Common names or abbreviations:
Description or definition:
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
all around, near, enclosing, surrounding
of, relating to, or situated near the anus
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.
A) Possible anal sac
problems. An infection which starts in the anal sacs, spreading back into the
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
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
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
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
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
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.
Additional Links about this disease:
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
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
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
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