4.1 Definition

Constipation is a symptom indicative of an abnormality in stool or its elimination: the stool is too large or too hard; passage is too infrequent, painful or incomplete. There is an extremely wide range in what constitutes normal bowel habit, and this changes markedly between birth and adolescence. As a generalization, stool frequency is less in the formula-fed than in the breastfed infant. The formula-fed infant tends to pass 3 to 5 bowel motions per day; breastfed infants, however, can be very well and pass soft stool without difficulty with a frequency that may range from 10 stools per day to 1 stool every 10 days. At 2 to 3 years of age the modal frequency of defecation is 2 bowel motions per day. From age 3 to adulthood bowel motions are passed between 3 times per day and 3 times per week in 96% of individuals. One-quarter of all cases of chronic constipation begin during the first year of life, but the majority of children affected develop problems in the preschool years. Chronic constipation is a very common cause of referral to pediatric gastroenterology practices and tends to affect males slightly more often than females (by a ratio of 1.5:1).

Encopresis is a term that has become synonymous with a voluntary or involuntary passage of stool in an inappropriate place (usually the underclothing). Soiling refers to the constant involuntary seepage of stool associated with fecal impaction. Chronic constipation complicated by encopresis or soiling is reported to make up 3% of referrals to large teaching hospital clinics. It occurs in 1-2% of 7-year-old primary school children, and is more prevalent in males than females (by a ratio of 5:1).

The colon absorbs water and electrolytes, and collects and packages indigestible residue as a formed stool for later evacuation. Colonic motor function is specialized to perform these functions. Repeated ring contractions or haustral contractions cause to-and-fro shuttling of luminal contents, delaying their transit and enhancing absorption. One to three times a day mass movements transport colonic contents distally. Normal defecation is a combination of autonomic and voluntary functions. Distention of the rectum is the stimulus that initiates reflex defecation. When the fecal bolus distends the rectum, sensory receptors in the rectal wall are stimulated, leading to conscious perception of rectal distention and involuntary relaxation of the internal anal sphincter. In the absence of voluntary contraction of the puborectalis muscle and the external anal sphincter, the fecal bolus is expelled.

Intestinal transit time is closely related to defecation frequency. The reduction of frequency of defecation with age is associated with an increase in intestinal transit time. In the first month of life transit time is 8 hours, at age 2 it is 16 hours, between 3 and 13 years it is 26 hours and in an adult it is 48 hours or more. Transit time is largely influenced by the amount of fiber in the diet. Fiber-rich diets favor the retention of water and result in increased stool weight and volume, shorter transit time and more frequent defecation. Normal stools have a water content of 60-85% of mass. An increase or decrease in volume of stool water of as little as 100 mL in the adult can represent diarrhea or constipation, respectively. In constipation the increased desiccation of colonic contents is due to increased duration of mucosal contact rather than an alteration of mucosal absorptive function.

In the child who presents as having a difficulty with elimination, the physician must determine whether the problem is functional, organic or a parental misinterpretation of symptoms. Examples of the latter include the healthy, breastfed infant who passes a soft stool without difficulty once every 10 days and the normal infant who passes soft stools on a regular basis but frequently becomes fussy, cries or turns red and grunts while defecating. Similarly, 1- to 2-year-old children will interrupt their other activities, become flushed, stand in a rigid posture, and appear to be concentrating on the passage of a bowel motion that is difficult to pass. Often there is no difficulty and these children are in fact attempting to utilize a newly acquired skill and withhold passage of a bowel movement.

Organic constipation may be the result of mechanical obstruction, perianal difficulties causing painful defecation, metabolic or medical disorders, neuromuscular disorders or medications that favor the development of constipation. Mechanical obstruction may occur as a result of congenital, postsurgical or inflammatory stenosis at the level of the anal canal; obstruction by an intrinsic mass such as adenocarcinoma in the adult; or obstruction by an extrinsic mass such as neoplasia or pregnancy. Painful defecation may result from trauma or surgery to the anorectal region, anal fissures, thrombosed hemorrhoids or a perianal abscess/infection. Metabolic and medical disorders that have been associated with organic constipation include hypercalcemia, hypokalemia, hypothyroidism, porphyria and conditions leading to polyurea and dehydration, including diabetes insipidus, diabetes mellitus and chronic renal failure. Organic constipation can result from dysfunction at all levels of the neuromuscular axis: central nervous disorders such as cerebral palsy or stroke; abnormalities of the peripheral nervous system, including myelomeningocele, trauma, polio or diabetic nephropathy; conditions affecting the enteric nervous system such as Hirschsprung's disease; and skeletal or smooth-muscle myopathies. Medications known to predispose to constipation include the opiates, anticholinergics, tricyclic antidepressants and phenothiazines, aluminum-containing antacids, diuretics, iron and vincristine.

Precipitants of functional constipation include decreased fluid intake or increased fluid losses; decreased physical activity; a diet that is low in fiber, contains excessive milk or is nutritionally insufficient; and anything that leads to chronic involuntary inhibition of defecation. Imposed schedules and some children's reluctance to use different facilities are examples of the latter; children may also be simply too busy to attend to the urge to defecate.

In the child who presents with encopresis, the physician must consider whether the incontinence of stool is due to a congenital or acquired neuromuscular disorder, or a behavioral disturbance. However, most of these children have soiling secondary to chronic fecal impaction and overflow. In such cases children may have secondary behavioral disturbance but their primary problem is one of gross rectal distention with loss of the rectal-anorectal angle and the continence function of the puborectalis sling. Whenever there is a mass movement the only residual continence mechanism in these children is the external voluntary anal sphincter, which rapidly fatigues, leading to involuntary soiling. It is not unusual for younger children to deny any knowledge that this is occurring, because if they admit to awareness their parents often expect them to be able to prevent soiling. Such children will regain continence only if their gross rectal distention is relieved.

The most frequently considered organic problem in the differential diagnosis of patients presenting with functional constipation is Hirschsprung's disease. These two conditions can frequently be distinguished by significant differences in the history and physical examination. These are detailed in Table 3.

If an organic cause of constipation is suspected, it should be investigated and treated; however, most patients with constipation have no underlying organic abnormality. In patients with mild constipation, dietary modification with an increase in fluid or fiber intake, establishment of a regular bowel habit with a prompt response to the urge to defecate, and appropriate physical activity may be a sufficient remedy. Many individuals will require a laxative in addition. Patients whose constipation is complicated by fecal impaction and soiling require very aggressive management, including education, clearing of the impaction, establishment of a regular bowel habit, laxative therapy titrated to achieve the passage of a soft bowel motion daily, appropriate diet and exercise, and (in younger children) positive reinforcement for appropriate behavior. Therapy must be aggressive and persist for three to six months until the distended and dysfunctional colon has an opportunity to return to normal caliber, tone and sensitivity.

The fecal impaction can generally be cleared by administration of Fleet^® enemas at intervals of 12 hours (generally 2-4 are sufficient). There is a variety of laxatives on the market whose mechanism of action includes hydrophilic (dietary fiber), lubricant (mineral oil), osmotic (glycerin suppositories, lactulose, magnesium citrate/sulfate and sodium phosphate/biphosphate), secretory (ricinoleic acid, free hydroxy fatty acids, dihydroxy bile acids, and dioctyl sodium sulfosuccinate) and motor stimulants (anthraquinones and diphenylmethene derivatives). Natural bran, methylcellulose, polycarbophil and psyllium are all forms of fiber that by virtue of their ability to bind water within their structure lead to an increase in stool bulk and weight, and are associated with more rapid transit and more frequent bowel motions. These are safe and effective in children if sufficient amounts are taken, but children's compliance is often poor. Mineral oil is the lubricant laxative of choice in the pediatric age group because of better compliance. It is an indigestible, tasteless oil that adds bulk, softens and lubricates the stool and exerts an additional osmotic effect. Its aspiration can lead to lipoid pneumonia; therefore this form of treatment should be avoided in patients known to aspirate or with a history of reflux. Taken with meals mineral oil will result in a degree of fat-soluble vitamin malabsorption. This problem can be addressed by giving it as a single dose several hours after the evening meal. Properly used, mineral oil is an inexpensive, well-tolerated, effective and safe children's laxative. In those children who refuse mineral oil the osmotic agent lactulose is a more expensive but effective alternative.

Constipation in the very young infant can often be managed by adding prune juice to the diet or brown sugar to the formula, or by feeding the infant purées with a natural laxative action (containing prunes, for example). Mineral oil is frequently not a good choice in this age group because of the frequency of gastroesophageal reflux.