Perianal Fistula in Dogs

What is perianal fistula?

Perianal fistula, also known as anal furunculosis, is a serious medical condition. It most commonly affects German shepherd dogs but may also occur in other purebred or mixed-breed dogs.

Perianal refers to the area immediately surrounding the anus or termination of the digestive tract. A fistula is an abnormal connection or tunnel that forms between two tissues, organs, or vessels that normally do not connect.

In affected dogs, the condition is usually associated with an infection in the perianal region, and there are usually one or more draining tracts (tunnels) present.

What are the clinical signs of anal furunculosis?

In its early stages of development, there may be few clinical signs and the condition may go unnoticed. Some cases are discovered during a routine physical examination or when the dog is being bathed or groomed.

As the disease progresses, the affected dog will usually strain during defecation, and there will be blood in the feces. A decreased appetite (anorexia) is common in dogs with perianal fistulas. Usually, the dog will lick excessively at its tail and rectal regions. Some dogs will be reluctant to sit, some may not wag their tail normally, and some may become aggressive if the tail or hindquarters are touched. Behavior changes are common. Some dogs will become withdrawn or act depressed, and others may appear agitated or even aggressive. If your dog demonstrates any of these signs, contact your veterinarian.

What tissues are affected by perianal fistulas?

Perianal fistulas are characterized by chronic, purulent (pus producing), smelly, ulcerating, tracts in the anal region and surrounding skin. The condition could be compared with a carbuncle - a many-headed abscess. This is why some veterinarians prefer use of the term furunculosis - a skin condition characterized by the development of recurring boils.

What causes perianal fistulas to form?

The cause of perianal fistulas is not fully understood, although impaction or infection of the anal sacs (anal glands) and adjacent sinuses and crypts has been suggested. Poor air circulation around the anal region has long been proposed as a major contributory factor. More recent studies indicate that the condition is more likely caused by an autoimmune disease. There also appears to be a genetic component to the condition, since some families of German shepherd dogs appear particularly prone. One study indicates that approximately 80% of cases occur in German shepherds.

Is there any sex or age predisposition?

Yes. Perianal fistulas are more common in intact males and occur primarily in middle-aged dogs.

How is the condition treated?

Surgical treatment of perianal fistulas was previously the treatment of choice. However, medical management with immune- modulating drugs is now the preferred therapy. Improvement can often be seen quickly; however, it can take several months of treatment to get the disease under control.

Medical management of this disease is divided into an induction phase and a maintenance phase that involves a topical medication such as tacrolimus (brand name Protopic®), and an oral medication such as cyclosporine (brand name Atopica®). Antimicrobials are also often prescribed in the induction phase to treat secondary bacterial infections. A hypoallergenic food trial may be recommended since many cases have been linked to an underlying allergy.

Symptoms can often be improved by clipping the hair in the perianal region, particularly in long-coated dogs, to increase ventiliation. Careful, systematic bathing and cleaning can also provide relief.

In severe cases, surgery to debride or remove as much infected tissue as possible may be beneficial, with or without simultaneous cryotherapy (or freezing). This process reduces the amount of infection and may stimulate improved healing. Surgery has a high risk of complications and is used only in cases where medical treatment fails.

Is treatment curative?

Many cases resolve after lengthy treatment. Regardless of whether medical or surgical treatment is pursued, these cases are often frustrating for pet owners and uncomfortable for the pet. Recurrence is possible. Up to 20% of cases will not completely resolve and will require intermittent treatment for life. In these cases, treatment does not cure, but reduces the pain and discomfort the dog experiences.