Sometimes there are topics that, as a dog owner you have to learn about...things you find yourself talking about at the dog park you never thought you would discuss with strangers. This is one of those things that as a German Shepherd dog parent and or lover, you should know about. (I do draw the line at pictures, though. Sorry)
Perianal fistula
Perianal fistula is characterized by multiple chronic fistulous
tracts or ulcerating sinuses involving the perianal region. The cause is not
known, but apocrine gland inflammation (hidradenitis suppurativa), impaction
and infection of the anal sinuses and crypts, infection of the circumanal
glands and hair follicles, and anal sacculitis have all been proposed. The
gastrointestinal system becomes involved because of excessive scar tissue
formation around the anus. Self-mutilation can also be a major problem
associated with this disorder.
signalment
Dogs German shepherd dog
and Irish setter most commonly affected breeds Mean age, 7 years (range, 7
months-12 years) No gender predisposition reported, but sexually intact dogs
have a higher prevalence A genetic basis has been proposed, but not proven
signs
Vary with the severity
and extent of involvement : Dyschezia, tenesmus, hematochezia, constipation,
diarrhea, malodorous mucopurulent anal discharge, fecal incontinence, painful
tail movements, licking and self-mutilation, anorexia, weight loss, reluctance
to sit, posturing difficulties, and personality changes
causes and risk factors
Proposed causes involve
an inflammatory component Low tail carriage and a broad tail base are risk
factors predisposing the dog to inflammation and infection because of poor
ventilation, accumulation of feces, moisture, and secretions High density of
apocrine sweat glands in the cutaneous zone of the anal canal of German
shepherd dogs Hidradenitis suppurativa may be associated with immune or
endocrine dysfunction, genetic factors, and poor hygiene
diagnosis: differential
diagnosis
Chronic anal sac abscess
Perianal adenocarcinoma that is ulcerated and draining Rectal fistula
CBC/Biochemistry/Urinalysis
Results usually normal.
Patients with inflammation may have an inflammatory leukogram.
other diagnostic
procedures
Presumptive diagnosis is
based on clinical signs and results of physical examination. Definitive
diagnosis is made by biopsy of the affected area.
treatment
Surgery is considered
the most effective treatment. However, a tremendous amount of controversy
exists as to which surgical method should be used, and none of those currently
employed result in consistent resolution of the problem. Surgical options
include electrosurgery, cryosurgery, surgical debridement with fulguration by
chemical cautery, exteriorization and fulguration by electrocautery, surgical resection,
radical excision of the rectal ring, tail setting, tail amputation, and laser
surgery. Each technique has advantages and disadvantages that must be weighed
when making a choice. The primary objective of surgery is the complete removal
or destruction of diseased tissue while preserving normal tissue and function.
Multiple procedures may be necessary for complete resolution.
medications
Medical treatment of
perianal fistulas is usually unrewarding and can be detrimental by delaying
more definitive treatment and allowing progression. Medical palliation involves
clipping hair from the affected area, daily antiseptic lavage, systemic and
topical antibiotics, hydrotherapy, elevation of the tail, and systemic
corticosteroids.
contraindications/possible
interactions
Corticosteroids are
contraindicated when infection is possible.
follow-up
After surgery for
appropriate healing, signs of recurrence, and associated complications
Complications associated
with the various surgical procedures include recurrence, failure to heal,
dehiscence, tenesmus, fecal incontinence, anal stricture, and flatulence. The
incidence of postoperative complications is directly related to severity of disease.
Prognosis is guarded for
complete resolution except in mildly affected patients. Clients often become
frustrated with the difficulty of attaining definitive resolution of this
disorder.
references
Matthiesen DT, Marretta
SM. Diseases of the anus and rectum. In: Slatter D, ed. Textbook of small
animal surgery. 2nd ed. Philadelphia: WB Saunders, 1993;627-644. van Ee RT.
Perianal fistulas. In: Bojrab MJ, ed. Disease mechanisms in small animal
surgery. 2nd ed. Philadelphia: Lea & Febiger, 1993;285-286. Author James L.
Cook
Consulting Editor Brent
D. Jones
Current Recommendations
for the Treatment of Perianal Fistula
Author Kyle Mathews,
DVM, MS, DACVS
Introduction
The surgical treatment
of perianal fistula has been fraught with complications and a high recurrence
rate (generally, 40% to 50%). Recommended treatments have included cryosurgical
destruction of diseased perianal tissues, electrofulguration, rectal
pull-through, and caudectomy (tail amputation). Complications have included
rectal stricture, recurrence, and fecal incontinence. Medical treatment with
cyclosporine may be effective in some cases.
Discussion
The underlying cause of
perianal fistula is not known. It is thought to be the extension of infection
or inflammation of superficial tissues (hydradenitis) or of the anal sacs.
Conformation has also been thought to play a role in the formation of a
fistula, such as a tight tail base or a sunken or recessed anus. These anatomic
peculiarities may result in a persistent fecal film in the perineal region,
predisposing to infection. Reports of clinical response to immunosuppressive
drugs suggest that perianal fistula may be a primary immune-mediated disease or
have an immune-mediated component.
In one canine study, 9
of 27 (33%) German shepherd dogs with a fistula and histologically confirmed
colitis had resolution of their fistula after being placed on a high dosage of
corticosteroids and a hypoallergenic diet.1
An important change in
the treatment of canine perianal disease occurred recently with the report that
the immunosuppressive drug cyclosporine results in marked improvement or
resolution of perianal fistula in many patients.2 After 16 weeks of treatment,
the fistula healed in 17 of 20 dogs (85%). Humans with a form of chronic inflammatory
bowel disease (Crohn's disease) may also develop perianal fistulation that
often responds to cyclosporine.3
I typically start
treatment of perianal fistula with administration of microemulsified
cyclosporine (Neoral, Sandoz Pharmaceuticals, East Hanover, New Jersey) at 3
mg/kg PO q12h. Neoral comes in 50-ml vials (approximately $300 per vial) and
the proper dose can be aspirated in a syringe and then added to an empty
gelatin capsule. The drug is also available in 100-mg gelcaps, which is often close
to the proper dose for the typical German shepherd with this disease.
I check the patient's
trough plasma concentration of cyclosporine 2 weeks after beginning the
medication and make appropriate dosage adjustments based on the results. The
target concentration is 300 to 500 ng/ml (using an HPLC assay) or 500 to 750
ng/ml (using the TdX assay at North Carolina State University). Make sure you
know which assay your laboratory is using. Most laboratories associated with
human hospitals run this assay, but they may not for veterinary patients or it
may be expensive.
Cyclosporine should be
kept in a dark cupboard at room temperature. Blood samples should be drawn in
the morning, 12 hours after the last evening dose was given, and before giving
the dog his or her morning medications. The blood should be mailed in an EDTA
(purple-topped) blood tube in a crush proof container to the laboratory by
next-day delivery. Samples should not be sent on a Friday or before a holiday
because they may not be delivered promptly. The sample does not have to be
frozen for shipment.
The cyclosporine dosage
is increased if the trough concentration is low, particularly if the response
is minimal or absent after 1 month of drug administration. Trough
concentrations as low as 75 ng/ml (HPLC) may be effective in some dogs.4
A decrease in fistula
size is not usually seen for the first 2 weeks. However, many clients report an
improvement in their dog's energy level, decreased licking at the area, and
diminished tenesmus within the first 2 weeks.
Unanswered questions
regarding cyclosporine and perianal fistulas include these:
What is the proper
duration of treatment? I administer the drug to fistula patients for at least 2
weeks after complete resolution based on visual examination. It is unclear if
these dogs should be treated longer in order to keep the disease in remission
or if it is better to treat only during recurrent episodes. Small fistulas
recurred in 7 of 17 dogs 2 to 24 weeks after discontinuing treatment.5 What is the
underlying cause and reason that cyclosporine works? What is occurring at a
cellular level before, during, and after treatment with cyclosporine?
Why do some dogs respond
and others do not? One study showed no difference in the mean blood or intestinal
tissue concentration of cyclosporine in human responders and non-responders
with Crohn's disease.6
What ancillary
treatments are appropriate (e.g., dietary modification and antibiotics)?
Should other medications
be given to inhibit cyclosporine metabolism and thereby decrease the cost of
treatment (e.g., ketoconazole)?
I currently recommend
cyclosporine administration for the treatment of perianal fistula; however,
medication costs and the surgical options and their potential complications
need to be discussed so that the guardian can come to an informed decision. In
addition, excision of persistent or recurrent fistulas may be required.
Summary
The cause of perianal
fistula and why many dogs respond to treatment with cyclosporine is poorly
understood. The cost of cyclosporine is prohibitive for some clients. However,
the cost and risk of multiple potential surgeries must be considered as well.
Cyclosporine has greatly simplified the treatment of perianal fistula in many
animal patient. Questions regarding recurrence rate and long-term therapy will
likely be answered within the next few years.
References
1. Harkin KR, Walshaw R,
Reimann KA, et al. Association of perianal fistula and colitis in the German
Shepherd Dog: response to high-dose prednisone and dietary therapy. J Am Anim
Hosp Assoc 1996;32:515.
2. Mathews Karol A,
Sukhiani HF. Randomized controlled trial of cyclosporine for treatment of
perianal fistulas in dogs. J Am Vet Med Assoc 1997;211:1249.
3. Present DH, Lichtiger
S. Efficacy of cyclosporine in treatment of fistula of Crohn's disease. Digest
Dis Sci 1994;39:374.
4. Wooldridge JD,
Gregory CR, Mathews KG, et al. Clinical evaluation of leflunomide alone,
leflunomide and cyclosporine, and cyclosporine at varying dosages in the treatment
of perianal fistulas in dogs. Submitted, J Am Vet Med Assoc, 1999.
5. Mathews KA, ibid.
6. Sandborn WJ, Tremaine
WJ, Lawson GM. Clinical response does not correlate with intestinal or blood
cyclosporine concentrations in patients with Crohn's disease treated with
high-dose oral cyclosporine. Am J Gastroent 1996;91:37.