Overview

• Chronic inflammatory condition characterized by multiple, painful, progressive, ulcerating sinuses or, much less frequently, true fistulous tracts involving the perianal region.
• Synonyms: anal furunculosis, perianal sinus, pararectal fistulae, fistulae-in-ano.

Signalment

• Dog
• German shepherd dogs primarily; Irish setters
• Middle-aged dogs with mean age of 5–7 years; range, 7 months–14 years
• Males more commonly affected in most studies

Signs

• Dyschezia
• Tenesmus
• Hematochezia
• Constipation
• Diarrhea
• Malodorous mucopurulent anal discharge
• Ulceration of the perianal skin with sinus tract formation
• Licking and self-mutilation
• Reluctance to sit; posturing difficulties; personality changes
• Pain on manipulation of tail and examination of perianal area
• Fecal incontinence
• Anorexia
• Weight loss

Causes & Risk Factors

• Cause not clearly defined, but a multifactorial immune-mediated mechanism is strongly suspected.
• Appears to be an inappropriate T-cell mediated response.
• An association with colitis has also been proposed, particularly in German shepherd dogs.
• A genetic predisposition, based on breed incidence, has been proposed but not proven.
• Anatomic factors have been implicated, particularly in German shepherds.
• Low tail carriage and a broad tail.
• High density of apocrine sweat glands in the cutaneous zone of the anal canal of German shepherd dogs.

Differential Diagnosis

• Other inflammatory processes-e.g., anusitis, hydradenitis suppurativa
• Chronic anal sac abscess
• Perianal adenoma or adenocarcinoma with ulceration and drainage
• Squamous cell carcinoma
• Atypical bacterial infection
• Oomycosis
• Rectal fistula

CBC/Biochemistry/Urinalysis

• Usually unremarkable.
• Patients with inflammation may have an inflammatory leukogram.

Diagnostic Procedures

• Presumptive diagnosis-based on clinical signs and results of physical examination.
• Definitive diagnosis-made by biopsy of the affected area.
• Colonoscopy with biopsy-may reveal associated colitis.

Appropriate Health Care

• Outpatient medical therapy recommended initially in all cases.
• Clipping and cleaning the perianal area facilitates local therapy.
• Bathing with an antimicrobial shampoo may be helpful.

Diet

• Dietary modification-novel protein elimination diet such as venison or fish and potato. Hypoallergenic hydrolyzed diets should also be considered.
• Stool softeners-with pain or tenesmus.

Surgical Considerations

• Surgery is primarily indicated for patients with incomplete resolution or pseudohealing of sinuses following appropriate medical therapy.
• Anal sacculectomy-perform if anal sac involvement is confirmed.
• Surgical options-resection of inflammatory tissue and/or ablation of remaining sinuses with carbon dioxide laser is preferred.
• Surgical debridement (deroofing) with fulguration by chemical cautery or electrocautery; surgical resection followed by primary closure or second intention healing are other options.
• Radical excision of the rectal ring with modified rectal pull-through is not commonly necessary and is associated with a higher risk of fecal incontinence.

Drug(s) Of Choice

• Cyclosporine (CsA) ± ketoconazole is treatment of choice but is expensive.
  • Cyclosporine A microemulsion as a single agent-give 4–8 mg/kg PO per day as induction dose, then taper dose based on clinical response.
  • Cyclosporine A and ketaconazole-give CsA orally at 2–5 mg/kg/day PO and ketoconazole at 5–10 mg/kg/day PO as induction dose and then taper CsA as clinical signs resolve.
  • Ketaconazole reduces dose of cyclosporine required by inhibiting CsA metabolizing enzymes.
  • Continue treatment at least 4 weeks after complete resolution of fistula(e), but many patients require chronic treatment at reduced frequency to prevent recurrences.
• Tacrolimus (0.1% ointment) applied topically as maintenance therapy may be sufficient to control lesions; begin application as dose of oral medications is reduced.
  • Apply topically q12h with gloved hand, then taper to q24–72h.

Or

• Oral prednisone and topical tacrolimus, appears to be efficacious and economical in less severe cases.
  • Prednisone-2 mg/kg PO q24h for 2 weeks, decrease to 1 mg/kg q24h for 4 weeks and then 1 mg/kg q48h for 10 weeks.
  • 0.1% tacrolimus ointment-(see protocol above)
  • Chronic maintenance therapy with tacrolimus and possibly prednisone likely necessary for long-term control.
  • Azothioprine alone or combined with prednisone using a decreasing dosage regimen is another treatment option.
  • Metronidazole-10 mg/kg q12h for 2 weeks at initiation of therapy to control secondary infection.
  • Elimination or hypoallergenic dietary therapy must be strictly enforced.
  • Fecal softener if needed.

Alternative Drug(s)

Analgesics may be necessary, especially during induction phase, to facilitate local therapy.

Patient Monitoring

• Assess cyclosporine trough levels especially when ketoconazole is used if toxicity is suspected.
• Re-examine to assess healing, signs of recurrence, and associated complications.

Possible Complications

• Reversible alopecia
• Vomiting, diarrhea, anorexia
• Weight loss
• Recurrence
• Failure to heal
• Dehiscence of surgical site
• Tenesmus
• Fecal incontinence
• Anal stricture
• Flatulence
• Iatrogenic Cushing's disease from corticosteroids

Expected Course and Prognosis

• Guarded for complete resolution except in mildly affected patients.
• Chronic treatment may be necessary.
• If all treatment is discontinued, patient should be closely monitored for recurrence.

Associated Conditions

• Colitis
• Constipation and/or obstipation may develop