Defecation Disorders After Surgery for Hirschsprung's Disease

A majority of treated children with Hirschsprung's disease suffer from chronic constipation, incontinence, and/or abdominal pain. Over half experience incontinence (1), and 20% endure constipation (2). Recent studies clarified causes for persistent symptoms after successful surgery (3). The child is not lazy or uncooperative, but has treatable physiological reasons for symptoms. Constipation there are three mechanisms for constipation following successful Hirschsprung's disease surgery: functional constipation (also called functional fecal retention or retentive constipation), neuropathy proximal to the aganglionic segment, and hypertensive anal sphincter. History and physical examination do not distinguish among these conditions. Colon and anorectal manometry clarify the diagnosis. Functional constipation arises most often following a painful bowel movement. The child avoids defecation, and after a few days has a bigger, more painful bowel movement. Children with Hirschsprung's disease are more likely to acquire functional constipation than healthy children, because of the many painful experiences around the pelvic floor. Post pull-through diarrhea may injure sensitive skin under the diaper, and the child recognizes pain after bowel movements. A few children require anal dilations when there is scar formation that narrows the neorectal lumen. Dilations without analgesia and sedation may be painful, frightening events that discourage defecation. Sometimes clinicians suspect that enterocolitis is brewing, and order repeated enemas and washouts. These procedures prevent the child from learning pelvic floor control, and provoke fear and retentive behavior. Then the infant's abdomen swells from retaining stool, and the clinician's concern grows, so that the cycle of fear (for clinician, parents, and child) and pain (for the child) is perpetuated. Treatment begins with educating the child and parents about functional constipation (4). Functional constipation is not a dangerous disease, but a maladaptive response to painful defecation. The colon cannot burst. Toxins do not leak back into the body. Non-stimulant laxatives are safe. The clinician prescribes an oral osmotic laxative to melt away the stool mass. Evacuating the stool mass is no emergency, and the more important goal is to return control of the child's pelvic floor to the child. Weekly visits reassure the family and clinician, who listens to the parents' concerns and evaluates the stool mass by feeling the abdomen. The child learns to relax the pelvic floor only after fears, real or imagined, disappear. After the stool mass is gone the laxative is continued for months, until the child and the parents are confident that toilet skills are complete. About 10% of children with Hirschsprung's disease have neuropathy proximal to the aganglionic segment. Children with neuropathy proximal to the aganglionic segment have abnormal colon manometry. There may be a segment with 1) persistent pressure that fails to relax, 2) simultaneous contractions, but no coordinated, propulsive contractions, or 3) no contractions. Most often neuropathy is congenital. Occasionally there may be a transient, treatable neuropathy due to persistent effects of inflammation after Hirschsprung's enterocolitis. When there is a history of enterocolitis anti- inflammatory drugs (eg sulfasalizine) or antibiotics (eg metrinidazole or clarithromycin) may speed recovery. When there is no history of enterocolitis, one treatment choice is laxatives to maintain watery stools for life, so that stools flow downstream without effective colon motility. When the neuropathy involves a long colon segment but small bowel is spared, surgery to remove the neuropathic colon is a better solution. Colon manometry discriminates functional constipation from colon neuropathy. The child is sedated for anorectal manometry and colon manometry catheter placement. Anal sphincter pressures are increased by fear, and frequent movement artifacts confound the interpretation of the recto-inhibitory reflex, so that anal sphincter testing is more accurate when accomplished under propofol anesthesia (5). A colon manometry catheter with recording sites spaced 10 or 15 cm apart is placed through the anus to the cecum. As the child wakes, the colon study begins. Parents are encouraged to comfort the child, and to ask questions about the study as they watch the results appear on the bedside computer screen. After an hour, the child eats lunch. Food increases contractions in healthy colons, defining the gastrocolonic response. In normal children and children with functional constipation the colon makes high amplitude propagating contractions (HAPCs), the physiologic marker for colon neuromuscular health. HAPCs are strong coordinated contractions that move colon contents towards the anus. During HAPCs children with functional constipation become distressed, or stiffen and straighten their legs in retentive postures. The examiner can point out to the child that the HAPC on the computer screen correlates with abdominal discomfort or the urge to have a bowel movement. This portion of the test provides an opportunity for biofeedback, as the examiner instructs the child that the sensations are normal, and suggests to the child that defecation relieves discomfort. In neuropathy HAPCs and the gastrocolonic response are absent. If there are no HAPCs before or after the meal, the examiner gives the stimulant laxative bisacodyl through the catheter into the proximal colon. In children with functional constipation bisacodyl stimulates HAPCs (6). In neuropathy, there are no HAPCs after bisacodyl. If HAPCs are present, the problem is functional constipation (7). Hypertensive anal sphincter is the least likely cause of constipation, affecting about 5% of symptomatic children after Hirschsprung's disease surgery (3). Experienced surgeons have moderate success with anal myotomy for constipation (8). In children with hypertensive anal sphincter, pressures are so high that stool cannot pass even when there is an HAPC. Hypertensive anal sphincter is diagnosed by anal manometry when the child is asleep (9). If the child is awake, false positive results occur because the child tenses with fear when a tube is inserted through the anus. Botulinum toxin injection treatment often fails, immediately or within a few months after a transient response (10). Surgical sphincterotomy should be considered when a hypertensive anal sphincter is documented by manometry under anesthesia. Fecal incontinence in postoperative Hirschsprung's disease may be a consequence of functional constipation or HAPCs through the neorectum. In a healthy colon several times each day HAPCs begin in the cecum and dump the colon contents into the rectum. Defecation is voluntary, in part because the rectum accommodates to stool volume. After Hirschsprung's surgery, the rectum is gone, and HAPCs move colon contents to the anal verge with neorectal pressures that often exceed the anal sphincter pressure. The child has two choices: relax the sphincter and experience incontinence, or hold tight and indure crampy pain. When the colon is transected, instead of several HAPCs each day, there may be several each hour (11). In health there are no HAPCs during sleep, but after colon transaction, HAPCs may occur during sleep, causing incontinence. Day and night incontinence improves in most instances with amitriptyline at bedtime, starting with 0.2-0.3 mg/kg/night, and increase by 0.2 mg/kg/w until the problem stops, or at 1 mg/kg/night, whichever comes first. Amitriptyline's anticholinergic effects probably reduce the pressure waves pushing out the stool, and its effects on sensory afferent nerves and central arousal reduce chronic pain. The second cause of fecal incontinence is functional constipation. A large stool accumulates in the neorectum as the child suppresses defecation. However, the child must pass flatus. The sensitive anoderm can detect the difference between hard stool and gas, and between hard stool and liquid, but not between gas and liquid. Occasionally, some liquid stool oozes around the fecal mass. When the child relaxes the anal sphincter and passes gas, liquid that has seeped around the hard stool leaks out at the same time. Many children over 4 years of age blame absence of anal and colon sensation for incontinence. Colon and anal sphincter sensation are never affected by Hirschsprung's disease. The child may be having a problem with misunderstanding the afferent signals, but restoring the brain's recognition of normal sensations is part of the child's responsibility as he acquires normal toilet behaviors. Abdominal pain may occur whenever the child senses a defecation urge, but tightens the sphincter to avoid defecation. Some children with a gastrocolonic response perceive those contractions as pain rather than a defecation urge, so that the child no longer recognizes the call to stool. This perception alteration from a sensation that does not hurt to one that does is called hyperalgesia. Hyperalgesia is caused by physiological changes in the pain nerves that run from the gut to the brain, and pain centers in the brain. A child who has had early life pain experiences like surgery for Hirschsprung's disease is at risk for developing hyperalgesia. Drugs such as amitriptyline and gabapentin slowly reverse visceral hyperalgesia. For school age children cognitive behavioral therapy (CBT) may be used instead of or in combination with drugs. CBT teaches the child to use adaptive ways of thinking to take control of pain centers that may seem out of control.