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Basics ⬇

Basics

Overview

  • Relatively common cause of colitis in boxer breeds and infrequently seen in French bulldogs and border collies.
  • Boxer colitis is also referred to as granulomatous colitis (GC) in light of the granulomatous inflammation (macrophages) in the colon.
  • Etiology of GC is an adherent-invasive E. coli (AIEC) strain.

Signalment

  • Dogs; primarily affects young boxers, usually less than 3 years of age.
  • Reported in French bulldogs and border collies less frequently.

Signs

  • Bloody, mucoid diarrhea with marked increase in the frequency of defecation.
  • Tenesmus.
  • Weight loss and anorexia can occur and debilitation may develop.

Causes & Risk Factors

  • GC appears to be a genetic disorder in boxer breeds associated with reduced macrophage phagocytic function and an inability to kills adherent-invasive E. coli.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Other causes of colitis-non-histiocytic IBD (lymphocytic plasmacytic, eosinophilic colitis, other infectious causes of colitis (pythiosis), parasitic colitis (whipworms), food-responsive diarrhea.
  • Cecal inversion.
  • Ileocolic intussusception.
  • Neoplasia-lymphoma, adenocarcinoma.
  • Foreign body.
  • Colorectal polyps. Dogs with colorectal polyps do not have diarrhea or increased mucus in their stools, and instead have a normal defecation frequency with formed stools coated with frank blood.
  • Irritable bowel syndrome.
  • Differentiate by clarifying the history (colitis vs. colorectal neoplaia), fecal flotations, abdominal imaging, and colonoscopy or proctoscopy and biopsy.

CBC/Biochemistry/Urinalysis

  • Usually unremarkable; microcytic anemia may be present in boxer dogs with GC secondary to intestinal bleeding.
  • Chemistry panel may reveal hypoalbuminemia, electrolyte abnormalities, and prerenal azotemia in dogs with severe diarrhea and anorexia.

Other Laboratory Tests

N/A

Imaging

Abdominal ultrasound in boxer dogs with GC often reveals mild or moderate mesenteric or sublumbar lymphadenomegaly, and the colonic wall can appear thickened.

Diagnostic Procedures

  • Proctoscopy or colonoscopy to obtain colonic biopsies.
  • Most boxer dogs with GC have involvement of the descending colon, underscoring the diagnostic utility of proctoscopy.
  • Common changes in appearance to the colonic wall include erythema, irregularity, and ulceration of the colonic and rectal wall.

Microbiologic Testing

E. coli is commonly isolated on routine bacteriologic media from feces of both healthy dogs and dogs with diarrhea. However, attempts to isolate E. coli from colonic biopsies is recommended for sensitivity testing and optimization of antimicrobial therapy.

Pathologic Findings

  • Histopathologic lesions include neutrophilic inflammation, epithelial ulceration, crypt hyperplasia and distortion, decreased numbers of goblet cells, and large numbers of macrophages that stain positive with periodic acid-Schiff (PAS) stain.
  • The presence of E. coli within macrophages can be confirmed using fluorescent in-situ hybridization (FISH).

Treatment ⬆ ⬇

Treatment

Medications ⬆ ⬇

Medications

Drug(s)

Antimicrobials-First-Line Therapy

  • Enrofloxacin (10 mg/kg q24h), for a minimum duration of 6–8 weeks is typically associated with rapid resolution of clinical signs and resolution of histopathologic abnormalities.
  • Because enrofloxacin resistance has been documented in some isolates from dogs with GC, attempts to isolate E. coli from colonic biopsies before treatment is recommended such that antimicrobial susceptibility testing can be performed.
  • Antimicrobials that penetrate intracellularly, such as fluoroquinolones, chloramphenicol, rifampin, or trimethoprim-sulfonamides, should be preferentially chosen for treatment based on the results of antimicrobial susceptibility testing.
  • Chloramphenicol and trimethoprim-sulfonamide should be considered for cases resistant to fluoroquinolones.

Anti-inflammatory/Immunosuppressive Drugs

  • Rarely indicated in dogs with GC, and used at anti-inflammatory dose in conjunction with appropriate antimicrobial therapy.
  • Diagnosis must be reconsidered if there is no dramatic improvement in clinical signs following administration of fluoroquinolone therapy because not all boxers with signs of colitis have GC.

Contraindications/Possible Interactions

Avoid anticholinergics or other motility modifiers such as Imodium in dogs with an infectious cause of their diarrhea.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Monitor clinical signs, stool consistency and frequency, and body weight.
  • Dogs showing a favorable response should improve within 3–5 days of starting fluoroquinolone therapy.

Prevention/Avoidance

N/A

Possible Complications

Colonic stricture if inflammation is uncontrolled for long periods.

Expected Course and Prognosis

  • Generally good prognosis following appropriate antimicrobial therapy.
  • Increasing injudicious administration of fluoroquinolones to dogs is increasing the resistance of E. coli to this class of antimicrobials, necessitating the use of alternative antimicrobials in a subset of dogs.

Miscellaneous ⬆

Miscellaneous

Pregnancy/Fertility/Breeding

  • Boxers, French bulldogs and border collies with GC should not be bred.

Abbreviations

  • IBD = inflammatory bowel disease
  • GC = granulomatous colitis
  • FISH = fluorescent in-situ hybridization
  • PAS = periodic acid–Schiff

Suggested Reading

Craven M, Dogan B, Schukken A, et al. Antimicrobial resistance impacts clinical outcome of granulomatous colitis in boxer dogs. J Vet Intern Med 2010, 24(4):819–824.

Author Stanley L. Marks

Consulting Editor Stanley L. Marks