Demodicosis most common underlying cause of persistent pododermatitis

Demodicosis most common underlying cause of persistent pododermatitis

Jul 01, 2005

There is nothing more frustrating than treating a dog with bacterial pododermatitis.

You can use antibiotics, foot soaks in antibacterial soaps, and sometimes a small dose of steroid, and this infection keeps lingering!

The most common underlying cause of a persistent pododermatitis is demodicosis. In some patients, only the feet will be involved. In some cases, just one foot is effected.

Photo 1: Inflamed, swollen foot with demodex mites and accompanying infection.
The clinical presentation of a dog with demodex pododermatitis is usually a swollen foot, particularly around the nailbeds often with accompanying deep infection. (See Photo 1.)

If skin scrapings are not performed or the mite is missed and the dog is treated with antibiotics and steroids, the feet improve. Unfortunately the steroid leads to more immunosuppression, and the patient's feet flare up worse than on the original presentation.

If the mite is missed again on scrapings, more of the same medications are dispensed typically. The patient enters a cycle of improvement, yet worsens over time. Another common mistake is to check the patient's feet for yeast and dispense appropriate anti-yeast medications yet when demodex is present, the yeast is a secondary problem. In essence, diagnosing the mite is essential to clearing up any secondary bacterial or fungal infection.

Photo 2: In some patients, plucking the hairs of the feet will enable one to visualize the mite adhering to the root of the hair.
The diagnosis of pododemodicosis is made by deep skin scrapings of the effected feet and observation of the mites in oil under low power. (See Photo 2.) In some patients, plucking the hairs of the feet will enable one to visualize the mite adhering to the root of the hair. Since a deep secondary pyoderma is usually present, a culture and sensitivity is usually performed. In some patients on chronic steroid use, demodex infections will develop.

Photo 3: Demodex of the feet/legs in a Shetland Sheepdog with transitional cell carcinoma of the bladder.
In those patients, in order to eradicate the mite, an alternate therapy to the steroid needs to be undertaken along with treatment for the mite. In older patients not on steroids that develop demodex of the feet, an internal medicine workup should be undertaken to rule out neoplasia, Cushing's disease, hypothyroidism or underlying chronic allergy. (See Photo 3.)

Long-term antibiotics Treatment of pododemodicosis can be difficult because of the accompanying infection.

Photo 4: Demodex of the feet—more chronic with crusting, hyperpigmentation.
Long-term antibiotics should accompany one of the three treatments for demodex. The only FDA-approved treatment for demodex is mitaban dip. These dips are approved for biweekly use, but the success rate doubles when dips are performed weekly. Dips should be preceded by a benzoyl peroxide shampoo of the feet for its follicular flushing activity. (See Photo 4.)

The patient should be discouraged from getting its paws wet between dips, which makes these dips difficult to use in patients that go outside. If the owner is performing weekly dips, they should be cautioned not to use the medication on dogs if they are pregnant, diabetic, on antihypertensives, cardiac medications or antidepressants.

Once the mites have been eradicated, we suggest that the patient have four more weekly dips as insurance. Along with the dip and benzoyl peroxide shampoos, antibiotics need to be prescribed for the entire treatment regimen. Do not prescribe steroids, not even a small amount! In some patients a "small" dose of steroids is enough to perpetuate immunosuppression that the demodex mite is causing anyway. Ivermectin at 200-800ug/kg/day orally is another treatment for demodex of the feet. It is not FDA-approved for use in the dog for demodex and should not be used in herding breeds, herding breed mixes, white German Shepherds or in elderly patients. The patient should be heartworm negative before starting therapy.