Inflammatory bowel disease (IBD) in cats is a complex disease in that some cats respond well to relatively simple changes like diet change, while others require significant medical management.
Part of the problem is we don't know what causes inflammatory bowel disease in every case. We commonly think of it as an allergic-type disorder, but not every cat's signs will resolve if we just treat it as an allergy. In other cats, it may be parasitic or bacterial in origin, while in others there seems to be no obvious trigger.
It is important to look at the diagnosis of IBD, especially when a cat has lost nearly half its body weight. IBD can cause significant weight loss as the nutrients in the food are not as well absorbed.
However, we have to keep in mind that other intestinal disorders can appear very similar. When we see intestinal thickening or inflammation on ultrasound, the two primary differential diagnoses are IBD or small cell lymphoma. The latter is a form of slowly progressive cancer which can look exactly the same.
Ask your vet what tests were done to get to the diagnosis of IBD.
Typically the workup looks something like:
- Bloodwork usually shows non-specific changes - perhaps a mildly elevated white blood cell count, or a slightly low protein
- Fecal analysis is usually negative for parasites, but not always
- X-rays may or may not show any specific changes - the intestinal changes with inflammatory bowel disease are often too subtle to show on x-rays
- Ultrasound will show intestinal thickening or abnormal intestinal wall layering in almost every IBD case. Sometimes the associated lymph nodes appear enlarged.
Biopsy is needed to reach a definitive diagnosis. This can be done endoscopically to sample the stomach, duodenum (part of small intestine), and colon. It requires anesthesia and a fair amount of skill to get good biopsies, but it does have its limitations. Only the proximal part of the small intestine can be sampled, and only the mucosa and submucosal layers of intestine can be obtained (the deeper muscular layer, where pathology often resides, may be missed). The other method of biopsy is full thickness (surgical biopsy), which is a more invasive procedure but does allow full thickness biopsies of intestine, possibly pancreas and other organs to be taken.
Biopsies can tell us which form of IBD your cat has - is it eosinophilic, or lymphoplasmacytic in origin, or is it suggestive of emerging neoplasia?
The reason I just spent so much time talking about the diagnostics is because I see a lot of patients come in with a diagnosis of IBD, based not on any diagnostics but just a history of chronic vomiting and diarrhea.
The reason we spend time - and money - on diagnostics is that they determine how we manage the disease. I understand that not everyone can do the gold standard workup, but if not then there has to be an understanding that some of the treatments may be somewhat 'blind'.
The treatment of inflammatory consists of a number of aspects:
- Diet: Hypoallergenic (novel protein) diets are often recommend. The idea is that there is less antigenic stimulation in the intestine with these diets. If your cat won't eat the hypoallergenic diet - they would not be alone - then a gastrointestinal diet would be a good alternative.
- Antibiotics and antiparasitics are sometimes indicated. Metronidazole, an antidiarrheal medication can also help if there is a component of bacterial overgrowth. These medications alone will rarely solve the problem.
- Steroids are usually needed long term for management of IBD. I will be honest in that I very rarely have success managing IBD with a long-acting injectable steroid. You did not say which steroid was used in your cat's case, but long-acting injectable steroids such as methylprednisolone (Depo-Medrol) or triamcinolone do not usually work for this purpose. Oral prednisolone is most commonly used, which can be compounded into a tablet or liquid form. In a cat that cannot be orally medicated, giving dexamethasone injections at home a few times a week can be good alternative and is something that is something most people can easily do once they (and the cat) gets used to it.
- If steroids alone are not doing enough, then I usually add in chlorambucil. Chlorambucil is an anti-neoplastic which can help with aggressive forms of IBD (which your cat may have) or small cell lymphoma.
- Vitamin B injections are often helpful. Cats with intestinal disease such as IBD are often deficient in vitamin B12 and other vitamins.
- Probiotics can be helpful to restore normal intestinal flora, as the IBD is treated.
For further reading, the Cornell Feline Health Center has a good article on Inflammatory Bowel Disease.
In summary, I would make sure your vet is confident in the diagnosis of IBD for your cat. Talk to them about trying an oral steroid such as prednisolone since the injections do not seem to be working (your cat is losing far too much weight).