Perianal fistula

From Dog
Small perianal fistula[1]
Severe perianal fistulas in a German Shepherd dog[1]

Perianal fistulas (anal furunculosis) are an immune-mediated disease characterized by a chronic, painful and progressive inflammatory disease of the perianal, anal and perirectal tissue.

Recent studies showing clinical resolution with diet changes emphasizes the important role dietary allergens play in the etiology of this disease[2].

This disease mainly affects large breed dogs such as the German Shepherd, Irish Setter, Labrador Retriever, Old English Sheepdog and Border Collie. In German Shepherds, an association between perianal fistulas and colitis exists, further emphasizing the role of inflammatory mediators in this disease[3].

Lesions vary from superficial microscopic fistulas to large ulcerations and sinus tracts. Secondary bacterial infections and anal sacculitis are common.

Clinically affected dogs present with anal licking, yelping when scooting, and increased straining and frequency of defecation.

Conventional treatments have included surgical excision, cryotherapy, laser[4] and chemical cautery and drugs such as azathioprine[5] and metronidazole[6], with variable success.

However, recent understanding of the immune-mediated role of etiology has changed therapeutic approach to this disease, with the use of cyclosporin, 1% topical tacrolimus[7] and ketoconazole showing excellent results in most cases.

Most dogs receive oral cyclosporin (1 - 5 mg/kg daily)[8] and/or ketoconazole (5 - 10 mg/kg daily)[9] in combination with topical tacrolimus twice daily with good responses in most cases.

Some cases have also responded well to tacrolimus, orally administered prednisolone and a novel-protein diet[10].


  1. 1.0 1.1 ACVS
  2. Lombardi RL & Marino DJ (2008) Long-term evaluation of canine perianal fistula disease treated with exclusive fish and potato diet and surgical excision. J Am Anim Hosp Assoc 44(6):302-307
  3. Harkin KR et al (1996) Association of perianal fistula and colitis in the German shepherd dog: response to high-dose prednisone and dietary therapy. J Am Anim Hosp Assoc 32(6):515-520
  4. Shelley BA (2002) Use of the carbon dioxide laser for perianal and rectal surgery. Vet Clin North Am Small Anim Pract 32(3):621-637
  5. Harkin KR et al (2007) Evaluation of azathioprine on lesion severity and lymphocyte blastogenesis in dogs with perianal fistulas. J Am Anim Hosp Assoc 43(1):21-26
  6. Tisdall PL et al (1999) Management of perianal fistulae in five dogs using azathioprine and metronidazole prior to surgery. Aust Vet J 77(6):374-378
  7. Misseghers BS et al (2000) Clinical observations of the treatment of canine perianal fistulas with topical tacrolimus in 10 dogs. Can Vet J 41(8):623-627
  8. House AK et al (2006) Evaluation of the effect of two dose rates of cyclosporine on the severity of perianal fistulae lesions and associated clinical signs in dogs. Vet Surg 35(6):543-549
  9. Patricelli AJ et al (2002) Cyclosporine and ketoconazole for the treatment of perianal fistulas in dogs. J Am Vet Med Assoc 220(7):1009-1016
  10. Stanley BJ & Hauptman JG (2009) Long-term prospective evaluation of topically applied 0.1% tacrolimus ointment for treatment of perianal sinuses in dogs. J Am Vet Med Assoc 235(4):397-404