Constipation is defined symptomatically as the infrequent passage of hard stools, straining while passing a stool, or pain associated with the passage of a hard stool. The range of normal defecation patterns in children is widely variable, though in general, formula-fed infants may have 4-5 stools per day in the 1st weeks of life while breast-fed infants usually pass softer and more frequent stools. Stool frequency in both gradually decreases to 1-2 per day by 1 year of age. Most children aged 1-4 years have 1 or 2 daily bowel movements, with a range of 3 daily bowel movements to 1 bowel movement every other day.
(See Nelson Textbook of Pediatrics, p. 868.)
Constipation is classified broadly either as functional or as secondary to underlying conditions, such as anatomic abnormalities, metabolic disorders, neurologic dysfunction, or medication effects ( Table 16.1 ). The majority of childhood constipation is functional. The Rome III Criteria for Functional Gastrointestinal Disorders defines functional constipation in 2 age groups as noted in Tables 16.2 and 16.3 .
Functional
Anatomic
Endocrine
Genetic/Metabolic
Infectious
Abnormal Innervation/Neurologic
| Neurologic/Spinal Cord Lesions
Psychologic
Medications
Other
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Diagnostic criteria Must include 1 mo of at least two of the following in infants up to 4 yr of age:
Accompanying symptoms may include irritability, decreased appetite, and/or early satiety. The accompanying symptoms disappear immediately following passage of a large stool. |
Diagnostic criteria * Must include two or more of the following in a child with a developmental age of at least 4 yr with insufficient criteria for diagnosis of IBS:
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* Criteria fulfilled at least once per week for at least 2 mo prior to diagnosis.
Changes in diet, such as formula changes or the addition of solid foods, may lead to transient constipation in infants. Minor illnesses, including infectious diarrhea, can subsequently result in episodic constipation as well. More long-standing constipation is often secondary to inadequate intake of dietary fiber, fluid, or both. The evaluation of constipation involves first determining whether the change in the frequency or consistency of stools is secondary to functional constipation or is related to an underlying organic disorder. This determination is based on identifying historical features and examination findings that suggest an underlying disorder and prompt further investigation.
Physiology of Normal Defecation and Constipation
Fecal continence and physiologic defecation are dependent on the anal inhibitory reflex , which is in turn dependent on the proper structure and function of the internal and external anal sphincters and the pelvic floor. The internal anal sphincter is an involuntary muscle that is contracted at rest. When a bolus of stool distends the rectum, the internal anal sphincter relaxes. This process generally results in the child sensing the need to defecate. The external anal sphincter and the puborectalis muscle of the pelvic floor, under voluntary control, contract upon rectal distention, respectively closing the anus and decreasing the rectoanal angle, thus allowing the child to hold stool until it is socially convenient to defecate. Voluntary relaxation of the puborectalis muscle and the external anal sphincter straightens the anorectal angle and allows the child to stool. In situations where there is encopresis secondary to overflow incontinence , the child typically consciously withholds stool by refusing to relax the external anal sphincter in the setting of a relaxed internal anal sphincter. Over time, the child is not able to keep the external anal sphincter fully contracted and stool leaks out of the anal canal. The presence of overflow incontinence is an important indicator that the anal inhibitory reflex is likely intact, as patients with anatomic or neurologic abnormalities of the distal colon and internal anal sphincter are unable to reflexively relax the internal anal sphincter to allow for the passage of stool.
Patients with chronic constipation have physiologic abnormalities upon anorectal manometric evaluation. The most consistent abnormality is blunted rectal sensation, rendering the patient unable to feel the bolus of stool in the rectum. Other findings include incomplete relaxation of the internal anal sphincter and paradoxical contraction of the external sphincter during attempted defecation. Patients who have paradoxical anal contraction are less likely to respond to routine medical therapy or may be more likely to have recurrent constipation if treatment is withdrawn.
Data Collection and Assessment
History
Functional constipation may be distinguished from secondary causes of constipation by assessing the age of symptom onset, the stool consistency, and the presence of associated signs or symptoms.
The age at symptom onset differentiates disease processes that are congenital versus those that are acquired. Failure to pass meconium within the first 48 hours of life suggests a diagnosis of Hirschsprung disease ; however, up to 50% of patients with Hirschsprung disease will pass meconium prior to this. In addition to Hirschsprung disease, constipation in the 1st month of life or a history of constipation since infancy suggests organic causes ( Table 16.4 ). The appearance of symptoms beyond infancy suggests acquired organic constipation or functional constipation.
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Stool consistency in constipation can differ by etiology. Functional constipation tends to produce large, bulky stools, whereas constipation secondary to Hirschsprung disease or other organic etiologies tends to produce harder, pebble-like, or ribbon-like stools. Stool consistency may be objectively rated via use of the Bristol stool scale ( Fig. 16.1 ), and can be used to follow response to therapy.
The assessment of associated signs and symptoms should include evaluating for a history of blood in the stool, as well as for the presence of urinary symptoms. Bright red blood on the surface of the stool suggests an anal fissure indicative of straining, which is seen in approximately 25% of patients with constipation. Blood on the periphery of the stool may suggest pathology in the distal colon or anorectal vault.
Urinary symptoms may take the form of either retention or incontinence. Retention may be secondary to congenital or acquired abnormalities in the neurologic regulation of bladder voiding and may be associated with similar abnormalities in the regulation of defecation. Alternately, retention may be secondary to urinary tract outflow obstruction, which is secondary to a large stool burden. Incontinence may be due to a large stool mass distending the rectum and placing pressure on the posterior bladder wall, or may indicate overflow incontinence in the setting of a neurogenic bladder. Urinary retention is also seen in patients with chronic intestinal pseudoobstruction and is thought to be secondary to autonomic dysregulation.
Abdominal pain is common in constipated patients; when present, it is often mild, nonspecific, and periumbilical. Older children may describe discomfort in the lower abdomen and a history of relief of pain after a stool is passed. Appetite is often diminished. A diary recording the passage of stools, the timing of meals, and the onset of abdominal pain over a period of several days to a few weeks can aid in the diagnosis of constipation and in monitoring of therapy. The personal medical history and the family history may reveal illnesses and conditions associated with constipation ( Table 16.5 ; see Table 16.1 ).
