Overview and Risk Factors

The term "constipation" refers generally to the difficult or infrequent passage of stool. A common definition of constipation is fewer than 3 spontaneous, complete, bowel movements per week. It is the most common gastrointestinal complaint in the United States, with an adult prevalence of about 15% to 20%.

Constipation is also a common pediatric condition. Many cases are related to behavioral issues. However, the condition in children can result from dietary causes, which include fiber deficiencies, dehydration, and dairy intolerance.¹ Constipation also occurs in cystic fibrosis and lead poisoning.

Primary Causes

The most common primary cause of constipation is slow transit of stool through the colon, which accounts for 95% of cases. Less common primary causes include pelvic-floor dysfunction, anismus, and an irritable colon.

Secondary Causes in Adults

Common identifiable secondary causes in adults include:

• Medications. Constipation is a common side effect of antihistamines, narcotics, antacids, calcium channel blockers, tricyclic antidepressants, and many other drugs. Drugs are a particularly common contributor in older adults.
• Smoking cessation. Constipation is a temporary result of nicotine withdrawal.²
• Parkinson's disease.
• Anatomical obstruction (eg, tumor, stricture, or third-trimester pregnancy).
• Hemorrhoids, abscesses, fistulae, and fissures can decrease the desire to defecate due to pain and induce constipation.
• Diet (see Nutritional Considerations).
• Hormonal factors (eg, hypothyroidism).

Symptoms and Signs

• Hard, dry stool, which is difficult to pass or leaves the sensation of incomplete evacuation.
• Infrequent bowel movement.
• Bloating and abdominal discomfort. These symptoms are more common in irritable bowel syndrome (IBS) than in simple constipation. IBS can be differentiated from simple constipation by the presence of other digestive symptoms (see Irritable Bowel Syndrome chapter).
• Lower back pain. However, pain is uncommon in idiopathic chronic constipation.
• Rectal bleeding (eg, stercoral ulcerations/erosions).
• Hemorrhoids or, uncommonly, headaches due to straining in adults.

Risk Factors

The highest reported prevalence of constipation occurs in persons over 60 years of age, followed by children under age 10. The association with age is largely attributable to other factors, such as medication and diet. For unclear reasons, whites report constipation less frequently than other racial groups, and women are affected approximately twice as often as men. The condition is more common in individuals with relatively low incomes and less education.

Additional possible risk factors include:

• Family history.
• Pelvic floor dysfunction.
• Pelvic and abdominal surgery.
• Childbirth.
• Anorectal problems.^3,4

Diagnosis

Careful history and rectal examination can establish the diagnosis, and physical examination may help identify causes of secondary constipation.

Identification of drug side effects in adults, including over-the-counter products such as antacids and iron supplements, does not negate the need for further evaluation-for example, in patients at risk for colorectal cancer. Drugs may make evident a problem that had not previously been apparent.

A detailed bowel diary, submitted by a patient or parent, may be helpful. Many people misjudge normal bowel function as abnormal.

Laboratory evaluation is indicated if hypothyroid disease, anorexia, hypercalcemia, or diabetes is suspected. These conditions may also apply in children, as may celiac disease, lead poisoning, cystic fibrosis, and urinary tract infection.

Plain film imaging of the abdomen can detect megacolon/rectum and assist in monitoring progress in a hospitalized patient. However, in cases of intra-abdominal bowel distention, plain films often cannot distinguish ileus from mechanical obstruction.

If history and physical examination are normal, colonoscopy or barium enema can help rule out obstruction. Gastrografin should be used if perforation or partial obstruction is suspected. Barium can become desiccated behind a partial obstruction. 

Final diagnostic steps may include:

Marker studies to determine normality of colon transit 

Anorectal manometry to assess the appropriateness of internal and external anal sphincter tone, and intrarectal pressure during defecation.

Treatment

Treatment of any identified cause should be attempted before medications are considered. Unfortunately, most constipation treatments are not well-supported by clinical trials.

For idiopathic constipation, the most effective treatment is to stepwise increase fiber intake and fluids, consume foods that reduce transit time (see Nutritional Considerations), and take advantage of the body's normal rhythms of colonic motility, which occur after meals, especially in the morning.

Biofeedback and behavioral changes may be helpful in outlet dysfunction, especially in children.

Severe constipation may require a multidimensional approach that includes manual disimpaction.

Drug Therapy

Many of the following drugs can be used in children, but doses must be adjusted accordingly. Many of these remedies are available in oral form and as rectal suppositories and enemas.

Simple therapies, such as those mentioned above, supplemental corn syrup and fruit juices with sorbitol (for infants already eating solid foods), should be tried first. Enemas and stimulant laxatives should not be used in infants.

Laxatives are not generally recommended, because they prevent the bowel from recovering normal function and often need to be continued. Although they are generally well-tolerated, laxatives may cause abdominal distention, nausea, anorexia, cramps, gas, and (rarely) malabsorption or dangerous electrolyte imbalances, which may worsen with continual use. Laxative abuse is common and often hidden. Clinicians should try to wean patients from laxatives for these reasons.

Bulk-forming agents (eg, oral fiber supplements such as psyllium, methylcellulose, and polycarbophil) hold water in the intestinal contents, making them easier to pass.

Emollients, such as docusate and mineral oil, soften stools, but are not very effective.

Hyperosmolar agents, which cannot be absorbed, produce diarrhea through an osmotic fluid shift. These include:

• Magnesium salts are effective for rapid emptying and intended for one-time use. Hypermagnesemia can occur with frequent use.
• Lactulose works more slowly than salts, and may be used for long-term treatment when diet therapy is not possible or ineffective. It may cause gas.
• Sorbitol is less expensive than lactulose and functions similarly.
• Glycerin is available as a suppository.
• Polyethylene glycol (MiraLax) formulations have varying electrolyte compositions. Although still relatively expensive, they may produce less gas than sorbitol and lactulose.

Stimulants or contact irritants increase peristalsis. They include senna, bisacodyl, and castor oil. These agents are not for chronic use, as they may cause electrolyte abnormalities.

Additional Treatments for Adult Patients

Drugs that act as prokinetics may be helpful (an exception is metoclopramide, which has not been shown to be helpful for severe constipation). Effective agents include:

• Misoprostol⁵ and colchicine.⁶
• Tegaserod, a serotonin agonist (5-HT4), which is approved for chronic constipation.⁷

Patients with refractory slow-transit constipation may be considered for colectomy with ileorectostomy. However, this procedure is experimental and currently can only be recommended as part of a research protocol. Long-term outcome data are not available.

If slow transit is not present, the patient may have pelvic floor dysfunction, which may respond to pelvic floor exercises or biofeedback.⁸ The value of exercise is not limited to such patients; individuals who report daily physical activity have roughly half the risk for constipation, compared with those who are least active. When higher levels of both activity and fiber intake are paired, the risk for constipation drops roughly 70%, compared with individuals who are least active and eat the least fiber.⁹

The rationale for biofeedback treatment is based on the observation that inappropriate (paradoxical) contraction or a failed relaxation of the puborectal muscle and of the external anal sphincter often occurs during attempts to defecate, and is considered a form of maladaptive learning.¹⁰ Although additional long-term studies are required, the available evidence indicates that biofeedback training provides a significantly higher probability of successful outcome in treatment of functional constipation and functional fecal incontinence than standard medical care.¹¹

Nutritional Considerations

Constipation is common in developed countries. According to most estimates, 20% of North Americans are affected, which is similar to the percentage of people affected in other Westernized cultures.^12,13 The most common cause is a diet low in fiber, which is found only in plant-derived foods such as beans, vegetables, fruits, and whole grains. Americans eat an average of 5 to 14 grams of fiber daily,¹⁴ far less than individuals residing in developing countries. In persons eating more traditional, higher-fiber diets, constipation is rare.^15-17 The following considerations are important in preventing or alleviating constipation:

Increasing intake of high-fiber foods. A lower intake of dietary fiber differentiates children with chronic constipation from those with regular bowel habits.^18,19 Increasing dietary fiber improves constipation and significantly reduces the need for laxatives in children,²⁰ the elderly,²¹ and postsurgery patients.²²

Although high-fiber foods should generally be the first choice, there may be a role for fiber supplements in some individuals (eg, edentulous patients or those with dysphagia). Evidence indicates that fiber supplements permit discontinuation of laxatives in about 70% of constipated patients.²³ Several types of fiber supplements have been shown to be effective for constipation relief, including psyllium (Metamucil)²⁴; methylcellulose (Citrucel)²⁵; and Japanese konjac root (glucomannan).²⁶

Increasing fluid intake. A hypohydrated or dehydrated state contributes to constipation.²⁷ Poor fluid intake is often found in constipated children.¹⁸ A combination of 25 grams of fiber and 1.5 to 2.0 liters of fluid daily was more effective for constipation relief than fiber intake alone in patients with functional chronic constipation.²⁸

Avoiding cow's milk. Many children with chronic constipation are allergic to cow's milk, manifesting IgE antibodies to cow's milk antigens. Cow's milk consumption is also significantly higher in infants and children with constipation and anal fissure than in those without these disorders.²⁹ In roughly half of constipated, cow's-milk-allergic children and adolescents who have had a colonoscopy, lymphoid nodular hyperplasia was found, compared with 20% of controls. In one third of all cow's-milk-allergic individuals, a significantly higher number of intraepithelial T cells were also found, indicating an enhancement of local immune responses against food antigens.³⁰ Immune activation is known to affect gastric motility,³¹ possibly indicating a role for an immune response to food antigens in constipation. Roughly one third to two thirds of constipated children with cow's milk sensitivity improve on milk-free diets.^30,32 A controlled clinical trial found that constipation returned within 5 to 10 days of reintroduction of cow's milk.³³ When calcium adequacy is in question, calcium-fortified soymilk, rice milk, or juices may be substituted for cow's milk.

Orders

See Basic Diet Orders chapter.

What to Tell the Family

Constipation is a common disorder that is usually preventable with a diet high in minimally processed, high-fiber foods, consumption of ≥1.5 to 2.0 liters of fluid per day, and regular exercise. Health practitioners can provide helpful information about dietary approaches to prevention and treatment. Most patients and their families are not fully aware of the best sources of dietary fiber (beans and other legumes, vegetables, fruits, and whole grains), or of the absence of fiber in animal-derived or heavily processed food products. They may also have been inappropriately influenced by advertisements for over-the-counter treatments or specific foods, such as breakfast cereals and snack bars. Children with milk sensitivity may respond to the removal of dairy products from their diet. Laxatives should be the treatment of last resort, because they prevent normal bowel function. Biofeedback training is an option for patients, especially children who do not respond well to other treatments.

References

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