Lick granuloma in dogs: causes, tests and treatment

Overview

Lick dermatitis usually develops on a lower leg within easy reach while the dog lies down. The wrist region of a front leg is a common site. Hindlegs can also be affected. One dog may repeatedly lick areas on several legs.

Constant licking breaks the skin's protective surface and can expose deeper tissues. Skin inflammation then increases itching and encourages further licking. Gradually, a thick, raised area develops and its surface may ulcerate. Damage can persist even when the original irritation has become less intense.

Causes

Itching, pain and skin disease

Allergic dermatitis is a common trigger for lick dermatitis. Your dog may lick because of itching from food allergy or atopic dermatitis, for example. Flea allergy can also start the itch–lick cycle. Concurrent recurrent ear infections or itching elsewhere make allergy more likely to be suspected.

Osteoarthritis pain may cause licking of skin over a painful joint. An old injury or surgical site may also feel uncomfortable and trigger licking. A foreign body beneath the skin can sustain local irritation. Nerve injury or compression can cause abnormal sensations that prompt licking or biting of a leg.

A ringworm kerion, Demodex mites or a deep fungal infection can resemble lick dermatitis. A tumour can also be the initial cause if it itches or hurts.

Behaviour and persistent inflammation

Stress or anxiety can increase compulsive licking. Changes in daily life, time alone or too little meaningful activity can sustain the problem. A licking-related behavioural disorder is assessed alongside investigations of itching, pain and inflammation.

Hair and keratin released from ruptured follicles can remain in the skin as foreign material. Retained keratin can cause a foreign-body reaction sustaining deeper inflammation and itching. Scar tissue and retained hair fragments can provide sheltered sites for bacteria.

Risk factors

Lick dermatitis is diagnosed particularly in medium and large dogs. It has been described in breeds including Dobermanns, Great Danes, Labrador Retrievers, Weimaraners and Boxers. However, any breed can develop it. Labrador Retrievers have a described tendency to lick their lower front legs excessively. A short coat is one predisposing feature. An old injury site may remain a licking target later in life.

In one northern European behavioural survey of almost 4,500 dogs, low exercise levels were associated with a greater likelihood of compulsive behaviour. The survey covered several repetitive behaviours, including repeated licking of a particular target.

Typical symptoms

Initially, the skin may look red and develop a crust. Over time, the lesion becomes noticeably thicker and may rise above surrounding skin.

• Your dog repeatedly returns to lick the same part of a leg.
• The licked area loses hair.
• Skin may become red and crusted.
• The area feels thickened or firm.
• Skin may break or ulcerate.
• Pus or blood-stained discharge may seep from the inflamed site.

Deep inflammation may also cause red or purplish raised lesions and subcutaneous nodules. Absence of visible pus does not exclude deep bacterial infection. Your dog may lick while lying down because the area is easily accessible then.

Complications and consequences

In deep pyoderma, bacteria extend into the dermis and sometimes subcutaneous tissue. An inflamed follicle can rupture and release its contents into surrounding tissue. Severe or longstanding inflammation can heal with scarring. Repeatedly licked, scarred skin may remain susceptible to further infection.

In one study of 31 lesions, deep tissue cultures grew bacteria in 30 cases. A bacterium classified within the Staphylococcus intermedius group grew in 58% of samples. Some bacteria were resistant to antibiotics commonly used for skin infections.

Diagnosis at the vet

How licking began and examination of the skin

Your vet asks whether licking began before or after the skin lesion appeared. Examining other skin areas and ears may reveal signs of allergic skin disease. Skin scrapings can look for Demodex mites. Hairs and scales can be cultured for dermatophytes if needed. Joint examination helps locate pain that might cause leg licking. The leg may be X-rayed if injury or joint disease is suspected.

A neurological examination looks for findings consistent with nervous system disease. MRI may be needed for a longstanding problem or one accompanied by neurological signs.

Cytology, culture and biopsy

Cytology looks for bacteria and inflammatory cells in the lesion. Ideally, the sample comes from deeper discharge expressed by gently pressing the lesion. Deep tissue culture helps identify the infecting organism. Susceptibility testing establishes which antibiotics work against the sampled bacterium.

Surface culture does not always reflect bacteria in deeper tissue. In one comparison, surface and deep cultures matched in 8 of 22 cases. In that study, 57% of tissue isolates were susceptible to amoxicillin combined with clavulanic acid. Susceptibility to cefazolin was 55%.

A biopsy helps distinguish lick dermatitis from a tumour or deep fungal infection. Tissue samples may show follicular inflammation, ruptured follicles and scarring.

Behavioural assessment

The timing of licking, time alone and recent household changes help assess behaviour. A home video can help if your dog does not lick at the practice. Diagnosing a compulsive disorder also requires investigation of physical diseases causing licking.

Treatment

Preventing licking and treating inflammation

Your vet plans treatment according to the underlying cause of licking and the skin inflammation. Care usually includes settling inflammation and preventing further damage. A protective collar can stop your dog reaching the lesion. Its fit is checked because otherwise your dog may reach around it or rub the leg against its edge. Protection continues until your vet considers healing sufficient.

Deep bacterial skin infection usually requires an oral or other systemic antibiotic. Where possible, selection is based on culture and susceptibility results. A painless area can also receive a topical antimicrobial or antiseptic chosen by your vet. Anti-inflammatory and anti-itch medication may reduce skin irritation.

Treating the underlying cause and behaviour

Long-term control of allergic skin disease is needed if it sustains licking. Treatment of a painful joint or nerve pain targets the problem identified during investigation. When allergy is suspected, care may include a veterinary-planned diet trial. Treating the skin alone may lead to recurrence if underlying allergy remains untreated.

Behavioural care reduces anxiety and adds suitable, meaningful activity. Predictable responses from you and familiar routines may reduce anxiety. Your dog can be rewarded for calm alternative behaviour. Your vet may consider behavioural medication if compulsive licking continues alongside other treatment.

In a randomised drug trial, owners reported less licking and improved lesions in fluoxetine-treated dogs at the 6-week assessment. Another trial of compulsive disorder in 51 dogs found short-term symptom improvement with clomipramine. It included 12 dogs that damaged their skin by licking. Clomipramine can cause lethargy and reduce appetite. Dogs participating in follow-up still showed repetitive behaviours after 1–2 years.

Follow-up and additional treatments

Response of deep skin infection is checked at the practice, including repeat cytology. If infection persists but is improving, reassessment may take place every 2 weeks. Success is assessed by both reduced licking and healing of the skin surface.

Laser removal of thick scar tissue may be considered in some persistent cases after the underlying cause and infection have been treated. Additional benefit from low-level laser therapy was investigated in a randomised, sham-controlled trial. Seven dogs received laser treatment. Six received sham treatment. Both groups also received an antibiotic and anxiety-reducing medication. Laser treatment did not reduce licking or lesion size significantly more than sham treatment. Increased hair growth was 24% greater in the laser group than the comparison group.

Prevention

Early treatment of itchy or painful disease may interrupt the licking–damage cycle. Allergy maintenance treatment helps reduce itching between inflammatory episodes too. Suitable exercise and meaningful activities reduce environmental stressors. A predictable routine and daily life meeting your dog's needs form part of behavioural problem prevention. Familiar settling activities and reward-based training can help manage anxiety. Changing your dog's environment can prevent situations that trigger repetitive behaviour. Your dog can be taught to rest on their own mat with a suitable chew in situations where licking usually starts.

Important for dog owners

Prevent licking with protection recommended by your vet and check that your dog cannot reach around it. Do not scold or punish licking because fear-inducing methods can increase anxiety. Watch other skin areas and ears too, so changes associated with more widespread itching are noticed.

Film a short home video of situations in which licking begins. Tell your vet about household changes, time alone and previous injuries. Return for checks as arranged because surface appearance does not always reveal continuing deep inflammation.

Frequently asked questions

Is lick dermatitis always caused by stress?

Licking may also be caused by allergic itching, joint pain, nervous system disease or a local skin lesion. Stress can nevertheless sustain it. Skin disease and possible pain are therefore investigated carefully before diagnosing a purely behavioural disorder.

Why is a deep skin culture needed?

Surface bacteria may differ from those in deeply infected tissue. In one comparison, surface and deep cultures matched in 8 of 22 cases. Deep culture and susceptibility testing help select an effective medicine.

Is a protective collar enough to heal the licked area?

A collar can prevent further damage by stopping your dog reaching the site. Care also treats any infection and the original cause of licking. Untreated allergy may cause dermatitis to recur once protection ends.

Does low-level laser therapy help?

In a small randomised study, laser treatment did not reduce licking or lesion size significantly more than sham treatment. Hair growth increased more in the laser group. All dogs also received an antibiotic and anxiety-reducing medicine, so laser was assessed as an additional treatment.

Why does my dog lick an area that has already healed?

Recurrence is possible if the disease causing itching or pain continues. Retained hair fragments and scarring can sustain inflammation. Learned or compulsive behaviour developed through repeated licking can also sustain skin damage for a long time.