Constipation and the use of laxatives are relatively common in patients with diabetes mellitus (79) but the mechanism of constipation remains unclear. Epidemiological studies in community-based practices suggest that physicians should not immediately assume that GI symptoms in patients with diabetes mellitus represent a complication of diabetes mellitus (80). Diabetic autonomic neuropathy may be implicated in some patients, but other factors might also be important. For instance, evacuatory dysfunction is another important factor (81). Jung et al. (82) showed in a study involving patients with type 2 diabetes mellitus that those with constipation had longer total colonic transit times than those without constipation. However, there was no difference in colonic transit times between patients with and without cardiovascular autonomic neuropathy. Another study by Ron et al. (83) in elderly, frail patients showed a high prevalence of constipation associated with prolonged colonic transit times. However, no significant differences were noted between patients with and without diabetes. Iida et al. (84) showed in type 2 diabetics an association between prolonged colonic transit measured by the radiopaque pellet method and autonomic cardiovascular dysfunction. In one study, constipation in type 1 diabetics was found to be associated with the use of calcium channel blockers (80).
Poor glycemic control is probably an important contributory factor (85). Indeed, acute hyperglycemia affects anorectal motor and sensory function (86). The natural history of constipation in diabetics does not seem to predict symptom change over time (87).
It is difficult to separate constipation in patients with diabetes from that occurring among the normal population because constipation is such a highly prevalent symptom (Table 3). The depth of diagnostic evaluation in a patient with diabetes complaining of constipation depends on the severity of constipation and on the associated symptoms. Digital examination, testing of stools for occult blood, proctosigmoidoscopy, and barium enema, or better yet, full colonoscopy should be performed to rule out colonic malignancy.
Anorectal manometry might be useful to evaluate the rectoanal inhibitory reflex (88), which is absent in Hirschsprung's disease. Colonic segmental transit time can be derived from the mean segmental transit time of radiopaque markers through right colon, left colon, and rectosigmoid area. These tests should help distinguish between diffuse colonic hypomotility and rectosigmoid dysfunction (outlet obstruction). Unfortunately, the sensitivity and the specificity of these procedures have not been specifically evaluated in diabetics.
Evaluation of Colonic and Anorectal Dysfunction in a Patient With Diabetes
Digital examination Stools: occult blood Barium enema Colonoscopy (biopsy) Colonic segmental transit time Anorectal manometry Fecal incontinence 24-hour stool weight Anorectal manometry Maximum basal sphincter pressure Maximum "squeeze" sphincter pressure Rectoanal inhibitory reflex Tests of continence Solids: solid sphere Liquids: rectally infused saline
Treatment of constipation in diabetics does not differ from those without diabetes. However, besides conventional anticonstipation measures, acarbose has proven valuable in the treatment of diabetics. Because it reduces prolonged colonic transit times in constipated diabetics in addition to its beneficial effect in the control of diabetes (89).
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