Slow Transit Constipation

The diagnosis of slow transit functional constipation is based upon diagnostic testing of patients with idiopathic constipation who responded poorly to conservative measures such as fiber supplements, fluids, and stimulant laxatives. These tests include barium enema or colonoscopy, colonic transit of radio-opaque markers, anorectal manometry, and expulsion of a water-filled balloon. Plain abdominal films can identify megacolon, which can be further characterized by barium or gastrografin studies. Colonic transit of radio-opaque markers identifies patients with slow transit with stasis of markers in the proximal colon. However, anorectal function should be characterized to exclude outlet dysfunction, which may coexist with colonic inertia. Because slow colonic transit is defined by studies during which patients consume a high-fiber diet, fiber supplements are generally not effective, nor are osmotic laxatives that consist of unabsorbed sugars. Stimulant laxatives are considered first-line therapy, although studies often show a diminished colonic motor response to such agents. There is no evidence to suggest that chronic use of such laxatives is harmful if they are used two to three times per week. Polyethylene glycol with or without electrolytes may be useful in a minority of patients, often combined with misoprostol. I prefer to start with misoprostol 200 mg every other morning and increase to tolerance or efficacy. I see no advantage in prescribing misoprostol on a TID or QID basis or even daily because it increases cramping unnecessarily. This drug is not acceptable in young women who wish to become pregnant. An alternative may be colchicine, which is reported to be effective when given as 0.6 mg TID. Long-term efficacy has not been studied. Finally, biofeedback is a risk-free approach that has been reported as effective in approximately 60% of patients with slow transit constipation in the absence of outlet dysfunction. Although difficult to understand conceptually, it is worth attempting and certainly so in patients with associated pelvic floor dyssynergia. Subtotal colectomy with ileorectal anastomosis is often effective in those patients with colonic inertia, normal anorectal function, and lack of evidence of generalized intestinal dysmotility. However, morbidity is significant both early and late in the disease process and must be balanced against current disability. Ileostomy is preferred in the presence of anorectal dysfunction or with associated impairment of continence mechanisms. Similar considerations apply to the patient with disabling functional megacolon. An alternative approach is ileostomy with disconnection of the colon, which is more acceptable to some patients who may hope for future reconnection if recovery occurs. An additional alternative approach for patients with colonic inertia or megacolon who are not good surgical risks is tube cecostomy (or in children, use of the appendix as a conduit to the cecum). This permits either decompression (in megacolon) or antegrade enemas (in colonic inertia). Our surgeons are not enthusiastic about this approach, and I have little experience with it. In general, the use of partial resections of the colon should be discouraged, because marker studies do not define pathophysiology in patients with slow transit constipation.