Dog skin disorders
Dog skin disorders are among the most common health
problems in dogs. Skin disorders in dogs have many causes, and many of the
common skin disorders that afflict people have a counterpart in dogs. The
condition of dog's skin and coat can also be an important indicator of its
general health. Skin disorders of dogs vary from acute, self-limiting problems
to chronic or long-lasting problems requiring life-time treatment. They also
need to be differentiated on the basis of being of primary or secondary (due to
scratching, itch) in nature, making diagnosis complicated. Dog skin disorders
may be grouped into categories according to the causes.
Immune-mediated
skin disorders
Skin disease may result from deficiency or over activity
of immune responses. In cases where there are insufficient immune responses the
disease is usually described by the secondary disease that results. Examples
include increased susceptibility to démodé tic mange and recurrent skin
infections, such as Malassezia infection or bacterial infections. Increased,
but harmful immune responses, can be divided into hypersensitivity disorders
such as atopic dermatitis, and autoimmune disorders (autoimmunity), such as
pemphigus and discoid lupus erythematous.
Canine Atopic
Dermatitis
Canine atopy is a hereditary and chronic allergic skin
disease. It usually starts between 6 months and 3 years of age with some breeds
of dog such as the Golden Retriever starting at an earlier age. Dogs with AD
are itchy, especially around the eyes, muzzle, ears and feet. In severe cases
the irritation is generalized. In cases where the allergens are seasonal the
clinical signs of irritation are similarly seasonal, but many dogs with house
dust mite allergy have perennial disease.
Some of the allergens associated with canine AD include
pollens of trees, grasses and weeds, as well as molds and House dust mite. Ear
and skin infections with the bacteria Staphylococcus pseudintermedius and the
yeast Malassezia pachydermatous are common secondary to canine AD. Flea allergy
is commonly associated with AD. AD is a lifelong condition in most dogs.
Food allergy can be associated with identical signs and
some authorities consider food allergy to be a type of atopic dermatitis.
Diagnosis of AD is by elimination of other causes of irritation
including fleas, scabies and other parasites such as Cheyletiella and lice.
Food allergy can be identified through the use of elimination diet trials in
which a novel or hydrolyzed protein diet is used for a minimum of 6 weeks and
allergies to aeroallergens can be identified using intradermal allergy testing
and/or blood testing (allergen-specific IgE ELISA).
Treatment for AD includes avoidance of the offending
allergens if possible, but for most dogs this is not practical or effective.
Other treatments modulate the adverse immune response to allergens and include
antihistamines, steroids, cyclosporine and immunotherapy (a process in which
allergens are injected to try to induce tolerance). In many cases shampoos,
medicated wipes and ear cleaners are needed to try to prevent the return of
infections.
New research into T-cell receptor peptides and their
effects on dogs with severe, advanced atopic dermatitis are being investigated
by Animal Health Consulting, LLC.
Autoimmune skin
diseases
Pemphigus foliaceus is the most common autoimmune disease
of the dog. Blisters in the epidermis rapidly break to form crusts and erosions
most often affecting the face and ears initially, but in some cases spreading
to include the whole body. The paw pads can be affected causing marked
hyperkeratosis (thickening of the pads with scale). Other autoimmune diseases
include bullous pemphigoid and epidermolysis bullosa acquisita.
Treatment of autoimmune skin conditions requires
treatment to markedly reduce the abnormal immune response; steroids, azathioprine
and other drugs are used as immunosuppressive agents.
Physical and
environmental skin diseases
Hot Spots
A Hot Spot, or acute moist dermatitis, is an acutely
inflamed and infected area of skin irritation created and made worse by a dog
licking and biting at itself. A hot spot can manifest and spread rapidly in a
matter of hours as secondary Staphylococcus infection causes the top layers of
the skin to break down and as pus becomes trapped in the hair. Hot spots can be
treated with corticosteroid medications and oral as well as topical antibiotic
application, as well as clipping hair from around the lesion. Underlying
inciting causes include flea allergy dermatitis, ear disease or other allergic
skin diseases. Dogs with thick undercoat are most subject to getting hot spots.
Acral lick
granulomas
Lick granuloma
from excessive licking
Related to Hot Spots are Lick granulomas, a raised,
usually ulcerated area on a dog's wrist or ankle area caused by the dog's own
incessant compulsive licking. According to the Merck Manual of Veterinary
Medicine, compulsive licking has the following necessary condition: licking in
excess of that required for standard grooming or exploration. The following
condition is sufficient: licking in excess of that required for grooming or
exploration that represents a change in the animal’s typical behavior and
interferes with other activities or functions (e.g., eating, drinking, playing,
interacting with people) and cannot easily be interrupted. One home remedy for
lick granuloma is to use marmite liberally around the area, this creates a
protective barrier which aids recovery.
Infectious skin
diseases
A dog with skin irritation and hair loss on its leg
caused by démodé tic mange
Infectious skin diseases of dogs include contagious and
non-contagious infections or infestations. Contagious infections include
parasitic, bacterial, fungal and viral skin diseases.
One of the most common contagious parasitic skin diseases
is Sarcoptic canine scabies. Another is mange caused by Demodex (Demodicosis),
though this form of mange is not contagious. Another contagious infestation is
caused by a mite, Cheyletiella. Dogs can be infested with contagious lice.
Other ectoparasites, including flea and tick infestations
are not considered directly contagious but are acquired from an environment
where other infested hosts have established the parasite's life cycle.
Ringworm is a fungal skin infection and is more common in
puppies than in adult dogs.
Non-contagious skin infections can result when normal
bacterial or fungal skin flora is allowed to proliferate and cause skin
disease. Common examples in dogs include Staphylococcus intermedius pyoderma,
and Malassezia dermatitis caused by overgrowth of Malassezia pachydermatis.
Flea allergy
dermatitis
Further information: Flea allergy dermatitis
Hereditary and developmental
skin diseases
Some diseases are inherent abnormalities of skin
structure or function. These include seborrheic dermatitis, ichthyosis, skin fragility
syndrome (Ehlers-Danlos), hereditary canine follicular dysplasia and
hypotrichosis, such as color dilution alopecia.
Puppy strangles is a developmental skin disease of
puppies of unknown etiology.
Cutaneous manifestations
of internal diseases
Some systemic diseases can become symptomatic as a skin
disorder. These include many endocrine (hormonal) abnormalities, such as
hypothyroidism, Cushing's Syndrome (hyperadrenalcorticism), and tumors of the
ovaries or testicles.
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