Perianal fistula
Perianal fistula is characterized by multiple chronic fistuloustracts or ulcerating sinuses involving the perianal region. The cause is notknown, but apocrine gland inflammation (hidradenitis suppurativa), impactionand infection of the anal sinuses and crypts, infection of the circumanalglands and hair follicles, and anal sacculitis have all been proposed. Thegastrointestinal system becomes involved because of excessive scar tissueformation around the anus. Self-mutilation can also be a major problemassociated with this disorder.
signalment
Dogs German shepherd dogand Irish setter most commonly affected breeds Mean age, 7 years (range, 7months-12 years) No gender predisposition reported, but sexually intact dogshave a higher prevalence A genetic basis has been proposed, but not proven
signs
Vary with the severityand extent of involvement : Dyschezia, tenesmus, hematochezia, constipation,diarrhea, malodorous mucopurulent anal discharge, fecal incontinence, painfultail movements, licking and self-mutilation, anorexia, weight loss, reluctanceto sit, posturing difficulties, and personality changes
causes and risk factors
Proposed causes involvean inflammatory component Low tail carriage and a broad tail base are riskfactors predisposing the dog to inflammation and infection because of poorventilation, accumulation of feces, moisture, and secretions High density ofapocrine sweat glands in the cutaneous zone of the anal canal of Germanshepherd dogs Hidradenitis suppurativa may be associated with immune orendocrine dysfunction, genetic factors, and poor hygiene
diagnosis: differentialdiagnosis
Chronic anal sac abscessPerianal adenocarcinoma that is ulcerated and draining Rectal fistula
CBC/Biochemistry/Urinalysis
Results usually normal.Patients with inflammation may have an inflammatory leukogram.
other diagnosticprocedures
Presumptive diagnosis isbased on clinical signs and results of physical examination. Definitivediagnosis is made by biopsy of the affected area.
treatment
Surgery is consideredthe most effective treatment. However, a tremendous amount of controversyexists as to which surgical method should be used, and none of those currentlyemployed result in consistent resolution of the problem. Surgical optionsinclude electrosurgery, cryosurgery, surgical debridement with fulguration bychemical cautery, exteriorization and fulguration by electrocautery, surgical resection,radical excision of the rectal ring, tail setting, tail amputation, and lasersurgery. Each technique has advantages and disadvantages that must be weighedwhen making a choice. The primary objective of surgery is the complete removalor destruction of diseased tissue while preserving normal tissue and function.Multiple procedures may be necessary for complete resolution.
medications
Medical treatment ofperianal fistulas is usually unrewarding and can be detrimental by delayingmore definitive treatment and allowing progression. Medical palliation involvesclipping hair from the affected area, daily antiseptic lavage, systemic andtopical antibiotics, hydrotherapy, elevation of the tail, and systemiccorticosteroids.
contraindications/possibleinteractions
Corticosteroids arecontraindicated when infection is possible.
follow-up
After surgery forappropriate healing, signs of recurrence, and associated complications
Complications associatedwith the various surgical procedures include recurrence, failure to heal,dehiscence, tenesmus, fecal incontinence, anal stricture, and flatulence. Theincidence of postoperative complications is directly related to severity of disease.
Prognosis is guarded forcomplete resolution except in mildly affected patients. Clients often becomefrustrated with the difficulty of attaining definitive resolution of thisdisorder.
references
Matthiesen DT, MarrettaSM. Diseases of the anus and rectum. In: Slatter D, ed. Textbook of smallanimal surgery. 2nd ed. Philadelphia: WB Saunders, 1993;627-644. van Ee RT.Perianal fistulas. In: Bojrab MJ, ed. Disease mechanisms in small animalsurgery. 2nd ed. Philadelphia: Lea & Febiger, 1993;285-286. Author James L.Cook
Consulting Editor BrentD. Jones
Current Recommendationsfor the Treatment of Perianal Fistula
Author Kyle Mathews,DVM, MS, DACVS
Introduction
The surgical treatmentof perianal fistula has been fraught with complications and a high recurrencerate (generally, 40% to 50%). Recommended treatments have included cryosurgicaldestruction of diseased perianal tissues, electrofulguration, rectalpull-through, and caudectomy (tail amputation). Complications have includedrectal stricture, recurrence, and fecal incontinence. Medical treatment withcyclosporine may be effective in some cases.
Discussion
The underlying cause ofperianal fistula is not known. It is thought to be the extension of infectionor inflammation of superficial tissues (hydradenitis) or of the anal sacs.Conformation has also been thought to play a role in the formation of afistula, such as a tight tail base or a sunken or recessed anus. These anatomicpeculiarities may result in a persistent fecal film in the perineal region,predisposing to infection. Reports of clinical response to immunosuppressivedrugs suggest that perianal fistula may be a primary immune-mediated disease orhave an immune-mediated component.
In one canine study, 9of 27 (33%) German shepherd dogs with a fistula and histologically confirmedcolitis had resolution of their fistula after being placed on a high dosage ofcorticosteroids and a hypoallergenic diet.1
An important change inthe treatment of canine perianal disease occurred recently with the report thatthe immunosuppressive drug cyclosporine results in marked improvement orresolution 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 inflammatorybowel disease (Crohn's disease) may also develop perianal fistulation thatoften responds to cyclosporine.3
I typically starttreatment of perianal fistula with administration of microemulsifiedcyclosporine (Neoral, Sandoz Pharmaceuticals, East Hanover, New Jersey) at 3mg/kg PO q12h. Neoral comes in 50-ml vials (approximately $300 per vial) andthe proper dose can be aspirated in a syringe and then added to an emptygelatin capsule. The drug is also available in 100-mg gelcaps, which is often closeto the proper dose for the typical German shepherd with this disease.
I check the patient'strough plasma concentration of cyclosporine 2 weeks after beginning themedication and make appropriate dosage adjustments based on the results. Thetarget concentration is 300 to 500 ng/ml (using an HPLC assay) or 500 to 750ng/ml (using the TdX assay at North Carolina State University). Make sure youknow which assay your laboratory is using. Most laboratories associated withhuman hospitals run this assay, but they may not for veterinary patients or itmay be expensive.
Cyclosporine should bekept in a dark cupboard at room temperature. Blood samples should be drawn inthe morning, 12 hours after the last evening dose was given, and before givingthe 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 bynext-day delivery. Samples should not be sent on a Friday or before a holidaybecause they may not be delivered promptly. The sample does not have to befrozen for shipment.
The cyclosporine dosageis increased if the trough concentration is low, particularly if the responseis minimal or absent after 1 month of drug administration. Troughconcentrations as low as 75 ng/ml (HPLC) may be effective in some dogs.4
A decrease in fistulasize is not usually seen for the first 2 weeks. However, many clients report animprovement in their dog's energy level, decreased licking at the area, anddiminished tenesmus within the first 2 weeks.
Unanswered questionsregarding cyclosporine and perianal fistulas include these:
What is the properduration of treatment? I administer the drug to fistula patients for at least 2weeks after complete resolution based on visual examination. It is unclear ifthese dogs should be treated longer in order to keep the disease in remissionor if it is better to treat only during recurrent episodes. Small fistulasrecurred in 7 of 17 dogs 2 to 24 weeks after discontinuing treatment.5 What is theunderlying cause and reason that cyclosporine works? What is occurring at acellular level before, during, and after treatment with cyclosporine?
Why do some dogs respondand others do not? One study showed no difference in the mean blood or intestinaltissue concentration of cyclosporine in human responders and non-responderswith Crohn's disease.6
What ancillarytreatments are appropriate (e.g., dietary modification and antibiotics)?
Should other medicationsbe given to inhibit cyclosporine metabolism and thereby decrease the cost oftreatment (e.g., ketoconazole)?
I currently recommendcyclosporine administration for the treatment of perianal fistula; however,medication costs and the surgical options and their potential complicationsneed to be discussed so that the guardian can come to an informed decision. Inaddition, excision of persistent or recurrent fistulas may be required.
Summary
The cause of perianalfistula and why many dogs respond to treatment with cyclosporine is poorlyunderstood. 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 manyanimal patient. Questions regarding recurrence rate and long-term therapy willlikely 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 GermanShepherd Dog: response to high-dose prednisone and dietary therapy. J Am AnimHosp Assoc 1996;32:515.
2. Mathews Karol A,Sukhiani HF. Randomized controlled trial of cyclosporine for treatment ofperianal fistulas in dogs. J Am Vet Med Assoc 1997;211:1249.
3. Present DH, LichtigerS. Efficacy of cyclosporine in treatment of fistula of Crohn's disease. DigestDis 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 treatmentof perianal fistulas in dogs. Submitted, J Am Vet Med Assoc, 1999.
5. Mathews KA, ibid.
6. Sandborn WJ, TremaineWJ, Lawson GM. Clinical response does not correlate with intestinal or bloodcyclosporine concentrations in patients with Crohn's disease treated withhigh-dose oral cyclosporine. Am J Gastroent 1996;91:37.
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