Motility Disorders in Humans: Slow Transit Constipation and Irritable Bowel Syndrome
ACVIM 2008
Gianrico Farrugia, MD
Rochester, MN, USA

Definitions

Slow Transit Constipation (STC)

Less than one bowel movement every three days associated with documented slow colonic transit. Slow transit constipation needs to be distinguished from idiopathic normal transit constipation/constipation predominant irritable bowel syndrome and from pelvic floor dysfunction.

Irritable Bowel Syndrome (IBS)

The Rome II diagnostic criteria for this disorder are: At least 12 weeks, which need not be consecutive, in the preceding 12 months, of abdominal discomfort or pain that has two out of these three features: 1. Relieved with defecation; 2. Onset associated with a change in frequency of stool; 3. Onset associated with a change in form (appearance) of stool. The newly published Rome III criteria require a lower frequency of symptoms than Rome II (at least 3 days/month, that is, at least 10% of the time over the past 3 months for Rome III, compared with at least 25% of the time over the past 12 months for Rome II). The new criteria also distinguish more clearly between IBS subtypes that are now defined as IBS with diarrhea, IBS with constipation, or IBS mixed.

Epidemiology

Chronic constipation is a common complaint. About 5% of the US population complains of constipation, defined as less than 3 bowel movements a week with some studies quoting a much higher prevalence of up to 18%. A subset of patients with constipation have predominantly pelvic floor dysfunction as a cause of their constipation, and a third subset (less than a fifth of patients who seek help for constipation) have slow colonic transit. This subset are referred to as STC. There is a strong female predominance in STC (about 8:1).

Irritable bowel syndrome. IBS is a common disorder effecting 15-20% of the population. There is a slight female predominance in the community, with a more marked predominance in tertiary referral centers.

Etiology

Slow transit constipation: Normal colonic motility is a complex process that required input from nerves extrinsic to the colon, an intact enteric nervous system, an intact interstitial cell of Cajal network, and functional smooth muscle cells. The main features of STC are loss of high amplitude propagated contractions, loss of enteric nerves and loss of interstitial cells of Cajal. Interstitial cells of Cajal are specialized mesenchymal cells that are required for normal gut motility. Interstitial cells of Cajal are found throughout the gut and have 4 main functions. Interstitial cells of Cajal generate the slow wave, required to initiate smooth muscle contraction, they amplify neuronal signals and therefore are required for normal gut neurotransmission, they also serve as mechanosensors and set the smooth muscle membrane potential. In two series of patients with slow transit constipation who came to surgery, a loss of the pacemaker cells was seen in all patients and this loss was not restricted to a particular region of the colon but involved all regions including the cecum. Loss of Interstitial cells of Cajal is very often accompanied by loss of enteric nerves.

Irritable bowel syndrome: Features of IBS include visceral hypersensitivity, increased central processing of peripheral signals and disordered motility. The etiology of IBS is still unknown but there have been recent fairly major advances in our understanding of the disease. There are now data that IBS develops in a subset of predisposed patients after an infectious event and that the composition of the bacterial flora of the gut can markedly influence enteric neuronal function.

Diagnosis

Slow transit constipation: Exclude metabolic disorders (sTSH and Ca2+) and use of drugs used that may cause constipation and exclude other systemic disorders and obstruction. In the patients who do not respond to first line therapy further investigation is warranted. Pelvic floor dysfunction can be assessed by the use of a balloon expulsion test or barium defecography. Dynamic pelvic MRI provides detailed information on pelvic floor function. Transit should be measured using radiopaque markers or scintigraphy. Colonic manometry can provide information on the size of the left colon, baseline motor activity and response to a meal and stimulants such as neostigmine.

Irritable bowel syndrome: There is no specific test for IBS. IBS is diagnosed on the basis of a complete medical history that includes a careful description of symptoms and a physical examination. Diagnostic tests are performed to rule out other problems. These tests may include stool sample testing, blood tests, breath testing, and colonoscopy with biopsies.

Treatment

Slow transit constipation: Despite our classification of constipation into three groups, idiopathic constipation, pelvic floor dysfunction and slow transit constipation, often patients may have both pelvic floor dysfunction and slow transit constipation. As pelvic floor dysfunction may result in slowing of transit through the left colon, it should be treated first before assuming that constipation is refractory to therapy. Dietary fiber supplementation is an effective method of treating constipation, however it may not be of significant benefit in slow transit constipation. The bloating occasionally seen with fiber supplementation is usually more marked in slow transit constipation, perhaps secondary to decreased transit. It is reasonable to attempt a trial of fiber supplementation but the patient should be told to stop after an adequate carefully titrated trial period if symptoms worsen. Laxatives are often useful for mild to moderate slow transit constipation. Choices include osmotic laxatives such as Milk of Magnesia and Polyethylene glycol, and stimulant laxatives such as bisacodyl. I usually use Milk of Magnesia starting at 30cc and titrating up as needed and add Miralax 17g daily if needed. I use Bisacodyl and/or enemas on an as needed basis when the above two medications do not provide adequate relief. The chloride channel opener lubiprostone can also be useful to treat slow transit constipation. In a subset of patients who fail medical management a subtotal colectomy with an ileorectal anastomosis can provide significant symptom relief and is well tolerated. Anorectal manometry is required to ensure adequate anal sphincter function and gastric and small bowel transit needs to be assessed to exclude a pan-intestinal motility disorder. Laparoscopic surgery is now the surgery of choice. Segmental colectomy is not recommended as histological studies point towards a pan-colonic defect in the vast majority of patients with slow transit constipation. Colonic manometry can provide useful information on the response, or lack of, to a meal or a stimulus such as neostigmine. The information provided is useful in informing the decision making process prior to proceeding to surgery.

Irritable bowel syndrome: Treatment of IBS currently focuses on reducing visceral hypersensitivity, usually by using a tricyclic, dietary changes, fiber supplements or laxatives for constipation or medications to decrease diarrhea, such as diphenoxylate hydrochloride and atropine sulfate (Lomotil) or loperamide (Imodium). An antispasmodic may be useful to help to control colon muscle spasms and reduce abdominal pain. Stress management can also be of benefit. Recent data suggest that probiotics may be of significant use in helping with altered bowel habits, bloating and abdominal pain.

References

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Speaker Information
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Gianrico Farrugia, MD
Mayo Clinic College of Medicine
Rochester, MN


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