What is a Perianal Fistulae?

By Emily Hoppmann, DVM

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 the rear end on the ground, or seem to be in pain when sitting or raising the tail. When the tail is lifted and the anus inspected, a dog with perianal fistulae will show deep open crevices and some oozing pus all around the anal sphincter. Odor may be noted, and the dog might 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 this 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 this condition. 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.

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


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


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

Pain Medication/Anti-Inflammatory

This disease is very painful and the area surrounding the fistula is very inflamed.  It is very important to address the pain and inflammation to allow the area to heal.

Immunosuppressive drugs

The most important drug for treatment is cyclosporine. The drug is relatively expensive, but all other treatment plans are not effective and most dogs fail to respond to them at all.
A topical crème called tacrolimus can be used in addition to oral medications or alone for very mild cases. This is also an immunomodulator and is much stronger than cyclosporine.  It is best to re-evaluate the patient in 2 weeks, then as often as the veterinarian feels is necessary.