Acral Lick Dermatitis causes and treatment

Acral lick dermatitis is an ulcerated lesion, usually on the lower legs, caused by self-trauma due to licking or gnawing. It is not a disease, but a symptom of an underlying condition.

Aetiology and pathogenesis

Acral lick lesions are caused by self-trauma. There are many reasons for a dog to lick obsessively at the legs, the most common reason being pruritus. Pruritus of the legs is most often caused by atopic dermatitis, but ectoparasites should be ruled out as well. In addition, abnormal sensory perception is a possible reason for licking. Acral lick lesions have been reported over surgical implants, at arthritic joints and following nerve pathways, indicating that pain plays a role in some cases. Excessive licking can be a sign of gastrointestinal or dental disease.  Anxiety or compulsive disorders may play a role in some dogs, by either causing this condition or exacerbating it. It is important to recognise that these are not mutually exclusive and many dogs have multiple triggers. In some cases, a small initial injury to the skin may be a focus of licking, causing a secondary bacterial folliculitis and furunculosis, which leads to more pain or pruritus, causing more licking and enlarging the lesion.

Clinical features

Middle-aged to older and large breed dogs are predisposed. Lesions are plaque like, firm and often ulcerated on the surface. A rim of hyperpigmented, lichenified skin and saliva-stained hair usually surrounds the lesion. Dogs start these lesions on the dorsal lower legs and feet and, where the dog has a favourite limb that is focused on, the front limbs are often preferred (Fig. 2.1).

A well-developed acral lick granuloma with well-demarcated swelling

Fig. 2.1 A well-developed acral lick granuloma with well-demarcated swelling, erythema, alopecia, erosions and hyperpigmentation.

Atopic dermatitis and/or a food allergy is the most common underlying reason for this condition, and so other symptoms such as pododermatitis, otitis and skin infections may be concurrent. Other causes typically have no skin lesions other than those created by the animal. Very precise and focal lesions (e.g. single digits) often have a neuropathic cause, especially if bilateral.

Diagnosis

These lesions are usually easy to diagnose visually; it is the underlying cause of the condition that can be more difficult to establish, especially if the dog has no other signs or history of atopic dermatitis. A careful history and thorough physical examination is required to rule out systemic illness, musculoskeletal problems, neuropathies and behavioural factors. These lesions almost always involve a deep staphylococcal bacterial infection, so cytology and deep bacterial culture/sensitivity is ideal. Multiple biopsies or surgical removal with histopathology may be needed to confirm diagnosis and rule out infectious or neoplastic causes of this condition.

Treatment

This condition can be very frustrating to manage if an underlying condition is not found and if owners are not compliant. Owners should be warned of the low likelihood of curing the condition once it has become chronic, especially if an underlying condition is not found and, no matter what, it is likely that the dog will need some form of long-term management:

  1. In mild cases, start by treating the secondary staphylococcal infections (usually for 6–8 weeks), and investigate and treat the underlying condition. It is best to be very diligent to make sure that the lesions are resolving well with your choice of treatment, to stop them becoming chronic and severe.
  2. In severe cases, no matter the underlying reason, the following protocol can be attempted using all medications and barriers constantly until resolution (smooth, non-lichenified skin and hair regrowth), which usually takes 1–2 months.

 

Bear in mind that glucocorticoids frequently mask underlying diseases, so diagnostics should be performed before starting therapy. Also remember that glucocorticoid therapy has many adverse side effects:

  1. Prednisone/prednisolone 0.5–1 mg/kg per day.
  2. Oral antibiotics based on culture; topical antibiotics may be sufficient for less severe lesions.
  3. Twice-daily topical DMSO/fluocinolone 1 drop per cm of ulceration, followed by a thin layer of antibiotic/antifungal/steroid ointment.
  4. An Elizabethan (e-)collar and/or other barrier method (wrapping, basket muzzle, sock, etc.) is essential to break the self-trauma cycle.
  5. Naltrexone (2 mg/kg po q12–24 h) or hydrocodone (0.25 mg/kg po q8–12 h) can be used to help break a compulsive cycle, if suspected.

Underlying causes of acral lick dermatitis must be diagnosed and treated long term.