My name is***** and I am sorry to hear that Earl has chronic vomiting.
When I see a kitty with chronic vomiting, the first thing that comes to mind is inflammatory bowel disease. This can be related to a food allergy, so I like to start with a hydrolyzed protein diet (vs a limited ingredient diet). There are several on the market you can ask your regular vet about. IBD can also be an immune problem where the immune system is clogging up the intestines with white blood cells leading to maldigestion, diarrhea and weight loss. Another possible cause of weight loss and low appetite would be pancreas problems (either inflammation- pancreatitis or lack of production of digestive enzymes- exocrine pancreas insuffiency). The best way to diagnose this is with a "GI Profile" blood work (both Antech and Idexx have this profile as well as the GI Lab at Texas A&M University). The last cause that comes to mind would be intestinal lymphoma. This can appear very similar to inflammatory bowel disease and biopsies can be needed to differentiate the two diseases.
Abdominal ultrasound is a great next step for your kitty. Your veterinarian can measure the thickness of the intestines as well as look for inflammation around the pancreas. I would ask about the "GI Profile" as this can also aid in the diagnosis of intestinal disease. The last step to consider would be an abdominal exploratory. This is where your veterinarian would anesthetize your cat, open up their abdomen, visually examine all of the organs and collect biopsy samples for analysis. This is the gold-standard for diagnosing IBD vs intestinal lymphoma.
If all of the above tests have already been run, the next question is have you done a "prednisone trial?" This is where we give prednisone to chronic vomiting and diarrhea kitties just to see if there is any response to treatment. This is an older technique that we used to use before the GI profile was available, but I still sometimes try it when there aren't other good answers.
Best regards, ***** ***** this answer helps you.
Feel free to contact me if you have any more questions.
Kansas State University,
College of Veterinary Medicine Class of 2001