Diagnostic Evaluation

By | 2011-08-05

History and Physical Examination

Inflammation is the most important pathophysiologic condition of the colon. Colitis is responsible for the major clinical signs of hematochezia, mucus in the feces, dyschezia, abdominal discomfort, tenesmus, urgency, and increased frequency of defecation. The colon is an important target organ for inflammatory bowel disease in the dog, whereas the upper gastrointestinal tract (stomach and small intestine] is more frequently involved in feline inflammatory bowel disease. Clinical signs are useful in localizing the anatomic site of the diarrhea to the small or large bowel (Table Clinical Signs Associated unth Diarrhea — Large Bowel versus Small Bowel), although some animals will have diffuse involvement of the small and large intestines.

Clinical Signs Associated unth Diarrhea — Large Bowel versus Small Bowel

Signs Small Bowel Large Bowel
Weight loss May be present Uncommon
Vomiting May be present Uncommon
Flatulence Present with malossimilation Unusual
Defecation frequency Normal to mild increase Marked increased frequency
Fecal volume Increased Normal to mild increase
Urgency Absent Usually present
Tenesmus Absent Usually present
Mucous in feces Usually absent Frequently present
Hematochezia Absent Often present
Melena Sometimes present Absent
Steatorrhea Present with malossimilation Absent

 

The history should include specific questions about diet, parasite control, environment, travel history, concurrent medical disease, and drug history. Dietary sensitivity reactions and parasitism are major causes of colitis in many pet populations. Dietary history should include information regarding type of diet, incidence of dietary indiscretion, supplements, snacks, and treats. Information concerning previous fecal examinations and anthelmintic use may provide useful clues to the cause of the diarrhea. Environmental history should identify other pets in the household, the composition of their diets, and any behavioral interactions or hierarchies that might influence the development of clinical signs. The travel history may yield important information about exposure to histoplasmosis, pythiosis, and heterobilharziasis, all of which have regional distributions. Concurrent medical disease (e. g., Addison’s disease, inflammatory bowel disease, pancreatitis) will also help place the current episode of colitis in context. The drug history should include information about the use of alternative and complementary medicines that could contribute to clinical symptomatology.

The physical examination may be normal in many cases of colitis. The most consistent physical examination findings are pain and irregularities of the colonic mucosa on digital rectal examination. The perineum should be examined carefully to exclude perineal diseases such as perineal hernia and perianal fistula. Physical examination may reveal other important findings, including fever (inflammatory bowel disease, cecal or colonic perforation, fungal infection), abdominal pain (inflammatory bowel disease, colonic neoplasia, cecal or colonic perforation), abdominal mass (colonic neoplasia, granulomatous colitis, intussusception), small intestinal thickening (concurrent small intestine inflammatory bowel disease, small intestine lymphoma), mesenteric lymphadenopathy (small intestine inflammatory bowel disease, small intestine lymphoma), hepatosplenomegaty (lymphoma, disseminated fungal infection), and uveitis (protothecosis, lymphoma). A scoring system has been developed to relate clinical signs with histologic findings in canine inflammatory bowel disease.

Constipation is the second most important pathophysiologic condition of the colon. Clinical signs include reduced, absent, or painful defecation for a period of time ranging from days to weeks or months. Physical examination findings will depend on the severity and pathogenesis of constipation. Dehydration, weight loss, abdominal pain, and mild to moderate mesenteric lymphadenopathy are common findings in cats with idiopathic constipation. Physical examination might also reveal abdominal mass (cecal or colonic neoplasia, granulomatous colitis), abdominal pain (foreign bodies, colonic perforation), autonomic neuropathy (dysautonomia), hindlimb paresis (lumbar spinal cord pathology), pelvic fracture (pelvic outflow obstruction), and perineal hernia (cause or complication of constipation).

Laboratory Data

For both inflammation and constipation, the scope of the medical investigation will be shaped by prior history, suspected cause, chronicity, and signs of systemic illness.

Complete blood count (CBC), serum chemistry, and uri-nalysis should be considered in animals with signs of colonic disease, particularly those with signs of systemic disease. These tests may provide evidence of anemia (chronic disease, gastrointestinal blood loss), leukocytosis (inflammatory bowel disease, neoplasia, cecal or colonic perforation), eosinophilia (parasitism, Addison’s disease, mast cell disease, hypereosinophilic syndrome), thrombocytopenia (concurrent immune thrombocytopenia), hypoproteinemia (protein-losing enteropathy (protein-losing enteropathy]), hyperglobulinemia (FIP, inflammatory bowel disease, infection, neoplasia), hypercalcemia (neoplasia, fungal disease), hypoglycemia (leiomyosarcoma), and hyponatremia and hyperkalemia (Addison’s or pseudo-Addison’s disease). This minimum data base is also useful to screen animals prior to anesthesia and colonoscopy. If fungal, Oomycetes, or algal infections are possible causes in the pet’s geographic area, special serologic tests are available for the diagnosis of some of these diseases (Table Definitive, Suspected, and Unproved Pathogens of the Large Intestine of Dogs and Cats). Feline leukemia virus (FeLV) and Feline immunodeficiency virus (FIV) testing are warranted in cats with unexplained, chronic diarrhea.

Fecal Parasitic Evaluation

Direct fecal smears and fecal flotation studies should be performed to evaluate for helminth, protozoa, and some bacterial infections (see Table Definitive, Suspected, and Unproved Pathogens of the Large Intestine of Dogs and Cats). Direct fecal smears may be useful in detecting Giardia, Tritrichomonas, and Campylobacter organisms. Zinc sulfate flotation is the most accurate and practical fecal flotation test available, and it may be more sensitive for the detection of Giardia and Tritrichomonas infections. Some animals may have intermittent shedding of helminth ova, Giardia trophozoites and cysts, or both; therefore suspected infections should always be treated with anthelmintics or antiprotozoal agents before animals are subjected to colonoscopy.

Definitive, Suspected, and Unproved Pathogens of the Large Intestine of Dogs and Cats

Classification / Organism Tissue Trophism Evidence Of Pathogenicity Diagnosis
Helminths
Trichuris vulpis Cecum, colon Good evidence Fecal flotation
Trichuris serrata, Trichuris campanula Cecum, colon Moderate evidence Fecal flotation
Ancylostoma caninum Intestine, colon Good evidence Fecal flotation
Heterobilharzia americana Colon Good evidence Fecal flotation, histology
Protozoa
Balantidium coli Colon Poor evidence Fecal flotation
Entamoeba histolytica Colon Weak evidence Fecal flotation
Ciardia spp. Intestine, colon Moderate to good evidence Fecal flotation, ELISA, IFA, duodenal / colonic aspiration
Isospora obioenesis — dogs Intestine, cecum, colon Weak evidence Fecal flotation
Tritricbomonas foetus — cats lleum, cecum, colon Moderate to good evidence Fecal flotation, culture, polymerase chain reaction
Fungi
Histoplasma capsulatum Intestine, colon Good evidence Exfoliative cytology, histology
Oomycetes
Pythium insidiosum Stomach, intestine, colon Good evidence Histology, immunohistochemistry, enzyme-linked immunosorbent assay. PCR
Algae
Prototbeca zopfii / wickerbamii Eyes, skin, colon, CNS Good evidence Exfoliative cytology, histology
Bacteria
Brachyspira pilosicoli lleum, colon Moderate evidence Culture, PCR, histology
Campylobacter coli, C. jejuni, Campylobacter upsaliensis, C. helveticus Intestine, colon Moderate to good evidence Culture, polymerase chain reaction
Clostridium perfringens Colon Moderate to good evidence Gram staining, culture, enzyme-linked immunosorbent assay, PCR
Clostridium difficile Colon Weak to moderate evidence Culture, Toxin A enzyme-linked immunosorbent assay, genotyping
E. coli (ET, EI, EP, EH, EA) Intestine, colon Good evidence Culture, serotyping, polymerase chain reaction
Salmonella spp. Intestine, colon Good evidence Culture, serotyping, PCR
Yersinia enterocolitica Colon Poor evidence Culture

ELISA, Enzyme-linked immunosorbent assay; IFA, indirect fluorescent antibody; PCR, polymerase chain reaction.

Fecal Bacterial Culture

Fecal cultures should be considered in animals with suspected bacterial infections of the intestine and colon. Risk factors for bacterial colitis include young age, crowded or poor hygienic environmental conditions, co-infection with helminth or protozoal parasites, viral immunosuppression, boarding or kenneling conditions, and multiple-pet households. Bacterial pathogens associated with colitis or enterocolitis lesions in dogs and cats have included Brachyspira pilosicoli, Campylobacter spp., Clostridium perfringens and C. difficile, certain Escherichia coli (enterotoxigenic, enteroinvasive, enteropathogenic, enterohemorrhagic, enteroadherent), Salmonella spp., and perhaps Yersinia enterocolitica (see Table Definitive, Suspected, and Unproved Pathogens of the Large Intestine of Dogs and Cats). Culture results should always be interpreted in light of clinical signs, other findings such as coinfections, and substantiating laboratory data such as serologies or polymerase chain reaction (polymerase chain reaction) results Feral cultures should not he performed for the purpose of diagnosing small intestinal bacterial overgrowth.

Molecular Diagnosis

A number of polymerase chain reaction and reverse transcriptase (RT)-polymerase chain reaction assays have been developed for gene amplification products and messenger RNAs of infectious organisms. Assays are now available for the molecular diagnosis of Tritrichomonas foetus, Pythium insidiosum, Campylobacter jejuni, Clostridium perfringens, C. difficile, E. coli, Salmonella spp., and Brachyspira pilosicoli, and many more are likely forthcoming. Molecular detection has become the standard for infectious disease diagnosis in many instances.

Exfoliative Cytology

Exfoliative rectal or endoscopic cytology may be useful in identifying causative agents (e. g., fungal elements, neoplastic cells) and inflammatory cells (e. g., lymphocytes, eosinophils). Rectal smears may be obtained with cotton-tipped applicator or conjunctival spatula during anorectal examination or with a cytology brush at the time of endoscopy. A good correlation (specificity: 97%; sensitivity: 93%) has been shown between exfoliative cytology and subsequent endoscopic or surgical biopsy in one study. Additional studies will be needed to verify the diagnostic value of this test.

Imaging

Survey abdominal radiographs may occasionally document colonic foreign objects, mesenteric or sublumbar lymphadenopathy, intussusception, and extraluminal compression; however, survey radiographs are generally nonspecific in the diagnosis of colonic disease. Contrast studies (i. e., barium enema) are performed infrequently because of their poor sensitivity and requirement for general anesthesia. Ultrasonographic imaging has proved more useful in documenting mass lesions, Iymphadenopathy, intussusceptions, and bowel thickening. Abdominal ultrasound may also be used to facilitate percutaneous aspiration of luminal masses, mucosal thickenings, and lymph nodes. Computed tomography (CT) colonography, also known as virtual colonoscopy, has been successfully implemented in human medicine and has been studied experimentally in the dog.

Colonoscopy

Colonoscopy is indicated for the diagnosis of colitis-type diarrhea unresponsive to dietary modification and medical therapy, suspected colorectal neoplasia, chronic constipation, unexplained stricture, and evaluation of prior surgical or medical treatment. Colonoscopy is performed after other noninvasive diagnostic tests (e. g., fecal parasitologic examination, fecal bacteriologic examination, exfoliative cytology, abdominal ultrasonography, survey ± barium contrast radiography) have failed to diagnose the disease.

Rigid or flexible endoscopy may be performed, but flexible endoscopy provides better visualization and examination of the entire colon. The normal colonic mucosa is pink in color, smooth in texture, and glistening in appearance. Unlike the esophageal, gastric, and duodenal mucosa, submucosal blood vessels are readily apparent. The mucosa should not hemorrhage when abraded by the endoscope; active hemorrhage usually implies an underlying disorder such as inflammation or infection. The colonoscopic procedure should include examination of the more proximal structures (e. g., ascending colon, cecum, ileocecal sphincter, distal ileum) whenever possible. The proximal colon is an important site of inflammation, parasitism, ileocolic intussusception, cecal inversion, and neoplasia.

Fecal materials must be completely evacuated before the colonic mucosa can be properly examined. Incomplete bowel preparation is the major reason for an unsuccessful colonoscopic examination. Patient permitting, food should be withheld for 36 to 48 hours so that fecal material does not accumulate in the colon. The patient should also be given warm-water enemas, gastrointestinal lavage solutions, or both. Lavage solutions are preferable to warm-water enemas, but both may be given to facilitate successful colonoscopy. Polyethylene plvcol solutions are isosmotic, administered orally, and induce a diarrhea that rapidly removes fecal material trom the bowel.

Large volumes may be administered without inducing significant changes in water or electrolyte balance. Electrolyte solutions should be given at a dose of 25 mL / kg at 24 and 12 hours prior to colonoscopy. Warm-water enemas should be performed gently, without irritating substances, at 24, 6, and 2 hours before colonoscopy. The combination of a 36 to 48 hour food-fast, gastrointestinal lavage solution, and enemas will usually result in a colon that is free of fecal fluids and solids. Endoscopic examination of the colon is described in detail. Diseased tissue, nondiseased tissue, and the transition zone between diseased and nondiseased tissue should be biopsied during colonoscopic procedures. This standard helps to verify the extent of the disease, ensures that disease in the submucosa has not been missed, and provides representative tissue samples to the pathologist to diagnose the disease. In some cases of severe inflammatory bowel disease or colonic neoplasia, advanced tissue necrosis may prevent the diagnosis of the disease process in the central part of the lesion. In the absence of gross mucosal abnormalities, three to five biopsy specimens should be obtained from each of the midascending, midtransverse, and mid-descending colonic regions.