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September 25, 2003
Treatment Options for Perianal Fistulas in Dogs

Perianal fistulas are abnormal passages into the rectum near the anus. Bacteria, moisture, feces, and other secretions can accumulate in the sinus of a fistula. Most affected dogs, such as German shepherds, have a low tail carriage, broad tail, and long hair, which may mask the lesion. Owners may report the dog licks of the perianal area; may have bloody stools, diarrhea, constipation, or foul discharge; and may be lethargic, and have personality changes and loss of appetite, perhaps due to chronic pain.

There may be an immunologic basis for perianal fistulas, because dogs often respond to immunosuppressive drugs. Mathews et al evaluated treatment with oral cyclosporine vs. placebo for 16 weeks. All lesions increased in size and depth in the placebo group, while surface area and depth decreased by 78% and 62% in the cyclosporine-treated group. By 16 weeks, fistulas had healed completely in 85% of the dogs; however, fistulas recurred in almost half of the dogs when treatment was discontinued. Even in dogs in which fistulas were not completely healed, cyclosporine administration appeared to be beneficial, because the surgical procedures that were required were less extensive than those that would have been necessary if cyclosporine had not been given.

The current recommendation is to treat dogs for as long as there is progressive improvement, and for 4 additional weeks after all fistulas resolve. Cyclosporine blood levels should be monitored. Ketoconazole can be administered concurrently with cyclosporine to reduce the amount and cost of cyclosporine required in large animals.

Tacrolimus is 10-100 times more potent than cyclosporine, is reported to have fewer side effects, is effective topically, and is less expensive than cyclosporine. Misseghers et al evaluated ten dogs with perianal fistulas who were treated with topical tacrolimus 0.1% ointment once to twice daily for 16 weeks. Full healing of the fistulas occurred in 50% and was noticeably improved in 90% of dogs.

Oklahoma State Univ College of Veterinary Medicine newsletter, Vol. 10, No. 1, 2003
Can Vet J. 2000 Aug;41(8):623-7
J Am Vet Med Assoc. 1997 Nov 15;211(10):1249-53
J Am Vet Med Assoc. 2002 Apr 1;220(7):1009-16 - Aust Vet J. 2002 Apr;80(4):207-11

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