Interdigital Cysts on Dogs

What Are Interdigital Cysts on Dogs?

Interdigital cysts are not true cysts. They are inflamed and infected tissue in the webbing between a dog’s toes. Once inflamed, these lesions are called furuncles. Furuncles are more commonly found on the top of the front feet; however, all four feet can be affected. With little space between the toes to spread, the furuncle ruptures through the skin and produces a draining tract.

Interdigital cysts or furuncles are painful and are the most common cause of draining tracts between the toes in dogs. Other causes of draining tracts are a reaction to a foreign object in the foot, infection of the hair follicle, or cancer.

Any dog can develop interdigital cysts, but dogs that are short-haired, allergy-prone, overweight, or obese are more likely to develop them.

Short bristly hairs in the webbing and increased webbing between the toes make these breeds more likely to get interdigital cysts:

• Shar-Pei

• Labrador Retriever

• English Bulldog

• Mastiff

• Great Dane

• Boxer

• Basset Hound

Symptoms of Interdigital Cysts on Dogs

Symptoms of interdigital cysts on dogs include inflamed, reddened skin in the webbing between the toes that may have extended from the bottom to the top of the paw. The swellings are deep reddish-purple, shiny, and hairless and range in size from 1-2 centimeters. They are also movable, which is why they are misnamed as cysts. They can break through the skin and produce a bloody discharge.

Interdigital cysts are painful, so dogs may limp, lick, and bite on the affected paw. There may be several nodules with new lesions developing as others resolve. 

Causes of Interdigital Cysts on Dogs

Interdigital cysts develop when hair follicles are traumatized, causing the microscopic opening of the hair follicle to enlarge. With limited space to expand, these follicles rupture and release their contents. The body sees this released material as foreign and creates an inflammatory reaction to it, as it does with bacteria, fungi, or mites.

The initial trauma is usually related to excessive weight on the feet, conformational changes (presence of increased webbing or gait abnormalities), or foreign material embedded in the skin. The presence of foreign material in the skin prevents complete healing of the infection. Until it is removed, the cyst or furuncle will recur.

The Demodex mite, a skin parasite, can cause interdigital cysts or furuncles as well as canine atopic dermatitis, an underlying skin condition. Until the mites are killed and the allergy causing atopic dermatitis is controlled, interdigital cysts will recur.

How Veterinarians Diagnose Interdigital Cysts on Dogs

The veterinarian diagnoses interdigital cysts or furuncles on your dog based on their history. First, they examine the dog’s paws looking for any discharge. To identify the cause of the initial trauma, the vet performs a combination of the following skin tests:

• Skin scraping or examining plucked hairs to rule out infection due to Demodex mites

• Impression smears, cytology, or culture to rule out other contaminants and determine the best antibiotic choice

• Skin biopsy to confirm changes to the hair follicle

• Bloodwork including hormone levels to rule out underlying disease

• Elimination diet trial to rule out food allergies

• Intradermal skin testing to rule out environmental allergens

Treatment of Interdigital Cysts on Dogs

There are three major treatment options of interdigital cysts in dogs: medical therapy, surgery, and CO2 laser:

• Medical therapy: Medications include oral or topical anti-inflammatories, like steroids, and antibiotics. In severe cases, treatment is continued for four weeks after symptoms improve.

  • Antibiotics alone may result in improvement, but without controlling the underlying cause of trauma the lesions tend to recur. Dogs often need systemic antibiotics of oral or long-lasting injectable medications for at least four weeks.

  • Anti-inflammatories applied topically work best with only one lesion. Oral anti-inflammatories are needed for resistant cases or for dogs with multiple lesions.

• Surgery: Surgery removes the affected webbing and stitches the adjacent toes together, preventing the webbing from regrowing. This procedure changes the shape of the paw and can cause future orthopedic problems. Postoperative care is time-intensive and requires bandage changes 1-2 times daily. Foot licking and pain may still occur, so underlying conditions must be controlled.

• CO2 laser: Carbon dioxide lasers remove unhealthy, thin layers of skin with minimal damage to the surrounding area. Healthy skin can return without altering the shape of the paw. To achieve the best outcome, multiple laser procedures are needed.

Despite treatment and identification of an underlying disease, some dogs have chronic recurrent lesions. These lesions are best controlled with long-term topical medications, like cyclosporine, and weekly or biweekly medicated baths.

Recovery and Management of Interdigital Cysts on Dogs

Successful recovery and management of interdigital cysts on dogs can take months to achieve. It is dependent on managing the cause of the underlying trauma, decreasing re-exposure to traumas, and rebuilding healthy skin. Factors like wet, hard, or uneven environments, dirty kennels, or uncontrolled allergies prevent complete resolution of interdigital cysts.

Lifelong routine management is required to maintain remission. In most cases, medication to moderate the immune system’s response to environmental trauma is needed for long-term control.