Constipation, a common complaint in the pediatric age group, may be associated with significant functional disability and family discord. Although it is usually easily remedied in the acute stage, the patient frequently presents long after its initial appearance when the symptoms may be more intractable and difficult to tolerate. The symptoms are difficult to define because interpretation of the normal defecation pattern is to some extent subjective and varies with the observer. There is a lack of general agreement on the norms for stool frequency, size or consistency, with considerable uncertainty on how much deviation is required to warrant the label of constipation.
Stool frequency is the easiest parameter to quantify. Studies have shown that most adults pass at least three stools per week. ' Infants and children appear to show decreasing frequency with age, so that review of a number of studies reveals a decline from more than four stools per day during the first week of life to 1. 2 per day at 4 years of age.2'5 Infants with no difficulty other than fewer numbers of stools than average seem to constitute a disproportionate percentage of those who later develop frank constipation.6 This implies that recognition of the trend toward decreased stool frequency in the first years of life may lead to more timely intervention and possible avoidance of chronic constipation in later years.
Our knowledge of the interrelationship of the various autonomic and conscious controls over the sensory and motor components of the anorectal region is far from complete. Although a detailed description of the region is beyond the scope of this article, some review of its features is necessary to elucidate some of the pathophysiologic concepts.7
The specialized anatomy and physiology of the anorectal region determines the combination of physical factors and reflexes that control defecation. The lumen of the rectum ends at the pelvic floor where it passes through the levator ani muscles and continues as the anal canal. This canal is surrounded by the internal and external sphincters, which overlap each other to a considerable extent (Figure). The downward continuation of the circular smooth muscle layer of the rectum becomes three to four times thicker to form the internal sphincter. The external sphincter is made up of striated muscle with various attachments at different levels. Both the internal and external sphincters have a resting tone which creates the high pressure region of the anal canal. This zone represents a barrier to rectal pressure and is thought to be a mechanism for anal continence. The axis of the rectum forms approximately a right angle with the axis of the anal canal and is created by the continuous tonic contraction of the striated puborectalis muscle. This angle is present except when the hips are flexed more than 90 degrees or during defecation. This angulation is one of the most important mechanisms for gross fecal continence.
Distention of the rectum by a bolus of stool from more proximal bowel results in characteristic reflex relaxation of the internal anal sphincter and simultaneous contraction of the striated external sphincter. This reflex relaxation of the upper anal canal allows rectal contents to come in contact with the highly sensory epithelium in the canal. This helps distinguish the nature of the contents as solid, liquid, or gaseous, and produces the urge to defecate. For defecation, the external anal sphincter is relaxed, and the puborectalis sling is adjusted such that the lower rectum and anorectal canal propel stool out upon an increase in abdominal pressure (Valsalva's maneuver).
PATHOPHYSIOLOGY OF FUNCTIONAL CONSTIPATION
Failure of any portion of the mechanism for defecation results in difficulty with evacuation. Recent research, consisting principally of anorectal manometric studies, has provided some explanation for chronic constipation. Studies have demonstrated failure of external sphincter relaxation during defecation in some encopretic children,8,9 and impaired rectal and sigmoid sensation10,11 particularly in the constantly stretched rectum of encopretic children. However, it is unclear whether these are primary or secondary to prolonged constipation. Although these types of studies give hope for a better understanding of the mechanism of prolonged constipation, the role of these abnormalities remains unclear.
Genetic predisposition to the condition appears to be a major factor. Between 38%12 and 65%6 of children with constipation demonstrated a tendency toward constipation before 6 months of age, often in the earliest weeks of life before there were significant variations in diet, habits, or attitudes. In one study of twins, concordance for constipation was demonstrated to be six times greater among identical compared with fraternal twins. This finding is generally taken to indicate the importance of heredity over conditioning for a symptom.13
Waves of increased pressure in the rectum of constipated infants with colic have been shown to be similar to those in some adults with constipation or irritable bowel syndrome.14 The increased ability of constipated children to absorb water in the distal colon has also been shown. 15 The infant with a tendency to constipation thus may have increased tonus in the distal colon associated with delay in stool passage and excessive drying of the intraluminal contents. The early tendency for constipation is often missed in the neonate, since the infant who eliminates stool once or twice a day is usually not considered to be constipated, even though these numbers represent a lower than average frequency. However, between 6 and 12 months of age, as the number of stools per day decreases in accordance with normal growth,5 such an infant often begins to skip days and starts to eliminate small dry scybala. This constipated state might have been anticipated in the neonate.
Figure. Drawing of anorectal anatomy.
Between the ages of 1 to 2 years, some constipated children may develop a new set of problems related to fecal retention. It develops gradually in some as a consequence of the decreased frequency of stool passage, with increasing difficulty in passing the resultant excessively firm stools. In other children, an acute episode of constipation may follow a change in diet (eg, human to cow's milk), febrile illness, period of dehydration, or bedrest. With increasing awareness that defecation is under voluntary control a child might begin to withhold stool in an attempt to avoid the pain of these severely constipated stools.
The "stool withholding" behavior is often erroneously interpreted by the parents to be extreme straining to pass a stool. The child will often retire to a corner of the room to hide or to grip a piece of furniture for reinforcement, squeeze the buttocks together, assume a longitudinal posture by standing or lying supine, and turn red with or without crying. The rectum accommodates the contents and the urge to defecate passes. This behavior initiates a vicious cycle in which successively greater amounts of stool are built up in the rectum. The resultant larger bowel movements ultimately are passed with even greater pain, reinforcing the desire to withhold. Persistence of this situation leads to permanent stretching of the rectal wall, which produces the state of rectal distension known as megarectum. Ultimately, the rectum reaches a maximal size and can be stretched no further because of the enclosing pelvic bones and contained structures. The force of the fecal mass shortens the anal canal and softer stool begins to leak to the outside involuntarily. This condition of incontinent stool soiling unrelated to any organic defect or illness is called encopresis. ,6 Levine found a mean age of 7 years 4 months for encopresis.12 That this overflow soiling without the perceived urge to defecate is involuntary is often difficult for parents to accept and is frequently a major issue of contention between parent and child. The parents often date the onset of their child's problem to the sudden appearance of this soiling. Rectal manometric studies suggest that the constantly stretched rectum of encopretic children exhibits decreased sensitivity to distention.17 The child, therefore, has a lessened sense of rectal fullness with infrequent urge to defecate.
Conditions Associated with Constipation
Drugs Used in Children That May Cause Constipation
The term "psychogenic constipation" is unfortunately often applied to those children with functional constipation in whom fecal retention and megarectum occur. Although emotional and behavioral problems may be significantly associated with stool withholding and soiling, use of appropriate therapy which corrects the physical problems often leads to resolution of the emotional tensions. This suggests that generalizations should not be made regarding psychological factors as the cause or effect of constipation and encopresis. It is a disservice to the child, the family, and the practice of medicine that some physicians look for the cause of encopresis solely in the emotional relationships between the child and family. By contrast, an uncommon state of nonretentive soiling exists which is often associated with serious underlying psychiatric problems.
DIFFERENTIAL DIAGNOSIS OF CHRONIC CONSTIPATION
The symptom of constipation is associated with many disorders. Table 1 lists some of the conditions associated with constipation. Table 2 lists some of the medications that may promote constipation principally by hypomotility. However, in the vast majority of children no associated abnormality is found, and the term chronic functional (idiopathic) constipation is usually applied. The distinction among the specific diagnoses rests principally on a detailed history and physical examination, with knowledge of the natural history of functional constipation. Extensive laboratory, radiologic, and endoscopic examinations are usually unwarranted.
When taking a patient's history, special attention should be paid to stool frequency and size, the age of onset, dietary patterns, family history of constipation and functional bowel difficulties, evidence of whether the child perceives the urge to defecate, withholding behavior, and the presence of soiling. The physical examination is important for assessing the abdominal contents and wall strength, neurological status of the lower extremities and abdominal wall, anal tone, and size of the ampulla. Abdominal distention is frequently not marked in patients with functional constiparion, but fecal masses are often felt above the pubic symphysis and in the lower quadrants. Rectal examination may reveal an ectopic anal opening, anal fissures, stool outside the anus in the gluteal area as evidence of soiling, a tight rectum with small scybala, or the presence of a large amount of low-lying stool in a capacious rectum. Physical signs of underlying disorders include a patulous anus with neurologic disease, flat buttocks with sacral agenesis, and a pilonidal dimple with spina bifida occulta.18
The most frequent organic differential problem in patients with constipation is Hirschsprung's disease (congenital megacolon). The conditions may almost always be distinguished, except in the newborn period, by significant differences in history and physical examination. The urge to defecate is not appreciated by patients with Hirschsprung's disease since their obstipated stools are held up proximal to the lower portion of the rectum, where the proprioceptors for defecation are located. Regardless of whether a child is attempting to have a bowel movement or to withhold, evidence of stiffening, squeezing and crying indicates that stool is regularly being propelled to the rectum and renders unlikely the diagnosis of a problem more proximal. Patients with Hirschsprung's disease rarely soil since the retained stool is proximal to the rectum and involuntary passage of feces from an overfilled rectum is unlikely. On digital examination, the anal canal and rectum are almost always free of feces in the child with Hirschsprung's disease, whereas in the child with retentive constipation this region is usually packed with stool.
Therapy for chronic constipation should be appropriate to the particular developmental stage of the disorder. In patients with acute constipation, various dietary maneuvers may be employed to control mild symptoms. For example, between 6 and 12 months of age infants have less difficulty with constipation when ingesting mother's milk or formulas with a higher lactose content than that of cow's milk. Addition of laxative fruits (eg, prunes, apricots, plums) and fibrous vegetables may compensate for an inherent tendency to constipation. In some instances a mild laxative must be prescribed to increase stool softness via colonic fermentation and gentle stimulation. Carbohydrate preparations such as malt soup extract which are difficult to digest and pass largely unchanged to the colon to undergo bacterial action are preferable. Addition of senna extract to the malt soup preparation may be required to offer a mild stimulant in cases of severe early constipation.
If stools become so hard that they are difficult for an infant under 4 to 5 months of age to pass, glycerin suppositories or rectal stimulation with a thermometer are preferable to fermentative laxatives. During the first months of life, excessive gaseous distention from fermentation might make a constipated colicky infant more uncomfortable and irritable.
Treatment of Chronic Retentive Constipation
Overbearing preoccupation with bowel movements is certainly not desirable in the vast majority of children, but attention is necessary for constipated toddlers because benign neglect can result in a pattern of chronic constipation which progresses to voluntary stool withholding and eventual development of megarectum and encopresis. Therefore, early attention to the possible need for laxative foods or medications in the first year of life continues to be important through the second year and beyond.
For children with chronic constipation and an enlarged rectum who progress to encopresis, the principles of therapy are different from those for simple "spastic" constipation. Before therapy is outlined, parents should be educated to the natural history of constipation and be made to understand that stool withholding is induced by attempts to avoid painful defecation. Any accompanying soiling occurs involuntarily without the knowledge or control of the child.
The initial phase of therapy is disimpaction (Table 3). This can be achieved most efficiently by instructing the parents to administer a sodium biphosphate enema (3 mL/kg) each morning and evening until the effluent contains no solid stool (usually two to six enemas). Since sodium biphosphate enema abuse can result in hypematremia or hyperphosphatemia, no more than two enemas each day for the initial three days should be advised.
The next phase of treatment is aimed at preventing the reaccumulation of retained feces and overcoming stool withholding. Prescribing a sufficient dose of stimulant laxative containing senna, milk of magnesia, or cascara to "force" one or two stools daily should be sufficient. The usual dosage of senna for children greater than 1 year of age is 1 to 2 teaspoons daily. Occasionally the medication can be timed to have its effect (usually six to eight hours later) when the child is most likely to use the toilet.
Children in whom an impressive megarectum has developed often require that this regimen be continued on a prolonged basis.. To achieve a more definitive solution to the problem, the rectum must return to a more normal caliber, which would allow for daily urges to defecate. To accomplish this, an empty state in the rectum must be maintained for three to four months. This could be approximated by the use of laxatives in sufficient dosage to ensure passage of four to six loose stools daily. Because there would be too much pain and discomfort with such doses of any stimulant laxative, Davidson6 introduced the use of a high dose mineral oil regimen. The usual starting dose was 5 mL/kg divided twice daily to limit the possible interference with lipid absorption. However, this rigorous, high dose mineral oil regimen is distasteful and difficult for most, and thus has largely been abandoned. Forcible administration to a resistant child should never be attempted for fear of aspiration.
The third stage of treatment is aimed at establishing a behavioral pattern of regular bowel movements. Although evidence is sparse for recommending regular bowel habits for normal individuals, the patient with chronic constipation should be encouraged to establish a routine. If such an individual relies on the normal physiologic urge, there may be recurrent difficulty from accumulation of hard stools. Conditioning to more frequent elimination assures softer stools and seems reasonable in children old enough to cooperate (ie, those over 3 to 4 years of age). To take advantage of the gastrocolic reflex the child should sit on the commode for 15 minutes after a particular meal with proper foot support for leverage. Over the ensuing months the laxatives should be gradually withdrawn in those with normal sized rectums, and a regular bowel habit should be formed, with success rates approaching 90%. 6 The nonresponders frequently may benefit from more formalized behavior modification therapy. Parents should be cautioned to expect occasional bouts of acute constipation which should be treated promptly to avoid a recurrence of chronic problems.
Children with voluntary fecal incontinence without megarectum and impaction (a distinct minority of less than 1%) are tesistant to treatment.16 These children often have severe behavioral disorders and require psychiatric evaluation and treatment.
The role of diet in chronic constipation of toddlers and school age children should be reviewed with the parents. Pediatrie constipation is engendered by a sequence of maladaptive behaviors. Although dietary therapy may be helpful, attempts at major changes in diet ate usually unproductive and often promote greater parent-child discord. General mention should be made of the benefits of adequate fluid ingestion, limited milk consumption, and the benefits of dietary fiber. Bran in the form of muffins, or a psyllium seed preparation can be used in the older child with spastic constipation.
Although constipation is considered by many to be a trivial condition not worthy of careful attention, the amount of disordered family interaction and functional disability which can be relieved promptly by proper therapy continually confirm its importance to the caring physician.
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Conditions Associated with Constipation
Drugs Used in Children That May Cause Constipation
Treatment of Chronic Retentive Constipation