Lick Granuloma/Acral Lick Dermatitis In Dogs

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When I graduated from Auburn University’s College of Veterinary Medicine in 1980 the syndrome was called Lick Granuloma. At some point veterinary dermatologists decided on a new name, Acral Lick Dermatitis (ALD). Lick Granuloma continues to be the most commonly-used term among general practitioners.

In the 80s the leading causation theory was injury. The pathogenesis was believed to go something like this: Lesions are almost always on the front surface of a front leg or outside surface of a rear leg. In those locations bone is closer to the surface than anywhere else in the body. If a dog runs into an immovable object the skin, fascia, muscles, tendons, blood vessels and nerves would be “trapped” between the immovable object and the hard bone below. Finding itself between a bone and a hard object, a nerve becomes injured. The nerve’s attempts to heal result in a tingling sensation, which then causes the patient to lick at the spot as if something were there. The more it tingles the more the pet licks and the more he licks the moister it becomes, begetting excellent conditions for infection. Once infection invades it adds to the itchiness and tends to become very, very deep in the lesion.

“Acral” comes from the Greek word “akron,” which means “extremity,” which is where the lesions are located. Granuloma refers to a type of tissue that is attempting to heal, but ineffectively.

Today there are known to be many more contributing factors, yet little research is reported on ALD. Dr. John Angus, Board Certified Veterinary Dermatologist, of the Animal Dermatology Clinic in Pasadena, CA, says, “Since 1980 only ten original research articles have been published on canine ALD; most were treatment trials…with only three reporting histopathologic and microbiologic findings.2

Any breed of dog can be affected, but the majority of ALD patients are large-breed dogs with short hair coat over the limbs. A list of breeds is provided in the footnotes1.

According to Dr. Angus, veterinary dermatologists divide the causes into three categories: predisposing, primary and perpetuating.

A predisposing factor is not a cause, but large-breed dogs with short hair on the legs (regardless of the length of hair on the trunk) are more likely to be affected by Lick Granuloma.

Primary causes are factors that initiate itchiness and are led by food allergy and atopy. Dr. Angus lists trauma next, (see opening statement) followed by cancer, fungal infection, foreign body, osteoarthritis, parasthesia/neuropathy and behavioral problems.

Perpetuating factors are conditions that keep the process going after it starts. They include deep bacterial infection, trapped hair or ruptured hair follicles, sweat gland inflammation, fibrosis (scarring) and reinforced behavior.

Regardless of the initial cause, after a patient has licked the skin until it is macerated and inflamed it is a perfect place for bacterial infection to persist. The nature of the tissues involved prevents thorough antibiotic penetration and the bacteria tend to be highly resistant to many antibiotics. Infection causes the itchiness to escalate.

As licking persists, hair follicles are ruptured. Short, stiff hair shafts are then forced into the lesion. Hair is high in keratin protein, which Dr. Angus describes as “phenomenally irritating to tissues and stimulates a profound acute and chronic inflammation. Hair shaft foreign bodies are very painful. This combination of pruritus [itchiness] and pain results in an amplification of the desire to lick at the region. “

Notice that food allergy is the first predisposing factor listed. Dr. Steven LeMarie’, Board Certified Veterinary Dermatologist, of Southeast Veterinary Specialists in Metairie, LA,  (www.svsvets.com) concurs that a food allergy trial is essential in the workup of these cases. Failure to address predisposing factors dooms therapy. Atopy, or Allergic Inhalant Dermatitis, and all other primary causes must be controlled by whatever means necessary.

Bacterial culture and sensitivity is necessary to identify the (usually multiple) bacteria that cause infection in acral lick dermatitis. Merely swabbing the surface for culture is insufficient. Instead, deep biopsies should be obtained or deep infection squeezed up through pores to the surface.

I have had great success with surgical removal of these lesions when they are small. Small is the key word, because in the areas of the body where ALD lesions occur there is little redundant skin for closing a large surgical resection. Surgical removal also has the advantage of giving the clinician access to the deep tissues for bacterial culture and sensitivity, as well as tissue to send for histopathology for confirmation of the diagnosis. Obviously, preventing self-trauma during the postoperative healing time is crucial. Elizabethan collars and foul-tasting topicals can be effective for keeping the patient’s mouth from the surgery site.

Your pet’s doctor has many tools in his treatment arsenal. You should plan for treatment to be a lifetime challenge and for therapies to change periodically as conditions change.
MMLICK

  • 1Doberman Pinscher
  • Great Dane
  • Labrador retriever
  • Boxer
  • Weimaraner
  • German shepherd
  • Golden retrieever
  • Irish setter

2Reference:  Canine Acral Lick Dermatitis, Angus, JC, Proceedings of the NAVDF, Portland, Oregon 2010, pp. 175-179

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