Functional Constipation and Encopresis

William J. Klish

Chronic constipation is a common complaint in children. It accounts for 3% of office visits to a primary care physician and 20% to 25% of the referrals to a pediatric gastroenterologist. Because stool habits are a major concern of many parents, the physician or health care worker should become familiar with both normal and abnormal patterns of defecation to properly advise parents. Distinguishing functional constipation (i.e., without evidence of a pathologic cause) from constipation with an organic cause is important. Beyond the neonatal period, the most common cause of constipation is functional constipation.

Constipation is defined as a delay or difficulty with defecation, present for 2 or more weeks. Children with chronic constipation have infrequent bowel movements that are unusually large, hard, dry, and painful to pass. The frequency of defecation and the consistency of stool are related to the patient’s age and diet. Infants have a mean of four stools per day during the first week of life. However, some infants have a bowel movement after each feeding because of an active gastrocolic reflex, and others, particularly breast-fed infants, can have stools every 2 to 3 days. Breast-fed infants usually have stools more frequently than do formula-fed infants. This frequency gradually declines to a mean average of 1.7 stools per day at 2 years of age and 1.2 stools per day at 4 years of age. After 4 years of age, the frequency of bowel movements remains unchanged. Less frequent stools should be of concern if they are hard, dry, unusually large, or difficult to pass.

Encopresis is involuntary fecal soiling or incontinence secondary to chronic constipation. Physiologic encopresis occurs most commonly and is manifested as overflow incontinence that occurs as a result of severe constipation, fecal impaction,
and a dilated rectum. Children with encopresis frequently have related behavioral components, including active withholding of stool, fear, and embarrassment that frequently resolve with adequate treatment. A less common form of psychological encopresis usually is manifested as full bowel movements in the underwear. The diagnosis of psychogenic incontinence should be reserved for older and previously toilet-trained children who have full bowel movements in their underwear on a regular basis.

PATHOPHYSIOLOGY

For defecation to proceed, a normal rectum and puborectalis muscle, normal internal and external anal sphincters, and normal innervation of these structures through both the autonomic and somatic nervous systems must be present. The rectum functions not as a storage area for fecal material but rather as a sensing organ that initiates the process of defecation. When stool moves into the rectum from the sigmoid colon, pressure is put on the wall and the rectal valves. This pressure initiates an impulse within the intrinsic nervous system of the rectum resulting in relaxation of the internal anal sphincter, which is experienced as the urgency felt just before defecation. If defecation is inconvenient, contraction of the external sphincter is initiated, first by reflex and then intentionally. The external sphincter is assisted by contraction of the puborectalis muscle, which helps constrict and angulate the anal canal. If the external sphincter is held contracted long enough, the reflex to the internal sphincter wanes and the urge to defecate disappears. When defecation is convenient, the external sphincter is relaxed consciously, and stool is propelled by colonic peristalsis through the open anal canal. As stool enters the anal canal, a secondary reflex is initiated via the somatic nervous system that results in contraction of the abdominal musculature and assists in emptying the lower colon.

Many general causes exist for constipation. Often it is a familial complaint, and the parents of constipated children often report being constipated when they were children. This history implies a genetic component to constipation, which may be the result of increased efficiency of water extraction from fecal material caused by a congenitally long or hypomotile large bowel. Diet plays a role in the volume and hardness of fecal material throughout life. Some dietary residue, such as plant fiber, tends to make stools soft, whereas other residue, such as the calcium salts in cow’s milk, tends to make stools firm. Elemental and chemically defined diets decrease dietary residue and thus decrease the frequency of having stools.

Hospitalized children may become constipated because of decreased stimulus for defecation resulting from inactivity. Diseases associated with fever may result in acute constipation. Some chronic diseases, such as hypothyroidism, are associated with constipation. The differential diagnosis of constipation is discussed later.

Children who develop functional constipation associate discomfort with defecation. The most common reason for discomfort is an anal fissure resulting from either hard stool or the use of suppositories, enemas, or a rectal thermometer. Occasionally, the sense of discomfort results from a bad toilet-training experience. Whatever the cause, the result is the same. Whenever the child feels the sensation associated with relaxation of the internal anal sphincter, he or she aggressively contracts the external sphincter to prevent expulsion of stool and the pain it is expected to bring. Increased amounts of stool collect in the rectum, and over a period of months, the rectum gradually dilates. As it enlarges, it becomes less capable of propulsive peristaltic activity, which results in more retention of stool. As the volume of the rectum increases, its sensory capacity diminishes, so that retention is easier. Eventually, the constipation becomes self-perpetuating.

Encopresis develops when the rectal vault enlarges sufficiently to exert pressure on the structures of the floor of the pelvis, including the levator muscle. This muscle interdigitates with the anal sphincters. As it is pushed downward, the anal sphincters become distorted and the anal canal is shortened. If the external anal sphincter is allowed to relax, it assumes a slightly open position. During activity, loose or mushy stool then can flow around firmer stool present in the rectum and can leak out. Affected children instinctively know they have little control over the leakage at this point, so they often adopt a casual attitude that is frustrating to parents. They constantly smell of fecal material, which may result in ridicule by their peers and secondary psychological problems.

CLINICAL FINDINGS

The most common symptom associated with constipation is chronic recurrent abdominal pain, which occurs in approximately 60% of patients. The pains are intermittent and localized to the periumbilical region and resemble functional abdominal pain. Enuresis is reported in approximately 30% of the children with encopresis. Many of them have daytime as well as nocturnal enuresis, which resolve when the constipation is treated. Urinary tract infection is a common complication in girls with chronic constipation.

Stools of very large caliber are another associated symptom. Parents often must break up stools mechanically to flush the toilet. The size of the stool is a function of the size of the colon.

In children with encopresis, fecal incontinence tends to occur in the late afternoon and early evening, but it can occur at any time of day or night. The pattern of incontinence tends to parallel the child’s activity, with soiling occurring less frequently when the child is sedentary. Most children insist that they do not feel the stools coming and do not perceive the sensation of impending soiling until they actually feel stool in their underwear.

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