Perianal Fistulas (anal Furunculosis) is a disease encountered most frequently (although not exclusively) in the German Shepherd Dog, and is characterized by chronic infection and ulceration of the tissues around the anus. More importantly, there are often unseen, but deeply infiltrating, fistulous tracts which run under the skin and along the rectal wall up to 3 and 4 inches (10cm) deep.
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 dogs predisposition to the development of Perianal Fistulas is lifelong. Relapses, although uncommon, may sometimes occur even after apparent care.
The primary lesions are deep, draining, fistulous openings around the anus which will not heal. They may spread to involve a large portion of the perianal area. Many dogs with perianal fistulas will show few signs of discomfort apart from licking the anal region, but in advanced cases there may be damage and scarring which prevents normal defecation. These dogs may experience constipation and pain when passing feces. Other dogs with severe perianal fistulas may not be able to close the anus properly and become incontinent.
No single technique has been shown to result in a consistent cure for perianal fistulas. Nevertheless, surgical removal of the infected tissue followed by reconstruction of the surrounding skin has met with good results. The key to success is to resolve the chronic, deep, fistulous drainage while maintaining fecal continence. The damage to the anal sphincter from the deep fistulas determines fecal continence and thus, its preservation is of paramount importance to the surgeon.
Lesions will completely resolve in considerably more than 75% of those dogs which receive surgical reconstruction. Some of these dogs, however, will need more than one surgery.
It is vitally important that they are routinely examined until complete resolution of the tracts is achieved. When a second surgery is required, its purpose is to remove the smaller, residual perianal fistulas and, therefore minimize the chance of recurrence.
Regrettably, a small percentage of dogs will not respond to surgery and will continue to have problems or incontinence. These are often identified at the initial examination and are documented as high risk patients prior to treatment.
Recent developments in the medical management of perianal fistulas suggest there is not only a bacterial, but also a possible immune component to the disease. Immunomodulating drugs are therefore under investigation for the prevention of fistula recurrence and may be recommended for your pet.
Copyright 1998, Southern
California Veterinary Surgical Group