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Anal Furunculosis

Other Names: Perianal Fistula, Perianal Sinus

Anal Furunculosis (Perianal Fistula): An Overview

The development of Perianal Fistuals, a condition also referred to as Anal Furunculosis, is associated with the formation of severe lesions around the anus of the dog. These lesions are chronic, often resulting in persistent ulcers. 

Causes of Furunculosis

While the specific cause of Perianal Fistuals remains unknown, it is speculated that they result from inflamed sweat and sebaceous glands which produce oil in the anal area. Bacteria proliferate in the moist, warm environment under the base of the tail, exacerbating the condition.

Prevention of Furunculosis

There are currently few preventative treatment options available for dogs with Anal Furunculosis. The anal area of breeds that traditionally have a broad tail base, low tail carriage, or history of immune-mediated disease should be examined regularly for symptoms of Perianal Fistula development.

Symptoms of Furunculosis

According to the Merck Veterinary Manual, Ninth Edition, symptoms of Perianal Fistulas include:

  • Attitude variance
  • Tenesmus (persistent feeling of needing to pass stools with an empty bowel)
  • Dyschezia (inability to defecate/constipation)
  • Anorexia (eating disorder associated with reduced appetite and/or aversion to food)
  • Lethargy
  • Diarrhea
  • Biting and licking at the anal area

Diagnosing Furunculosis

Diagnosis of Anal Furunculosis occurs through physical examination of the dog’s hindquarters underneath the base of the tail, evaluation of the dog’s history, and also results from skin biopsy.  Depending on the progression of the lesions, veterinary sedation may be necessary to prevent additional pain during the examination. The lesions associated with Perianal Fistulas are often found in male dogs between the ages of 5 and 8; however, the range can be extended to affect young and aging dogs of both sexes between 1 and 14 years old. Dogs over age 7 are statistically at a higher risk. Perianal Fistuals commonly develop in German Shepherd Dogs. Biologically, German Shepherds have a significantly larger number of glands located beneath the tail.  Anatomically, they have a broad tail base and low tail carriage. These combined characteristics may result in poor ventilation of the anal area and lodging of fecal material in the anal folds.  Such conditions encourage bacterial growth and infection of anal glands and hair follicles, which results in perpetual inflammation. Because inflammation of the sweat and sebaceous anal glands may lead to the onset of severe lesions, immune-mediated reactions could also be a contributing factor.  Immune-mediated reactions involve the inappropriate, and often harmful, response of the body’s immune system. A dog’s immune system may over-react to something assumed to be foreign, or it may trigger an immune response against the body’s own tissues. White blood cells induce an inflammatory response as a protection mechanism against bacteria and viruses.  German Shepherds are particularly known for immune-mediated disorders. Labrador Retrievers, Irish Setters, Spaniels, Old English Sheepdogs, Border Collies, and Bulldogs are breeds with the highest risk for Perianal Fistulas, but many mixed breeds also develop these painful lesions.

Treating Furunculosis

Once diagnosed, treatment of Anal Furunculosis varies from antibiotics to immunosuppressive therapy to surgery. Because of the suspected multifaceted nature of Anal Furunculosis, numerous treatment methods may be recommended in conjunction. Cyclosporine, which is an immunosuppressive drug that works by disabling helper T cells, often serves as effective short-term treatment for minimizing immune-mediated disease response. Ketoconazole is often prescribed in conjunction with cyclosporine for its antifungal properties. Stool softeners may be given to decrease the effects of dyschezia. Surgery is usually avoided unless medical therapy treatment options are exhausted. According to the Merck Veterinary Manual, Ninth Edition, surgical options include excision, debridement (removal on non-living tissue from around the lesions), fulguration (use of high-frequency electric current to destroy unwanted tissue), and cryosurgery (localized exposure to extreme cold to eliminate abnormal cells). Amputation of the tail is an archaic surgical treatment method that is no longer commonly recommended. 

Care for dogs with Furunculosis

For basic management of a diagnosed Anal Furunculosis case, the external anal area should be kept clean and surrounding hair should be clipped under sedation, if necessary. Humidity and moisture may be managed by applying baby powder, or a similar substance recommended by your veterinarian, to the perineum. The perineum is the area located between the anus and scrotum in the male, or between the anus and vulva in the female. Under the supervision of a veterinarian, lesions may be flushed with chlorhexidine or povidone iodine, both of which function as disinfectants that control bacterial growth. Antimicrobial shampoo may also be used.  If medical management techniques are ineffective, surgery may be recommended. Ulcer tissue may also be removed using a carbon dioxide laser technique, which is usually performed by a dermatologist.

Cure for Furunculosis

Anal Furunculosis is a chronic disease and therefore can be managed, but not permanently eliminated. Because the lesion formation is suspected to be associated with an immune-mediated disease response, long-term therapy may serve as effective management.
1. Cleveland Clinic 
2. Pet Education
3. Go Pets America
4. Merck Veterinary manual, ninth edition p.149-150

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