A German Shepherd plays in the park.

How Do You Treat Perianal Fistulas in Dogs?

Perianal fistulas, otherwise known as anal furunculosis, are painful lesions that may be found in or around the anal and rectal regions of dogs. The defining feature is one or more ulcerative, foul-smelling lesions that may or may not be associated with a secondary infection. As the name implies, these lesions are located around the anus and they may be associated with fistulas, which are regions connecting an area of infection or inflammation deep under the skin with the skin’s surface. Perianal fistulas are chronic, painful, and often affect a patient’s overall quality of life.

What Causes Perianal Fistulas in Dogs?

The definitive cause of perianal fistulas remains widely debated, but most experts agree that they result from multiple factors. Some believe that perianal fistulas are due to an anatomic predisposition, meaning that the individual anatomy of a dog may make it more likely for the disease to occur. This theory was derived from the fact that the most common breed suffering from perianal fistulas, German Shepherds, have broad-based and low-carrying tails. Additionally, dogs with a higher density of sweat glands in the perianal region may also be more predisposed to the condition. The anatomy of the tail and high density of sweat glands create an ideal environment of poor air flow, moisture build-up, and bacterial overgrowth due to the location by the anus.

Another theory is that these patients may have an immunological defect. Interestingly, this stems from research done in humans, which has shown an association with Crohn’s disease and the development of perianal fistulas. German Shepherds, one of the breeds predisposed to this condition, often also suffer from concurrent colitis, or inflammation of the colon and chronic diarrhea. The fact that many of these patients respond well to immunosuppressive and immunomodulatory drug therapy supports this theory.

What Age and Breeds Are Most Affected?

The average age of dogs suffering from perianal fistulas is 5 – 7 years old, but reports have shown the condition in dogs as young as 1 and as old as 14. Male intact (unneutered) dogs tend to be overrepresented.

In one study, German Shepherds represented 84% of the dogs suffering from perianal fistulas. The second most common breed is believed to be the Irish Setter. Other breeds affected include Labrador Retrievers, Old English Sheepdogs, Border Collies, Bulldogs, and various mixed breeds.

What Are Clinical Signs of Perianal Fistulas?

The lesions associated with perianal fistulas can range from small to large ulcerative regions that may even involve the anal sacs and/or rectal tissue.

The clinical signs a dog exhibits are the result of the location of the lesions and associated discomfort. Signs include:

How Are Perianal Fistulas Diagnosed?

There are other diseases that can present similarly to perianal fistulas, such as chronic anal sac infections, colitis, perianal tumors, injury, and infected bite wounds.

The diagnosis of perianal fistulas is typically made using a combination of the patient’s signalment (age, sex, and breed), history, clinical signs, and physical examination.

In one study, 50% of the patients suffering from perianal fistulas also had a confirmed histopathologic diagnosis of colitis. Because colitis and perianal fistulas often occur together and some of their clinical signs may overlap, patients with suspected perianal fistulas typically benefit from an Internal Medicine workup (including colonoscopy and biopsy) to evaluate for underlying colitis.

How Are Perianal Fistulas Treated for Dogs?

Treatment of perianal fistulas involves medical management, surgery, or a combination of the two. Conventionally, mild cases tend to be targeted with medical management, while the more moderate and severe cases have been approached surgically. Regardless of the severity, however, many clinicians may still elect to start with medical management, given potential consequences and complications that can be associated with surgery.

Medical Management

There are two steps to medical management, the induction phase, in which the clinical signs need to be resolved, and the maintenance phase, which keeps the clinical signs in remission. Placing patients on antibiotics, anti-inflammatory agents, pain medications, and/or keeping the area clean may be recommended, but this merely addresses the secondary side effects of perianal fistulas without targeting the underlying cause.

Given the fact that the disorder is thought to result from an immunological defect, patients should also be treated with immunosuppressive drugs, which is often done in combination with dietary and hygiene therapy. One of the most frequently used immunosuppressive drugs is cyclosporine. This drug is quickly metabolized by the body, so some veterinarians will give it in combination with ketoconazole, an antimicrobial that can be used to treat secondary infections and reduce the metabolism of the cyclosporine. Other drugs may include high-dose prednisone, azathioprine, and topical tacrolimus.

Dietary and hygiene therapy are often a core part of medical management. Since many of these patients also suffer from concurrent colitis, they may benefit from being on a novel protein or hydrolyzed protein diet to reduce the chance of their body reacting poorly to the protein in the food. Your veterinarian can speak with you about the various types of diets that exist and help you choose the best one for you and your pet. Hygiene therapy involves keeping the affected area clean and dry in order to help reduce the chances of secondary infections, which may make clinical signs worse. Secondary infections can be treated with antimicrobial agents, but it is always recommended that you talk to your veterinarian regarding culture and susceptibility testing to identify the infectious agent prior to initiating treatment. Placing your pet on the incorrect antimicrobial medication or one that they don’t need can lead to overall antimicrobial resistance in your pet, the environment, and the community.

Surgical Removal

Neutering of intact male dogs is always recommended for multiple health reasons, including reducing the risk of perianal fistulas. Various surgical approaches can also be taken in order to treat the perianal fistulas themselves. The main goal of surgery is to remove the diseased tissue and destroy its lining in order to help prevent recurrence.

Surgical procedures include:

Surgery is not without complications, and narrowing of the anus (anal stenosis), fecal incontinence, and flatulence are just some of the potential side effects. Additionally, some patients may even require a second surgical procedure.


Unfortunately, with both medical management and surgery, this condition still has a high recurrence rate, having been reported as high as 80%. Additionally, many of these patients will require lifelong management and frequent visits to the veterinarian.

You should always talk to your veterinarian about your pet’s condition and its severity, as they can help you choose the right method of therapy with the best chance for remission and minimize the chance for various complications.