Reader Question: What is causing my cat's chronic diarrhea?

Dear Dr. Plotnick,

My 16 year-old female cat has had chronic diarrhea for 2 years now amd our vet is stumped. She has gone from 7 lbs down to 5. She is also constantly hungry. Her water intake is normal. We feed her continually. She's had a blood test, an x-ray, and ultrasound, and everything is normal. We now have her on a high protein diet and it seems to be maintaining her weight now.  We're reluctant to do a biopsy because of her age. Any help would be greatly appreciated.

Lois F.

 Dear Lois,
Normally, I’d put hyperthyroidism at the top of my list for a 16 year-old cat with a ravenous appetite, weight loss, and diarrhea, but you said that your vet ran blood tests, so I’m sure a thyroid test was done.  X-rays don’t usually give much information regarding a cause for chronic diarrhea, but I would have hoped that the ultrasound would have revealed something, like increased intestinal thickness or enlarged lymph nodes.  A normal ultrasound report, however, does not preclude the presence of a gastrointestinal disease, and I suspect that your cat has either inflammatory bowel disease or perhaps low-grade lymphoma.  Lymphoma is lower on my list, because the symptoms have been present for two years, and if this were lymphoma, your cat would not have survived this long without proper treatment.  So I’m leaning toward inflammatory bowel disease.    I do think there are a few tests that you should consider running, though, if they have not been done yet.  I would have a fecal sample submitted for PCR analysis for gastrointestinal pathogens.  Most commercial veterinary laboratories now run a test like this.  It is a very sensitive test that detects infection with a number of bacterial and protozoal pathogens like Clostridium, Campylobacter, Salmonella, Giardia, and Tritrichomonas.  These organisms are capable of causing chronic diarrhea.  I also think a TLI test and a vitamin B12 and folate level should be run.  This test evaluates the ability of the pancreas to make digestive enzymes.  This condition is called exocrine pancreatic insufficiency (EPI).  Cats with EPI usually have chronic diarrhea and a ravenous appetite.  They often have concurrent bacterial overgrowth in the small intestine, which can be evaluated by measuring the vitamin B12 and folate levels.  If all of these tests come back negative, then your cat likely has inflammatory bowel disease (IBD).  To prove this, biopsies must be obtained. I understand your reluctance to have your 16 year-old, 5 lb. cat undergo anesthesia and surgery or endoscopy.  I think, given the circumstances, if you’ve ruled out most of the common causes of chronic diarrhea, and you’ve tried a variety of symptomatic treatments and your cat continues to decline, I think it would be reasonable to make a presumptive diagnosis of IBD and treat her for it.  The treatment is the anti-inflammatory drug prednisolone.  Your vet may want to consider giving her 5 to 10 milligrams daily for a month, and closely monitor her response.  If she responds well (diarrhea resolves and she gains weight), the dosage can be tapered to the lowest dose that still controls the symptoms, eventually giving the medication every other day.  Good luck with her.