Page 1522 - Cote clinical veterinary advisor dogs and cats 4th

772 Perianal Fistula

• Perianal licking/chewing Acute General Treatment Drug Interactions
• Scooting • Cyclosporine 2-5 mg/kg PO q 12h until no Interaction of cyclosporine with many drugs
VetBooks.ir • Constipation/obstipation ○ Preferred drug given reported high concentrations; consult a formulary before
can increase or decrease blood cyclosporine
evidence of lesions
• Painful defecation
response rates
giving with other drugs.
• Foul odor and exudate
• Large-bowel diarrhea (if colitis)
administration can reduce cyclosporine
• Tenesmus ○ Ketoconazole 10 mg/kg PO q 24h Possible Complications
• Hematochezia dosage to as low as 1 mg/kg PO q 12h • If lesions recur with drug dose reductions,
• Increased frequency of defecation and thereby reduce treatment cost. resume high-dose treatment.
• Ribbon-like stool ○ Microemulsified forms offer more con- • Surgical complications (recurrence, stricture,
sistent and predictable gastrointestinal incontinence)
PHYSICAL EXAM FINDINGS absorption. • Constipation, obstipation, or anorectal stric-
• Pain when tail is lifted • Tacrolimus 0.1% ointment applied topically tures may be managed with stool softeners.
• Epithelial ulcerations adjacent to or sur- to affected tissues q 12-24h is also associated • Azathioprine can cause hepatopathy, or bone
rounding the anal opening, potentially with with high response rates. marrow suppression that usually manifests
fistulous tracts extending into the deeper ○ May be given in conjunction with as thrombocytopenia or neutropenia in
underlying tissue prednisone dogs.
• Purulent perianal discharge ○ For dogs initially too painful for topical
• Foul odor application, may implement after improve- Recommended Monitoring
• Thickened or ruptured anal sacs or rectal ment is achieved with cyclosporine Physical exam at intervals to document
stricture possible • Prednisone 2 mg/kg PO q 24h until no resolution or persistence of lesions is typically
evidence of lesions, then tapered to lowest sufficient. Improvement in many dogs is appre-
Etiology and Pathophysiology effective dose ciated within 2-4 weeks of starting cyclosporine.
The underlying pathophysiology has not been • Azathioprine 1-2 mg/kg PO q 24h until • Therapeutic monitoring of cyclosporine
determined. Improvement with immunosup- lesions improve, then q 48h; often given in can be considered, especially for dogs not
pressive therapy and/or diet modifications conjunction with prednisone improving in response to treatment.
incriminates a pathologic immune response • The benefits of the immunosuppressive drugs ○ Trough drug concentrations are often
to bacterial and/or dietary antigens. mycophenolate mofetil or leflunomide have suggested, but the analyzing laboratory
not been explored. should be consulted for the timing
DIAGNOSIS • Cleaning of perineum (under sedation or of sample collection and target drug
anesthesia) may be needed for some dogs. concentration because results and recom-
Diagnostic Overview • Analgesics mendations can vary with assays and drug
Diagnosis is usually made by observing • Antibiotics (e.g., cephalexin 22 mg/kg PO formulations.
characteristic perianal lesions during physical q 8h, metronidazole 10 mg/kg PO q 12h ○ Pharmacodynamic monitoring based on
examination of a dog with compatible history for 14 days) are commonly given before or suppression of T-lymphocyte function has
and clinical signs. in conjunction with immunosuppressive been available through the Mississippi
therapy, but their role in disease manage- State University College of Veterinary
Differential Diagnosis ment has not been critically evaluated. Medicine (http://www.cvm.msstate.edu/
• Anal sac neoplasia (primarily adenocarcinoma) Because antibiotics alone rarely resolved, animal-health-center/pharmacodynamic-
• Anal sacculitis or anal sac abscess or minimally improved, lesions in the cases laboratory).
• Chronic colitis of many causes (e.g., antibi- described in the literature, their value has to • For dogs administered azathioprine
otic responsive, diet responsive, infectious) be questioned. ○ Liver enzymes: weekly for the first month
• Colonic neoplasia (hepatopathy uncommon after 4 weeks)
Chronic Treatment ○ CBC: weekly for the first 6-8 weeks, then
Initial Database • Some dogs require maintenance immunosup- monthly
Results of CBC, biochemical profile, and pressive therapy to maintain remission.
urinalysis are usually normal/unremarkable. • Anal sacculectomy may benefit a population PROGNOSIS & OUTCOME
of dogs that respond incompletely to medical
Advanced or Confirmatory Testing therapy, those that have anal sac involve- Prognosis for most dogs is fair to good. Anal
Colonoscopic biopsies, if obtained, can show ment, or those with recurrence in the face sac involvement may decrease the likelihood
lymphocytic/plasmacytic mucosal infiltrates of diminishing doses of immunosuppressive of durable control with medical therapy alone.
characteristic of colitis of many causes. drugs.
• Some dogs may need surgical resection of PEARLS & CONSIDERATIONS
TREATMENT residual inflamed tissue.
• Some of the literature supports a period Comments
Treatment Overview of initial medical therapy to improve Tapering immunosuppressive drugs to the
A best treatment for this disease is not estab- lesions before surgery with the goal of lowest effective dose or longest dosing interval
lished. Resolution of inflammation and associ- reducing the amount of tissue to surgically to control lesions is encouraged. Transition to
ated clinical signs has been accomplished with remove. topical tacrolimus often reduces treatment
medical therapy (immunosuppressive drugs, costs, especially for dogs needing long-term
diet modification), surgery, or combinations Nutrition/Diet treatment.
of the two. The role of surgery in the early Feeding a novel protein/novel carbohydrate
management has diminished given the responses or hydrolyzed protein is often advocated with Prevention
typically expected with medical therapy, but the potential of allowing immunosuppressive There is no means of preventing this disease.
surgery may play a role for some dogs (see drugs to be given at low dosages, long dosing Given the genetic predisposition of German
Chronic Treatment below). Some have argued intervals, intermittently (tacrolimus), or not at shepherds, affected dogs should not be bred.
that surgery can reduce the long-term expense all. These diets can benefit dogs with concurrent This may be true of affected dogs of other
of medical treatment. colitis. breeds.

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