Introduction

Acral lick dermatitis (ALD) can be a very frustrating challenge for the small animal practitioner. It’s easy for clients and veterinarians alike to lose patience with the often slow process of workup and therapy. The purpose of this lecture is to present some tips that I have found useful in the management of acral lick dermatitis.

Factors that may contribute to ALD¹

Tip One

Prevention of further damage and treatment of secondary infection are the two most critical factors determining treatment success or failure.

Self-trauma creates a “damage à itch/discomfort à lick à more damage” cycle that can be almost unbreakable if the patient is allowed to continually traumatize the lesion. Physical intervention to prevent self-trauma will be required initially, although adjunctive medications (see below) may make the job easier. The most commonly used method is an Elizabethan collar, although the animal must be observed to make sure that they cannot reach around the collar or scrape the leg on the collar edge. Collars can be extended by taping X-ray film (or sections of another collar) to the edges. Alternately, a plastic bucket can be tied to the patient’s collar. Inflatable or foam-filled collars will probably not be sufficient on their own, but may be helpful when placed behind an Elizabethan collar to prevent it from being shoved backwards. The temptation to remove the collar early must be resisted, as dogs can undo weeks of healing in a single afternoon. Ideally, the collar should be kept on (except for feeding) until the lesion is re-epithelialized and nearly resolved.

Almost all ALD are complicated by secondary bacterial infection. This infection is perpetuated by the presence of hair foreign bodies and extensive fibrosis, both of which serve to create protected areas for bacteria. Antibiotic selection is best based upon the results of sensitivity testing. Ideally, the skin should be aseptically prepared and a deep skin biopsy obtained for culture. If finances are an issue, the lesion may be cleaned and squeezed to extrude infected debris. Prolonged courses of antibiotics (2–6 months or more) are often required. As a general rule, patients should be continued on antibiotics at least until the lesion is completely resolved.

Tip Two

A search for obvious underlying disease is indicated in almost every ALD case.

Investigation of Infectious or Neoplastic Factors

A number of infectious conditions may be complicated by significant secondary self-trauma. Examples include dermatophyte kerions, demodicosis and deep fungal infections (Pythium, phaeohyphomycosis, Blastomyces, etc.). Mast cell tumors may be associated with the elaboration of pruritogenic factors, while other tumors may be associated with discomfort and secondary self-mutilation. Skin scrapings and dermatophyte cultures should be performed at the initial visit, but may fail to demonstrate deeply sequestered organisms. Biopsy for histopathology and culture (bacterial, fungal, +/- Pythium, Lagenidium) is appropriate for large or chronic lesions.

Identify Sources of Pain

Patients may lick at the skin over arthritic joints, foreign bodies, wound sites (including tumors) or at locations of prior trauma. An orthopedic examination is easy and quick to perform on the initial visit, and may be helpful to identify painful joints or bones. In persistent cases, imaging (radiographs, CT, MRI, ultrasound) may help to reveal the presence of orthopedic abnormalities or foreign bodies.

Investigate the Possibility of Neuropathic Disease

Neurologic issues such as disk herniation, degenerative myelopathy and nerve damage/impingement may all trigger an unpleasant sensation and the desire to lick or chew. Other conditions that potentially could be associated with neuropathic pain/neuropathy include hypothyroidism, syringomyelia and caudal occipital malformation syndrome. A complete neurologic examination should be performed at the initial visit. Persistent disease (or the presence of other neurologic abnormalities) may warrant advanced imaging (MRI) or neurology referral. Alternately, gabapentin (see below) may be of benefit in some of these patients.

Allergic Skin Disease Workup

Flea allergy, food allergy and atopic dermatitis have all been associated with the development of ALD. Typically, patients will demonstrate ALD in addition to more “classic” signs of allergy, such as pruritus, pododermatitis and otitis. However, anecdotal reports exist in which allergic patients have only demonstrated ALD. Aggressive flea control is always indicated. Food allergy elimination diet trials may be implemented once the bacterial component is at least somewhat under control. Intradermal or serologic testing is usually performed last, unless the history strongly suggests this differential.

Behavioral Investigation

While boredom, isolation and separation anxiety can certainly be associated with the development of these lesions, it has been my experience that behavioral/psychological issues are not usually the primary problem. Nonetheless obtaining a thorough history is important as psychological stress can contribute to the persistence of the issue. Relevant questions would include the amount of time that the patient spends confined or alone, addition or loss of human or animal family members, whether overcrowding or inter-dog aggression has been a problem and whether the dog’s routine (timing, location, quality) has recently changed.

Tip Three

Symptomatic Therapy

In my hands, symptomatic medical therapy of ALD has been of limited benefit. I do believe that it helps in many cases (especially early or less severe disease), but I think it works best as a treatment adjunct, not as the sole means of treatment.

Topical Therapy

1.  Fluocinolone/DMSO 8 ml plus flunixin 3 ml: Apply to lesion twice daily

2.  Bitter apple 2 parts/liquid HEET 1 part: Apply to lesion twice daily

3.  Bitter apple: isopropyl alcohol, water, bitter extract

4.  Liquid HEET: 0.25% capsicin, 15% methyl salicylate, 3.6% camphor, acetone, alcohol

Systemic Therapy

1.  Gabapentin: 10–20 mg/kg three times daily. May be especially effective if neuropathic pain is suspected. Some sources will increase as far as 30 mg/kg if necessary.

2.  Clomipramine: 1–3 mg/kg once daily. May require 2–4 weeks for full effects

3.  Amitriptyline: 1–2 mg/kg twice daily, +/- hydrocodone 0.25 mg/kg two to three times daily.

4.  Fluoxetine: 1–2 mg/kg once daily. May require 2–4 weeks for full effects.

5.  Doxepin: 2–4 mg/kg twice daily.

6.  Oclacitinib: 0.4–0.6 mg/kg twice daily for two weeks, then once daily. May be most effective for patients with underlying allergic skin disease.

Miscellaneous Therapy

1.  Laser ablation: Laser treatment can be used to gradually resurface chronic, severely fibrotic lesions. The point is not to try to remove the lesion entirely as it is to decrease the amount of sequestered fibrous tissue, hair and bacteria so that antibacterial treatment may be effective. This is generally reserved for lesions that remain fibrotic and proliferative despite appropriate protection and antibiotic therapy.

References

1.  Angus JC. Canine acral lick dermatitis. In: Proceedings from the North American Veterinary Dermatology Forum; 2010; Portland, Oregon.