The Colorectal Quiz Episode 23: Hirschsprung Disease - The Soiling Patient Part 2 -The Dentate Line and Motility

The three components of continence are quality of sphincters, quality of dentate line, and motility.

In Hirschsprung's disease there are two sphincters of concern: the external sphincter (which patients have voluntary control of) and the internal sphincter (which tends not to relax due to absent recto-anal inhibitory reflex).

If a patient has voluntary bowel movements during the day but accidents at night when sleeping, their external sphincters are working but internal sphincters are not—when sleeping they relax the external sphincter and lose control.

The dentate (or pectinate) line is the transition from squamous epithelium to columnar epithelium, occurring about two-thirds of the way up the anal canal, with associated changes in blood supply (splenic versus systemic) and innervation.

The nerves in the dentate line region tell you gas versus liquid versus solid, how hard to squeeze, how long to squeeze, and how tight to squeeze—preserving this region is key to continence.

The rectum (not the anal canal) has proprioception capacity to detect stretch, which signals stool accumulation and triggers external sphincter contraction to hold stool until a bathroom is found.

In anorectal malformation patients, stool softeners are problematic because patients never feel the stretch—they just have loose stool flowing; they are better off with bulk kicked out by a laxative than a stool softener that slowly oozes out.

For children with anorectal malformation, Hirschsprung's disease, or spinal conditions, their ability to sense stool in the rectum or neorectum is so sensitive to success that the right consistency and bulk of stool is very important.

If clinicians make stool too soft or too loose through medications, they throw a child with borderline control over the edge into failure.

Loose stool is the enemy of borderline continence because you don't know for sure that it's there—we are very dependent on the stretch and bulk of stool in the rectum to trigger the external sphincter and relax the internal sphincter.

Patients with Hirschsprung's disease with absolutely intact sphincters are dependent on rectal stretch; they don't have a rectum (it's been removed) and their sigmoid has taken over that job—if they have injured sphincters they are particularly in trouble.

A patient with missing dentate line (from dissection started too low) loses all anal canal sensation but can still develop bowel control if sphincters are working, though they will be very sensitive to loose stool and need bulk to detect stool presence.

A patient with missing dentate line but intact sphincters is similar to an anorectal malformation anastomosis (rectum or colon mucosa to skin) and should be able to achieve continence if muscle is intact.

On contrast study, a colon that moves too fast shows smaller caliber with many haustrations (appearing as contractions), while a colon that moves too slow shows dilation with lack of haustrations.

For a hypomotile (slow-moving) colon with intact sphincters and dentate line, treatment can start with mechanical emptying then switch to laxative program; if sphincters and dentate line are deficient, mechanical enema program is needed.

For hypermotile patients (7-8 stools daily), treatment involves constipating them and then ensuring timed emptying—either spontaneous if sphincters intact or mechanical if deficient.

The treatment approach for hypermotile patients is to constipate them, then figure out how to empty them in a time-controlled fashion to maintain mechanical or social continence, depending on sphincter function.

Hirschsprung's is an obstruction problem that has been solved by surgery; the separate challenge is getting patients clean, which depends on whether they are too slow or too fast and whether they have the mechanisms for continence (sphincters and dentate line).

For hypermotile patients, treatment escalates through: skin care with cyanoacrylate barrier, proton pump inhibitor to reduce stool acidity, small volume enemas, water-soluble fiber for bulk, loperamide (0.5-0.8 mg/kg divided daily), cholestyramine, hyoscyamine (0.125 mg every 6 hours), and rarely diphenoxylate-atropine (which has cardiac side effects).

Tincture of opium is useful for slowing hypermotility but is a controlled substance and difficult to prescribe.

Botox may be needed for patients with good pull-through who are not emptying, to help them train and control non-relaxing sphincters and stop being withholders.

Some Hirschsprung's patients with good operations have super-strong sphincters that need relaxation (via Botox) to allow stool passage until they learn proper external and internal sphincter coordination for evacuation.

Anorectal manometry can provide objective data showing that resting pressures in some Hirschsprung's patients are on the higher end of normal, indicating need for relaxation therapy.

Patients with Hirschsprung's disease are very sensitive to some foods, particularly lactose, and paying attention to diet (from breastfed infants through older children) is important.

Every soiling patient can be made to do well with appropriate help (mechanical evacuations, Botox, etc.) and can be gotten on the right track.

Of all soiling populations (anorectal malformation, Hirschsprung's, functional constipation, and spinal), Hirschsprung's is the hardest group because the sphincters are so troublesome.

Within Hirschsprung's soiling patients, the hypermotile group is much harder to manage than the hypomotile group.