Inflammatory bowel disease (IBD) refers to the condition that results when cells involved in inflammation and immune response are called into the lining of the GI tract. This infiltration thickens the bowel lining and interferes with absorption and motility: the ability of the bowel to contract and move food. With abnormal ability to contract and absorb, the bowel’s function is disrupted. Chronic vomiting results if the infiltration is in the stomach or higher areas of the small intestine. A watery diarrhea with weight loss results if the infiltration is in the lower small intestine. A mucous diarrhea with fresh blood (colitis) results if the infiltration occurs in the large intestine. Of course, the entire tract from top to bottom may be involved.
Infiltration of the bowel with inflammatory cells occurs when something inflammatory (or, in other words, stimulating to the immune system) is on-going within the intestinal tract. In food allergy, the digested food stimulates the immune system and causes inflammatory cells to infiltrate the bowel lining. With intestinal parasites, the parasites themselves stimulate the immune system. In some cases, we think the bacteria that live in the bowel may be producing inflammatory products that call in the infiltrating immune cells. In most cases, the cause of the immune stimulation cannot be determined.
The World Small Animal Veterinary Association defines IBD as an inflammatory infiltration for which no specific cause can be found. This means that if no cause for the inflammation is definable, therapy is directed at suppressing the immunological/inflammatory infiltration and relieving the long-standing inflammation regardless of its cause.
A little vomiting or diarrhea here and there seems to be pretty standard for pet dogs and cats. After all, cats groom themselves and get hairballs. Dogs eat all sorts of ridiculous things they aren’t supposed to. Still, many owners notice that their pets seem to have vomiting or diarrhea a bit more often than it seems they should. It might be subtle where one notices that one is cleaning up a hairball or vomit pile rather more frequently than with previous pets or it could be the realization that one has not seen the pet have a normal stool in weeks or months. Typically, the animal doesn’t seem obviously sick. Maybe there has been weight loss over time but nothing acute. There is simply a chronic problem with vomiting, diarrhea or both. IBD is probably the most common cause of chronic intestinal clinical signs and would be the likely condition to pursue first.
If vomiting occurs weekly or more, this is reason to see the vet for an evaluation.
The diagnosis of IBD requires a tissue biopsy, which is obviously invasively collected with some expense. Since there are a number of other conditions that cause similar signs, a step-by-step testing sequence precedes biopsy.
The first step in pursuing any chronic problem is a metabolic database. This means running a basic blood panel and urinalysis to rule out biochemically widespread problems, such as liver disease or kidney disease, pancreatitis, or hyperthroidism in cats that could be responsible for the signs. Since IBD is localized to the GI tract, such a database is usually normal but might express a general inflammatory response in the blood or a loss of blood proteins as often there is a leak of albumin, an important blood protein, from the intestine into the bowel contents. The database not only serves to rule out metabolic causes for the patient's symptoms but also assesses other areas, potentially turning up unanticipated problems and identifying factors that could change what medications are used.
Fecal testing and broad spectrum deworming is often performed at this time to rule out parasitism as a cause of the chronic inflammation. If the patient is young or has been housed with multiple animals, more obscure parasites may be afoot and often special fecal testing is submitted to the laboratory for PCR testing. Typical organisms screened by this kind of testing include: Giardia, Cryptosporidium, Salmonella,Tritrichomonas and Clostridium perfringens.
In dogs, a condition called Addison’s Disease is able to create chronic waxing and waning intestinal disease, among numerous other possible manifestations. This condition, more correctly termed hypoadrenocorticism, is often referred to as "the Great Imitator" as it can mimic many other diseases besides IBD. This condition revolves around a deficiency in cortisol, a crucial hormone in adaptation to stress. Treatment is relatively straightforward so it is important not to forget to screen for this condition. This is done with a screening test called baseline cortisol blood level or with a longer test called an ACTH stimulation test, which is a more definitive test that requires an hour or two in the hospital.
In both cats and dogs, a trypsin-like immunoreactivity (TLI) test would be performed to rule out pancreatic exocrine insufficiency, a deficiency of digestive enzymes. This condition is relatively easy to treat but, like Addison's disease, cannot be diagnosed without a specific confirming test. Typically this test is run in combination with a vitamin B-12 level and a folate level. When intestinal bacterial populations alter (we used to say "overgrow" but that is not technically accurate), folate levels rise and B-12 levels drop. Antibiotics are likely indicated in this situation as well as vitamin B12 injections.
Somewhere in the course of this work up, ultrasound of the abdomen is generally recommended. Ultrasound is able to image and enable sampling of areas within the belly that cannot be accessed by endoscopy. The texture of the liver and pancreas are evaluated and the size of the mesenteric lymph nodes, which serve the bowel, are examined. The layering of the bowel is also evaluated to see if it is thickened, as is more typical of IBD, or more disrupted as with intestinal cancer such as lymphoma. Since cancer is a consideration for most adult animals with chronic intestinal disease, this kind of imaging is particularly valuable and if any unusual textures or even masses are discovered, they may be needle aspirated for analysis.
If this kind of non-invasive testing is not revealing, then the definitive test for IBD is needed: a biopsy. Tissue samples must be harvested from several areas of the GI tract. This can be done either surgically or via endoscopy.
Endoscopy involves the use of a skinny tubular instrument (an endoscope) which has a tiny fiber optic or video camera at the end. The endoscope is inserted down the throat, into the stomach and into the small intestine where small pinches of tissue are obtained via tiny biting forceps. If the large intestine is to be viewed, a series of enemas is needed prior to the procedure as well as a relatively long fast. The endoscope is inserted rectally and again tissue samples are harvested. The advantage of this procedure over surgery is that it is not as invasive as surgery. Patients typically go home the same day. Disadvantages are expense (often referral to a specialist is necessary) and the fact that the rest of the abdomen cannot be viewed. Growths that are seen via endoscopy cannot be removed at that time and a second procedure typically must be planned whereas, if surgical exploration is used to obtain the biopsy, any growths can also be excised at that time.
Surgical exploration may also be used to obtain samples. The recovery afterwards is typically a couple of days though some patients bounce back immediately. With surgery, other organs can also be sampled and abnormal sections of tissue can be removed. Surgery tends to be more expensive than endoscopy but this depends on the recovery period. Often these two procedures work out to be of similar expense.
Tissue samples obtained are processed by a laboratory and analyzed. The infiltration of inflammatory cells is graded as mild, moderate, or severe and the type of cells involved in the inflammation are identified.
Recent studies have shown that patients with normal albumin levels and without vitamin B12 deficiencies have a 50:50 chance of responding to diet alone - no drugs needed. What sort of diet? The diets that have shown most consistent success are the hydrolyzed protein diets.
Hydrolyzed proteins are "predigested" so as to create protein segments that are too small to stimulate the immune system. Further, they typically are made with medium chain fatty acids, which are easier to absorb than the more customary long chain fats, and favorable omega 3 to omega 6 fatty acid ratios. In other words, there is more to these diets than just their predigested proteins, but approximately 50% of patients showed good improvement after approximately one month on a hydrolyzed protein diet.
Another approach is the use of the novel protein diets. The idea here is that the patient cannot have an immunological reaction to a protein source it has never experienced. (It takes long-term exposure to a protein before the immune system will respond against it, so a new protein should be safe.) This means using an unusual protein such as rabbit, venison, fish (for dogs) or duck, so long as the patient has not been fed these foods before. Again, it takes about a month to see a good response.
Patients that are sick enough to have a low albumin level or low vitamin B12 level are too sick for an approach this conservative. They will need medication.
The cornerstone of treatment for IBD is suppressing the inflammation. In milder cases of large intestinal IBD, the immunomodulating properties of metronidazole (Flagyl®), might be adequate for control but usually prednisone or prednisolone is needed. Prednisone will work on IBD in any area of the intestinal tract. In more severe cases, stronger immune suppression is needed (as with cyclosporine, chlorambucil, or azathioprine). Higher doses are usually used in treatment at first and tapered down after control of symptoms has been gained. Some animals are able to eventually discontinue treatment or only require treatment during flare-ups. Others require some medication at all times. Long-term use of prednisone should be accompanied by appropriate periodic monitoring tests due to the immune suppressive nature of this treatment.
In cases where it is particularly important to spare the patients from the side effects of long-term steroids, a medication called budesonide can be used. This medication is not readily absorbed from the GI tract and serves as a topical treatment for the lining of the intestine.
Possibly. Certainly, with IBD the diagnostic tests tend to be much more costly than the treatment. The problem is making sure there is enough confidence in the diagnosis of IBD that there will be no harm in skipping diagnostics. It is not unusual to take the work-up all the way through ultrasound and making a treatment decision based on the information obtained up to that point. If the patient is stable enough, there is time to change the diet or try medications and see how it goes.
The biggest problem in simply putting the patient on prednisone or prednisolone involves the possibility of intestinal lymphosarcoma, also called lymphoma. This type of cancer produces chronic diarrhea or vomiting just as IBD can. Lymphoma is temporarily responsive to prednisone but better responses can be obtained from stronger chemotherapy agents. Exposure to prednisone will make the lymphoma much more difficult to diagnose should biopsies be obtained later. Plus, exposure to prednisone can lead to resistance to other medications. (This is less of a problem for cats, but in dogs even a few days of prednisone can make a lasting remission impossible to achieve.)
In short, if you try prednisone or prednisolone without confirming a diagnosis, harm can be caused should the pet have lymphoma instead of IBD. Sometimes it is financially impossible to complete the ideal test sequence so it is important to discuss all the pros and cons with your veterinarian if going this route.
Inflammatory bowel disease continues to be a common cause of chronic intestinal distress in both humans and animals. Research for less invasive tests and for newer treatments is ongoing.