Functional Constipation (& Hirschprung, CF)

• Constipation is defined as a delay or difficulty in defecation sufficient to cause distress to the patient and refers to abnormalities in stool frequency, size, and character.

• Most children and adults pass from three stools daily to one stool every other day.

• Individuals on a high-fiber diet or vegetarians pass stools with greater frequency than those ingesting a diet low in fiber and high in meat and dairy products.

• Data on stool consistency and size are difficult to obtain, but stools should not be difficult or painful to pass and should not contain blood.

Up to 10% of pediatric patients develop constipation at some time during their childhood. In most, no underlying cause of the constipation can be identified. These patients are classified as having functional fecal retention.

• Voluntary stool withholding is due to fear of defecation (often associated with discomfort)

• Instead of relaxing the pelvic floor during a valsalva maneuver, the patient contracts the gluteal muscles in an attempt to avoid defecation.

• Eventually, the urge to defecate is lost.

• Functional fecal retention typically occurs during toilet training and again upon entrance to school. S

• ome children refuse to sit on the toilet for reasons other than rectal discomfort.

• In older children, the urge to defecate may be suppressed due to the unattractiveness of the school toilet or an unwillingness to interrupt an activity in which they are involved.

• Whatever the cause, failure to defecate is associated with fecal accumulation in the rectum, leading to abdominal pain and distension and a deterioration of mood and appetite. (see Abdominal masses)

DDx

• psychogenic factors (eg, abuse, coercive toilet training, toilet phobia)

• motility disorders (eg, Hirschprung disease, intestinal pseudo-obstruction)

• dehydration and malnutrition

• anorectal anatomic abnormalities

• endocrine or metabolic dysfunction (hypothyroidism)

• neuropathic conditions (eg, myelomeningocele)

• abnormal abdominal musculature

• connective tissue disorders

• pharmacologic ingestion, and botulinism.

If functional constipation persists, progressive fecal retention will occur, resulting in distension of the rectum, rectal inertia, and the presence of large volumes of fecal material in the distal colon, as reported for the boy in the vignette. Intermittently, a firm stool of unusually large size may be passed with significant effort.

The management of functional constipation can be difficult and frustrating to the child, his or her family, and the medical professional. Unless there is an understanding of the etiology, pathogenesis, and treatment of this disorder, successful therapy is difficult.

• Once functional fecal retention is identified, treatment can be started without embarking on a series of tests.

• Evaluation should be considered in cases in which therapy is unsuccessful or the constipation recurs after successful treatment.

• treatment focuses primarily on education, softening and elimination of retained feces, prevention of further fecal retention, and patient and parental support.

Meds

• lubricants (eg, mineral oil)

• osmotic agents (eg, lactulose or milk of magnesia)

• stimulants (eg, senna derivatives).

• Dosages should be titrated to produce the desired results, typically the passage of one large, soft, nonpainful stool daily.

• Sitting on the toilet with foot support in an unhurried time of day is a helpful adjunct to pharmacologic therapy.

• Treatment failures occur in approximately 20% of patients, often due to poor compliance, premature  discontinuation of therapy, or significant psychosocial abnormalities.

Rectal prolapse

Although cystic fibrosis can present with constipation and rectal prolapse, the disorder is much less common than functional constipation. In most children, prolapse is associated with malnutrition rather than due to cystic fibrosis alone. In patients who have rectal prolapse, a sweat chloride analysis may be useful.

Hirschsprung

Hirschprung disease and hypothyroidism rarely cause rectal prolapse and present with normal or increased rectal tone. In Hirschsprung disease, the rectal vault is empty.

Intestinal pseudo-obstruction (primary intestinal myopathy or neuropathy) can present in a similar fashion to functional constipation, but it is a rare disorder. Abdominal radiographs reveal signs of obstruction, including distended bowel loops with air-fluid levels.

References:
Hyman PE, Fleisher DR. A classification of disorders of defecation in
infants and children. Semin Gastrointest Dis. 1994;5:20-23
Nolan T, Oberklaid F. New concepts in the management of encopresis.
Pediatr Rev. 1993;14:447-451
Seth R, Heyman MB. Management of constipation and encopresis in
infants and children. Gastroenterol Clin North Am. 1994;23:621-636