Page 430 - Small Animal Internal Medicine, 6th Edition

402 PART III Digestive System Disorders

and the serum albumin is well within the normal range (a
serum albumin at the lower end of the reference range may BOX 26.12
VetBooks.ir not be “normal” enough), then it is often most appropriate Major Causes of Hematochezia*
to try therapeutic trials after a few basic diagnostic tests.
Fecal examination to detect whipworms, fecal ELISA to
Anal-rectal disease
detect Giardia (a small bowel problem that can mimic large Dog
bowel disease), and fecal PCR to detect Tritrichomonas (cats) Anal sacculitis (important and common)
are indicated. Therapeutic trials usually consist of high-fiber Neoplasia
diets, elimination diets, antibacterials to control “clostridial” Rectal adenocarcinoma (important)
colitis, and/or treatment for parasites. Rectal polyp (important)
Additional diagnostic tests that may be done instead Colorectal leiomyoma or leiomyosarcoma
of therapeutic trials principally include biopsying colonic Perianal fistulas (important)
Anal foreign body
mucosa by colonoscopy, and fecal assays for toxins (e.g., Rectal prolapse
clostridial toxin) and/or specific organisms (e.g., Campylo- Anal-rectal trauma (e.g., foreign body, thermometer,
bacter, Salmonella). Fecal cultures and antigen tests for spe- enema tube, fecal loop, pelvic fractures)
cific pathogens should be considered if history indicates a
strong likelihood of a contagious disorder. Fecal ELISA and Colonic/intestinal disease
PCR assays should be done before performing enemas or Parasitism
administering lavage solutions. Unless there is a good epide- Whipworms (important and common)
miologic reason to strongly suspect infectious bacteria, fecal Hookworms (severe infections can involve the colon)
cultures and antigen/DNA tests tend to be very low-yield Dietary responsive (intolerance or allergy; common)
procedures that are difficult to interpret. Colonoscopy/ “Clostridial” colitis (common disease but uncommonly
causes hematochezia)
biopsy is principally useful to diagnose histoplasmosis, his- Acute hemorrhagic diarrheal syndrome (important and
tiocytic ulcerative colitis, protothecosis, Heterobilharzia, or common)
neoplasia in dogs, whereas cats are often diagnosed with Parvoviral enteritis (important and common)
colonic inflammatory bowel disease. Histoplasmosis (regionally important and common)
If the results of these tests are not diagnostic, the clinician Pythiosis (regionally important)
must consider three main possibilities. First, the biopsy spec- Intussusception (more common in young animals)
imens may not be representative of the entire colonic mucosa. Ileocolic
For example, if the disease is localized to the region of the Cecocolic
ileocolic valve, it will be necessary to use a flexible endoscope Inflammatory bowel disease
to reach the area. Second, the pathologist may not have rec- Colonic trauma
ognized the lesions. Third, there may be no mucosal lesions. Coagulopathy
This typically occurs in animals with a dietary intolerance or Colonic vascular ectasia
allergy, “clostridial” colitis, or fiber-responsive diarrhea, all Cat
common problems in dogs. Dietary responsive (intolerance or allergy)
Inflammatory bowel disease (important)
Coccidia
HEMATOCHEZIA Rectal tumors (uncommon)

If the patient has hematochezia (fresh blood in the feces) and *These diseases do not consistently produce hematochezia, but
diarrhea, the problem should usually be approached in the when hematochezia is present, these are the most common causes.
same manner as for animals with large bowel diarrhea (see
Chapter 26, pp. 401-402). The patient with normal stools not helpful, then colonoscopy and biopsy are indicated.
plus hematochezia is approached slightly differently. Streaks Barium enema is not recommended. Biopsy specimens of
of blood on the outside of otherwise normal feces usually masses must include submucosa or many neoplastic lesions
indicates a distal colonic or rectal lesion, whereas blood will be missed. Hematochezia is rarely severe enough to
mixed into feces suggests that bleeding is occurring higher cause anemia; however, a CBC can be performed to look for
in the colon. Coagulopathies rarely cause bleeding from the and characterize anemias.
rectum only. Focal bleeding lesions in the distal colon,
rectum, or perineal region (Box 26.12) are especially impor-
tant. Acute hematochezia may also result from trauma (e.g., MELENA
passing a foreign body).
A thorough digital rectal examination is the best initial Melena is caused by digested blood and is seen as “coal tar”-
step (even if anesthesia is necessary). The clinician should black (not just “dark”) feces. Clinicians must distinguish
express each anal sac repeatedly and examine the contents. melena from stools that are intensely dark green. Melena is
If the problem is chronic and digital rectal examination is strongly suggestive of upper alimentary tract bleeding or