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  Perianal Fistula


Common names or abbreviations:

bulletPerianal Fistula
bulletAnal Furunculosis

Description or definition:

A perianal fistula (anal Furunculosis) is a chronic inflammatory, ulcerative disease most frequently found in, but not exclusive to the German Shepherd Dog.  What is a perianal fistula, you ask? Let’s break it down, piece by piece.


Peri:  all around, near, enclosing, surrounding


Anal: of, relating to, or situated near the anus


Fistula: an abnormal passage leading from an abscess or hollow organ to the body surface, or from one hollow organ to another and permitting the passage of fluids or secretions.

Perianal fistulas, also known as Anal Furunculosis, are ulcerated tracts that develop around the anus.  The tracts are similar to the root system of a plant, spreading out in all directions. These abscesses eat out the flesh around the anus and often into the intestinal tract.  There are often unseen, but deeply infiltrating fistulous tracts that can spread up inside the tail and down into the back legs, along the rectal wall up to 3 and 4 inches deep, and into the dog’s internal organs, eventually causing death.  Perianal fistulas are becoming more widespread by the day, and they hit without care to gender or age. They are most commonly diagnosed between the ages of two and five, but have been diagnosed in dogs as old as ten.

The symptoms of the primary lesions are deep, draining, fistulous openings around the  anus which will not heal.  They may spread to involve a large portion of the perianal area.  Some dogs will show few signs of discomfort other than licking the anal region.  But as the problem advances, there may be damage and scarring that prevents normal defecation. These dogs may experience fever, constipation, pain when passing feces, bloody feces, diarrhea, weight loss, lethargy, butt  scooting, and open sores often with a malodorous discharge, similar to the odor of having the anal sacs expressed. Some dogs with severe perianal fistulas may not be able to close the anus properly, leading to incontinence.


The cause of perianal fistulas has not been determined. There are many theories as to the cause, and several studies have been performed to investigate the possible immunological, bacterial, endocrine, or anatomic basis for the disease.  


Theories include:

A) Possible anal sac problems. An infection which starts in the anal sacs, spreading back into the rectum.

B) The basic conformation of the German Shepherd Dog, with a broad base tail which hangs down doesn’t allow much air circulation in the anal area, keeping it warm and moist and prone to breeding bacteria. Another known fact is that German Shepherd Dogs have an increased density of perianal apocrine sweat glands.  It is not known if this could make the breed more prone to fistulas. Perianal fistulas are found in German Shepherds more (approximately 70 %) than any other breed. They are also found commonly in setters and retrievers, which carry their tails down, covering the anal area.  However, they have also been diagnosed in beagles, which carry their tail up for the most part, and in Australian Shepherds, which don’t have much tail at all.


C) Genetics is also a suspect, many feeling that we have done so much line breeding and inbreeding that we have turned our beautiful breed into a genetic nightmare causing immune system problems. Similarities in the clinical appearance of canine perianal fistulas and perianal fistulas in humans with Chron’s disease have been reported.  In humans with Chron’s disease, the immune system is thought to play an important role.


D) Stress as a whole is being studied as another factor many feel may be involved.  It is a known fact that stress affects the body’s ability to defend itself against disease.


E) Irritable bowel disease (IBD) and /or food allergies are also being considered as a possible link to perianal fistulas.  Many dogs with fistulas have a black tar-like substance on and around their rear area. It is believed this to be the result of old dried blood coming from the small intestines, indicating something internally is amiss.


F) Some believe that over-vaccinating could be factored in as a perspective trigger.  Yearly vaccinating directly involves the body’s immune system. This may be why some dogs develop perianal fistulas and others do not. 


The course of treatment varies, as does the success rate. Although many different methods of treatment have been proposed for this problem, none have been reported routinely successful in the control of the disease. There are some that believe the only course of treatment is surgery. And there are many different types of surgical treatments, as well as drug treatments.


A) Chemical cauterization is the excision of superficial fistulas with a chemical solution inserted in the deeper tracts. The wound is allowed to heal by second intention. Success is claimed to be in excess of 80%, but with fecal incontinence occurring in about 20 %.


B) Heat cauterization is the excision of the diseased tissue, followed by heat cauterization.


C)  Deroofing and fulguration is where all chronic tissue and scar tissue is excised and the lining electrofulgurated.  This method spares the sphincter muscle, but fistulas do return in a high percentage of cases.  It is not successful if more than half of the anal circumference is involved.


D) Cryosurgery is the application of nitrous oxide into the fistulous tracts with second intention healing. Success rates are claimed to run from 50-95%.   Fecal  incontinence  and stenosis is low compared to some of the other surgical options.


E) Surgical excision is a complicated surgery.  It involves removing all diseased tissue and much of the surrounding tissue. All fibrosis causing rectal or anal stricture is also removed.  Incontinence runs 13-29% due to damage to the sphincter muscle.


F) Laser surgery is claiming a 95 % success rate. A synthetic sapphire tip and continuous impulse of 13-15 watts is used to excise the fistulas.   Flatulence increases in some dogs, fecal tone is reduced, and fecal incontinence develops 20% of the time.


G) Tail amputation must include the lateral skin folds up to the second or third cocygeal certebra.  Superficial lesions may heal but deeper fistulas will still require surgery.  This generally is a last choice of dog owners.


H) Prednisone has been showing some limited success. An experiment at Michigan State University showed one-third of the dogs responded well, one-third showed a reduction in the inflammation, and one-third showed no response. The treatment begins with high doses of the drug, reducing down to one-half the prescribed dosage over a period of time. Prednisone does have many side effects, including increased thirst and appetite, increased urination, hair loss, damage and weakening of the skeletal system,   just to name a few.


I) Cyclosporin, an anti-rejection drug used in humans who have had organ transplant surgery, has been tested. The theory behind this experiment is that perianal fistulas are related to autoimmune problems. Cyclosporin suppresses the immune system of the dog, allowing the dog’s body to stop attacking itself and the fistulas to heal.  Cyclosporin can be started and stopped fairly safely though experience has shown that a certain level has to be reached and maintained in the bloodstream to get optimal use of the drug. Testing of the blood must be done to maintain the proper level of the drug. Initially, the success rate was 100%, but the fistulas returned in about one-third of the cases. The drug, as well as the testing, is  extremely expensive, making it beyond the reach of most dog owners. Cost of treatment can run into thousands of dollars.


J) A relatively new study, which was done in Australia, has shown to be successful at a more moderate price.  The use of Imuran and Flagyl was involved in an experiment  in 1999. The dogs showed anal irritation to be reduced or eliminated  within two weeks. Non-healing areas were usually associated with anal sac rupture or chronic fibrosis. Visible improvement reached a plateau 4-6 weeks after starting treatment.  Immunosuppressive therapy continued for 5-24 weeks before surgical removal of anal sacs and/or residual fistulae.  All dogs remain disease free 7-10 months postoperatively.


K) Several years ago, a German Shepherd Dog was presented to Michigan State University for treatment of perianal fistulas. It was also discovered that the dog had multicentric lymphosarcoma. A multi-drug chemotherapy treatment was started to treat the lymphosarcoma. After 4 weeks of chemotherapy, it was noted that the perianal fistula problem had completely resolved. The doctors conducting this experiment now believe that perianal fistulas are just an external manifestation of a systemic disease.  The  German Shepherd breed also has a problem with infiltrative/inflammatory bowel diseases, particularly affecting the colon and rectum. A prospective study was initiated to investigate the possible association between perianal fistulas and colitis/proctitis.


L) In a 2001 study in Italy, it was noted that two German Shepherd Dogs, and one Pomeranian dog with perianal fistulas were found to be carriers of Babesia spp, without showing specific clinical symptoms and sign of babesiosis. These dogs were treated with imidocarb dipropionate once a week for 4 weeks.  This therapy led to a complete recovery from the perianal fistulas without subsequent relapses; no surgery was needed. This is the first time a relationship between perianal fistulas and  babesiosis was noted, and is suggested that examinations of blood smears should be recommended as a laboratory routine in the diagnosis of perianal fistulas.

For years, there have been many speculations as to the cause and the best method of treatment for perianal fistula. However, recently more veterinarians and scientists are leaning toward a relationship between perianal fistulas and a dogs immune system. With the defect thought to be immunological rather than anatomical, surgical excision and tail amputation can likely be unsuccessful. A thorough search for underlying disease with consequential chemotherapy is suggested today as the proper answer to the problem. As more studies are done, and as medical advances are made, it is hoped that perianal fistulas can be controlled or cured.



http://www.geocities.com/Heartland/Pointe/1672/msuarticle.html   Perianal Fistula is a Medical (Not a Surgical) Problem by Richard Walshaw  02/19/02


http://www.geocities.com/Heartland/Pointe/1672/canadaarticlae.html   Canadian Cyclosporin treatment of perianal fistulas in dogs by Karol A. Mathews, Sara A. Ayres,  Cheryl A. Tano, Steve M. Riley, Hanif R. Sukhiani, Catherine Adams   02/19/02


http://www.geocities.com/Heartland/Pointe/1672/australiapfreport.html   Successfully Treating PF Dogs Using IMURAN & FLAGYL  by PLC Tisdall, GB Hunt, JA Beck, and R Malik  02/19/02


http://www.inno-vet.com/articles/2001/0401/5931.html   Babesiosis as an Underlying Factor Influencing the Severity an Duration of Perianal Fistulas in Three Dogs  by W Tarello   02/21/02


http://www.geocities.com/Heartland/Pointe/1672/treatments.html  Important Information About Treating PF Dogs  02/19/02


http://www.geocities.com/Heartland/Pointe/1672/explanation.html  Perianal Fistulas-What Are They  02/19/02


http://www.geocities.com/Heartland/Pointe/1672/carticle.html   02/19/02




Pathophysiology by Kathryn L. McCance and Sue E. Huether  Chapter 38, pages 1387-1389

Additional Links about this disease:

  2012 Update


Perianal Fistulas

Perianal fustula (PF) or anal furunculosis (AF) is a chronic progressive disease characterized by ulceration of the perianal tissue (tissue surrounding the anus). The definition of a fistula is an abnormal passage or communication between an internal organ and the surface of the body or between two organs, and it is typically seen as multiple draining tracts surrounding the rectum. These fistulas communicate between the rectum and the perianal area. At first these lesions appear as a tiny, sometimes weeping hole. Most dogs experience significant pain and discomfort with this condition. Dogs may present with tenesmus (feeling of constantly needing to pass stool) or dyschezia (difficulty passing stool), pain while passing stool, excessive licking or biting the anal area, scooting, mucus or blood in stools, ribbon-like stool, diarrhea, or constipation. It is very important to distinguish perianal fistulas from chronic anal sac abscessation (abcess) with secondary fistulas. Dogs can have a single draining tract or numerous tracts surrounding the entire anal area. Bacterial infections are a frequent secondary problem with perianal fistulas.

Originally it was thought that perianal fistulas were caused by a broad-based, low carriage tail with increased density of sweat glands. However, that has been replaced with an immune-mediated theory because of the favorable response to certain medications. There also seems to be a strong correlation between PF and colitis. The classic symptom of canine colitis is chronic diarrhea. Very often the stool starts out normal but becomes loose. Sometimes the amounts are small and are soft or slimy. The stool can be mixed with blood and mucus. PF is found in many breeds besides German shepherds (Irish setters, collies, Border collies, Old English sheepdogs, Labrador retrievers, English bulldogs, beagles, Bouvier des Flandres, spaniels, and mixed breeds). PF does appears in both sexes and is most common in middle aged (4-7 years) dogs. However, younger dogs have been diagnosed.

In the early stages of PF some dogs are relatively asymptomatic and the owner does not notice the small clinical signs. As PF progresses in severity, the dog may have weight loss, lethargy, pyrexia (fever), and rectal or anal bleeding. In chronic cases, fibrosis of the rectal and perirectal tissues may result in worsening of tenesmus and constipation due to inflamation and narrowing of the anal diameter.

It should be noted that anal sac disease is not the primary cause of PF. However, they may become secondarily involved due to inflammation from adjacent sinus tracts or from dysfunction of the external anal sphincter muscle which impairs expulsion of the glandular secretion of the anal sacs. Involvement of the anal sacs only as a secondary event is supported by histologic evaluation in a large number of German Shepherd dogs and non-German Shepherd dogs with PF. The histopathologic changes associated with the anal sac were centered mostly on the duct of the anal sac, and when the body of the anal sac was significantly affected, these lesions were generally adjacent to inflamed sinus tracts. These findings were interpreted as representing local extensions of inflammation
from the sinus tracts.

If the source of PF is dissecting abscessation from infected anal glands, then infection would be the primary component of the disease process. In fact, bacterial infection has not been shown to play a role in the initial development of canine perianal fistula. It is believed that it is initially a sterile disease with bacterial contamination and secondary infection only after epidermal ulceration has occurred.


Anal Sacs - PF can also involve anal sacs and make treatment difficult with a high recurrence rate. Therefore, it is highly recommended to remove the affected anal sacs. If the anal sacs are not involved, having them removed should be discussed with your veterinarian. However, the anal sacs should be closely monitored should they become irritated or infected.

Dietary therapy - Since there is a strong correlation and similarities with colitis, modifying the dog's diet to a single source, novel protein (i.e., fish and potato diet), preferable a protein that the dog has not had previously or one that is known to cause few reactions is recommended. Grains and dairy are also eliminated from the diet. Dietary options include kibble, home cooked or raw diet. Keeping ingredients to a minimum is the best way to monitor if a particular food is causing a flare up.

Hygiene therapy - Involves keeping the perineal area clean and free of secondary bacterial infection. This involves keeping the area clipped (groomers can do “sanitary clips”) and clean, especially if the area gets soiled after the dog has had a bowel movement. Using soft unscented baby wipes have been used by some pet owners to keep the area clean. The sanitary clip will also provide better air flow, thus eliminating excess moisture in the area. Metronidazole, cephalexin, cefpodoxime, or amoxicillin-clavulanate have been used as antibiotic therapy. Adjunctive topical antibiotic therapy with mupirocin ointment can be useful if the dog can tolerate topical application.

Drug therapy - Medical management of PF is done in two phases. The first phase is the induction phase, used to resolve the clinical signs. The second phase, or maintenance phase, is to keep the clinical signs in remission. There are several immune suppressive drugs that have been used, including cyclosporine (Atopica), tacrolimus, ketoconazole, Immuran, azathioprine (Immuran) and prednisone. Thorough research should be made to understand each drug, how it works, it’s side effects, and any monitoring (blood testing) that would be required, to make the best decision for the dog.

Cyclosporine - Many cases have had good success with this immune suppressor. Once all lesions are in remission, cyclosporine therapy can be tapered. There are different options for tapering and should be discussed with your veterinarian. Some feel cyclosporine levels require monitoring. The recommended trough levels of cyclosporine in dogs are based on data established for humans and animals receiving organ transplants. A relationship has not been established between cyclosporine trough concentrations and efficacy of treatment for PF. Adverse effects of cyclosporine therapy include primarily gastrointestinal signs (vomiting, soft stool, or diarrhea). Cyclosporine is best absorbed on an empty stomach, although some dogs cannot tolerate cyclosporine without food due to gastrointestinal upset. Pepcid AC, Tagamet, or Slippery Elm bark are options to help with gastric upset.

Concurrent use of ketoconazole will decrease the clearance (removal) of cyclosporine by the liver through its competitive binding action, thereby extending the useful life of the cyclosporine and decrease the associated cost of therapy. Adverse effects of ketoconazole include gastrointestinal signs (anorexia, vomiting, and diarrhea). Pepcid AC, Tagamet, or Slippery Elm bark are options to help with gastric upset.

Tacrolimus is a topically applied immunosuppresive ointment that has similar mechanism of action to cyclosporine and may be used with cyclosporine or alone if small fistulas recur. Although tacrolimus is much more potent than cyclosporine, it is not used systemically due to the severity of the side effects. When used topically it has potent anti-inflammatory effects with minimal systems absorption. Individuals should wear gloves during the topical application.

Immuran (Azathioprine) has also been used successfully. It takes about 2 to 3 weeks to reach optimal blood levels, so treating concurrently with prednisone is advised. The initial dosage will be lowered once remission is achieved. Blood work needs to be monitored for myelosuppression and liver toxicity. Myelosuppression can resolve in some dogs with dosage reduction.

Prednisone - There is much controversy between prednisone and cyclosporine. For some, prednisone is not the drug of choice because it is less efficient than cyclosporine, while others prefer it because it is less expensive. Prednisone protocols are followed daily until lesions are in remission, then tapering down to maintenance doses given every other day. The most common side effects of prednisone are polyuria (excessive passage of urine), polydipsia (excessive or abnormal thirst), and ployphagia (excessive appetite or eating).

Cold Laser Therapy -This treatment has been shown to significantly improve therapeutic outcomes, both in wound, injury, and surgical applications. When deep penetrating photobiostimulation occurs there is pain relief, reduction of inflammation and accelerated tissue healing time. The best results are when a sufficient number of photons reach the target tissue. The therapeutic dose is measured in Joules (J) delivered per cm2. Treatment protocols include correct power, dosage, and wavelengths (continuous wave) to produce the best therapeutic results. The therapeutic cold laser can be a very important tool to heal PF (tissue) and speed healing of surgical sites.

Surgery - Once widely used, is presently reserved for cases that involve the anal sacs or for selective cases that do not respond to medical management. Complications frequently associated with surgery include permanent fecal incontinence, anal stricture, and recurrence of fistulation.

Pathogenesis - The complete pathogenesis of perianal fistulas is unknown, but several theories exist as to the underlying cause, which is likely complex and multifactorial. Due to the favorable response to treatment with immunosuppressive or immunomodulatory medications, an immunemediated basis has been suggested. It is also felt that there is and a strong genetic association with the DLA-DRB1*00101 allele. Research is still ongoing.

Vaccines - Vaccines are designed to stimulate the immune system. If the dog's immune system is suppressed - either by drugs (PF treatment), ill health/illness (PF), poor nutrition, genetic weaknesses, or stress - then he isn't going to be able to mount that immune response, and the results could be very serious. You do not want to stimulate your dog’s immune system by giving any vaccination. So all dogs diagnosed with PF may not be able to have vaccines. Please do your research and speak with your vet about whether or not  you should  vaccinate you dog during treatment for PF.

For vaccinations legally required, sometimes titers can be substituted to determine level of protection. Or obtaining a medical exemption for the vaccine could be another option. Many states are considering bills to allow dogs with health problems an exemption to rabies vaccination. Research what is required in your state, and what avenues can be taken to protect your dog’s health.
Flea and Heartworm Treatments - While some stay away from any medications of this type due to the concern at how these medications will affect their dogs, others research the options to find what they feel would work best for them.

All treatment options should be thoroughly examined with you and your veterinarian to come up with the best plan for your dog.

Support Groups - There are also support groups (Yahoo PF Group) that are very helpful. Their members have very good information and experience to share with one another.
This can be very beneficial if your vet is not very knowledgeable about PF or doesn’t have the latest treatment information.

**The most important treatment you can provide to your canine is fast treatment”. PF is not a disease that you can wait a couple of weeks to treat. PF will continue to grow/spread while your success rate diminishes and is very painful for your dog. Please act quickly!**

1. Pieper J, McKay L Perianal Fistulas
2. Misseghers BS The Histologic Characterization of Perianal Fistulas During Treatment with Cyclosporin
3. Barnes A, O'Neill T, Kennedy LJ, Short AD, Catchpole B, House A, Binns M, Fretwell N, Day MJ, Ollier WE. Association of canine anal furunculosis with TNFA is secondary to linkage disequilibrium with DLA-DRB1*.
4. Muller Esneault S Canine Perianal Fistula or Anal Furunculosis

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All rights reserved. Revised: January 2008

The information on this website was written by ISSR breeders and other concerned individuals, however we are are NOT veterinarians. This information is being provided as a general overview, from information we were able to find about each disease through our own research. These summaries are not intended to be relied upon as medical or veterinary advice, nor do we consider ourselves experts in the veterinary field or in any of these conditions. While we do our best to provide the most up to date information, new research is constantly being done on these diseases. We recommend that you do further study and talk to your veterinarian on any topics you see here, as we cannot guarantee that the information posted here is the most current information available.  This site was originally designed and maintained by Debbie Knatz.