The article Pediatric Anorectal Disorders provides a review of defecation dynamics as well as a discussion on functional constipation and other disorders that may cause constipation. Functional constipation describes all constipation in patients that have no underlying “organic” cause, which means there is no bodily organ causing the problem. In 90-95% of patients, no specific organic cause can be found for their constipation.
For the body to have a bowel movement, the sensitive intestinal lining in the rectal area knows the stool is there, but a conscious decision is made by the individual about whether to push it out or hold on to it. If having a bowel movement is put off to a later time, pushing it out into the anal canal to produce the bowel movement takes a lot of effort that requires contracting abdominal muscles and relaxing the pelvic floor. If this cannot be produced effectively or is difficult, constipation will happen.
In some babies, the first episode of constipation may happen with a change in diet. Retentive posturing, or holding onto poop, is probably the main cause for constipation in toddlers. Other causes of stool withholding behavior include the previous passage of large, hard, or painful stools; anal fissures; significant behavioral problems; lack of time for regular toileting; and distaste for toilets other than the child’s own. When the child has the urge to defecate, he or she assumes an erect posture and holds the legs stiffly together to forcefully contract the pelvic and gluteal muscles. As a result, the rectum accommodates to its content, and the urge to defecate goes away. The retained poop becomes increasingly more difficult to push out, leading to a vicious circle in which the rectum is distended by large fecal contents. Chronic rectal distension may cause overflow incontinence (encopresis), loss of rectal sensitivity, and in the end, loss of normal urge to poop.
The general approach to the child with functional constipation includes education, disimpaction, prevention of re-accumulation of stool and close follow up. A very important first step is managing anxiety for both children and parents, which is followed by behavior modification for regular toileting habits. For children with resulting encopresis, the social impact can be significant. Therefore, a non-accusatory approach is important which includes reassurance and not placing blame. Disimpaction is best accomplished with enemas and/or medications taken by mouth. The goals of medication management are to remove any impacted stool, then to restore normal bowel habits with soft stools that are passed without discomfort and to help patients achieve self-toileting and toileting at appropriate places.