Perianal means around the anus, and a fistula is a channel that opens onto the skin. Perianal fistulas, also called anal furunculosis, are painful open sores that show up on their own in the skin around a dog’s anus [1]. Under the skin they form narrow tunnels, called sinus tracts, and some of these tunnels reach as far as the inside of the rectum [2].
If your dog has sores or draining wounds around the anus, strains to pass stool or keeps licking the area, see your vet.
Which dogs get it
Any breed can be affected, but German Shepherds make up the large majority of cases [1]. A UK study of German Shepherds seen in general practice lists anal furunculosis among the problems this breed is known to be prone to [3].
Researchers describe it as an immune-mediated condition [1]. Immune-mediated means the body’s own defense system drives the damage, rather than an outside germ alone.
Wound signs
The sores are ulcers, which are open breaks in the skin [1]. A dog may have one tract or several, and the number of openings can grow when the disease is more active [2]. Under the microscope, the tissue shows long-lasting inflammation with pus-like secretions collecting in the tracts [1], which is why the area can look wet or draining.
Itching around the anus can be an early sign, and in one study it was the first sign that the problem was coming back [1].
Signs beyond the skin
Dogs with this condition often strain to pass stool and find it painful to do so [2]. Many German Shepherds with perianal fistulas also have signs of an inflamed large bowel (colitis) [2], which can show up as loose stool or diarrhea.
Why prompt care matters
Left without effective treatment, the condition can become debilitating for the dog [1]. Getting your dog checked early gives your vet the best chance to bring it under control.
How vets diagnose it
Your vet will look closely at the area around the anus and examine it by hand. A small tissue sample (biopsy) can confirm what the sores are [1]. Other problems near the anus, such as anal gland trouble, can look similar, and only a vet can tell them apart.
Treatment
Your vet will advise on treatment for your dog. Perianal fistulas are often a long-term problem: current treatments aim to control the disease but cannot always cure it, and it can come back [1].
At home, as directed by a vet:
- do not give your dog human or leftover medicines unless your vet says so;
- do not stop or change any medicine without talking to your vet;
- give any treatment exactly as your vet prescribes, for as long as your vet says;
- go back for any recheck your vet books.
When to see your vet
See your vet if your dog has:
- open or draining sores around the anus [1];
- straining or pain when passing stool [2];
- itching, biting or licking at the anal area [1];
- loose stool or diarrhea along with sores near the anus [2];
- any sore or swelling near the anus you are unsure about.
The bottom line
Perianal fistula causes painful, draining sores and tunnels around a dog’s anus, and German Shepherds are affected far more often than other breeds. It is an immune-driven, often long-term condition, so see your vet early if you notice these signs.
This article is for general information only and does not replace advice from your veterinarian. If your dog has sores or draining wounds around the anus, see your vet.
Sources
- Enciso N, et al. In Situ Treatment of Refractory Perianal Fistulas in Dogs with Low-Dose Allogeneic Adipose-Derived Mesenchymal Stem Cells. Animals (Basel). 2024;14(22):3300. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC11591124/
- Maldonado-Contreras A, et al. Dysbiosis in a canine model of human fistulizing Crohn’s disease. Gut Microbes. 2020;12(1):1785246. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC7524328/
- O’Neill DG, et al. Demography and disorders of German Shepherd Dogs under primary veterinary care in the UK. Canine Genet Epidemiol. 2017;4:7. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC5532765/