Perianal Fistulae

Perianal fistulae (anal furunculosis) are encountered most frequently in the German Shepherd, and are characterized by chronic infection and ulceration of the tissues around the anus. There are often deeply infiltrating, fistulous tracts which run under the skin and up to three to four inches along the rectal wall.

While the precise cause is unclear, some German Shepherds seem to be unable to resist superficial infections which may arise in the skin. This may be the result of an ineffective immune response resulting in predisposition to the development of persistent skin infections. Additionally, the conformation of the German Shepherd allows for the broad base of the tail to remain in almost continual contact with the anus, thereby spreading a thin film of feces over the perianal region.

The anal sacs (scent glands) are usually involved and are removed as part of the initial treatment. It should also be emphasized that a dog’s predisposition to the development of perianal fistulae is lifelong. Relapses, although uncommon, may occur even after treatment.

Symptoms

The primary lesions are deep, draining, fistulous openings around the anus which will not heal. They may spread to a large portion of the perianal area. Many dogs with perianal fistulae will show few signs of discomfort apart from licking the anal region, but in advanced cases there may be damage and scarring which prevents normal defecation. These dogs may experience constipation and pain when passing feces. Other dogs with severe perianal fistulae may not be able to close the anus properly and may become incontinent.

Treatment

No single technique has been shown to result in a consistent cure for perianal fistulae. Nevertheless, surgical removal of the infected tissue followed by reconstruction of the surrounding skin has met with good results. The key to success is to resolve the chronic, deep, fistulous drainage while maintaining fecal continence. Damage to the anal sphincter from the deep fistulae can lead to fecal continence so preservation of the anal sphincter is of paramount importance to the surgeon.

Lesions will completely resolve in considerably more than 75% of those dogs that undergo surgical reconstruction. Some of these dogs, however, will need more than one surgery.

It is vitally important that dogs are regularly examined until complete resolution of the tracts is achieved. When a second surgery is required, its purpose is to remove the smaller, residual perianal fistulae and therefore minimize the chance of recurrence.

Regrettably, a small percentage of dogs will not respond to surgery and will continue to have problems or incontinence. These dogs are often identified at the initial examination and are documented as high risk patients prior to treatment.

Recent developments in the medical management of perianal fistulae suggest there is not only a bacterial but also a possible immune component to the disease. Immunomodulating drugs are therefore under investigation for the prevention of fistulae recurrence and may be recommended for your pet.