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Perianal Fistula in Dogs

What Is a Perianal Fistula in Dogs?

Perianal fistula in dogs refers to an abnormal opening near the anus, which should not be present. The condition, also known as anal furunculosis, can manifest as one or a few small openings or as multiple large, draining wounds resembling ulcers near the anus. It causes significant discomfort and pain to affected dogs.

The anus serves as the passage for stool during bowel movements. When a perianal fistula develops, pet owners may observe a small opening or discharge near the anus. This opening forms a tunnel, or tract, connecting the anus to the surrounding skin, typically infected.

Although perianal fistulas can become serious if left untreated, they do not typically constitute a medical emergency and can be managed during regular veterinary hours.

Symptoms and Types

  • Presence of a draining tract or hole near the anus
  • Redness, discharge, pus, or moist skin around the anus
  • Difficulty or straining during bowel movements
  • Presence of blood in the stool
  • Issues with fecal control such as incontinence, constipation, or diarrhea
  • Loss of appetite
  • Excessive licking or biting of the rear end
  • Reluctance to sit or wag the tail
  • Signs of discomfort or aggression when the hind end is touched


The cause of perianal fistulas in dogs remains uncertain, though it is believed to stem from an autoimmune condition where the immune system erroneously targets healthy cells and tissues. There’s likely a genetic predisposition involved, with German Shepherds being the most frequently affected breed. Statistics show that 84% of dogs diagnosed with perianal fistulas are German Shepherds, with middle-aged dogs being more susceptible.

The involvement of the anal glands, also referred to as anal sacs, varies. Infection of these sacs might elevate the risk of developing perianal fistulas. Additionally, many dogs with fistulas may also develop colitis, an inflammation of the colon.


Veterinarians typically diagnose perianal fistulas in dogs through a thorough physical examination. During the examination, the veterinarian will palpate the anus, fistula, and anal sacs. Sedation might be necessary as perianal fistulas can cause discomfort, and sedation helps keep the dog relaxed and stress-free during the examination.

To confirm the diagnosis and rule out other conditions, various factors must be considered. These include anal sac abscesses, tumors of the anal sac and adjacent tissue, as well as other autoimmune and inflammatory diseases, which may present similar symptoms.

Before commencing treatment, your veterinarian might recommend bloodwork to ensure your dog can safely tolerate any oral medications that may be prescribed. Additionally, stool and urine samples, x-rays, and even a tissue biopsy may be required to aid in diagnosis and treatment planning.


Treatment options for perianal fistulas in dogs vary, with management being the primary goal as complete cure is often elusive.

Previously, surgery was commonly considered the best treatment option, but many dogs experienced recurrence of perianal fistulas post-surgery, especially if the anal sacs were involved, prompting their removal.

Currently, oral medications that suppress the immune system are more frequently prescribed. Cyclosporine is a commonly used immunosuppressive medication, although its cost can be prohibitive. Combining it with ketoconazole can reduce the required dose of cyclosporine and alleviate costs.

Prednisone, a steroid, can induce remission in about one-third of dogs with perianal fistulas, though it comes with side effects such as increased thirst, urination, appetite, and weight gain.

Azathioprine, another immunosuppressive medication, may be used alone or with metronidazole to treat perianal fistulas, but it carries risks of serious side effects like bone marrow suppression, liver toxicity, and pancreatitis, necessitating regular bloodwork monitoring.

Tacrolimus, a topical product, offers localized treatment without systemic immunosuppression and is effective in about half of treated dogs. It is often combined with oral medications for comprehensive resolution.

Other experimental therapies like platelet-rich plasma (PRP), stem cell injections, and fluorescent light therapy have been explored. Pet owners should consult with their veterinarians to determine the best treatment approach for their dogs.

Recovery and Management

The road to recovery from perianal fistulas in dogs is often lengthy, but many affected pets can enjoy long and good-quality lives. While most pets exhibit improvement within a few weeks of therapy, treatment typically spans the dog’s lifetime and necessitates regular monitoring. Recurrence of perianal fistulas is not uncommon, prompting pet owners to vigilantly observe the affected area for any signs of relapse.

A potential correlation has been noted between perianal fistulas and food allergies in pets, mirroring findings in human patients with conditions like irritable bowel syndrome (IBD) and perianal fistulas.

Can a perianal fistula in dogs heal itself?

Perianal fistulas in dogs cannot heal by themselves. They always necessitate veterinary intervention. If left untreated over time, perianal fistulas can escalate into severe and debilitating conditions.

How long can dogs live with a perianal fistula?

Dogs with properly managed perianal fistulas can enjoy a lengthy and healthy life. Although some dogs may suffer from more severe manifestations of the condition, potentially shortening their lifespan, most affected dogs can attain remission.

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