Diarrhea in cats is not a disease.  It is a symptom of an underlying medical condition, and the challenge for both the cat's caregiver and the attending veterinarian is in finding the cause for the smelly, runny stools which we call diarrhea.

Our twelve year old Jaspurr, has been suffering from diarrhea for several months at the time of this writing. Jaspurr also is hyperthyroid, so far controlled by methimazole.

He also has arthritis, particularly in his rear quarters, and is showing evidence of potential kidney problems. Because of the kidney factor, he is not a particularly good candidate for Radioactive Iodine Therapy, which both our Bubba had in 2004, and our Joey in 2011.

Jaspurr also is prone to flatulence, which often accompanies diarrhea, and he sometimes leaves small, very firm poop pellets on the floor near the litter box. I associated the latter with possible anal gland impaction, which he had when he was younger, and our veterinarian expressed his anal glands. However the tiny "poops" still appear from time to time. Jaspurr also occasionally vomits shortly after eating, (either dry or canned cat foods), which is also commonly associated with diarrhea.

Diseases and Conditions Associated With Diarrhea

Diarrhea can be caused by any number of conditions in cats. However in Jaspurr's case, the fact that one of our recently adopted young cats, Gaither, also had diarrhea shortly before it showed up in Jaspurr made me think there might be a connection.

The following are some of the diseases and conditions which are commonly associated with diarrhea:

1. Giardia:  Giardia, an intestinal parasite, was found to be the cause of Gaither's diarrhea, and he was successfully treated for it. However, Jaspurr has been tested negative for it twice thus far.
2. IBD (Inflammatory Bowel Disease): Inflammatory Bowel Disease, aka Inflammatory Bowel Syndrome, is often associated with diarrhea in cats. Treatment includes a limited ingredient diet, as well as l-lysine. Also see idiopathic inflammatory bowel disease.
3. Liver Disorders:   PetEducation.com  writes, "Liver disease may be due to viral or bacterial infection, parasites, cancer, inflammation, obstructive bile duct disease, fatty liver disease, toxic reactions, or as a result of certain medications."
4. Bacterial Infections: Includes salmonella, e coli, Clostridia, Campylobacter.  E coli is more commonly found in kittens. This bacteria may be found in both humans and cats, but does not always cause disease. It is more common with kittens who have limited natural immunity., although it is sometimes seen in older cats. Salmonella is often the result of eating dry cat food contaminated by moisture and mold in storage, and is frequently the subject of cat food recalls. Even people can contract salmonella by handling contaminated bags or the food, and it is considered a zoonotic disease.
5. Viral Infections: Most commonly including Panleukopenia (distemper), FeLV  (feline leukemia), or FIV (Feline Infectious Virus) While feline distemper can be prevented by a vaccination, both vaccinations for FeLV and FIV have proven controversial. I personally would not use them for my own cats as they are all indoor-only, and have no contact with cats other than their housemates. If I were to adopt any more cats in the future, I would certainly make sure they were tested for FeLV and FIV before adopting.
6. Hyperthyroidism: It was interesting to find that one of the symptoms of hyperthyroidism is diarrhea. As that is consistent with Jaspurr's history, as well as his lab tests, it does give me another starting point to work with my veterinarian to curb Jaspurr's diarrhea.
7. Diabetes Mellitus: While diarrhea is not a normal symptom of feline diabetes, it can be one of the warning symptoms of  ketoacidosis. According to the Cornell University Feline Health Center, "A dangerous, sometimes fatal condition called ketoacidosis may develop, indicated by loss of appetite, vomiting, diarrhea, lethargy, weakness, dehydration, and breathing abnormalities."
8. Pancreatitis: Pancreatitis is not to be dallied with, as left untreated, the body starts to digest itself, until the cat dies a painful death.
9. Lymphoma: Lymphoma is the most common form of cancer in cats, constituting 33 percent of all feline tumors.

If you get nothing else from this article, I hope you will treat diarrhea in your cat seriously. Cats with continual diarrhea can become dehydrated, and if the cause is a serious condition, delay in seeking treatment, can only worsen the problem.

Disclaimer: I am not a veterinarian, nor a feline health professional. Your veterinarian should always be your first and foremost resource for health treatment for your cat. This article is meant only to give you a basic understanding of diarrhea in cats,  along with a starting place to do your own research so you can fully understand the potential causes for diarrhea, should your cat ever develop it.