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Perianal Fistula 771

○ Cyclosporine 5-10 mg/kg PO q 24h with hyperadrenocorticism, urinary tract infec- • A significant percentage of cases can be cured.
glucocorticoids for PF; first choice in cats, • Persistent use (daily for > 14 days) of potent • Side effects of drug therapy are a major cause
tions, pyoderma).
VetBooks.ir ○ Chlorambucil 0.1-0.2 mg/kg PO q 24-48h topical glucocorticoids can create skin • Combination drug therapy is generally more Diseases and Disorders
for euthanasia, and this can be avoided.
or
in conjunction with prednisolone (cats),
effective and acceptable than monotherapy.
atrophy, alopecia, and comedone formation.
or
○ Mycophenolate mofetil 15 mg/kg PO Recommended Monitoring • Although acantholytic keratinocytes and
neutrophils on skin cytology exams suggest
q 12h with prednisone/prednisolone; • Semiannual CBC, serum biochemistry pemphigus, clinicians may also see these
more recent promising option, potentially profiles, urinalysis, and urine cultures cells in cases of pustular dermatophytosis
less myelotoxicity/hepatotoxicity than for all patients receiving long-term oral (Trichophyton spp) and in some cases of
azathioprine glucocorticoids canine pyoderma. Biopsies (including special
• Alternative immunosuppressive drugs • Azathioprine, chlorambucil: CBC monitoring stains such as periodic acid–Schiff) are needed
○ Tetracycline and niacinamide: milder or for cytopenias q 2-3 weeks for the first 3 for confirmation.
localized cases of PF and PE (250 mg months, then q 3-6 months. For azathioprine, • Clinicians should consider prophylactic
of each PO q 8h for dogs < 10 kg; also monitor liver and pancreatic enzyme antibiotic treatment during initial immu-
500 mg of each PO q 8h for dogs activity. nosuppression or (in milder cases) before
> 10 kg) for 2-3 months to achieve starting immunosuppressive therapy (p. 851).
remission, then gradually decrease to q PROGNOSIS & OUTCOME • If new cutaneous lesions occur during
12-24h or alternate days if remission is treatment, first rule out pyoderma, demodi-
maintained • PF: fair to good prognosis, with the majority cosis, or dermatophytosis before increasing
• Topical therapy is indicated as a sole treat- achieving partial or complete remission with immunosuppression.
ment for some localized forms of PF and PE oral glucocorticoid ± other immunosup-
and in conjunction with systemic therapy pressive drugs. Time to improvement with Technician Tips
for persistent focal lesions that remain active therapy is 2-6 weeks; time to complete remis- Acanthocytes, which are acantholytic keratin-
despite satisfactory control of the overall sion is 3-9 months. Mortality (euthanasia) ocytes, are uncommonly seen on microscopic
disease. Person applying treatment must rate for dogs with PF is 20%-30% within the cytologic exams. They appear as large, rounded,
wear gloves. first year due to lack of response or adverse dark blue cells with a violet nucleus. When
○ Potent topical glucocorticoid initially: effects of treatment, notably glucocorticoids seen, especially in clusters, they should alert
fluocinolone acetonide, triamcinolone, (implying a need to use combination therapy the clinician that biopsies may be required.
betamethasone valerate; when adequate before triggering adverse effects that are
response, treatment is changed to 1%-2% unacceptable to the owner, deleterious to Client Education
hydrocortisone for maintenance the patient, or both). Mortality rate for Owners must be well informed about the
○ Tacrolimus 0.1%: has shown efficacy for cats with PF is < 10% in first 6 months of chronic nature of the disease, as well as the
treating both PE and PF. therapy. Persistence of long-term remission potential side effects of immunosuppressive drug
of PF after discontinuation of therapy has therapy. Gloves must be worn when applying
Drug Interactions been reported for 7%-22% of cases. topical immunosuppressive medications.
• Ketoconazole potentiates cyclosporine activ- • PV: 39% mortality rate (death or euthanasia);
ity; adjust dosage accordingly and monitor milder variants have better prognosis. SUGGESTED READING
serum cyclosporine levels (p. 1333). • PNP: poor prognosis Miller WH Jr, et al: Muller & Kirk’s Small animal
• Azathioprine is contraindicated in cats dermatology, ed 7, St. Louis, 2013, Saunders, pp
because of a profound myelosuppressive PEARLS & CONSIDERATIONS 438-448.
effect in this species.
Comments AUTHOR: Caroline de Jaham, DMV, MScV, DACVD
Possible Complications • Because response to treatment and prognosis EDITOR: Manon Paradis, DMV, MVSc, DACVD
• Side effects are common with long-term oral vary with the forms of pemphigus, it is
glucocorticoid therapy (signs of iatrogenic essential to make a specific diagnosis.

Perianal Fistula Bonus Material
Online

Epidemiology
BASIC INFORMATION greater risk for developing perianal fistulas than
SPECIES, AGE, SEX those that do not express the allele.
Definition Dogs, often middle-aged (4-7 years); no sex
Potentially severe inflammation of the perianal predisposition ASSOCIATED DISORDERS
tissue leading to draining tracts/fistulas in Colitis has been described in approximately
the tissue adjacent to and/or surrounding the GENETICS, BREED PREDISPOSITION 50% of dogs with perianal fistulas. Anal sac-
anus. German shepherds are the most com- culitis occurs in some.
monly affected breed, but others can be
Synonyms affected. Clinical Presentation
Anal furunculosis HISTORY, CHIEF COMPLAINT
RISK FACTORS Historical complaints:
German shepherds that express the dog leuko- • Low tail carriage/reluctance to lift tail
cyte antigen allele DLA-DRB1*00101 are at • Pain on lifting tail

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