Basic approach to chronic diarrhea
Chronic diarrhea (i.e., that which persists > 2-3 weeks) usually necessitates a systematic diagnostic approach (which may
mean classic tests and/or therapeutic trials). The first question in the patient with chronic diarrhea is whether the patient
has an obvious problem such as parasites or an obviously inadequate or poor quality diet. At this point, we are not talking
about dietary allergy or intolerance; we are simply talking about obviously bad choices or totally erratic diets in which
the animal is fed anything and everything. While it is possible that parasites are unlikely in your area, it is always a
good idea to check for them; perhaps the dog or cat has been traveling or boarding with an animal that has been traveling
where parasites are common. Besides, having intestinal parasites will lower the threshold for diarrhea caused by other problems.
The second question is whether the patient has large intestinal disease or small intestinal disease. It is important to realize
that diarrhea is simply increased fecal water. Severe, life-threatening small bowel disease may cause minimal or no diarrhea
if the colon can absorb enough water to make the feces firm or solid by the time they are evacuated. In particular, if the
patient has been in a cage and unable to exercise (a potent stimulus for defecation), the feces may be normal despite significant
intestinal disease. It is only when the colon's water absorbing capacity is exceeded that diarrhea occurs. Even when small
bowel disease does cause diarrhea, the weight loss from nutrient malabsorption may precede diarrhea by months.
Use the history to help differentiate large bowel from small bowel disease.
- • Weight loss, especially in the face of a reasonable appetite, strongly suggests nutrient loss from the small intestine. Hepatic disease
can closely mimic intestinal disease in this regard, but the intestines are usually a better place to start looking. Weight
loss is probably the most important area to look at in differentiating large bowel from small bowel disease. Any animal with
chronic small intestinal disease that is clinically significant should have weight loss or loss of condition. Any animal with
chronic diarrhea and no loss of weight or condition has large bowel disease until proven otherwise. Some animals with severe
large bowel disease will have weight loss, but these usually also have hematochezia, mucus, hypoalbuminemia and/or marked
• Red blood (hematochezia) comes from the large bowel or the ileum. This finding is specific but insensitive for large bowel diarrhea
- • Mucus in the feces comes from the large intestine or ileum. This finding is specific but insensitive for large bowel diarrhea.
- • Tenesmus and dyschezia suggest large bowel disease; however, any animal with chronic diarrhea can have anal irritation causing tenesmus.
- • Vomiting can occur with either large or small bowel disease.
Once small intestinal disease is diagnosed, the next question is whether there is a protein-losing enteropathy (PLE) or not.
Check the serum albumin concentration (NOT the total protein) to make this determination. While it is certainly possible
to have PLE and a normal serum albumin concentration (i.e., the disease has not gone on long enough yet to cause hypoalbuminemia),
we generally reserve using the term PLE for those dogs which have hypoalbuminemia even though this is not technically correct.
If the patient has a serum albumin < 2.0 g/dl that is not caused by renal loss or hepatic insufficiency, then we typically
diagnose PLE by default. If you suspect PLE, you should skip down to that section.