Rudolph's Pediatrics, 22nd Ed.

CHAPTER 386. Constipation and Fecal Incontinence

Manu R. Sood

Constipation is a common problem in children and is often associated with maladaptive behavior triggered by a painful or otherwise unpleasant defecation. There is no universally accepted definition of constipation, although the term is generally describes infrequent or painful bowel movement due to stool that is too large or hard to pass.1,2 The Rome Committee, consisting of a group of pediatric gastroenterologist from Europe and North America, defined constipation as 2 or more of the following symptoms in a child with a developmental age of at least 4 years: 2 or fewer defecations in the toilet per week, at least 1 episode of fecal incontinence per week, history of retentive posturing or excessive volitional stool retention, history of painful or hard bowel movements, presence of a large fecal mass in the rectum, and history of large-diameter stools that may obstruct the toilet.3,4

EPIDEMIOLOGY

The incidence of constipation in 5 to 21 year olds is estimated to be 3.9 per 1000 person-years. The prevalence of constipation in children ranges from 0.7% to 29.6% (median 8.9%).5,6 About 3% of children experience constipation in the first year of life and about 10% in the second year of life.7 Constipation accounts for almost 3% of general pediatric outpatient clinic visits and 10% to 25% of visits to a pediatric gastroenterology clinic. Most cases of functional constipation present between ages 2 and 4 years. The incidence of constipation in children younger than 13 years is similar between genders, but in older children, girls seek medical help more often than boys. In school-aged children, fecal soiling is 3 times more common in boys than in girls. The incidence increases when a parent, sibling, or twin has constipation. Monozygotic twins are 4 times more likely than dizygotic twins to have constipation.

PATHOPHYSIOLOGY

A normal pattern of defecation requires the removal of water from the liquid chyme that enters the cecum and propulsion of soft, formed colonic contents through the colon to the rectum, which stores stool until defecation. Sensation of the need to pass stool by rectal smooth muscle contraction and reflexive partial inhibition of the internal anal sphincter allows stool to impinge on the sensory area of the mucosa of the upper anal canal. To achieve continence, the child must be able to perceive this urge to defecate, and then, if in the appropriate setting, the child must plan to find a lavatory depending on the urgency. This is not an innate ability but requires learning in a supportive environment. If the child has learned that stooling is painful, or if appropriate access to a socially acceptable location for passing stool is unavailable, the child withholds the stool by external anal sphincter and pelvic floor contraction. The expulsion of the stool requires an increase in intra-abdominal pressure by bearing down.

Constipation results from either slow transit of the stool through the colon due to an underlying neuromuscular disorder or from outlet obstruction due to mechanical obstruction (tumors, stricture), abnormal defecation (dysnergia), or stool-withholding behavior. Whatever the cause of stool retention, fluid absorption desiccates the stool, resulting in increased hardness. Causes of incontinence other than function fecal retention are discussed further in this chapter.

CLINICAL FEATURES AND DIFFERENTIAL DIAGNOSIS

Constipation is a symptom, not a disease, and can be associated with a number of disorders (Table 386-1). The majority of children with chronic constipation have no clearly identifiable disorder, and their condition is therefore labeled functional or idiopathic constipation. Passage of a large-diameter or hard stool is painful. Repeated painful experiences can scare the child and prompt stool-avoidance behavior. Almost 75% of children with functional constipation have experienced painful bowel movements, and 97% have a fear of defecation. Therefore, prompt treatment of constipation is important to prevent further difficulties.8,9

Some children can withhold stool for up to 2 to 3 weeks. They adopt various “stool retentive” postures in an attempt to avoid defecation, such as standing in the corner on tip toes with stiffening of the body to contract the gluteal muscle while screaming or breath holding in response to the sensation of an urge to defecate. This behavior (often called the “potty dance”) is often confusing to caretakers who interpret it as discomfort due to constipation rather than as stool-withholding behavior. As stool accumulates in the rectum, mood deteriorates, appetite decreases, and the child experiences abdominal pain and distension.

The child ultimately develops overflow incontinence in which the liquid stool seeps around the rectal fecal mass and the child passes small amounts of soft stool several times a day (Fig. 386-1). Sometimes this can be confused with diarrhea, but a good clinical history distinguishes between the two. The loss of control over defecation confuses the child and often angers the parents. Overflow incontinence should be distinguished from fecal incontinence secondary to fecal urgency seen in patients with irritable bowel syndrome, neurologic disorders, and spinal disorders. Children with behavioral disorders and sexual abuse can also present with fecal incontinence. Urinary tract infection occurs in 5% to 10% of chronically constipated children, probably secondary to partial urethral obstruction or ascending infection from chronically soiled underwear.

In infants, constipation is somewhat more likely to be due to an underlying organic disorder such as an anatomic disorders (anterior ec-topic anus, rhabdomyosarcoma, stricture) or Hirschsprung disease, but in most cases, constipation is functional. It often results from dietary issues. Hard stool is more common in formula-fed infants than in breast-fed infants because of the higher protein-to-carbohydrate ratio and a lack of oligosaccharides in formula. Therefore, a change from breast milk to formula is associated with firm and less frequent bowel movements. Cow milk protein has also been implicated in chronic intractable constipation in infants and children. Breast-fed infants often pass stools infrequently (up to every 5 days), which may be normal if the stool is soft and passage is not painful.

In toddlers, conflict can arise out of overzealous or inappropriate toilet-training practices. The parents may have unrealistic expectations that can be influenced by socioeconomic factors. Working single parents or families in which both parents are working may be under pressure to toilet train their child before the child is eligible for preschool placement. Because of the need to get the child toilet trained, parents may seek medical help for toilet training. School-aged children may prefer to postpone defecation until they reach home because the school toilets are unhygienic. Repeated avoidance of bowel movements at school can lead to rectal fecal mass, which is painful to pass and may trigger fecal retentive behavior.

Table 386-1. Causes of Constipation in Children

It is important to differentiate fecal soiling associated with functional fecal retention from nonretentive incontinence. Children with this condition present with a history of passage of part or the entire stool in the underpants. The incontinence is sporadic rather than the continuous seepage seen in functional fecal retention. There is no history of passage of hard or large-diameter stool. In most cases, fecal incontinence is one of many difficult behaviors exhibited by the child. An ongoing struggle with the parents over many aspects of daily living is not unusual. Fecal incontinence is a behavioral manifestation of emotional disturbance and requires psychological evaluation and treatment. Laxative therapy frequently worsens the problem.

Spinal cord injury or dysraphism may results in slow-transit constipation and external anal sphincter and levator ani muscle dysfunction. In addition, the motor and sensory function of the rectum may be affected. Fecal incontinence, with or without constipation, is present in 11% to 30% of patients with myelomeningocele.10 Biofeedback training has been helpful in patients with preserved sensorimotor function in the perianal region and who are cooperative. High-fiber diet and daily digital rectal stimulation, suppositories, or enemas will allow acceptable control of fecal incontinence. Administration of antegrade colonic enemas through an appendectomy, a cecostomy, or a sigmoid colon button is beneficial in selected patients.11

Constipation is also common in children with neurodevelopmental disorders in whom abnormal skeletal muscle tone can cause poor defecatory effort, and enteric neuromusculature abnormalities may also cause slow-transit constipation. In addition, medications frequently administered to these children and diets low in fiber contribute to problems of constipation.

FIGURE 386-1. Fecal incontinence results from the rectal fecal mass stretching open the anal sphincter; the liquid stool seeps around it and leaks out of the anal canal.

Children with irritable bowel syndrome may present with constipation and abdominal pain. Diagnosis and management is discussed in Chapter 384. Cow milk intolerance can present with constipation. In these cases, symptomatic improvement is usually achieved following a 2-week trial of dairy-free diet. Children with poor abdominal musculature (eg, prune belly syndrome) are unable to increase the intra-abdominal pressure and thus have difficulty with defecation.

DIAGNOSTIC EVALUATION

The history begins by determining the age at onset of symptoms, frequency of bowel movements, and appearance and consistency of the stool. A history of retentive posturing suggests a functional etiology, but if stool passage is painful from another disorder (such as perianal streptococcal infection or anal fissure), this behavior may ensue. Anatomic obstruction, Hirschsprung disease, and the other organic causes of constipation must be considered, especially in cases when soft, small-caliber stools are passed or if there are episodes of explosive passage of soft stool preceded by a lack of stool passage and abdominal distension. Abdominal distention, nausea, vomiting, a decrease in appetite, lethargy, fever, weight change, and failure to thrive are all signs of a possible organic disorder. However, in most cases of pediatric constipation, dietary or functional causes explain the symptoms.

Perianal examination may reveal an anal fissure, erythema due to a streptococcal infection, anal stenosis or an anterior displaced anus. Digital rectal examination is not essential in every child but is necessary if the history is not typical of functional constipation. The lumbosacral region of the back should also be examined for evidence of myelodysplasia and sacral agenesis. A patulous anus, absent ano-cutaneous reflex (anal wink), cremasteric reflex, sacral dimple, tuft of hair in the sacral region, or absent ankle reflex suggest an underlying vertebral or spinal neurological disorder. In children with various causes of constipation, abdominal distension with a palpable rectal fecal mass may be observed but is most common with functional fecal retention. The skin examination may show pigmentary changes such as those seen with neurofibromatosis, and the neurological examination may suggest underlying disorders such as hypothyroidism or a generalized neuromuscular disorder.

In most patients, a good clinical history and physical examination is usually sufficient to differentiate between functional constipation and Hirschsprung disease (Table 386-2 and Chapter 407) which is the most potentially dangerous diagnosis to overlook. Laboratory studies may include electrolyte, calcium, and magnesium measurements and tissue transglutaminase and thyroid hormone levels. However, no investigations are required in children with a history and findings typical of functional constipation. If simple treatment measures fail to resolve the symptoms, then further diagnostic test may be necessary.

Table 386-2. Differentiating Functional Constipation from Hirschsprung Disease

Judicious use of plain radiograph of the abdomen to document a rectal fecal mass in children who refuse digital rectal examination is helpful occasionally. Barium enema can be used to document the transition from aganglionic to ganglionic bowel if Hirschsprung disease is suspected, but it is not sensitive in the child under 1 year of age. Barium enema, pelvic ultrasound, computerized tomography, or magnetic resonance imaging may all be useful if an anatomic obstruction due to a mass is suspected. Suction rectal biopsy is the most useful test to exclude Hirschsprung disease. Anorectal manometry may be helpful, but it is most useful when biopsy is normal. In these cases, it may aid in diagnosis of anal achalasia (eFig. 386.1 )12 (see Chapter 407). Bowel transit time to evaluate for slow-transit constipation is most easily measured using sitz marker studies.13 These are performed by ingestion of different shaped markers daily for 3 successive days, followed by an abdominal x-ray on day 4. Normal colonic transit time ranges from 50 to 62 hours in healthy children. Single-shape markers ingested once and an abdominal x-ray performed 72 hours later can be sufficient for clinical evaluation of colon transit and is easier and cheaper to perform. In slow-transit constipation, the markers are present in the right colon, and in children with fecal retention, the markers are retained in the rectum. Colonic motor function can be evaluated by colonic manometry in children with chronic intractable constipation not responding to conventional medical therapy.14

TREATMENT

Goals of treatment vary depending on the cause of constipation. In infants, a change to a milk-based formula with a lower casein component or administration of 2 to 4 oz of diluted fruit juice (pear, apple, or prune) is often useful. The value of probiotic and prebiotic formula to attain soft bowel movements is under investigation.15,16 In older infants, administration of higher-fiber foods such as peas, beans, apricots, and prunes is often helpful. In infants over 6 months, treatment with polyethylene glycol 400 or lactulose may be considered.17 If these measures are ineffective, a more thorough evaluation may be indicated. Phosphate-containing laxative should not be used in infants because of a risk of severe hypocalcemia and tetany.18

In toddlers and children, functional constipation is most common. Treatment consists of education, clearance of a rectal fecal mass if present, and then maintenance therapy with laxatives to ensure regular soft bowel movements.1,2Education of the parent and child must include a description of the pathophysiology of the condition. Most parents are convinced that their child has an underlying serious medical condition and need reassurance. Constipation associated with fecal retention is best viewed as an acquired behavioral problem whereby the child has “forgotten” the mechanism for normal stooling. It is especially important for the parents to understand that soiling and overflow incontinence is not a willful and defiant behavior.

The “clean-out” is usually achieved with oral laxatives. Mineral oil or polyethylene glycol electrolyte solution, or both, soften the rectal fecal mass before it is expelled. If the child has not managed to pass the mass within a couple of days, a mild stimulant like senna may be helpful. Rectal disimpaction with an enema is quicker, but passing a large, hard stool can be extremely painful and traumatic for the child.16Polyethylene glycol outpatient clean-outs are successful in most patients such that inpatient admission for a clean-out is rarely necessary. In small children and those with other complicating behavioral or medical conditions, an inpatient clean-out may be preferable to avoid dehydration or fluid overload, both of which can occur during a prolonged clean-out procedure.

Once the rectal fecal mass has been passed, oral maintenance therapy with osmotic agents such as polyethylene glycol 3350 (0.75 g/kg), lactulose (1–3 ml/kg/day of 70% solution, divided BID), or magnesium hydroxide (1–3 ml/kg/day of 400 mg/5 ml liquid), sorbitol (1–3 ml/kg/day of 70% solution, divided BID); lubricants such as mineral oil (not recommended for < 1 yr old, 1–3 ml/kg/day); and stimulants such as senna derivatives or bisacodyl are used.17-22 Polyethylene glycol powder can be mixed with water or juice to make a tasteless, colorless, and odorless solution. Polyethylene glycol is superior to mineral oil or lactulose and senna combination in controlled trials. Advice regarding adequate fiber intake should be given. The role of fiber supplements in treatment of childhood constipation is controversial. The cellulose in the fiber is converted by bacterial cellulase produce by the colonic flora into water and short-chain fatty acids, which produce an osmotic cathartic. There is only 1 controlled trial that shows fiber supplements are better than placebo in the treatment of constipation.20 Frequent follow-up visits and/or phone contact with supportive health care personnel is important in successful management. After several months of painless defecation, medical therapy can be weaned. In some intractable cases, consultation from a psychologist regarding behavioral strategies to modify a child’s defiant behavior and reluctance to sit on the toilet may be beneficial.

In children with underlying organic causes of constipation, correction of the underlying disorder often improves symptoms. In those with uncorrectable disorders, management is directed toward symptomatic relief with dietary measures that assure adequate fiber intake, daily laxative regimens, and, occasionally, enemas to achieve a daily soft bowel movement. In some patients with severe constipation or fecal incontinence, placement of a cecostomy and administration of antegrade enemas may achieve symptom relief and allow a degree of independence in bowel function, especially for adolescents (such as those with spina bifida).23-25

Complications of constipation requiring acute intervention are infrequent. Rarely, the fecal accumulation is so massive that it can result in respiratory compromise from impaired diaphragmatic movement, or there may be a bowel obstruction that contraindicates oral or nasogastric clean-out approaches. Occasionally, repeated vomiting from bowel obstruction can result in dehydration. Hypertonic enemas or excessive oral phosphates may cause dehydration, shock, hypernatremia, hyponatremia, and hyperphosphatemia and are contraindicated in infants or children with renal disease.

OUTCOME

Treatment failure occurs in about 20% of children with functional fecal retention regardless of the treatment approach.26 Children likely to fail are those with onset of symptoms within the first year of life27and those with a long duration of constipation and fecal retention symptoms without therapy. Those children with a negative self-image and children who achieve secondary gain from their persistent behavior also tend to do poorly. Children with attention deficit disorders can be resistant to treatment because they are unable to focus and respond to the urge to defecate. Almost 30% of children suffer from relapses or have constipation in adult life. Some may go on to develop irritable bowel syndrome as adults.