Physiopathology

It is known that destruction of the intramural plexuses alters colonic motility. In Chagasic colopathy, there is hyperreactivity to cholinergic stimulation, as confirmed by manometric test. Using of 0.05 mg/kg of methacholine, uncoordinated contraction of the rectum and sigmoid colon are recorded. The result is the opposite to that observed in patients with Hirschsprung's disease. A similar result is obtained with the use of neostigmine.29,30

It has been reported that motor incoordination is also present during spontaneous activity of the rectum and sigmoid colon, with simultaneous contraction of both segments. Normal patients do not exhibit this uncoordinated activity. After resection of a segment of dilated colon and coloanal anastomosis, patients with Chagas' disease continue to display the same pattern of colonic motor activity.31 These data indicate that the entire colon and not only the dilated segment is affected with Chagas' disease. However, after the Duhamel operation the pulled-through colon and the rectal stump synchronism disap-pears.30 This motor synchronism may disappear after surgery due to the anatomic continuity between the two segments (lateral-lateral anastomosis). Contradictory data have been obtained after manometric study of basal motor activity. In chagasic megacolon, the gastrocolic reflex is absent. This absence is probably due to hypore-

Figure 25.3. Achalasia of the internal anal sphincter in a patient with Chagasic megacolon. Rectal distention (R) fails to relax the internal anal sphincter (E).

activity of the denervated colon to the action of pentagastrin, cholecystokinin, and other peptides released into the duodenun.32,33 Another very important alteration encountered in Chagasic colopathy is the lack of relaxation of the internal anal sphincter when the rectal wall is distended. This loss of the rectoanal inhibitory reflex is known as sphincter achalasia.34 This phenomenon emphasizes the importance of anorectal manometry in the evaluation of constipation. Figure 25.3 shows achalasia of the internal sphincter; rectal distention fails to relax the internal anal sphincter (the rectoanal inhibitory reflex is absent).

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Constipation Prescription

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