CHAPTER 124

Constipation

Doron D. Kahana, MD, CPNS, and Khalid M. Khan, MD

Constipation is a common and significant complaint that accounts for approximately 3% of visits to pediatric clinics and up to 25% of pediatric gastroenterology visits. Constipation is often associated with fecal incontinence and abdominal pain, can cause significant distress to the child and family, and has a significant effect on health care costs. Stools that are dry, hard, and difficult to pass define constipation. Although reduced stool frequency is a common characteristic of constipation, it is not universal. The guidelines of the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition define constipation as “a delay or difficulty in defecation, present for two or more weeks and sufficient to cause significant distress to the patient.” This definition is less stringent that the Rome III criteria, which classifies constipation into 2 groups based on patient age, with children younger than 4 years needing to meet 2 criteria for at least 1 month and those older than 4 years for at least 2 months. The 6 Rome III criteria are defecation frequency 2 times or fewer per week, fecal incontinence, retentive posturing, pain during defecation, large-diameter stools, and palpable rectal fecal mass. The average stool frequency is 3 to 4 per day during the first weeks after birth, which decreases to 1 to 2 per day with introduction of table foods by 1 year of age. After age 4 years and into adulthood, normal stool frequency can range from 3 per day to 3 per week.

Many factors influence the stool frequency in normal newborns, infants, and young children, including diet, familial pattern of intestinal motility, personal sensitivity, hygiene habits, hydration status, variable stressors, and intake of medications. Newborns and infants who are fed mother’s milk exclusively may have long intervals—sometimes several days—between normal bowel movements, usually starting in the third month after birth, although the stool will remain loose and seedy. Introduction of solids starting at 6 months of age is often associated with additional slowdown in bowel frequency, and functional constipation may initiate as early as this time.

Functional constipation is constipation in the absence of organic disease; however, it is important to note that chronic constipation is also a condition that begets disease and, thus, must be managed appropriately. Constipation is 1 of several unique medical conditions that create a positive feedback loop—stool withholding results in worsening constipation as stretch receptors accommodate a distended rectum and contractile forces fail to result in a complete evacuation.

In infancy, peristaltic motility may be weak or poorly coordinated, and the lack of physical mobility or ambulation requires the infant to exert a physiologic effort (ie, Valsalva maneuver) to allow passage of stool. Parents or guardians may interpret “straining” as a sign of constipation despite the passage of soft, normal stools. Therapy in such cases, if necessary, is usually nonmedical and involves manual stimulation of the anal sphincters and bringing of the knees toward the chest in a “bicycle kick.” Older infants and toddlers may have constipation secondary to food intolerance, such as cow’s milk protein allergy, and removal of the inciting agent may result in complete resolution. Toilet training can prove to be a challenge, especially in toddlers with constipation, and stressful parent/guardian-child interactions may result in resistance to toilet training on the part of the child.

Commonly, chronic constipation in childhood is triggered by a painful evacuation that results in an unpleasant experience. School-age children may elect to withhold stool because of fear of toileting outside the home or because of social stressors (eg, parental divorce, bullying). Assessment of the etiology of constipation requires a careful medical history to determine the age of onset, characteristic of the stool, and presence of contributing or confounding factors. Comorbidities, such as anal fissures or overflow encopresis, may manifest over time and usually signify a more chronic course.

Epidemiology

Functional constipation is a common problem in childhood, with an estimated prevalence of 3% worldwide. Prevalence of constipation in infants is lower, but it increases between the ages of 2 and 4 years. The onset often coincides with toilet training and dietary changes and is partially a product of increased colonic transit time. Prevalence of constipation in infants and toddlers is equal among males and females, but it becomes 3 times more frequent in boys than girls by age 5 years. Fecal soiling is a significant comorbidity and is reported in up to one-third of females and one-half of all males with severe, chronic constipation (see Chapter 56).

Clinical Presentation

Infants often present with infrequent passage of stool, with some parents or guardians reporting facial grimacing and grunting during defecation as well as apparent discomfort or fussiness with bowel movements, defined by Rome III as infant dyschezia. History of delayed passage of meconium or onset of symptoms before 1 month of age, recurrent vomiting, poor weight gain, or family history of congenital megacolon (ie, Hirschsprung disease) or cystic fibrosis indicate the need for further evaluation. Toddlers usually present with abdominal pain and report the passage of hard or large stools. School-age children may present with fecal soiling, which usually represents overflow incontinence. (Only 10%–15% of all cases of encopresis consist of non-fecal retention.) Parents and guardians describe a stool-withholding posture in which the legs are clamped together and the gluteal muscles are contracted in an effort to suppress defecation (Figure 124.1). Poor appetite and episodic vomiting in severe cases are secondary to a persistent sense of fullness from a dilated and impacted colon. In infants, toxic megacolon resulting from Hirschsprung disease can present with lethargy and signs of sepsis, peritoneal signs, and bloody diarrhea. Hydronephrosis, urinary tract infections, and enuresis also are historically associated with chronic constipation and an impacted colon.

Physical examination should include growth parameters, abdominal examination, perianal inspection, digital rectal examination, inspection of the lumbosacral region, and neurologic evaluation for tone and deep tendon reflexes. The abdomen may be distended and contain a fecal mass on palpation; anal position must be confirmed, and the presence of stool present around the anus or on the undergarments, erythema, rash, skin tags, or fissures should be noted. Lumbosacral dimple, hair tuft, gluteal cleft deviation, and sacral agenesis must be excluded.

Figure 124.1. Child exhibiting retentive posture.

Pathophysiology

The Colon

The colon is a muscular organ that processes dietary residue through bacterial fermentation, salvaging nutrients and reabsorbing more than 90% of the water that enters, and prepares stool for transient storage and eventual excretion (Figure 124.2). Fermented food residue produces gas (eg, hydrogen, methane) and short-chain fatty acids; the latter provide colonocytes with readily available fuel (via butyric acid) that enters the portal circulation for calorie salvage in the liver (eg, propionic acid, acetic acid). The fermentation process may release other micronutrients and vitamins (eg, vitamins K₂ and B₁₂, folic acid, biotin) and is thus an important component of colonic function.

Normal Physiology

Digested food normally takes approximately 2 to 6 hours to reach the cecum from the duodenum (following gastric emptying, which has a normal half-time of 60–90 minutes). The propagation of food in the small intestine occurs via peristaltic waves called the migrating motor complex. Once chyme is in the cecum, peristalsis slows, and it may take several hours or days for it to be expelled as stool. The longer the transit time, the more extensive the water resorption and the more likely it is for the stool to be dry and hard. The rectosigmoid is the sensing organ that initiates the process of defecation and can store stool until it is socially acceptable to expel it. Contraction and emptying of the rectosigmoid is stimulated by eating, a process called the gastrocolic reflex. In the rectum, the pelvic floor muscles (ie, levator ani, puborectalis muscle) regulate fecal retention and defecation. The puborectalis muscle suspends the rectosigmoid and imposes constraints that facilitate voluntary stool retention (ie, continence). Continence is also promoted by contraction of the internal and external anal sphincters.

Figure 124.2. Diagram of the anus, rectum, and sigmoid colon.

Defecation

The urge to defecate is signaled by the propulsion of feces from the sigmoid colon to the rectum. Distention of the rectum causes relaxation of the internal anal sphincter; the external anal sphincter and puborectalis muscle must voluntarily relax through parasympathetic action. The pelvic floor muscles descend, permitting straightening of the anus and rectum (Figure 124.2). Thus, defecation is facilitated by squatting or sitting and by increasing intra-abdominal pressure. The urge to defecate can be consciously repressed by voluntary contraction of the external anal sphincter and likely subconscious sympathetic reflex inhibition and contraction of the puborectalis muscle. The process of defecation is learned early in childhood and remains spontaneous throughout life. The spontaneity of this process may be lost for a variety of reasons, including secondary to trauma, pelvic floor dysfunction, pseudo-obstruction, and surgical resection.

The Vicious Cycle of Constipation

If the urge to defecate is suppressed, the rectosigmoid and eventually the entire colon become dilated and impacted, and defecation may become difficult. The increased caliber of the colonic lumen makes contractions weaker and less effective in propagating stool. Moreover, the child with constipation may become desensitized to rectal distention. Eventually, delayed defecation results in the formation of hard, bulky stool, which makes defecation difficult and painful. The child learns to tighten the external anal sphincter and gluteal muscles, pushing feces higher into the rectal vault and suppressing the urge to defecate; this is the vicious cycle of constipation (Figure 124.3). In children, the initiating event may be a painful evacuation, possibly after an acute illness (eg, cold, respiratory infection) or a course of antibiotics. Intentional and prolonged suppression of defecation is an important factor in the pathogenesis of chronic constipation.

Familial Factors

Some families are predisposed to constipation. Concordance for constipation is 4 times more common in monozygotic twins than dizygotic twins. It may be related to increased absorption of water or an unusually long or poorly motile colon. Poor sensitivity to a critical rectal volume or the need for a particularly large rectal volume may delay the initiation of defecation in genetically predisposed individuals.

Differential Diagnosis

The differential diagnosis of constipation can be divided into congenital versus acquired and then into the following etiologic categories: anatomic; neurologic; hormonal; infectious/toxic; drug-induced/metabolic; functional; and other, such as genetic or allergic (Box 124.1). Functional constipation is often supported by a history that includes poor dietary and hydration habits, stool-withholding behavior, and a normal physical examination. Dietary history may reveal high consumption of cow’s milk (>24 oz/day), cheese, or sugary fruit juice, as well as poor intake of fruits, vegetables, and whole grains. Stool withholding most commonly occurs in young, school-age children and often is a product of a stressful environment, such as a new sibling, a move, parental struggles, or a new school environment.

Chronic constipation that is resistant to medical therapy should not be ignored. Conditions such as congenital megacolon and congenital intestinal malrotation can present past the neonatal period and may result in intestinal devastation (eg, volvulus, ischemia). Several conditions are particularly important to consider when evaluating constipation in infants, including congenital megacolon, hypothyroidism, anal stenosis or atresia, meningomyelocele, and cerebral palsy. Failure to pass meconium or a delay in the passage of meconium beyond 24 hours should raise suspicion for a congenital or genetic aberration (eg, congenital megacolon, cystic fibrosis).

Figure 124.3. The vicious cycle of constipation.

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