Investigation

In order to understand the pseudo-obstructive disorder and plan rational treatment, there are three steps in diagnosis: definition of the presence of functional obstruction. definition of the areas involved and the physiology of the affected areas; and delineating the disease process causing the functional obstruction.

CIP is due to disordered motor activity, and this results from disturbance of the control mechanisms of motor activity and disease of the smooth muscle coats. This may occur as a consequence of primary disease of the gut motor apparatus or because of involvement of the neuromusculature of the gut secondary to disease, which either affects the gut as part of a multisystem disease or is primarily elsewhere. It is useful to consider that the obstruction may be caused at different levels of control of gut motor activity: the end-organ smooth muscle; the enteric nervous system; the humoral environment provided by gut endocrine cells or immunocytes; or the extrinsic innervation. Disruption at one or all of these levels results in the lack of effective co-ordinated propulsive movement. Initial investigations were designed to demonstrate this.

Radiology and transit studies

Plain abdominal X-rays and abdominal ultrasound examinations may show the presence of large distended loops of gut, but it is difficult using such studies to define the area of the gut involved. Conventional contrast radiography will delineate anatomical abnormalities and together with studies by radioisotope and computed tomography (CT) scanning, may provide a measure of transit time and/or demonstrate disordered peristalsis. Limited descriptions of transit can be obtained using breath hydrogen or radio-opaque pellets and plain abdominal X-ray for whole bowel transit times. All of these methods provide a limited description of the disease but no clues to the nature of the disorder.

Surface electrogastrography

Electrogastrography (EGG) is defined as the recording of myoelectric activity of the smooth muscle of the stomach by means of electrodes attached to the abdominal skin surface. EGG was first devised by Alvarez in the 1920s using mechanical means of recording from a string galvanometer. The advent of powerful personal computers and the development of signal processing algorithms has allowed such data to be objectively analyzed. A great advantage of the methodology is that it is non-invasive and readily detects disturbance of gastric antral slow waves and, by suitable positioning, duodenal slow waves. This method has been used in patients with diffuse CIP to detect abnormal myoelectric activity. Persistent entral dysrhythmias have been found in the fasting state in both myopathic and neuropathic disor-ders.9

Manometry

Motor activity may be studied by measurement of intraluminal pressure changes and known manometry. This is helpful in delineating both the extent of the disordered motility and possibly the disease processes causing the disorder. In patients with suspected functional obstruction at least three areas of the gastrointestinal tract should be studied: the esophagus, the upper small intestine and the left colon, as the disease process may not be restricted to any one of these areas. In these areas swallow-induced peristalsis, fasting small intestinal motor activity and the gastrocolonic response to food or the induction of highamplitude propagated contraction by bisacodyl can be used as tests of the integrity of the enteric nervous system and of the contractile activity of the smooth muscle.

Esophagus

Swallow-induced peristalsis and the associated relaxation of the lower esophageal sphincter can be studied using a Dent sleeve assembly modified for use in infants or young children.10 Particular attention should be paid to the nature of the primary peristaltic sequence and whether secondary peristalsis occurs in response to reflux. The presence of tertiary contractions and the amplitude and form of the contractile waves should also be noted, as should the behavior of the lower esophageal sphincter.

Small intestine

Most studies of intestinal motor activity in children with CIP have utilized small intestinal manometry. The cyclical nature of fasting small intestinal motor activity is determined by the inherent activity of the enteric nervous system. This intrinsic property can be used to test the integrity of the enteric nervous system and whether extrinsic nervous modulation is present. Disruption of fasting activity and the establishment of postprandial activity results from the humorally mediated responses to food and clarifies whether enteroenteric responses are intact. In addition, these responses can be further tested by utilizing the motilin agonists erythromycin and somatostatin. The algorithm that the author uses to test motor functioning in pseudo-obstruction is shown in Figure 18.1. Some studies have shown that myopathic processes produce low-amplitude poorly propagated contractions5,11 whereas neuropathic processes are associated with contractions of normal amplitude which are bizarre in wave form, abnormally propagated and, in phase 3 activity ill formed.11,12 In addition, clustered phasic activity in phase 2 is often present. Disturbance of the neuroendocrine environment can also be shown where there are changes in frequency of

Plain abdominal X-ray Contrast study

Hirschsprung's disease surgery

Ileostomy and

+ve histology

Antroduodenal manometry ^ -ve

Radio-opaque pellet transit study

Rectal biopsy Full thickness

Colonic Ileostomy manometry or colostomy

Ileostomy and histology

Radiology Transit study

Rectal suction biopsy

Electrogastrography Antroduodenal manometry

Figure 18.1 Investigation of intestinal pseudo-obstruction.

slow-wave activity and in frequency of phase 3 contractions. In conditions where there is increased secretion of catecholamines such as hyperthyroidism, ganglioneuroma and pheochro-mocytoma there is increased frequency of slow-wave rhythm; in preterm infants and hypo-thyroidism, there is decreased slow-wave frequency.

Colon

It is often useful to record simultaneously left-sided colonic motor activity and post-prandial small intestinal motility as a feed will also induce increased rectosigmoid contractions. In addition, the response of the descending colon to bisacodyl in inducing a high-amplitude propagated contraction can be demonstrated, and also whether this propagated contraction halts in the sigmoid colon. Thus, information regarding smooth muscle, local enteric nerves and those involved in the gastro-colonic response and colocolonic reflexes can be obtained.13

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