(also called “perineal fistulae,” “anorectal abscesses”,
“perianal fissures,” “perianal sinuses,” and “pararectal fistulae.”)

Most people are not in the habit of inspecting the area under their dog’s tail unless the dog seems to be doing something that indicates a problem. A dog will lick under the tail, scoot his or her rear end on the ground, or seem painful sitting or raising the tail. When the tail is lifted and the anus inspected, a dog with perianal fistulae will show deep open crevices, some oozing pus, all around the anal sphincter. Odor may be noted as may be straining to defecate. This condition waxes and wanes but ultimately over time is progressive, ulcerating the surface of the anus and its surroundings.

WHAT CAUSES THIS CONDITION?

At the present time, no one knows but recent information suggests an immune-mediated basis. There seems to be some genetic basis as the German shepherd dog seems predisposed to development of this condition, though this phenomenon may be more about conformation than about a specific genetic factor for the disease. The German shepherd dog also has an increased number of apocrine sweat glands, the type of sweat glands that produce stinky oily sweat (as opposed to watery sweat), in the anal area relative to other breeds. The average age of onset is 5 years and approximately twice as many males are affected as females. The anal glands may or may not be involved in the fistulation.

Approximately 80% of affected dogs are German shepherd dogs.

WHAT ELSE COULD IT BE?

A biopsy is necessary to confirm the diagnosis as the following conditions can appear similar to perianal fistulae:

• Squamous Cell Carcinoma of the anus (cancer)
   
• Hyperplastic Anus (common in older unneutered male dogs)
   
• Perianal Adenoma (benign tumor also common in older unneutered male dogs)
   
• Anal Sac rupture

TREATMENT

After the diagnosis is confirmed, there are several aspects to therapy. It should be realized from the beginning that it will take 2-5 months to get the lesions under control and that maintenance therapy will likely be needed for the remainder of the animal’s life.

• ANTIBIOTICS

Since these lesions are commonly infected at least at the beginning of treatment, antibiotics are typically prescribed. A topical antibiotic may be helpful for long term infection control.

• STOOL SOFTENERS

Because of the ulcerations, defecation may be painful. To minimize the straining, stool softeners may be prescribed.

• NOVEL PROTEIN DIET

Food allergy seems to be a possible etiology in this condition so using foods that the patient could not possibly be allergic to has been a recommended adjunctive therapy. Such diets are typically made from unusual protein sources such as rabbit, duck, kangaroo, fish, or venison. Most veterinary hospitals stock an appropriate food.

• IMMUNOSUPPRESSIVE DRUGS

The drug that seems to have emerged as drug of choice is cyclosporine, an immunomodulator originally used for organ transplant patients. The drug is relatively expensive and its dose can be effectively decreased by concurrent use of the antifungal drug ketoconazole (which increases blood levels of cyclosporine). Because cyclosporine absorption varies between individuals, therapeutic blood levels are monitored (meaning blood tests are needed to make sure adequate cyclosporine levels are achieved).

Another immunosuppressive protocol involves prednisolone, azathioprine, and metronidazole and is particularly helpful to patients with concomitant inflammatory bowel disease. This protocol is substantially less costly than cyclosporine but 30% of dogs can be expected to fail to respond.

A topical crème called tacrolimus can be used along with oral medications or alone for very mild cases. This is also an immunomodulator and is much stronger than cyclosporine.

Whatever the immunosuppressive protocol, it is best to re-evaluate the patient every 3-5 weeks to see if modifications are necessary. Most of the medications listed above are reviewed in our pharmacy library if more details are desired.

• SURGERY

Before the advent of cyclosporine, perianal fistulae were treated surgically with mixed results. Presently, surgery is only recommended for patients for whom immunosuppression has failed or where the anal glands are involved. The goal of surgery is to remove the proliferative or dead tissue, prevent or treat any anal or rectal strictures (narrowed areas caused by scarring), and change the “environment” of the perineal region. Tail amputation may be required; in fact, in one study, tail amputation alone was 80% successful in preventing recurrence of the fistulae.

If the anal glands are involved in the fistulae, they will have to be removed. In milder cases, chemical cauterization of fistulae (which destroys abnormal tissue and allows normal tissue to heal in) may be helpful. Cryotherapy, where a freezing agent is used instead of a chemical one, has been less effective (more scarring, less control over the area treated etc.) Laser therapy, on the other hand, has been 95% successful in preventing recurrence and controlling pain (20% of patients developed fecal incontinence but most of these cases were controlled with diet).

The more extensive the surgery, the more the potential for complications. Stool softeners are typically needed for a month after surgery and the owner should be comfortable cleaning the anal area. Fecal incontinence, narrowed anus, and inability to control the fistulation are the chief complications with surgery.

Despite innovations such as cyclosporine, perianal fistulae can be extremely frustrating.

For more information, visit the American College of Veterinary Surgeons page at:

www.acvs.org/AnimalOwners/HealthConditions/SmallAnimalTopics/PerianalFistulasinDogs/