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Acral Lick Dermatitis

David Grant continues his series looking at dermatological conditions.

ACRAL LICK DERMATITIS
REFERS TO A SELF-INFLICTED
FOCAL LESION
usually found
occurring on a distal (acral) extremity.
Favoured sites for the excessive
compulsive licking, which produces
the lesion, are most commonly on the
anterior carpal or metatarsal skin.

The problem tends to occur in
middle-aged to older breeds such as
the Doberman, Great Dane, Golden
Labrador, Labrador retriever, German
shepherd and
Boxer, although it
may occur in other
breeds including
crossbreeds.

Clinical features

  • Initially the lesion, in one of the
    sites mentioned, tends to be quite
    small but with increased licking slowly
    enlarges.
  • If untreated the lesion passes
    through various stages (Hnilica, 2011).
    Alopecia develops and the lesion
    becomes firm, raised, thickened and
    plaque-like. Later
    there is nodular ulceration, fibrosis
    and hyperpigmentation.
  • Secondary infection at the later stage is
    very common and is a deep pyoderma.
    Untreated cases may progress to
    furunculosis.
  • Damage to hair shafts due to the
    licking may penetrate into the dermis
    and will accentuate the deep pyoderma.
    In one study, deep pyoderma was
    present in 94% of acral lick lesions
    (Shumaker and others, 2008).
  • Whatever the initiating cause, the
    problem can quickly become self-
    perpetuating with the development of
    an itch-lick cycle.

Differential diagnosis

(Hnilica, 2011)

  • Atopic dermatitis.
  • Food hypersensitivity.
  • Trauma.
  • Foreign body reaction.
  • Deep pyoderma.
  • Pododemodicosis.
  • Hypothyroidism.
  • Neuropathy.
  • Osteopathy.
  • Arthritis.

Underlying factors

In addition to the diseases listed in the
differential diagnosis, many authorities suggest that a
major component in acral lick
dermatitis is
psychological.

One specialist
states that
although environmental stress may be a
factor, other causes are usually more
important (Hnilica, 2011) and these are
listed under the differential diagnosis.
It is suggested that differential
diagnosis rule-outs are investigated
before considering psychogenic
underlying causes.

An additional complication is
that even if the original cause is
psychogenic, secondary infection is
very common and will need to be
treated before further evaluation. The
list of possible psychological causes
cited here has not changed from that
in previous editions of a standard text
in the last 20 years or so of previous
editions.

Possible psychological factors

(Miller, Grif n and Campbell, 2013)

  • The dog is left alone all day.
  • The dog is confined for long periods
    to a crate, kennel, cage or run.
  • There is a new pet in the home.
  • A female dog is in heat nearby but not accessible to the dog.
  • A new dog has come to the
    neighbourhood.
  • A death has occurred in the family.
  • A long-time companion of the dog
    has died.
  • Children or other members of the
    family have moved away.

Diagnosis

  • The history (breed predisposition,
    licking) and clinical findings are very
    suggestive.
  • Investigation of underlying causes listed under differential diagnosis
  • Biopsy for histopathological
    examination. Biopsy may also be used
    for bacterial culture as secondary
    infection is likely to be deep. In these
    cases, sterile preparation of the surface
    is required.
  • Histopathological findings are
    often helpful in confirming the
    diagnosis if doubt exists. Findings
    include epidermal hyperplasia with
    marked rete ridge formation, compact
    orthokeratotic hyperkeratosis, which
    strongly suggests chronic surface
    irritation, and fibrosis of the dermal
    papillae.
  • The orientation of the collagen
    is perpendicular to the skin surface,
    though not to the basement membrane
    (Yager and Wilcock, 1994).

Clinical Management

The treatment of the lesion will depend
on how long it has been present and
what stage has been reached.

Acral lick dermatitis has
multifactorial causes and some aspects
are still poorly understood. As a result
many treatments have been advocated.
In more advanced cases a collaboration
between dermatology and behavioural
specialists is more likely to be effective
than individual specialists alone.

For early mild lesions

  • Topical glucocorticoids and
    bandaging to prevent further trauma.
    This is often not successful. Licking
    elsewhere while a bandage is protecting
    the lesion tends to suggest an
    unresolved underlying psychological
    problem, however.
  • Sub-lesional injections of
    glucocorticoids may break the itch-
    lick cycle, but should not be used in
    more chronic cases where secondary
    pyoderma is a likely complication.

For chronic lesions

  • Chronic lesions with secondary
    deep pyoderma require long-term
    antimicrobial systemic therapy based
    on sterile deep biopsy sampling.
    Treatment will be required for six to
    eight weeks and as long as four to six months in severe cases (Hnilica, 2011). The predominant pathogen is
    Staphylococcus pseudintermedius with some
    strains having methicillin resistance
    (Schumacher and others, 2008).
  • Systemic therapy is continued until
    the lesion clears and an assessment
    is then made as to whether licking
    remains a problem. Some cases will
    clear up with long-term antimicrobial
    therapy without relapsing. In those
    that don’t, further investigations will be
    necessary preferably in association with
    a behavioural specialist.
  • Surgical removal of the lesion is
    possible with small lesions, but there
    is a considerable risk of the dog
    traumatising the wound and making the
    situation much worse. It is generally not
    recommended.

Treatment with behaviour-modifying drugs

  • Preferably, in those cases with identified
    stress factors, behavioural therapy is the
    optimal approach. Behaviour-modifying
    drugs may be of short-term use in
    conjunction with these cases and if no
    obvious underlying psychological cause
    is found may be useful as stand-alone
    treatment. There are a number of drugs
    reported to be of benefit (Hnilica,
    2011).
  • Anxiolytics (phenobarbital, diazepam,
    hydroxyzine).
  • Tricyclic antidepressants
    (fluoxetine, amitriptyline, imipramine,
    clomipramine).
  • Endorphin blocker (naltrexone).
  • Endorphin substitute (hydrocodone).

References and further reading

Hnilica, K. A. Small Animal Dermatology: A
Color Atlas and Therapeutic Guide
; pp189-191.

Elsevier, 2011.
Miller, W. H., Grif n, C. E. and Campbell,
K. L. Muller & Kirk’s Small Animal
Dermatology
; pp650-653.

Elsevier, 2013.
Shumaker, A. K. and others (2008)
Microbiological and histopathological
features of canine acral lick dermatitis.
Veterinary Dermatology 19 (5): 288-298.

Yager, J. A. and Wilcock, B. P. Color Atlas and
Text of Surgical Pathology of the Dog and Cat
Dermatopathology and Skin Tumours
, volume 1;
pp57-58. Wolfe, 1994.