexes were regarded as positive. Indistinct reflexes often occur in neonates, possibly because the constriction of the anal canal is weak. However, when prostaglandin F2 alpha was intravenously administered during the examination, all ambiguous reflexes became distinct. Of patients with Hirschsprung's disease, 4% had a distinct reflex and 19% an atypical one. Most of the atypical reflexes were regarded as being artifacts and were mostly attributed to distension by a balloon. In these patients, the reflex was abolished in case of examination with electric stimulation or stimulation with cold water, procedures which do not dilate the rectum. Moreover these atypical reflexes did not fit the criteria for the normal rectoanal relaxation reflex prepared by the Japan Study Group of Pediatric Intestinal Manometry. The use of electric stimulation, cold water, or intravenously administered prostaglandin F2 alpha improves reliability of the conventional anorectal manometry. A clear and accurate definition of the normal reflex should aid in excluding the atypical reflex.

Hirschsprung's disease and idiopathic megacolon in adults and adolescents

The distinction between Hirschsprung's disease and idiopathic megacolon in childhood dates from the classic clinical, radiological, and histological studies of Bodian, Stephens, and Ward. This article describes clinical experience over 15 years of 94 patients in whom megacolon of these two types was recognised for the first time after the age of 10, to illustrate the problems of diagnosis and treatment in later years. Just as it is now recognised that patients with the clinical characteristics of Hirschsprung's disease may have one of several abnormalities of the myenteric plexus, including not only absence of ganglion cells, but also patchy or zonal loss, abnormal neurones or neuronal dysplasia, so idiopathic megacolon may also be a heterogeneous group of cases. This paper suggests on clinical grounds that those patients with idiopathic megacolon whose symptoms start in childhood differ from those whose symptoms develop in later years.

Restorative proctocolectomy. Clinical results and manometric findings with long and short rectal cuffs

Clinical results and manometric findings were compared in 82 patients following restorative proctocolectomy. There were 41 patients with long rectal cuffs measuring 8 to 10 cm. There were 39 J-shaped pouches and 2 S-shaped pouches in this group. Forty-one patients had short rectal cuffs measuring 2 to 3 cm. There were 28 J-shaped pouches and 13 S-shaped pouches in this group. Anal manometry was performed in ten patients with long rectal cuffs and in ten patients with short rectal cuffs matched for age, sex, and stool frequency. Postoperative complications were significantly greater in patients with long rectal cuffs. Functional results and manometric findings were similar. No patient demonstrated a normal rectoanal inhibitory reflex. The data in this study suggest that a short rectal cuff can be used safely for restorative proctocolectomy with satisfactory results. A normal rectoanal inhibitory reflex may be absent after restorative proctocolectomy, and this does not interfere with the attainment of continence.