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."

A 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.

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).