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Perianal Fistulas in Dogs
Veterinary & Aquatic Services Department, Drs. Foster & Smith
Skin Conditions
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Perianal fistulas are chronic and progressive lesions that occur around the anus in dogs. Deep and draining ulcers form, which are painful. The disease may also be referred to as "anal furunculosis."

What causes perianal fistulas?

The exact cause of these fistulas is not known, but is thought to start as an inflammation of the sweat and sebaceous (oil) glands in and around the anus, followed by infection of the area. Abscesses form, open, and then drain. The warm, moist area around the anus and under the tail, and the large numbers of bacteria in the area, make an excellent environment for bacteria to multiply.

What dogs are at risk for perianal fistulas?

Perianal fistulas most commonly occur in middle-aged (5-8 years old) male dogs, but can occur in dogs as young as 1 year and as old as 14 years. German Shepherds are particularly prone to this disease, and in one study accounted for 84% of the dogs diagnosed. This may be due to the larger number of glands in the perianal area when compared to other breeds, or the way the tail is set and carried. German Shepherds are also more prone to immune-mediated diseases, which may be a component of this condition. Other breeds that have been reported as having perianal fistulas include Labrador Retrievers, Irish Setters, Old English Sheepdogs, Border Collies, Bulldogs, Spaniels, and mixed breeds.

What are the signs of perianal fistulas?

Dog licking perianal areaA dog with perianal fistulas will often chew or lick the perianal area more frequently, or may scoot his anal area across the floor or ground. A dog with this disease may be constipated, have diarrhea, or pass stools more frequently. The dog may also have difficulty or show pain on passing stool, strain, have fecal incontinence (cannot control the bowel movements), or have blood in the stool.

Ulcers and bleeding may be seen around the anal area, as well as foul-smelling discharge. The ulcers may be very small, or over several inches in diameter, and may extend up the tail. The anal glands and rectal tissue may also be involved. Some dogs will become lethargic, lose their appetites, and start to lose weight. Because of the discomfort and pain, owners may notice a change in behavior of the dog. Even lifting the tail may cause extreme pain. The area around the anus may become darker in color as the chronically inflamed skin develops more pigment.

How are perianal fistulas diagnosed?

Diagnosis is based on physical examination and history. Sedation may be necessary to perform a thorough examination since the condition can be very painful. Biopsy samples will confirm the diagnosis.

How are perianal tumors treated?

Medical and surgical treatments have both been used. Mild conditions may be treated with clipping the hair in the anal region, cleansing the area with an antiseptic solution, and flushing with large amounts of water (hydrotherapy). For more serious conditions, a combination of oral cyclosporine and ketoconazole has been shown to be effective in treating these fistulas. Treatment usually must last for 7-9 weeks. Most dogs will show remission with this treatment, however, recurrence is common after treatment is stopped, especially in dogs that had moderate or severe disease.

Treatment with dietary changes and high doses of prednisone has also been attempted, however, it does not appear to be as effective.

Surgical treatment of perianal fistulas can be difficult because of the many nerves and blood vessels in the area. In addition, some of the ulcers are very deep. Surgical treatments including removal of the affected tissue, cryosurgery (freezing the tissue), laser surgery, cautery, and even tail amputation have been used. Complications after surgery include fecal incontinence and anal stenosis (scarring of the anal area, making it difficult to pass stool).

What is the prognosis for dogs with perianal fistulas?

Regardless of the treatment used, the earlier the condition is diagnosed and treated, the better the outcome. In most cases the prognosis is guarded to fair, understanding that recurrence is common. In more severe cases, and those involving surgery, fecal incontinence is a major concern.

 
References and Further Reading

Day, MJ; Weaver, BMQ. Pathology of surgically resected tissue of 305 cases of anal furunculosis in the dog. Journal of the Small Animal Practitioner. 1992;33:583-589.

DeNovo, RC; Bright, RM. Recto-anal disease. In Ettinger, S. (ed). Textbook of Veterinary Internal Medicine. W.B. Saunders Co. Philadelphia, PA; 2000.

Patricelli, AJ; Hardie, RJ; McAnulty, JF. Cyclosporine and ketoconazole for the treatment of perianal fistulas in dogs. Journal of the American Veterinary Medical Association 2002;220:1009-1016.

Sherding, RG. Anorectal diseases. In Birchard, SJ; Sherding, RG (eds.) Saunders Manual of Small Animal Practice. W.B. Saunders Co. Philadelphia, PA; 1994.

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