Perianal fistulae are a painful disease of the perianal, anal and perirectal tissue in dogs. They are primarily seen in German shepherd dogs. The cause is unclear, but a dysregulated immune system is suspected to be the cause. Historically, aggressive surgical debridement of the ulcers or cryotherapy were the primary treatments, although recurrence and postsurgical complications were common. In recent years, the treatment of choice has become immunomodulation with cyclosporine or tacrolimus.
Perianal fistulae often have a classic clinical appearance of fistulous tracts to severe ulcerative dermatitis in the peri-anal region. The main differential diagnoses are neoplasia or anal sac abscess. If possible, one should try to palpate the anal sacs to determine if they are intact. Admittedly, this is often not possible in dogs with severe peri-anal fistulae due to the dog’s pain level. Frequently, the clinical appearance of peri-anal fistulae is distinctive enough to initiate therapy.
I typically will start patients on Atopica initially at 5 mg/kg per day. Steroids are not usually effective at inducing remission of perianal fistulae. Once the lesions are in remission, I will begin gradually tapering Atopica to the lowest effective dose to maintain remission. I do not start with generic cyclosporine modified unless there are financial constraints. Atopica typically provides a better response than generic cyclosporine modified, although many dogs can eventually be switched to the generic version with no worsening of their clinical signs. Compounded cyclosporine should not be used in animals, as there is significant variability in the amount of active drug, and the drug is not reliably absorbed in compounded form.
Once the lesions are nearly in remission, I will also add topical tacrolimus ointment (Protopic). This is drug related to cyclosporine, and is administered as an ointment. Eventually, many dogs can eventually be transitioned entirely to Protopic, and can have Atopica discontinued. If the dog has relatively small lesions at the time of diagnosis, one could prescribe this as the initial sole therapy. If the dog has severe peri-anal fistulae and is exceedingly painful, this is not my initial treatment of choice!
Antibiotics are often needed initially for secondary infection (which is understandably common given the location!). Treatment for perianal fistulae is unfortunately usually life long, although dogs can usually be maintained on lower Atopica doses or tacrolimus.
Is food allergy an underlying cause?
Dermatologists often will put dogs with peri-anal fistulae on hypoallergenic diet trials. There is no proven link between perianal fistulas and food allergy, and in my experience food allergy is rarely a trigger for fistulae. A diet trial can be performed, as this is an easily treatable potential underlying cause, but do not be surprised if response is not seen.