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Inflammatory Bowel Disease in Cats (IBD)


As a veterinary internal medicine specialist, I have done my best to explain inflammatory bowel disease (IBD) to countless cat owners (and veterinary interns, and externs, and random people at dinner parties...). On many occasions I've said that I need write down my little spiel, so I can just let everyone read about it while I kick back and drink chai latte...just kidding about that part, but it is time to blog about this ubiquitous topic.

First of all, let me clear up one confusion: it's inflammatory bowel disease, not irritable bowel syndrome. I know you are forever hearing about people with IBS and how they should take this drug or eat that yogurt...what kitties get is entirely different and it is IBD, not IBS.

So what the heck is inflammatory bowel disease, in pets? What this term really means is that when a pathologist looks at a biopsy of that cat or dog's intestine under the microscope, the pathologist sees white blood cells that shouldn't be there. There are different types of inflammatory bowel disease, based on what kind of white blood cells are the culprits; the most common kind in cats is called (take a deep breath) "lymphocytic-plasmacytic inflammatory bowel disease". Don't panic - I can explain.

We all have lots of different kinds of white blood cells, whose main job is to fight infection. Some of the most common types are neutrophils, lymphocytes, plasmacytes, and eosinophils. So when a pathologist says that a cat has "lymphocytic-plasmacytic IBD", she means that under the microscope, she sees lymphocytes and plasmacytes lining the small intestines and/or the stomach.

Here's a really bad, very simplified drawing of a normal intestinal wall, and an intestine with lymphocytic-plasmcytic IBD:

IBD and LSA 004
IBD and LSA 005

Your next question is: why do the white blood cells come to the intestine? Good question, and the answer is that we don't really know. Probably there are different reasons in different animals. Whatever the reason, the intestinal immune system gets overexcited and sends all these soldiers (the white blood cells) to do battle and then the white blood cells lining the intestines make it hard for the GI system to function the cat loses weight (because he can't absorb nutrients effectively) or vomits, or has diarrhea, or doesn't want to eat, or any combination of the above.

Unlike most of the body, the intestinal immune system has to be like a bouncer at one of those hot clubs where everyone lines up - it has to really pick and choose about who gets in and who is rejected. In most of the body, anything foreign is bad and the immune system attacks and gets rid of the invader. For example, there should be no bacteria hanging around in the bladder, or the lungs. If there are, they get kicked out, hopefully. But if you think about it, the intestines are different. There are bacteria that normally live there, and also, if you're a cat, there are things like chicken, beef, and fish all hanging around. So the intestinal immune system has to be very selective: "OK, all you normal bacteria can stay, as long you behave and there aren't too many of you, but Mr. Giardia, you need to leave, and Ms. Salmonella, I'm not thrilled about you either...". We think what happens with inflammatory bowel disease is that the intestinal immune system gets confused, and starts seeing normal bacteria or food proteins as enemies that need to be evicted. 

I said that one of the things that might be pissing off the immune system is food proteins. That's called food intolerance or allergy. In some cases of IBD, a change to a hypoallergenic diet can help. A hypoallergenic diet is food that has very limited ingredients, of types that tend to be less allergenic, and generally composed of ingredients that the animal has never had before. So a cat who has been fed chicken and fish and beef might be switched to duck or lamb. When using a hypoallergenic diet, it's really important that it's made of a "novel protein" (a protein source that is new to the animal) and that there are no other protein sources in there. There would be no point to feed a venison diet, for example, that also had some chicken broth in it. It's also really important that the animal is not fed any treats or anything else that contain ingredients other than those in the diet. There is no point to have your cat on a hypoallergenic lamb diet but also give her a little piece of turkey once in a while, or chicken-flavored treats or medicine. 

Unfortunately, right now there is no accurate way to test for a food allergy. The only way we can really tell is to try feeding a novel protein diet and see if the animal improves. There are prescription novel protein diets, there are some being sold over the counter (read the ingredients carefully to make sure there is nothing extraneous in there!), or you can make a balanced homemade novel protein diet with the help of websites like

OK, so we don't know exactly what causes inflammatory bowel disease in cats, but some theories include excess carbohydrates in the diet (like dry food), bacterial flora imbalances, food allergies, or infections (such as bacteria, viruses, or parasites). I hope that one day we understand the causes better, so treatment can be more specific, but right now we end up treating many cases of IBD in a somewhat similar fashion.

Before we talk about treatment, let's talk about diagnosis. This is a step that sometimes gets skipped, to the detriment of the cat. Signs of inflammatory bowel disease in cats are very nonspecific; one of the most common signs is weight loss, and other signs include vomiting, diarrhea, or poor appetite. These signs can all also be caused by plenty of other things, such as cancer, pancreatic inflammation (pancreatitis), liver disease, ulcers, parasites, etc. So it is very important to obtain a definitive diagnosis before jumping into treatment! Especially since treatment may involve strong drugs like corticosteroids, which you wouldn't want to give without a specific reason. 

One disease that can cause identical symptoms to IBD in cats is called "small cell lymphoma". This is a slow, low-grade type of intestinal cancer that is very treatable. It's essential to differentiate whether a cat has IBD or small cell lymphoma because the treatment regime is different. And cats with small cell lymphoma can live happily for years on proper treatment (my own cat lived almost five years with this disease and died at close to 18 from something else entirely). In small cell lymphoma, the intestines are infiltrated by the white blood cells called lymphocytes (similar to inflammatory bowel disease), except there are lots and lots of them and they are more invasive.

The question has arisen whether inflammatory bowel disease is a precursor to small cell lymphoma, i.e. whether some cats with untreated (or treated?) IBD may go on to develop small cell lymphoma; does IBD in some cases "morph" into small cell lymphoma? We aren't sure. We do know that small cell lymphoma if unchecked can turn into a more malignant cancer called lymphoblastic lymphoma, where the cat actually develops a tumor.

Some bad illustrations are below:

IBD and LSA 001
IBD and LSA 002
IBD and LSA 003

The bottom line is that it is crucial to accurately diagnose and properly treat feline inflammatory bowel disease and small cell lymphoma. This is generally done through a combination of ultrasound and biopsies. We usually do an ultrasound first, to evaluate the stomach and intestines, see which parts of the GI tract (if  any) look abnormal, evaluate all the other organs such as the pancreas, liver, and spleen, and see if something else entirely may be causing the cat's symptoms. On ultrasound, the intestines of a cat with inflammatory bowel disease may look perfectly normal, or they may be somewhat thickened or have abnormal layering (disproportionate thickness of particular intestinal layers). Some cats with IBD or small cell lymphoma may have enlarged lymph nodes near the intestines.

It's essential that a skilled clinician performs your cat's ultrasound; some more information is here.

If the ultrasound is most consistent with the cat's symptoms being caused by IBD or small cell lymphoma (these cannot be differentiated on ultrasound), then a biopsy is performed. This can be done in one of three ways: endoscopy, surgery, or laparoscopy. Each has pros and cons, and your vet or internist can help you decide which is best for your cat. Endoscopy is least invasive and least expensive, but the biopsies are smaller and cannot be taken from as many different parts of the intestine. Surgery tends to be very accurate as long as good biopsies are taken from different sections of the intestinal tract, but obviously is more invasive and costly. Laparoscopy (minimally invasive surgery) is available at some facilities, and allows good biopsies to be taken with smaller incisions than the incision required for surgical biopsies. Being an internist, I do a lot of endoscopy, but I counsel pet owners about the pluses and minuses of each method.

It is essential to obtain biopsies before any medication is initiated, because medication, particularly corticosteroids, affect our ability to ever get a definitive diagnosis. They will mask symptoms, cause temporary improvement even with cancer, and can change the appearance of biopsy samples. It is NOT a good idea to do what is sometimes called a "steroid trial", where the cat is given steroids to see if symptoms improve. The symptoms of almost anything will temporarily improve on steroids, and once the cat has been given steroids, our ability to obtain a true diagnosis is greatly hampered. The cat can really be harmed if this causes accurate diagnosis or proper treatment to be delayed.

What is the treatment for inflammatory bowel disease? And small cell lymphoma? For inflammatory bowel disease, it depends somewhat on the severity and type. Treatment may include hypoallergenic diet, certain antibiotics such as metronidazole (Flagyl) and/or corticosteroids such as prednisolone. In cases of inflammatory bowel disease, the corticosteroid is very slowly tapered down based on the cat's progress; for example a cat might be on 10 mg a day for 2-3 months, then 5 mg a day for 2-3 months, then 2.5 mg a day, and so on. Unfortunately, most cats on corticosteroids for IBD cannot get off the drug entirely without relapsing.

For small cell lymphoma. the situation is different. Corticosteroids are also used, but the dose is never tapered, unless necessitated by side effects or other health issues. Generally cats are left on the same high dose for the rest of their life, and luckily they seem to do fine with this regime. In addition, cats with small cell lymphoma are usually treated with a drug called Leukeran (chlorambucil), also for the rest of their life. For example, a cat might receive one 2 mg tablet of Leukeran every other day. The combination of prednisolone and Leukeran works very well long-term in many cats. You can see why it is so important to obtain a definitive diagnosis if possible; if you did not know a cat had small cell lymphoma and treated presumptively for IBD, as the corticosteroid dose was tapered, the cat would relapse or potentially develop the much more devastating cancer called lymphoblastic lymphoma.

Some cats with IBD or small cell lymphoma will become deficient in certain B vitamins, particularly cobalamin (B12) and folate. This occurs because the inflamed intestines cannot properly absorb these vitamins. It is easy to test for B12 and folate deficiencies; a blood test is drawn after the cat has not eaten for about 12 hours. This test is important for several reasons: one, if either vitamin is low, it is a good clue that the cat may have intestinal disease, and two, it is essential to treat a deficiency if one exists. I often perform a test called a feline maldigestion profile, which measures these vitamins as well as checking for a deficiency of pancreatic digestive enzymes (a deficiency of digestive enzymes can cause similar symptoms to IBD or small cell lymphoma).

One of the most important things to monitor in cats with GI disease is their weight; if they are responding well to treatment they should gain back their weight and then maintain it. I encourage cat owners to purchase a good scale and monitor their cat's weight at home; my favorite scale is the Redmon Electronic Weigh-To-Grow Baby Scale.

Phew! Well, there you have it in a nutshell: IBD is a disease frequently seen in cats, which should be definitely diagnosed before treatment, and for which we don't really know the cause. Hopefully one day the veterinary profession will know more about this incredibly common problem, and in the meantime now YOU know more about it than you did 10 minutes ago!


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Thanks so much for explaining IBD. My 4 month old kitten just had an ultrasound yesterday because he was experiencing chronic vomiting, stomach pain, nausea to name a few. The ultrasound showed a thickening of the stomach closer to the esophagus. I guess the next step in a biopsy. They said they didn't have a scope small enough so I think he will have to have surgery. I do have him on a grain free diet and that has helped. Thanks again!!

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When you are ill and visit the doctor, he or she is in a position of trust. They have undertaken a duty to make an accurate diagnosis of your ailment and provide adequate treatment for it. Should they be negligent in that duty and either fail or delay to make a correct diagnosis, this could result in you having serious health issues and be entitled to make a delayed diagnosis compensation claim.

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my cat had colitis (inflammation of the colon)...i switched him to Hills Z/D canned ultra allergen... after a day blood in stools went away and vomiting also...he definitely had a food allergy and the hydrolyzed protein in Z/D tookaway the problem...dry Z/d doesnt work... but the canned did the trick...

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