Constipation

Emerg Med 37(4):43-47, 2005

Among the issues addressed by the author are differing patient and physician definitions of constipation, the roles of pelvic floor dyssynergia and slow transit, the efficacy of supplemental dietary fiber, the risks and benefits of laxatives, and possible medical and surgical therapies.

By Ronald Fogel, MD, MHSA

For many patients, constipation indicates subjective dissatisfaction with the act of defecation. Patients use the term to describe a bowel pattern that can include hard, small, infrequent stools; the sensation of difficulty in passing stool, specifically excessive or ineffectual straining; or the sensation of incomplete evacuation. In some instances, patients will consider themselves constipated despite having a daily bowel movement. In fact, the problems of straining, hard stools, and the sensation of inability to defecate are more frequent complaints than the symptom of infrequent stools for individuals who consider themselves constipated.

In contrast to the patient's subjective definition, the physician defines constipation as the passage of stool less than three times per week. These differences in understanding of the term constipation can affect research related to constipation as well as the clinical interaction of patient and physician, as will be discussed below.
 

Who suffers from constipation?

Surveys reveal variability in the prevalence of constipation, with estimates from 2% to 27%, reflecting different definitions of constipation and the characteristics of the populations being studied. For older populations (age over 65 years), the prevalence of constipation exceeds 30%. Women, non-whites, and those of low income and lower educational background are more likely to suffer from constipation.
 

What are the causes of constipation?

The many possible causes of constipation are listed in the box below. Among the secondary causes for constipation, it is necessary to exclude structural problems. These conditions require specific therapy or emergent intervention for successful relief of symptoms. An etiologic role for systemic illness or medication can be suggested by the history or physical findings. One approach to organizing the neurologic etiologies is an anatomical classification: central nervous system, spinal cord, autonomic nerves, nerves extrinsic to the colon, and enteric nervous system. Finally, conditions affecting the gastrointestinal smooth muscle can also cause constipation.
 

What is functional constipation?

Most patients with constipation do not have a specific identifiable cause and are classified as having primary or functional constipation. The criteria for functional chronic constipation are listed in the box below. It should be emphasized that a patient may have more than three bowel movements per week and still be classified as having chronic constipation based on the presence of other criteria, and that secondary causes for constipation should be sought in all patients with symptom duration of less than 12 weeks.
 

Three subtypes of chronic constipation have been described: normal transit, slow transit, and disorders of rectal emptying (pelvic floor dyssynergia). Some authors use the description "constipation-predominant irritable bowel syndrome (IBS)" to identify patients with normal transit constipation, thereby confusing the terminology.
 

What is pelvic floor dyssynergia?

Pelvic floor dyssynergia is the underlying etiology for 25% of cases of primary constipation. Although it is considered a disorder of the rectum and anus, these patients also have abnormal contractions throughout the colon. Dinning and colleagues recently showed that patients with pelvic floor dyssynergia had abnormal colonic pressure waves prior to defecation. Patients with pelvic floor dyssynergia present with symptoms that may include a sensation of incomplete evacuation, excessive straining, a need for digital disimpaction, perianal heaviness, and tenesmus. Soft stools and even enema fluid may be difficult to pass.
 

What is slow transit constipation?

Slow transit constipation is often a problem of young women, frequently starting at puberty. In this condition, patients have one or fewer bowel movements per week. They are not concerned about the infrequent urge to defecate but rather complain of bloating and abdominal pain.
 

How should patients with constipation be evaluated initially?

A detailed history is necessary to formulate a differential diagnosis and to develop a cost-efficient diagnostic approach. A review of medications is mandatory. It is important to ask whether there has been a change in diet and what therapies the patient tried before coming to the physician. Physical examination should search for perineal causes of constipation such as anal fissure, anal stenosis, rectal prolapse, scars, or external hemorrhoids.

Plain films of the abdomen and barium studies are usually not helpful in the evaluation of patients with chronic constipation because of the rarity of structural abnormalities. In my practice, barium studies are used infrequently.

Controversy surrounds the utility of endoscopy in the evaluation of patients with constipation but without other symptoms of colonic disease. In a retrospective study using diverse hospital populations, Pepin and Laudabaum showed that constipation without other signs or symptoms of colonic disease did not predict an increased probability of colorectal neoplasm. The investigators concluded that in this subset of patients, colonoscopy should be performed only if screening is indicated based on other factors, such as age or family history of colorectal neoplasm.

When a patient is suspected of functional constipation, a trial of fiber supplementation (30 gm daily) should be prescribed. Almost 70% of patients resolve their constipation and do not require further testing if given an adequate dose of fiber.
 

What are the physiologic tests that may be ordered in a workup of functional constipation?

Several investigations can be used to identify the physiologic abnormality responsible for functional chronic constipation.

A colonic transit study can demonstrate slow transit as well as pelvic floor dyssynergia. After the patient swallows a capsule containing 24 radiopaque markers, daily abdominal x-rays demonstrate movement of the markers through the colon. Normal transit is 72 hours. At 120 hours, no more than five markers should remain in the colon; a greater number suggests colonic inertia. If markers pass through the colon normally but accumulate in the rectum and sigmoid, pelvic floor dyssynergia should be considered.

Anorectal manometry evaluates sphincter pressures, rectal anal inhibitory reflex, and rectal sensation. Both basal and squeeze pressures (measurements of internal and external sphincter function, respectively) are determined. The rectal anal inhibitory reflex assesses the coordination of internal and external sphincters. Under normal circumstances, rectal distension relaxes the internal anal sphincter and causes contraction of the external sphincter. Sensory thresholds for first sensation and maximal tolerable volume can be measured by distending a balloon in the rectum. Expulsion of a balloon filled with 50 ml of water provides information regarding defecatory function. Failure to expel the balloon within one minute suggests pelvic floor dysfunction.

Defecography evaluates the anorectal anatomy, providing information regarding anorectal angulation, pelvic floor descent, and anatomic defects such as rectocele that can be associated with constipation. The test is not performed frequently because of poor interobserver reproducibility of findings and patient aversion to the test.
 

What is the initial treatment for the constipated patient?

Patients with chronic constipation require reassurance that their condition is not fatal and education regarding the variation of normal bowel patterns. Although lifestyle changes (daily designated time for passing bowel movements, increased fluid intake, physical activity) are the initial therapies recommended by many physicians, the clinical efficacy of these modifications has not been proved.

One of the cornerstones of treatment is increased fiber ingestion. The prevalence of constipation has been found to be inversely related to the quantity of fiber intake. The quantity of fiber ingested should be at least 25 gm, although those under age 50 may need as much as 35 gm. In my experience, most patients overestimate their daily intake of fiber. Although many physicians encourage patients to eat vegetables and fruits, it is very difficult to attain 25 gm of fiber intake with these foods alone. No matter how much fiber the patient claims to eat, I recommend daily consumption of a bowl of high-fiber cereal such as Fiber One, which provides 14 gm of fiber in a half-cup serving. I also suggest that patients record daily fiber ingestion to confirm that dietary fiber is adequate. Increasing fiber intake is more likely to help patients with normal transit constipation than the other causes of chronic constipation. If fiber does not provide an adequate response, laxatives can be used.
 

What are the benefits and risks of laxative use?

Although laxatives are widely used, their efficacy is controversial. A meta-analysis concluded that laxatives caused only a transient, limited improvement in stool frequency and did not demonstrate any significant benefits over placebo in the treatment of patients with chronic constipation.

Bulking agents are nonstarch polysaccharides frequently recommended for the long-term treatment of constipation because of a favorable safety profile. Bulking agents are not useful for the acute management of constipation because of a slow onset of action, requiring several days to produce a clinical effect. These agents should not be used if intestinal obstruction, fecal impaction, or appendicitis is suspected. Patients with swallowing disorders may develop esophageal obstruction. The bioavailability of digitalis glycosides, salicylates, tetracycline, and anticoagulants is reduced if the drugs are taken with laxatives. Finally, bulking agents can delay gastric emptying, causing bloating and anorexia.

Osmotic agents include poorly absorbed ions and other molecules that hold water in the lumen, such as salts of poorly absorbed cations (magnesium citrate, magnesium hydroxide, magnesium sulfate), and anions (phosphate and sulfate), poorly absorbed sugars (mannitol, lactulose, and sorbitol), and polyethylene glycol (PEG), a large inert polymer not degraded by bacteria.

Saline laxatives have a rapid onset of action (0.5-3 hr), making them useful for patients seeking quick relief, but their use should be limited because of the risk of dehydration and electrolyte abnormalities. Only the PEG compound should be considered for long-term daily use. Saline laxatives are contraindicated for patients with renal impairment or congestive heart failure. Polyethylene glycol solutions should not be used for patients with known sensitivity to PEG or suspected bowel obstruction.

All osmotic laxatives cause abdominal cramping and gas, although PEG has been said to cause less of these symptoms because the polymer is not digested by colonic bacteria. The divalent ion laxatives can cause dehydration. Depending on the laxative formulation used, patients with renal impairment may develop hypermagnesemia, hyperphosphatemia, or hypocalcemia and the clinical manifestations associated with these electrolyte abnormalities.

Stimulant laxatives can be classified into three groups: diphenylmethanes (bisacodyl), anthraquinones (cascara, senna), and surfactant laxatives (castor oil, docusates). These agents have been used extensively and are considered effective by many patients. Although the older medical literature attributes irreversible enteric nerve damage and cathartic colon (a term for colonic changes including loss of haustrations, pseudostrictures, colonic dilatation, and a gaping ileocecal valve) to the use of stimulating laxatives, this conclusion is not confirmed in recent publications.

Lubricating agents (such as mineral oil, glycerine, and docusates) and enemas or suppositories are used intermittently by many patients and frequently by a subset of patients with refractory constipation. Depending on the agent used, laxation can occur minutes to hours after use. Although occasional use is safe, regular frequent use should be discouraged because of side effects. The lubricating agents may interfere with the absorption of anticoagulants, oral contraceptives, digitalis glycosides, and the fat-soluble vitamins A, D, E, and K. Additionally, elderly users may be at risk for aspiration and consequent lipoid pneumonia.
 

What other treatment options are available?

Tegaserod maleate is a serotonin agonist (partial agonist for 5HT₄ receptors) approved for the short-term treatment of female patients with constipation-predominant IBS and for men and women under 65 years old with chronic constipation. Tegaserod is contraindicated for patients with severe renal impairment.

Transient diarrhea occurs in 10% of patients, usually during the first week of tegaserod therapy. Drug discontinuation is necessary in only 1% to 2% of subjects. Patients also report abdominal pain, nausea, flatulence, and headache. To date, there is no evidence for clinically significant effects on cardiac repolarization or QT intervals.

Tegaserod treatment has been associated with cases of colonic ischemia. The postmarketing experience with tegaserod includes 26 reported cases of suspected ischemic colitis as of June 2004. Whether the drug is responsible for this condition is debatable. Confusion results, in part, from reports that the incidence of ischemic colitis is higher in patients with IBS than in non-IBS controls.

Biofeedback, originally thought to help only patients with pelvic floor dyssynergia, is also effective for those with colonic inertia and IBS. Monitoring external anal sphincter muscle contractions or sphincter pressure during defecation can teach patients to control and reduce these sphincter actions. Although there have been no controlled trials on the efficacy of biofeedback in chronic constipation, improvement rates of 50% to 90% have been reported in uncontrolled studies.

Surgical intervention should be considered for patients with slow transit constipation, either alone or in combination with pelvic floor dyssynergia. The medical literature suggests that colectomy with ileorectal anastomosis relieves slow transit constipation that is refractory to medical therapy. Preoperative testing is mandatory to exclude patients with normal transit who would not benefit from surgery.

The site of the anastomosis has a major impact on the success of the surgery. Anastomosis of ileum to the sigmoid colon is frequently associated with recurrent constipation, while diarrhea and incontinence are common outcomes if the ileum is attached to the distal 7 to 10 cm of the rectum.

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