Perianal fistulas
From Felipedia
Perianal fistulas are a rare disease of the anus in cats. Current evidence suggests that immunological factors are involved in the primary aetiology, although no simple defect is likely. The disease appears to be modulated through cell-mediate immunity (T-cell involvement)1.
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Clincial signs
In cats, clinical signs of anal fistula include overt attention to tail region, painful defecating (dyschezia), blood in feces (haematochezia), meowing during defecation.
Diagnosis
Perianal fistulas can be very easy to identify by simply looking under the tail There are at least two situations in which diagnosis can be confusing. First, sometimes one will be examining a patient before the fistulas break open to the outside (i.e., they are still internal and will break open and form the fistulas tracts in the future), in which case it can be much harder to find them by digit examination and maybe proctoscopy. Second, there are a few other diseases that can look like exactly like perianal fistulas during a rectal exam, such as rectal pythiosis if it has formed fistulas. It is important to make the correct diagnosis because perianal fistulas have a much better prognosis than pythiosis. If you practice in an area without pythiosis, then physical examination is generally sufficient for a diagnosis (although sedation is often needed to get a good examination of the anal area).
Treatment
While surgery was once the treatment of choice, now immunosuppressive medications (e.g., cyclosporin or azathioprine) combined with antibacterial therapy (e.g., erythromycin, metronidazole) are clearly preferred. While quite effective, the biggest disadvantage of cyclosporin is its cost. Some dogs need to be treated for months and then may relapse and have to be treated again, and the only way to know if you are administering enough is to do measure blood levels of cyclosporin (which is also expensive). Therefore, cost can be a major impediment to therapy. In an effort to lower the cost, some people simultaneously administer ketoconazole in an effort to prevent metabolism of the cyclosporin and thereby achieve higher blood levels with lower dosing. However, therapeutic blood monitoring becomes critical as you cannot begin to anticipate what the blood levels will be. Therefore, some clinicians just treat with azathioprine which, although slower and not as reliable as cyclosporin, is considerably less expensive3.
References
1. Patricelli AJ, Hardie RJ, McAnulty JF (2002) Cyclosporin and ketoconazole for the treatment of perianal fistulas in dogs. J Am Vet Med Assoc 220:1009-1016
2. Misseghers BS, Binnington AG, Mathews KA (2000) Clinical observations of the treatment of canine perianal fistulas with topical tacrolimus in 10 dogs. Can Vet J 41:623-627
