Other chronic intestinal diseases, especially infiltrative ones (Proceedings)
Intestinal biopsy may be accomplished two ways: endoscopy and surgery. CBC, serum chemistry profile, and urinalysis are useful and may point out systemic manifestations of the disease which will aid in correctly diagnosing and prognosing the problem (e.g., hypoalbuminemia due to histoplasmosis), but are also useful as a preanesthetic work up before endoscopy. Ultrasound is useful to look for enlarged mesenteric lymph nodes, focal intestinal/gastric lesions, and loss of mucosal layering. Focal enlargements may suggest a tumor (e.g., alimentary lymphoma or carcinoma), as may lymphadenopathy. However, animals with severe IBD may also have mesenteric lymphadenopathy (as may dogs with histoplasmosis or pythiosis). If the lymph nodes are enlarged, it is reasonable to aspirate them percutaneously with ultrasound guidance. Mesenteric lymph nodes are typically reactive, making it more difficult to interpret cytology from them. However, finding obvious sheets of lymphoblasts or fungal organisms (e.g., histoplasmosis) allows diagnosis. Sonographic examination of the intestines is important (i.e., you may make a diagnosis), but it does not detect intestinal mucosal disease in many patients that are afflicted with such disease. If loss of mucosal layering is seen, then severe infiltration is likely (either inflammatory or neoplastic), but normal-appearing mucosa may have marked disease present. Most of the time, ultrasound's major use is to help you decide whether to perform intestinal biopsy using endoscopy or laparotomy. If there is an obvious lesion where an endoscope cannot reach, it is best to perform laparotomy instead of endoscopy. In contrast, abdominal radiographs (plain or contrast) are rarely helpful or cost-effective in these patients.
For our purposes, inflammatory bowel disease (IBD) will be defined as inflammatory infiltrates in the intestines that cannot be attributed to a specific cause; hence, IBD is idiopathic intestinal inflammation. This is a very important concept. If there are inflammatory infiltrates in the intestines and they subside when the patient is fed an elimination diet, then that patient had dietary intolerance or allergy, not IBD. Likewise, if a patient with inflammatory infiltrates of the intestines responds to antibiotics, then that patient has an antibiotic-responsive enteropathy, not IBD. The important point is that canine and feline IBD is NOT simply a histologic diagnosis. Unfortunately, accurately excluding the other causes of intestinal inflammation is time consuming and can be frustrating to the client who is dealing with ongoing diarrhea/vomiting/weight loss. Additional difficulties involved in diagnosing intestinal inflammation include the lack of agreement among pathologists over what constitutes normal, mild, moderate, and severe inflammation in the intestinal mucosa. Adding to this problem is the fact that many endoscopic biopsies (and a good number of full thickness biopsies) are so hopelessly inadequate that asking a pathologist to make any kind of meaningful statement about them is questionable, at best. This means that one cannot blindly believe pathology reports on intestinal biopsies. However, this makes the situation difficult for the average primary care practitioner who cannot sit down with the pathologist and discuss the slides with a multi-headed scope. A common question is, "When do I doubt a diagnosis or a histologic description?" Perhaps the best guidelines about when to ask for a second opinion center around two questions that should be asked every time a diagnosis is made. The first question is, "Does the diagnosis fit the patient?" (i.e., do the signalment, history, physical examination, laboratory finding and imaging fit the diagnosis?). The second question is, "Does the response to therapy fit the diagnosis?" If the answer to either question is "no", then the diagnosis is suspect.