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Perianal Fistula in Dogs

By Ernest Ward, DVM

Medical Conditions, Pet Services

What is perianal fistula?

perianal_fistula_in_dogs-1_2009Perianal fistula, also known as anal furunculosis is a serious medical condition that 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 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 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."

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 Behavior changes are common, some dogs will become withdrawn or act depressed and others may appear agitated or even aggressive.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, you should contact your veterinarian.

What tissues are affected by perianal fistulas?

Perianal fistulas are characterized by chronic, purulent (pus producing), smelly, ulcerating, sinus 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?  

perianal_fistula_in_dogs_2_2009The cause 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. In fact, tail amputation was an early attempt to treat this frustrating condition.

"...condition may have an autoimmune cause."

Recent work indicates the condition may have an autoimmune cause. There may also be a genetic component to the condition, since some families of German shepherd dogs appear particularly prone.

Is there any sex or age predisposition?

No. Adult dogs of either sex can become victims of the disease, although there appears to be a higher prevalence of the disease in non-neutered animals of either sex. It is most commonly diagnosed in dogs over seven years of age.

How is the condition treated?

Since the cause of the condition is not well understood, it is not surprising that many forms of treatment have been suggested.

  • In mild cases, the condition will improve with medical treatment, but frequently the improvement is not permanent. Currently, the treatment of choice is both cyclosporine and ketoconazole, prescribed simultaneously for a prolonged period, often up to sixteen to twenty weeks. Antimicrobials may also be prescribed to treat secondary bacterial infections. Topical tacrolimus is also prescribed in many cases.
  • A hypoallergenic food trial is recommended since many cases may have an underlying allergic or autoimmune cause.
  • Increasing ventilation of the perianal region by clipping the area, particularly in long-coated dogs, combined with careful systematic bathing and cleaning is a useful palliative measure.
  • In severe cases, surgery to debride or remove as much infected tissue as possible, with or without simultaneous cryotherapy (or freezing) may be beneficial. This will reduce the amount of infection and may stimulate improved healing. Surgery has a high risk of potential complications and is used only in cases where medical treatment fails.

Is treatment curative?

"Many cases will resolve after lengthy treatment."

Many cases will resolve after lengthy treatment. Regardless of whether medical or surgical treatment is pursued, these cases are often frustrating for the pet owners and uncomfortable for the pet.

Up to 20% of cases are unresponsive and require intermittent treatment for life. In these cases, treatment, although not curative, is certainly palliative and reduces the pain and discomfort that the dog experiences.

Contributors: Ernest Ward, DVM

© Copyright 2009 Lifelearn Inc. Used and/or modified with permission under license.

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