In the dog, diarrhea represents a significant proportion of all visits to veterinary clinics. Acute-onset diarrhea usually responds well to treatment against intestinal parasites, dietary modification and/or symptomatic therapy, however successful approach of chronic diarrhea is usually more challenging. Affected dogs often receive treatment with different diets, antimicrobials or anti-inflammatory drugs without success. A systematic approach including diagnostic testing and therapeutic trials is required to narrow down the list of possible differential diagnoses. Finally, close cooperation between the veterinarian and the dog's owners is a pre-requisite to optimize treatment success.

Key Diagnostic Points

The causes of chronic diarrhea in dogs are multiple, numerous factors are involved, and the prevalence of different diseases can vary depending on the geographical location. Some diseases can generally be ruled out using relatively simple exams (e.g., intestinal parasites). However, the diagnostic approach to other diseases may require therapeutic trials (e.g., adverse reaction to food) or more detailed investigations. In severely sick animals (with obvious systemic signs), it is preferable to immediately adopt a more aggressive, global approach involving blood tests, diagnostic imaging, and possible endoscopy or laparotomy with sampling of mucosal biopsies.

Parasite Infestation

This must be ruled out. A 'practical' alternative to multiple fecal exams consists in systematically administering a broad spectrum anthelminthic drug to treat locally prevalent endoparasites (e.g., fenbendazole 50 mg/kg p.o. daily during 5 days).

Diet

When parasites have been ruled out, dietary problems are probably the most frequent cause of chronic diarrhea in dogs. Food can elicit gastrointestinal inflammation in several ways: in genuine food allergy an immunological reaction against one or several of the dietary components (allergen) is at the origin of the problem. In such cases, it is recommended to feed the dog with a diet consisting of nutrients to which it had no previous contact (individually tailored hypoallergenic diet) during several weeks. To confirm the diagnosis and find out what exactly the dog is allergic to, it is necessary to perform a dietary challenge with different allergens which were part of the original diet (e.g., beef, chicken, milk, etc.) and to wait for the recurrence of clinical signs. Food intolerance is probably a more frequent cause of chronic diarrhea than food allergy. It is due to a non-immunological reaction against one or several components of the diet. It could be caused by the inability to adequately digest some of the dietary components or to substances added to the diet during industrial food processing.

Specific Laboratory Tests of Interest in Dogs With Chronic Diarrhea

Serum albumin may be mildly to moderately decreased with many intestinal diseases with involvement of the small intestine. However, severe decreases (< 20 g/l) are usually associated with protein-losing enteropathy, and are often associated with panhypoproteinemia. Possible causes include IBD or lymphangiectasia. Patients with severe hypoproteinemia are usually severely affected and may present with ascites, hydrothorax, and/or subcutaneous edema. They usually require more aggressive and intensive treatment. Hypoalbuminemia has been identified as a risk factor for unfavorable outcome in dogs with chronic enteropathies. Fecal alpha1-proteinase inhibitor can be a useful early marker of intestinal protein loss. In patients with protein-losing enteropathy, it may also be used for monitoring the evolution of disease and/or to assess response to treatment. Rectal cytology is a simple test that may be very useful for the diagnosis of intestinal infections (especially fungal infections). Fecal culture can be useful if specific bacteria are suspected (e.g., Campylobacter spp.), but can be difficult to interpret (is the identified bacterium at the origin of the problem or does it just represent an opportunistic growth in the inflamed intestine?). The possibility of exocrine pancreatic insufficiency must be ruled out in patients presenting compatible clinical signs (serum trypsin-like immunoreactivity or TLI). Low serum cobalamine and/or folate concentrations may indicate severe dysfunction of the ileal and jejunal mucosa, respectively. Cobalamine supplementation has been demonstrated to be beneficial in hypocobalaminemic cats with intestinal diseases. Hypocobalaminemia was identified as a risk factor for poor outcome in dogs with chronic enteropathies, and supplementation is recommended.

Key Therapeutic Points

Diet

Based on the high prevalence of diet-related problems in dogs with chronic enteropathies, it is recommended to prescribe a hypoallergenic diet to all dogs which did not respond to treatment against GI parasites. Such diets are available commercially or, alternatively, can be home-prepared by the owners. Commercial hypoallergenic diets are based on novel proteins and must be selected based on the dog's dietary history. Diets made of hydrolyzed proteins may also be a good choice, although they may be more expensive. At this time there is no published evidence that diets based on hydrolyzed proteins are superior to novel protein diets. The diet change must occur progressively. Strict compliance from the owners is essential. In the author's experience, most dogs respond within 7-10 days with a significant improvement of stool consistency and clinical status (although some of them may require more time). In a recent study 31 of 39 dogs (79%) with food responsive disease could be returned to a commercial diet after 14 weeks of elimination diet. The remaining 21% had to be maintained on a strict diet to avoid recurrences. When the clinical signs have subsided, it is advisable to maintain a strict diet to avoid recurrences. Some gastroenterologists postulate that food allergic dogs may become allergic to the protein source of the hypoallergenic diet, and recommend offering new diets (based on novel protein or hydrolyzed peptides) if clinical signs recur.

What To Do If Parasiticide Treatment and Elimination Diet Fail?

In cases of predominantly large bowel diarrhea (colitis with typical clinical presentation), a therapeutic trial can be initiated with metronidazole (20-25 mg/kg p.o. BID during 5-10 days), and addition of fiber to the diet (e.g., psyllium at 0.5 tablespoon (T) for toy breeds, 1 T for small dogs, 2 T for medium dogs, and 3T for large dogs). However, sampling of mucosal biopsies prior to further treatment may be the best course of action.

A number of dogs with chronic intestinal disease respond well to antimicrobial treatment (antibiotic responsive diarrhea or ARD). The aetiology of ARD is unknown, and a bacterial infection with unidentified bacteria cannot be ruled out at this time. German shepherd dogs may be predisposed to that disease due to insufficient production of immunoglobulin A (IgA). Clinical signs may vary considerably: chronic, recurring, mostly small intestinal diarrhoea is frequent (although large intestinal signs may also occur). Additional signs include borborygmus, flatulence, decreased appetite and weight loss. Once parasiticide treatment followed by 3-4 weeks elimination diet has been attempted without success, ARD is a possible diagnosis. Oral antimicrobial treatment with metronidazole (10-20 mg/kg BID), tylosine (10-20 mg/kg once daily or BID) or tetracycline (10-20 mg/kg TID) is recommended. Interestingly all 3 substances may also exert immuno-modulating or even anti-inflammatory effects on the intestinal mucosa in addition to their antimicrobial properties.

However, some dogs do not respond (or respond only partially or briefly) to the above treatment modalities. Additional testing is warranted in these animals, and includes blood work, abdominal ultrasonography, and endoscopic or surgical sampling of intestinal mucosal biopsies.

Treatment of IBD

Current treatment protocols for canine IBD most often involve the use of immunosuppressive doses of corticosteroids for several weeks followed by slow tapering to reduce the intestinal mucosal inflammation and achieve clinical remission. The author recommends using up to 2 mg/kg BID predniso(lo)ne p.o. for a few days, followed by 10-14 days at 1 mg/kg BID. In case of success, the dose is progressively decreased by one third to one half every 10-14 days. Dogs are usually switched to alternate day therapy after 4 to 6 weeks of treatment. This slow tapering is continued for weeks to months.

However, a number of dogs treated with immune suppressive doses of corticosteroids will either not respond at all or will relapse after weeks to months of treatment. At high dosages, corticosteroids have numerous side-effects such as PU-PD which may become unbearable for the owners, especially in large breed dogs. In patients that require prolonged therapy but are sensitive to its side-effects, the more expensive drug budesonide has been used with good anecdotal success (3.0 mg/m², or 0.5-3.0 mg per dog, depending on body weight, once daily or every other day). In humans, budesonide undergoes a first pass hepatic extraction of approximately 80-90%. Therefore, only a fraction of the absorbed compound reaches the systemic circulation, theoretically decreasing the side-effects. It is not known if the first pass effect is comparable in dogs. It has been documented that budesonide suppresses the hypothalamic-pituitary-adrenal axis in dogs with IBD.

Other immunosuppressive agents such as azathioprine, chlorambucil, cyclophosphamide at the usual dosages may be used alone or in combination with corticosteroids. They may (a) decrease the required dosage of corticosteroids and the associated side-effects, or (b) allow the dogs to be weaned off corticosteroids as soon as possible. These drugs may have a delayed onset of action (weeks to months until maximal effect). Recently, the use of cyclosporine A (5 mg/kg once daily) was described in corticosteroid-refractory dogs with IBD, and was successful in 12/14 dogs.

References

Additional references are available upon request.

1.  Allenspach K, et al. Chronic enteropathies in dogs: Evaluation of risk factors for negative outcome. Journal of Veterinary Internal Medicine 2007; 21: 700-708