What is a “Lick Lesion”?

When dogs lick over and over at the same spot they eventually cause sores that veterinarians refer to as  “acral lick dermatitis” or an “acral pruritic nodule”.   These are itchy, thickened, centrally ulcerated or “raw” areas of skin, typically on the legs and forepaws, caused by excessive licking and complicated by bacterial infection and scarring.  When skin is rubbed often (in this case by the tongue), it responds by becoming thicker, similar to the formation of a callus on our feet or hands from exercising.  The center of the lesion often gets the most attention while having the least amount of blood supply, and therefore typically has a moist, ulcerated, necrotic or “raw” appearance.  Secondary bacterial overgrowth often develops at the site of the lesion. The skin around the lesion will often appear black, also due to necrosis of the skin.  It is not uncommon for a pet to form multiple lick lesions on one or multiple legs.

Causes of Acral Lick Dermatitis:

 

Allergy

– Underlying allergy and subsequent itch is the most common cause of acral lick dermatitis.  This may be environmental allergy (housedust mites, pollens, molds, etc.), flea allergy or food allergy.

Parasites

– Fleas or contagious mites such as scabies.

Pain

– Older pets may initiate a lick lesion secondary to arthritis.  They lick the overlying skin to soothe the joint pain below, eventually the damaged skin itself becomes a stimulus for the itch.  Rarely, an underlying bone tumor can trigger the same response.  Sometimes, the infection of the lick lesion will extend and involve the joint below it, resulting in further discomfort.

Neurologic pain

– Occasionally nerve irritation caused by multiple primary disease may cause stimulus of the nerves and a “tingling” sensation that is soothed by the dog by licking.

Foreign body or puncture wound

 

Deep bacterial infection

 

Boredom/OCD (obsessive compulsive disorder)

– Some pets form an acral lick lesion as a result of a nervous, obsessive compulsive habit.  While this is a commonly suggested cause, this is in fact quite rare.  An underlying itch or pain generally starts the behavior before it became “habit”.

Skin tumor or growth

– Either cancerous or benign, it can mimic the appearance of inflamed skin.  These tumors are rare and occur usually in older pets.

Dermatophytes (ringworm or superficial fungal infections)

– Dermatophytes or other more serious fungal infections can occasionally form lesions that closely resemble a lick nodule.  This is a rare phenomenon.

Diagnosis

An acral lick nodule is most often diagnosed primarily by its clinical appearance.  However biopsies are important to rule out various growths or tumors that may be masking as an acral lick nodule.  Veterinarians will utilize other forms of diagnosis to determine the severity of infection (cytology and/or cultures), the cause of the change to the skin (skin scrapes), or the assessment of an underlying joint (radiographs).  It is important that these get evaluated by their veterinarian to prevent worsening and damage to the bony structures below.

Treatment

Acral lick dermatitis can be one of the most frustrating disorders for veterinarians and owners to treat.  The most important step in beginning treatment is to adequately assess the patient and to uncover the primary trigger for the problem.  Oral antibiotics, topical antibiotics and anti-itch therapies are important first steps in treating the secondary problem.  However, identifying and correcting the primary trigger  is essential to prevent recurrence of the condition.  Topical moisturizing grooming products to those areas and soothing agents can help when the condition is controlled to soothe the pet’s sensation of itch.  Mechanical restraint is often necessary as well (E-collars, bandages, booties or socks) to prevent the pet’s access to the area.  Additional topical sprays and ointments that taste bad (Grannick’s Bitter Apple® for example) can be helpful.  Rarely, surgical removal of the lesion is helpful.

It is important to understand that no treatment is uniformly successful because the cause of this clinical condition has many different triggers.  This disease is difficult to control without thorough workups and appropriate diagnostics.  It is critical for the owner to work closely with their veterinarian or dermatologist and to identify the underlying cause in order to successfully treat the lick lesions.

Dr. Mendelsohn is a 1997 graduate of UC Davis School of Veterinary Medicine and received Diplomate status with the American College of Veterinary Dermatology in 2004. After graduation from UC Davis, Dr. Mendelsohn completed an internship with the Animal Emergency Clinic and Animal Specialty Group in San Diego. She later practiced general medicine before starting her residency with the Animal Dermatology Clinic in 2000. Her love and appreciation of the human-animal bond is what drew Dr. Mendelsohn to this specialty. Another opportunity that Dr. Mendelsohn enjoys is the training of veterinary students, helping these students appreciate the hidden complexities of dermatologic disease.For more information please visit www.animaldermatology.com.