Q.How does one diagnose and manage chronic large bowel diseases in dogs?
A. Dr. Michael S. Leib of the Virginia-Maryland Regional College of Veterinary Medicine gave a lecture on chronic large bowel diseases in dogs at the at the 2004 Western Veterinary Conference in Las Vegas, Nevada. Some relevant points in this lecture are provided below.
Chronic large bowel diarrhea is often characterized by hematochezia, excess fecal mucus and tenesmus. The frequency of defecation is increased, and the quantity of feces/defecation may be reduced. Weight loss is uncommon. Common causes include highly digestible diet responsive diarrhea, whipworms, Clostridium perfringens enterotoxicosis, irritable bowel syndrome, fiber-responsive large bowel diarrhea and neoplasia. A thorough diagnostic plan should be followed to reach an accurate diagnosis efficiently. The diagnostic plan may include multiple fecal examinations, rectal cytology, elimination of dietary indiscretion, feeding a highly digestible diet for three to four weeks, treatment for whipworms, assessment of CBC, serum chemistry profile and urinalysis, and flexible colonoscopy with multiple mucosal biopsies.
After the diagnostic work-up, it is common to identify no abnormalities and, hence, make the diagnosis of chronic idiopathic large bowel diarrhea. The affected dogs usually have irritable bowel syndrome, fiber-responsive large bowel diarrhea or Clostridium perfringens enterotoxicosis in which rectal cytology has not identified an abnormal number of spores (Leib MS and Monroe WE. Practical Small Animal Internal Medicine. Philadelphia, WB Saunders, 1997:736-738).
Irritable bowel syndrome Irritable bowel syndrome (IBS) is a commonly diagnosed, but poorly described, functional disorder of the intestines that occurs in dogs. Synonyms include spastic colon, nervous colitis and mucus colitis. Colonic dysfunction exists in the absence of structural, biochemical, or microbiologic abnormalities. Diarrhea is often intermittent, and hematochezia is uncommon. Bloating, nausea, vomiting and abdominal pain may occur. Often stressors can be identified that are associated with development of cyclic clinical signs. Dogs might be nervous, high-strung or have abnormal personality traits.
The identification of abnormal personality traits or stressors that initiate episodes of diarrhea in a dog with chronic idiopathic large bowel diarrhea is strongly suggestive of IBS. If the dog responds to dietary fiber supplementation, the condition is referred to as fiber-responsive large bowel diarrhea. If the dog does not respond to fiber supplementation, then a trial and error therapy with antispasmodics, CNS sedatives, and opioids and have the owner attempt to reduce stress is used. The intermittent nature of clinical signs may make assessment of therapy difficult.
Pain can often be relieved by antispasmodic agents and the effects of stressors can be reduced by sedatives. Librax® (Roche) contains the sedative chlordiazepoxide (5 mg) and clidinium bromide (2.5 mg), an anticholinergic agent. A suggested dosage is 0.1-0.25 mg/kg of clidinium or 1-2 capsules PO BID-TID. The drug can be given when the owner first notices abdominal pain or diarrhea, or when stressful conditions are encountered, and can usually be discontinued after a few days. Other anticholinergics, such as propantheline (Pro-Banthine®, Searle), 0.25 mg/kg PO BID-TID, hyoscyamine (Levsin®, Schwarz Pharma Kremers Urban), 0.003-0.006 mg/kg PO BID-TID, or dicyclomine (Bentyl®, Lakeside Pharmaceuticals), 0.15 mg/kg PO BID-TID are suggested. Anticholinergics can decrease or inhibit GI motility that can worsen diarrhea.
The prognosis for cure of IBS in dogs is guarded. Affected dogs can have intermittent clinical signs for years. However, environmental and pharmacologic therapy can result in control or reduction of clinical signs. Dogs that respond to fiber supplementation have a very good to excellent prognosis.
Fiber-responsive large bowel diarrhea Fiber can be added to a highly digestible diet in dogs with chronic idiopathic large bowel diarrhea even if irritable bowel syndrome has been diagnosed. In cases of fiber-responsive large bowel diarrhea (FRLBD), chronic intermittent or continuous large bowel diarrhea is usually accompanied by hematochezia, excess fecal mucus and tenesmus. Abdominal pain and vomiting can occur in some dogs. Nervousness, abnormal personality factors, and stressors may be identified in some cases. However, in other cases, a temporal relationship to the diarrhea could not be established. Some of the dogs with FRLBD have classic signs of IBS. However, many of the dogs have hematochezia, a clinical sign considered uncommon in dogs with IBS.
Psyllium comes from the seeds or husks of the plant ispaghula and consists of approximately 90 percent soluble fiber. Psyllium hydrophilic mucilloid (Metamucil®, Procter & Gamble) when added to a highly digestible diet results in excellent or very good results in approximately 80 percent of dogs with chronic idiopathic large bowel diarrhea. The median amount of Metamucil® added to the diet is two tablespoons daily, which is approximately 1.3 g psyllium/kg daily. In some dogs, the amount of fiber added to the diet can be reduced or withdrawn entirely, while in others the highly digestible diet can be replaced with a grocery store brand of food after the diarrhea resolves.
Dietary fiber is a collective term for a wide variety of plant polysaccharides and lignins that are resistant to mammalian digestive enzymes. There are many types of dietary fiber, each with diverse chemical, physical and physiologic properties. Water-soluble fibers include pectin, gums, mucilages and some hemicelluloses. They are found in the parenchymatous portions of fruit and vegetables, and in the seeds of leguminous plants. Water insoluble fibers include cellulose, lignin and some hemicelluloses. They are found in cereal grains and seed coats.
There are several potential mechanisms by which dietary fiber supplementation may result in clinical improvement in dogs with FRLBD. Soluble fiber absorbs a large quantity of water, improving fecal consistency. Colonic bacteria, which make up approximately 40-55 percent of the dry-stool mass, ferment soluble fiber, which results in a vast increase in the numbers (but not types) of colonic bacteria and quantity of bacterial byproducts. Insoluble fiber greatly adds to fecal volume. Thus, dietary fiber can increase fecal bulk that increases colonic distention, the major stimulus for normal colonic motility.
With increased colonic distention, an improved motility pattern in dogs with FRLBD may result in resolution of clinical signs. In fact, dietary fiber has been shown to normalize colonic myoelectrical activity and colonic motility in people. Bacterial fermentation of fiber leads to the production of short-chain fatty acids, of which butyrate serves as an energy source for colonocytes.
Clostridium perfringens enterotoxicosis Acute and chronic large bowel diarrhea is associated with Clostridium perfringens type A enterotoxin. Vomiting, weight loss, flatulence and abdominal pain occur less frequently. The disorder occurs most commonly in dogs. Both naturally occurring and hospital-acquired cases do occur.
Diagnosis is commonly based on finding increased numbers of spores in rectal cytology samples, or demonstrating the toxin in the feces, which is primarily done at referral hospitals. The reason for including this syndrome in this discussion of chronic idiopathic large bowel diarrhea is that approximately 25 percent of toxin positive cases are negative on rectal cytology. Thus, in practices in which toxin is not analyzed, a case of Clostridium perfringens could be diagnosed as idiopathic. If fecal toxin cannot be routinely tested in a private practice, it may be indicated to treat a dog with chronic large bowel diarrhea with an appropriate antibiotic to eliminate the presence of C. perfringens enterotoxicosis.
Fecal sample confirmation Diagnosis can be confirmed by identifying enterotoxin in a fecal sample. Most commonly this was done with a reverse latex agglutination test (PET-RPLA Kit, Oxoid USA, Columbia, Mo.) However, this test may not be available at the present time. An ELISA test (Clostridium perfringens Enterotoxin Test, TechLab, Blacksburg, VA) is now also being used. Diagnosis should be suspected when greater than three to five spores per oil immersion field are found in a rectal cytology specimen. The spores are larger than most bacteria and assume a "safety pin" appearance. However, preliminary study has shown a poor relationship between fecal toxin and spores in rectal cytology samples.
A vegetative form of Clostridium perfringens is a normal inhabitant of the colon. The enterotoxin is a component of the spore coat and causes intestinal fluid accumulation, mucosal damage and diarrhea. The stimuli for sporulation and enterotoxin production are unknown. Enterotoxin has been identified in some cases of hemorrhagic gastroenteritis syndrome (HGE), parvovirus, giardiasis and IBD. The toxin may also be present in the feces of dogs without diarrhea.
Acute cases may resolve spontaneously. Chronic cases respond to antibiotic therapy in three to five days. Metronidazole at 6 mg/kg BID-TID for seven days is often effective. Ampicillin 22 mg/kg PO TID or amoxicillin 11-22 mg/kg PO BID-TID are also effective treatments.
Cases that show intermittent clinical signs require more long-term therapy. Tylosin can be used in these cases at 10-20 mg/kg BID. Some cases respond to feeding a high-fiber diet. The prognosis is excellent. Most effected animals respond to therapy within several days. Clinical findings have not been identified that predict which animals need long-term therapy.