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Perianal Fistulae

Issue Description
Canine anal furunculosis (perianal fistula) is a formation of an abnormal channel between the anal canal and the skin surrounding the anus. The continual discharge of watery pus from the fistula can irritate the skin and result in itching, discomfort and pain.
Other Names
Canine Anal Furunculosis, Anal Fistulae

While the precise cause of the disease is unclear, some German Shepherds seem to be unable to resist even superficial infections which may arise in the skin. This may be the result of an ineffective immune response resulting in predisposition to the development of skin infections as a persistent problem. Additionally, the conformation of the German Shepherd allows for the broad base of the tail to remain in almost continual contact with the anus, thereby spreading a thin film of feces over the perianal region. Hence this is the site which is affected most frequently. Recent evidence, however, points to an immune-mediated process as the underlying cause of this disease.

The anal sacs (scent glands) are usually involved in the disease process and are removed as part of the initial treatment. It should also be emphasized that a dog's predisposition to the development of Perianal Fistulas is lifelong. Relapses, although uncommon, may sometimes occur even after apparent care.

It is most common in German Shepherd and Irish Setter breeds. However, it has been seen in other breeds. Males outnumber females by 2 to 1. Clinical signs are characterized by multiple draining tracts and ulcers immediately surrounding the rectum. Animals may present pain and spasm when attempting to evacuate the bowels (tenesmus), difficulty in defecation and constipation. Affected area is usually very painful. An association between perianal fistulas and inflammatory bowel disease is suspected.

Clinical signs of anal furunculosis:

  • Pain or spasm when attempting to pass urine or evacuate the bowels (tenesmus)
  • Passage of red blood through the rectum
  • Constipation
  • Diarrhea
  • Ribbon like stool
  • Increased frequency of defecation
  • Perianal pus-filled discharge and/or bleeding
  • Perianal licking
  • Self mutilation
  • Perianal pain
  • Scooting
  • Offensive odor
  • Low tail carriage
  • Weight loss

  • Diagnosis
    Diagnosis is based on physical examination and history. Sedation may be necessary to perform a thorough examination since the condition can be very painful. Biopsy samples will confirm the diagnosis.

    In the past, treatment for perianal fistulas included surgical ablation (removal of the fistula) or deroofing (removal of the skin covering each tract). In general, surgery has been replaced by the use of immunosuppressive drugs. The response to cyclosporine, prednisone, and tacrolimus has been encouraging. Cyclosporine is generally considered to be the drug of choice and is typically used on a 16-week course of treatment. Surgery, once widely used, is presently reserved for cases that involve the anal sacs or for selective cases that do not respond to medical management.

    Regardless of the treatment used, the earlier the condition is diagnosed and treated, the better the outcome. In most cases the prognosis is guarded to fair, understanding that recurrence is common. In more severe cases, and those involving surgery, fecal incontinence is a major concern.

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