Perianal fistula is a chronic inflammatory, ulcerative disease of the perianal tissues that is seen almost exclusively in the German Shepherd dog. The exact etiology of this disease has not been determined as evidenced by the failure of studies that have been performed to investigate a possible immunological, bacterial, endocrine, or anatomic basis for the disease. Consequently, although many different treatment methods have been proposed for this problem, none of those reported are routinely successful in controlling the disease. Previously reported medical management of perianal fistula has included cleansing the affected area, topical administration of antibiotic and steriod preparations, and the use of tail braces in combination with topical antiseptic and systemic antibiotic therapy. Generally, medical management to this point has been considered to be palliative at best plus it has been suggested that it many be detrimental as it delays surgical intervention.
Historically many different surgical procedures have been described in the veterinary literature for the treatment of perianal fistula. Chronologically, these have included surgical excision, chemical cautery, cryosurgery, tail amputation, electosurgery, and laser surgery. All of these surgical procedures have, to some degree, been associated with significant postoperative complications, for example, recurrence, anal stricture formation, fecal incontinence, tenesmus and dyschezia and none of them can be considered to be 100% successful at controlling this disease process.
A number of years ago a German Sherherd dog was presented to Michigan State University for treatment of perianal fistula. During the work-up of this patient it was also discovered that the dog had multicentric lymphosarcoma. Multi-drug chemotherapy was initiated to treat the lymphosarcoma. Within 4 weeks of chemotherapy it was noted that the perianal fistula problem had completely resolved. The response seen in this dog stimulated Dr. Ken Harkin and myself to think about whether perianal fistula was, in fact, just an external manifestation of a systemic disease. The German Shephered breed, besides being uniquely affected with perianal fistula, also has a significant problem with infiltrative/inflammatory bowel dieseases, particularly affecting the colon and rectum. Therefore a prospective study was initiated to investigate the possible association between perianal fistula and colitis/proctitis in the German Shepherd dog and to evaluate the response of perianal fistula to high dose prednisone and an alternative protein diet. The results of this prospective clinical trial have been published and can be summarized as follows:


1. A majority of the dogs had clinical signs that could be attributable to either perianal fistula and/or infiltrative/inflammatory large bowel diesase.
2. All of the dogs had histologic evidence of mild, severe, chronic, infiltrative/inflammatory large bowel disease on biopsy specimens obtained by colonoscopy/proctoscopy.
3. Inflammatory cell infiltration in the biopsy specimens was composed predominantly of plasma cells and lymphocytes, with eosinophilic infiltration being present in 25% of the cases.
4. In general, there was no significant histopathologic improvement in the post-treatment biopsies when compared to the initial biopsies apart from the substantial decrease in the eosinophilic component when present.
5. The treatment protocol resulted in the following response:

-1/3 of the dogs had complete resolution of the perianal fistula lesions and clinical signs.
-1/3 of the dogs has resolution of the clinical signs and significant improvement/stabilization of the perianal fistula lesions.
-1/3 of the dogs had little or no improvement of clinical signs or perianal lesions.
The findings from this study raised the following points and questions:


1. The results tend support the concept that perianal fistula is not an independent disease entity but is , in fact an external manifestation of a systemic process, namely infiltrative/inflammatory large bowel disease. A similar problem is seen in humans with Crohn's disease who can develop anal fistulae.
2. Perianal fistula may well be an immunologically mediated disease. A food allergy component may need to be considereed as an underlying cause.
3. It is known that improvement in clinical signs associated with infiltrative/inflammatory large bowel disease can occur without histologic improvement on biopsy. This suggests that the underlying disease is not cured but only kept under control. The implication of this is that German Shepherds with perianal fistula need to be followed over a long period as relapse is possible. This can be seen clinically, for example, where a dog is free of disease for over two years and then relapses.