Perianal Fistulas, Anal Furunculosis
Canine anal furunculosis (perianal fistula) is a formation of an abnormal channel between the anal canal and the skin surrounding the anus. The continual discharge of watery pus from the fistula can irritate the skin and result in itching, discomfort and pain. Most anal fistulas are caused by abscesses (pus-filled sacs) that spread from inside of the anus to the outer surface of the skin.
What causes this condition is unknown. Researches have explored many possible causes, including overproduction by local secretory glands, poor ventilation associated with low tail carriage, anal sac disease, or hip dysplasia. Dogs more than 7 years olad are at higher risk. Contamination of the hair follicles and glands of the anal area by fecal material may result in tissue damage and longterm inflammation of the skin and tissue surrounding the anus. Low thyroid hormone levels or an immune system defect may also contribute to susceptibility. The likelihood of contamination is greater in dogs with a broad-based tail; deep anal folds may cause feces to be retained within rectal glands and play a significant role.
The current theory involves a multifactorial immune-mediated disease process.
An immune-mediated process is suspected because both canine anal
furunculosis and Crohn’s disease respond to immunomodulation.
Accumulating evidence shows that Crohn’s disease is the result of an
unbalanced host immune response to intestinal triggers in genetically
susceptible humans. Because German Shepherds with canine anal furunculosis
also have clinical and histologic evidence of colitis (inflammatory bowel
disease [IBD]), it is possible that enteral triggers (dietary antigens, bacterial
antigens, superantigens) are initiators of canine anal furunculosis as well.
It is most common in German Shepherd and Irish Setter breeds. However, it has been seen in other breeds.
Males outnumber females by 2 to 1. Clinical signs are characterized by multiple draining tracts and ulcers immediately surrounding the rectum. Animals may present pain and spasm when attempting to evacuate the bowels (tenesmus), difficulty in defecation and constipation. Affected area is usually very painful. An association between perianal fistulas and inflammatory bowel disease is suspected.
Clinical signs of anal furunculosis
- Pain or spasm when attempting to pass urine or evacuate the bowels (tenesmus)
- Passage of red blood through the rectum
- Constipation
- Diarrhea
- Ribbon like stool
- Increased frequency of defecation
- Perianal pus-filled discharge and/or bleeding
- Perianal licking
- Self mutilation
- Perianal pain
- Scooting
- Offensive odor
- Low tail carriage
- Weight loss
Diagnosis Diagnosis is based on history, physical findings and skin biopsy. Culture and sensitivity are tests are performed if antibiotic therapy is being considered as part of the treatment. The most common organisms recovered from culture include: E. coli, Staphylococcus aureus, beta-hemolytic Streptococcus, and Proteus mirabilis. Keep in mind that antibiotic therapy has very little impact on the clinical outcome.
Treatment Management of these cases is often disappointing because they do not respond consistently to antibiotics, corticosteroids and surgery.
Keep the affected area clean by clipping the hair and flushing the lesions with chlorhexidine or povidone iodine. Immunosuppressive therapy is helpful in those dogs in which eosinophilic infiltration is most profound. Prednisolone at 1.1 mg/kg twice a day for 14 days, then weaning, is usually adequate but, add azathioprine in cases that did not respond well to prednisolone. Cyclosporine has been reported to be very effective at 5 mg/kg b.i.d. during an average treatment duration of 16 weeks. Surgery is recommended for those animals that fail to respond to medical therapy. Post-operative complications include recurrence of fistulas, fecal incontinence, tenesmus, and difficulty in defecation.
The carbon dioxide laser has been an effective adjunctive tool in treating
canine anal furunculosis in some dermatology practices in the US. Lasers are
used to ablate and/or excise ulcerative necrotic tissue in patients with canine
anal furunculosis.
It is important for owners to understand that canine anal furunculosis is a
chronic relapsing and remitting disease that can be managed but not
necessarily cured. Lifelong therapy may be required as with other immunemediated
diseases. If one drug combination does not achieve the defined
goal, another drug protocol is warranted.
The first goal of therapy should be to alleviate large bowel clinical signs such
as tenesmus, blood discharge from the rectum, constipation or obstipation, diarrhea,
ribbon-like stool, increased frequency of defecation, and perianal pain. The
second goal of therapy should be to reduce the diameter, depth, extent, and
recurrence of sinus tracts.
It is important to keep the perianal region clean and dry. Clipping and
cleaning the perianal region under sedation can assist. Baby powder lightly
applied to the surrounding perineum may reduce regional relative humidity. At
home, antimicrobial shampoo therapy may be helpful once the patient will
tolerate it.
Adapted from
1. Nesbitt G.E. & Ackerman L.J. Miscellaneous Canine Skin Diseases. In: Canine and Feline Dermatology: Diagnosis and Treatment. Veterinary Learning Systems, Trenton, New Jersey, 1998
2. Mathews KA et al. Cyclosporine treatment of perianal fistulas in dogs. Canadian Vet Journal
3. Dermclub 1, 2006: Managing Anal Furunculosis in Dogs
Go Pets America recommends seeking the advice of your local veterinarian for the most appropriate vaccination program and for the diagnosis and treatment of your pet's health problems. For vaccination requirements please contact your state and local licensing authorities.
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