Constipation is a symptom of a complex condition that results from different pathologic processes. The term constipation implies not only infrequent defecation but also difficult defecation. Perhaps the best general definition is that of Drossman et al.’s, “Two or fewer stools per week and/or straining at stool more than 25% of the time.” Extracolonic causes for constipation are legion and need to be excluded primarily. The colonic causes are either structurally or functionally based, with the latter being further divided into constipation caused by colonic dysmotility or disordered defecation.”
To achieve predictable success in managing constipated patients, it is important that underlying pathophysiologies are identified objectively; in this way patients amenable to aggressive surgical or medical intervention can be identified. We therefore developed an evaluation strategy to categorize constipated patients on the basis of physiologic tests, bearing in mind that documenting a physiologic abnormality may not necessarily mean that surgery is indicated. Indeed with a disorder such as constipation, one with multiple causes and possibly complicated by psychomotor overtones, the results of surgery, particularly abdominal colectomy and ileorectostomy, are unpredictable at best.
Our evaluation strategy (see Figure) aimed to determine the cause of colonic constipation using quantitative tests of colonic, rectal, and anal canal function. The hypothesis was that patients could be evaluated accurately and placed into the appropriate pathophysiologic category such that only patients suitable for surgery would be operated on, with improved results and a predictable outcome. Our aim was to evaluate patients referred for severe constipation systematically to first select operative candidates and then to determine operative outcome over time.
Patients and Methods
Between 1987 and 1990, 277 patients were referred for symptoms of severe constipation. Only patients with a protracted, chronic — sometimes lifelong — history of constipation and those who were deemed not amenable to further medical management by their referring physicians were assessed. Patients with recent onset of constipation were specifically not evaluated.
Moreover physical examination and an initial series of tests, including barium enema or colonoscopy, had failed to uncover a contributing abnormality in all patients. Specifically patients had an anatomically normal colon; patients with megacolon, megarectum, volvulus, prolapse, evidence of colonic pseudo-obstruction, tumor, or polyp were excluded.
Patients studied underwent a series of tests of colonic and pelvic floor function that had been validated previously.
Colonic Transit Test
Transit of solids through the colon was measured using a technique validated by Metcalf and others. Transit through the different segments of the colon (right, left, rectosigmoid) also was determined. Mean colonic transit among 73 controls was 36 ± 4 hours. The upper limit of normal was 72 hours (2 standard deviations above the mean). Patients with transit times longer than 72 hours therefore were deemed to have slow colonic transit.
Pelvic Floor Function
The next step in the evaluation was to perform objective tests of pelvic floor function to quantitate defecation efficiency.
Perfused four-channel manometry determined resting and squeeze anal canal pressures, the presence of the rectal anal sphincter inhibition response, and compliance of the rectal wall. High sphincter pressures have been associated with functional disturbances in some patients; an absent rectal anal sphincter inhibitory response implies loss of ganglion cells (Hirschsprung’s disease); and a highly compliant rectum implies impending megarectum.
Concentric needle electromyography (EMG) was performed to determine the electromyographic characteristics of the puborectal muscle and the external anal sphincter in response to squeeze and defecation straining. The normal response to defecation straining is silencing of the electrical activity and concomitant relaxation of the muscles. Some patients with defecation disorders have a characteristic paradoxical increase or no change in the motor activity of these muscles while straining, and the muscles do not relax.
Scintigraphic Balloon Topography
This study defines movements of the anorectal angle and pelvic floor using scintigraphic techniques with low radiation exposure. In previous preliminary studies, among controls the anorectal angle opened a mean of 17 ± 3°, whereas in patients with defecation disorders the change was only 4 ± 4° (p < 0.05). Moreover in controls the perineum descended a mean of 2.3 ± 0.2 cm with straining, compared with 0.5 ± 0.1 cm in patients with disordered defecation (p < 0.05).
The efficiency of defecation was quantified by measuring the amount of artificial radiolabeled stool evacuated from the rectum.0 In preliminary studies among healthy volunteers, the mean (± standard deviation [SD]) percent of stool evacuated in 10 seconds was 80 ± 3%, whereas in patients with defecation abnormalities it was 34 ± 6% (p < 0.05).
A test of integrated pelvic floor function, balloon expulsion, was introduced by Preston et al. We used a similar method. A balloon attached to a catheter was inserted into the rectum and inflated with 50 mL warm water. Subjects then attempted to pass the balloon spontaneously. If spontaneous evacuation did not occur, weight was added incrementally to the catheter until the balloon could be passed.
In preliminary studies we found that most control subjects could spontaneously evacuate the balloon. In controls who could not spontaneously pass the balloon, the mean amount of weight required to pass the balloon was 126 ± 41 g. Patients with defecation disorders, however, could not spontaneously pass the balloon, and the mean (± SD) amount of weight required to facilitate passage was 590 ± 114 g (p < 0.05).
This study, described by Mahieu and others, documents the anatomy of the rectum and anal canal during straining. Among patients with difficult defecation, occult rectal prolapse and physiologically significant rectoceles are visualized readily. It is imperative that the studies be interpreted with caution, however, because some degree of intussusception is demonstrated in nearly half of healthy young volunteers.
This series of tests of pelvic floor function was performed, because no individual study has been a reliable discriminator pathognomonic for pelvic floor dysfunction.
Upper Gastrointestinal Manometry
Multichannel perfused catheter studies have been described previously. Patients were candidates for study if symptoms of upper gastrointestinal distress were present. These included nausea, vomiting, and bloating within 30 minutes of eating, weight loss, and upper abdominal pain.
Patients were placed into the following four diagnostic groups based on results of the function studies.
I. STC (slow transit constipation) — in these patients, colon transit was abnormally slow and pelvic floor function normal.
II. PFD (pelvic floor dysfunction) — these patients had normal colon transit but abnormal pelvic floor function.
III. STC + PFD; slow transit constipation and pelvic floor dysfunction — these patients had abnormally slow transit and abnormal pelvic floor function.
IV. IBS (irritable bowel syndrome) — these patients had normal colon transit and normal pelvic floor function. They therefore had no quantifiable abnormality of transit or pelvic floor function and, for lack of a more precise term, these patients were diagnosed as irritable bowel syndrome.
Evaluation of Severe Chronic Constipation. Results. Management
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