Constipation is a common complaint which may refer to either infrequent bowel movements, passage of hard stools, or difficulty in passing stool. Many patients present because of a misconception of what is “normal” bowel habits, and others may just be victims of their own poor dietary habits which result in an extremely low amount of daily fiber and fluid intake. When bowel movements occur fewer than two times per week, constipation is likely and an evaluation is warranted. Constipation is not a disease, but rather a symptom of some underlying illness, and the differential diagnosis for this condition is extensive. The Rome criteria define constipation as the presence of two or more of the following conditions for at least 12 months: 1) fewer than three movements per week, (2) excessive straining required during defecation at least 25% of the time, (3) at least 25% of stools are hard and pelletlike, and (4) a sensation of incomplete defecation at least 25% of the time, or a 12 month history of fewer than two bowel movements per week.
When evaluating constipation it is helpful to break the differential diagnosis down into three main catagories: systemic causes, mechanical abnormalities, and functional abnormalities. Systemic causes include poor dietary habits (low fluid and fiber intake), a sedentary lifestyle, medication side effect, and underlying illnesses (hypothyroidism, hypercalcemia, hypokalemia, diabetic gastroparesis, Parkinson’s disease, multiple sclerosis, etc). Many medications are associated with constipation, and it is prudent to consider discontinuing any suspected medications prior to initiating an evaluation. Mechanical abnormalities include: partial obstruction (neoplasm, strictures), rectocele, and rectal prolapse. Irritable bowel syndrome, slow transit constipation, and pelvic floor dysfunction (failure to relax the pelvic floor during defecation) comprise the category of functional abnormalities.
The initial evaluation should include measurement of the serum TSH, calcium, and potassium. If possible any medications which may cause constipation should be discontinued. In persons from appropriate parts of the world, constipation may be a symptom of Chagas disease and an EKG would be prudent to monitor for the characteristic changes. Since the American diet itself is a common cause, patients should be instructed at the initial visit to greatly increase their intake of water and fiber. In patients unwilling to change their diet habits, suggesting a fiber supplement such as psyllium (metamucil) or methylcellulose (citrucel) with meals may prove curative. An exercise program should also be started in conjunction with the dietary changes. In patients who complain of passing extremely hard stools, docusate sodium (50-200 mg/day) may be beneficial. It is also prudent to perform a rectal examination with fecal occult testing to evaluate for impaction, hemorrhoids, anal fissures, and to screen for colon cancer on the initial evaluation. A more detailed inspection of the terminal rectum may then be performed via anoscopy. Female patients should also undergo a pelvic examination to evaluate for a rectocele. Female patients who have a rectocele and report that they are able to defecate only when applying vaginal digital pressure should undergo further evaluation and possible treatment for their rectocele. However, the presence of a rectocele on examination is not proof that it is the underlying etiology as many patients with rectoceles do not have constipation. If symptoms persist despite therapy and there are no obvious etiologies after physical examination and biochemical testing then evaluation with either barium enema or colonoscopy will help exclude mechanical etiologies.
If the above work up does not reveal a correctable etiology and if symptoms persist despite lifestyle (diet and exercise) changes, then more aggressive medical therapy should be offered. Initially, osmotic laxatives (lactulose or milk of magnesia) should be offered in conjunction with the above mentioned fiber supplementation and an exercise program. Stimulant laxatives (bisacodyl or senna) may be offered if the above therapies prove ineffective. If constipation still persists, then water enemas (5-10 ml of colace liquid may be added) may be used at regular intervals, also, polyethylene glycol electrolyte solutions (8-12 ounces daily), such as those used for bowel preps, may provide relief in refractory cases. Prokinetic agents (metoclopromide, bethanechol chloride, or erythromycin) should also be considered as possible therapeutic modalities especially when gastroparesis is suspected. Lubiprostone is another alternative therapy.
If the above therapies are all ineffective after a 2 to 3 month trial, then further work-up should be considered. Further testing will address evaluation of colonic transit. Two tests may be used to determine colonic transit. In the first, the patient ingests 20 radiopaque markers and then six days later, is subjected to abdominal flat-plate radiography. In the second test, the markers are ingested over the first three days and then on days 4 and 7, abdominal flat-plate films are obtained. Normal colonic transit is approximately 70 hours. In order for both tests to be reliable, patients should be instructed to follow a high fiber diet and avoid any laxatives during testing. Obstructed defecation is diagnosed by finding increased anal pressure and electromyographic activity on attempted defecation during anorectal manometry. If anal sphincter relaxation is not observed during rectal distention in patients undergoing anorectal manometry, then congenital megacolon (Hirshsprung disease) should be suspected. Pelvic floor dysfunction and anatomic abnormalities such as a rectocele, rectal intussusception, or rectal prolapse will result in an abnormal ballon expulsion test (an inability to expel air-filled or water-filled ballons from the rectum). To further evaluate these possible etiologies, defecography may prove useful. In this study, the rectum is filled with thickened barium and then fluoroscopic images are taken during attempted defecation of this stool like material.
Refractory cases may respond to surgery to treat any underlying etiologies which are discovered on the above mentioned studies. Slow-transit constipation may respond to misoprostol; however, many cases require surgery (subtotal colectomy with ileorectal anastomosis). It is important to exclude and treat pelvic floor dysfunction and psychiatric disease preoperatively as these are commonly discovered in patients with suspected slow-transit constipations whose symptoms persist postoperatively. Therapy for pelvic floor dysfunction is biofeedback training.