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Chronic Diarrhea in Dogs

  • September 8, 2017 3:44 PM EDT

    The onset of diarrhea in a pet is one of the more common reasons for a visit to the veterinarian. By definition, diarrhea is an increase in fecal mass or volume with or without an increase in the fluidity (water content). The character of the stool is typically soft or watery. However, even a dog that passes "normal" looking stools with an increase in frequency may be considered as having diarrhea.

    Diarrhea can develop for many different reasons. The history and details surrounding the onset of diarrhea can be very helpful in determining the cause. Furthermore, it's important for the veterinarian to determine the cause in order to successfully treat the pet's underlying condition, and not just the symptoms.

    Diarrhea can be a sign of gastrointestinal (GI) upset (with or without vomiting), or it can develop in association with disease in another organ system. Cases of diarrhea can be acute and self-limiting, and other cases can become chronic.

    Some of the more common causes of acute diarrhea include:

    • Dietary indiscretion - This is one of the more common reasons for a pet to suddenly develop a case of diarrhea. Usually there is a history that the "pet got into something," "ate something that he or she shouldn't have," was observed rummaging through the garbage, or was fed fatty or rich foods (table scraps), etc.
    • Abrupt change of diet - Changing a pet's diet abruptly (as opposed to gradually introducing the change) can result in diarrhea. This also includes the introduction of new treats.

    • Intestinal parasites

    • Infectious diseases - bacterial, viral, etc.

    At a minimum, dogs that present with acute diarrhea should have a fecal examination for intestinal parasites. Pet owners should bring a fresh stool sample along to the veterinary visit. Based on the pet's history and physical examination findings the veterinarian may recommend additional testing which could include blood tests, abdominal radiographs (x-rays), or other diagnostics.

    Chronic diarrhea is another matter. These dogs may pass abnormal stools intermittently or they may continually pass abnormal-looking stools. Causes of chronic diarrhea include primary gastrointestinal disorders or enteropathies as well as diseases that do not originate from within the GI tract (e.g. a manifestation of a pancreatic, liver, kidney, cardiovascular, or other disorder - also known as secondary enteropathy).

    In order to pinpoint the cause of chronic diarrhea, the veterinarian may need to do a bit of detective work and arrive at the diagnosis through a process of elimination or trial and error.  Certainly, a work-up consisting of fecal testing for parasites and Giardia, as well as comprehensive blood testing to survey the pet's overall health status to rule out systemic disease is essential. Based on the individual pet's history and condition, additional tests may be recommended including endoscopy, gastrointestinal biopsies, among others.

    Not uncommonly, veterinarians may prescribe medications and/or manipulate the diet in an effort to symptomatically treat the patient - as a first-line approach. An attempt to alleviate any gastrointestinal discomfort and bring resolution to the diarrhea before proceeding with additional tests or procedures. For example, prescribing a course of antibiotic therapy (e.g. metronidazole and/or tylosin), probiotics, and/or manipulation of the diet (a temporary change to a bland / highly digestible diet, or one higher in fiber). Many dogs may improve in response to these efforts. Some of these dogs that initially respond, however, may relapse with the diarrhea once the treatment plan is discontinued. 

    It's in these cases - the dogs with chronic diarrhea or in those that relapse with diarrhea after an initial response to a therapy- that a systematic approach should be taken to try and determine the underlying problem. In the past, some dogs have been prescribed "antibiotics for life" to control their diarrhea. Some dogs may, in fact, need this - as they truly have an antibiotic-dependent or antibiotic responsive enteropathy. However, there are other types of enteropathy - namely food responsive enteropathy (in which the patient has a food allergy or a food intolerance) and steroid responsive enteropathy (inflammatory bowel disease). These cases may show some improvement while on the antibiotic regimen because some antibiotics may quell the intestinal inflammation (that is contributing to the diarrhea). They are not, however, addressing the underlying situation and are merely serving as a "band-aid." 

    Dr. Elisabeth Zenger - a board certified veterinary internist - had this to say regarding a study of dogs with chronic diarrhea:

    The findings in this study suggest that dogs with chronic diarrhea and suspected of having a primary inflammatory enteropathy (where GI parasites and other systemic disease have been ruled out) should undergo a food trial to rule out a food responsive disease (food allergy or food intolerance) before lifelong antibiotic administration is implemented. In this case, food is the medicine! It's also important to recognize that GI health is complex and interdependent on many factors