Constipation is a symptom, rather than a disease, and represents a subjective interpretation of real or imagined disturbance of bowel function.¹ Although constipation can have many causes, it is most often functional or idiopathic.^2,3

Constipation is more prevalent in children and the elderly.^2,3 In children, few benign medical conditions are as distressing as a disorder of defecation. In adults, chronic constipation has been shown to diminish perceived quality of life. Constipation may also signal more serious underlying problems such as colonic dysmotility or mass lesions.⁴

Epidemiology

The exact prevalence of constipation in the U.S. population is not known, although one epidemiologic study⁵ found an overall prevalence of 14.7 percent. In adults, constipation occurs more frequently in blacks and women, and usually becomes more prevalent with increasing age.⁶ Constipation affects 3 percent of preschool-age children and 1 to 2 percent of school-age children; in the latter group, constipation is more common in boys.⁷

In the United States, more than $800 million is spent on laxatives each year. Constipation is also responsible for 2.5 million physician visits, with patients over 65 years of age accounting for the greatest number of these visits.^4,8–10 In children, constipation is the reason for nearly 5 percent of outpatient visits to pediatric clinics and more than 25 percent of referrals to pediatric gastroenterologists.^2,11

Definition of Constipation

Constipation has different meanings to different people. A patient's perception of constipation may include not only the objective observation of infrequent bowel movements but also the subjective complaints of straining at stooling, incomplete evacuation, abdominal bloating or pain, hard or small stools, or a need for digital manipulation to enable defecation.

Although constipation is often defined as decreased frequency of defecation, that alone is not a sufficient criterion.¹⁰ In fact, this parameter needs to be adjusted in young children, because of the wide variability in normal defecation frequency in this age group^2,11 (Table 1).²

An international committee has recommended operational definitions of chronic functional constipation in adults, infants, and young children (Table 2)^12,13 [Evidence level C, consensus opinion]. These definitions can be used to guide the evaluation and treatment of constipation.

Anatomy and Physiology

The process of defecation involves the propulsion of stool through the colon to the rectum, the recognition of stool within the rectum, and the conscious act of defecation.

The colon terminates in the rectum, which, in turn, passes through the levator ani muscles and becomes the anal canal. Two groups of muscles encircle the anal canal: the internal anal sphincter (involuntary control) and the external anal sphincter (voluntary control). The nearly 90-degree angle formed at the junction of the rectum and the anal canal is also important. This junction straightens with flexion of the hips, which explains the physiologic advantage of squatting for defecation.¹⁴

Within three to four hours after ingestion, food enters the cecum; after several more hours, it reaches the rectum. When the rectal wall is distended by stool, reflex contraction of the rectum occurs, the internal anal sphincters relax, and fecal material is pushed into the anal canal. At this point, the stretch receptors of the anoderm perceive the stool, and a decision is made on whether to expel the stool by relaxing the external anal sphincter, squatting, and increasing intra-abdominal pressure with the Valsalva maneuver, or to postpone defecation by contracting the external anal sphincter and the gluteal muscle.^11,15,16

Pathophysiology

Constipation can occur because of an alteration in stool consistency or colonic motility or caliber. It can also result from any change in the process of rectal evacuation. From a practical standpoint, constipation is generally caused by one of two mechanisms: obstruction of the movement of luminal contents or poor colonic propulsive activity. Obstruction of colonic flow may be caused by an anatomic or functional disorder. Poor propulsive activity may be caused by inhibition of motility (i.e., effects of a drug or metabolic disease) or diffuse nerve or muscle disease (e.g., multiple sclerosis, Chagas' disease).

The differential diagnosis of constipation in adults and children is broad (Tables 3¹⁷ and 4¹¹). However, most patients are found to have no discernible cause for this symptom and are labeled as having chronic functional or idiopathic constipation^11,17 [Evidence level C, expert opinion].

Diagnostic Approach

A thorough investigation of constipation may be indicated for one of two reasons: (1) to exclude systemic disease or a structural disorder of the intestines, or (2) to elucidate the underlying pathophysiologic process when constipation does not respond to simple treatment.

ADULTS

History

The evaluation begins with clarification of what the patient means by “constipation.” The assessment includes the nature of the bowel movements (size, consistency, frequency) and the duration of the complaint.

Acute constipation is more often associated with organic disease than is long-standing constipation. It is important to determine whether the patient has a history or signs and symptoms of a neurologic, endocrine, or metabolic disorder. The patient must be asked about “red flags” that suggest the presence of an underlying gastrointestinal organic disorder. Important red flags include abdominal pain, nausea, cramping, vomiting, weight loss, melena, rectal bleeding, rectal pain, and fever.

During the first visit, it is helpful to obtain a history of the patient's working, eating, and bowel habits. Questions should be asked about dietary fiber intake, level of physical activity, and use of medications, including over-the-counter agents (e.g., laxatives, vitamins, bismuth compounds). The patient's perspective and concerns should be elicited, and a careful psychosocial history should be obtained, with attention given to depression, anxiety, and stress management.

Physical Examination

The physical examination is directed at identifying underlying causes of constipation. The patient's weight is recorded, and overall nutritional status is noted. The patient's skin is checked for pallor and signs of hypothyroidism (e.g., reduced body hair, skin dryness, fixed edema), and the abdomen is examined for masses, distention, tenderness, and high-pitched or absent bowel sounds. The rectal examination includes careful inspection and palpation for masses, anal and perianal fissures, inflammation, and hard stool in the ampulla. The color and consistency of the stool should be noted.

A focused neurologic examination should be performed to search for focal deficits and delayed relaxation phase of the deep tendon reflex (suggestive of hypothyroidism). The patient should also be evaluated for signs of depression, anxiety, and somatization.

Diagnostic Studies

Laboratory studies and colorectal imaging are appropriate when constipation is persistent and fails to respond to conservative treatment, or when a particular disorder is suspected. Laboratory tests may include a complete blood cell count and thyroid-stimulating hormone, calcium, glucose, potassium, and creatinine levels. The stool should be tested for occult blood.

Flexible sigmoidoscopy and colonoscopy are excellent for identifying lesions that narrow or occlude the bowel. Colonoscopy, if readily available, is the examination of choice in adult patients with constipation who have iron deficiency anemia, a positive guaiac stool test, or a first-degree relative with colon cancer.¹⁸ An alternative examination is barium enema and flexible sigmoidoscopy, a combination that can demonstrate potentially diagnostic features such as colonic dilatation and strictures¹⁹ [Evidence level C, expert opinion].

If extracolonic and mechanical causes of constipation are excluded by laboratory studies and colorectal imaging, a complete physiologic evaluation is warranted. Possible tests include anal manometry, balloon insertion, defecography, and colonic transit studies.

Anal manometry is performed to assess the anal sphincter, pelvic floor, and associated nerves. A special pressure-sensitive catheter is inserted into the anus to measure resting and squeeze pressures of the sphincter. Increased anal sphincter pressures are often associated with pelvic floor dysfunction. However, the principal purpose of anorectal manometry in the setting of chronic constipation is to exclude adult-onset or short-segment Hirschsprung's disease (congenital megacolon), which should be suspected in the absence of a rectoanal inhibitory reflex.

Balloon insertion is the simplest and perhaps most physiologic test to demonstrate rectal evacuation. Studies have found that healthy volunteers can expel the balloon, whereas most patients with pelvic floor dysfunction cannot.^8,20

Defecography and colonic transit studies are particularly useful in patients with intractable constipation or pelvic floor disorders. Videodefecography is specifically designed to evaluate evacuatory disorders such as rectal prolapse and rectocele.²¹ For this study, the patient's rectum is filled with thickened barium (to simulate the consistency of stool). The patient is then seated on a water-filled commode and examined from a lateral view with fluoroscopy. Views are obtained with the patient at rest, squeezing to defer a bowel movement, and straining to evacuate the rectum.⁸

For colonic transit studies, serial abdominal radiographs are obtained after the patient swallows a capsule filled with radiopaque markers. In normal persons, most of the markers should pass by day 5; in a patient with slow colonic transit, the markers will be scattered throughout the colon. If the patient has pelvic outlet obstruction, more than 20 percent of the markers will be held up in the rectum.^9,17,18

A suggested approach to the evaluation and management of constipation in adults is provided in Figure 1²² [Evidence level C, expert opinion].

CHILDREN

There is an interesting dichotomy in the approach to constipation in children: the differential diagnosis is lengthy, but the likelihood of undertaking an extensive exclusionary evaluation is small.¹¹

History

A thorough history is recommended as part of the complete evaluation (Table 5).² Based on the symptoms, it may be possible to narrow the differential diagnosis to a specific anatomic or pathophysiologic disorder (Table 6).⁷

Constipation frequently begins with the transition from breast milk to formula, or from strained foods to table foods. Cow's milk is the most constipating component of the young child's diet.¹¹ The transition to a daycare setting or an all-day school, with consequent loss of privacy, may be a contributing factor to constipation.

When possible, the family should be asked to prepare a five- to seven-day symptom and diet history before the office visit. The frequency and character of the stool should be recorded, along with episodes of pain. Stool withholding and retention may occur as the child attempts to avoid painful defecation. In one study,²³ 63 percent of children with constipation and soiling had painful defecation that began before three years of age.

Physical Examination

A complete physical examination should be performed to search for an organic disorder (Table 7).² Childhood functional constipation is a clinical diagnosis that frequently can be made on the basis of a typical history and an essentially normal physical examination. A fecal mass in the suprapubic area is demonstrable in most children who present with constipation.²⁴

External examination of the perianal area and at least one digital rectal examination are essential. One study²⁵ assessing the frequency of digital rectal examination by primary care physicians found that this examination was not performed before referral in 77 percent of children with chronic constipation; 54 percent of these children were found to have fecal impaction [Evidence level B, nonrandomized study].

It is important to look for signs of spinal dysraphism, such as sensory and motor deficits, urinary incontinence, absent cremasteric reflex, pigmentary abnormalities, and hair tufts in the sacrococcygeal area. Other red flags, such as delayed growth, should raise suspicion for a malabsorptive disorder (e.g., celiac disease, cystic fibrosis).²⁴

Diagnostic Studies

In children with constipation, the initial history and physical examination usually reveal no other problems. In the absence of red flags, no testing or subspecialist consultation is needed before treatment is initiated.²⁴

Functional constipation is the most likely diagnosis in older children. In children younger than one year of age, the possibility of Hirschsprung's disease must be considered. This disorder, which occurs in one of 5,000 children, is diagnosed in 40 percent of affected children by three months of age, in 61 percent by 12 months of age, and in 82 percent by four years of age.⁷

Fecal occult blood testing is recommended in all infants with constipation, and in children of any age who have abdominal pain, failure to thrive, intermittent diarrhea, or a family history of colon cancer or colonic polyps. Blood tests, which may include thyroid function tests, urea nitrogen measurements, and electrolyte, calcium, magnesium, or lead levels, are indicated to exclude some systemic disorders that may be suggested by the findings of the history and physical examination.

Plain-film radiography is useful to assess the presence of a fecal mass in a child who is not cooperative with abdominal and rectal examinations. Barium enema is used primarily to rule out anatomic abnormalities or to evaluate Hirschsprung's disease and colonic strictures (necrotizing enterocolitis)¹¹ [Evidence level B, nonrandomized studies]. Magnetic resonance imaging of the lumbosacral spine can demonstrate intraspinal problems such as tethered cord, tumors, and sacral agenesis.

Anorectal manometry is indicated to demonstrate the rectoanal inhibitory reflex and to rule out Hirschsprung's disease. Suction rectal biopsy can be valuable in diagnosing Hirschsprung's disease. It is now possible to stain rectal tissue for ganglion cells (lacking in Hirschsprung's disease) and acetycholinesterase (increased in Hirschsprung's disease). A full-thickness rectal sample is obtained by the surgeon to document normal colonic segments at the time of diverting colostomy for aganglionosis.¹¹

A suggested approach to the evaluation and management of constipation in children is provided in Figure 2² [Evidence level C, expert opinion].