Week 6 - Dermatology Flashcards
What is Atopic Dermatitis?
-Allergic (inappropriate) reaction to
environmental antigens and other
triggers
-allergic response, mediated by IgE
-seasonal or year round
There is a genetic component to atopic dermatitis.
◦Multiple genes noted
◦Breed differences
strong genetic tendency in dogs, with golden retrievers, Labrador retrievers, terriers, Dalmatians, and Shar-peis
What CAUSES atopic dermatitis?
allergen gain access to body by
respiratory OR percutaneous route
- Hypersensitivity mediated by IgE antibodies
- Loss of Barrier function / barrier dysfunction
- Bacterial dysbiosis ?
How does HYPERSENSITIVITY cause atopic dermatitis?
Allergens interact with Langerhans’ cells, TH2 and B lymphocytes, cause allergen-specific IgE production
Allergens bind to allergen-specific IgE on
mast cells = degranulation & release of
inflammatory substances
Inflammatory cytokines released from keratinocytes and T-cells
Mast cells release what 2 things?
Histamine
Tryptase - most abundant mediator stored in
mast cell granules !!!!
How does LOSS OF BARRIER FUNCTION cause atopic dermatitis?
◦Abnormalities in lipid layer of the stratum corneum
◦Tight junction abnormalities
◦Decreased epidermal (functional) filaggrin
-Clinical importance not proven yet in dogs
-filaggrin: important component of the stratum corneum (the outer most, ‘horny’ layer of the epidermis - may translate into more susceptibility to both allergen and infective organism access to the skin
-not seen in westies (WHWT)
Allows:
◦allergen ‘penetration’ via stratum corneum
◦Staphylococcus spp (& Malassezia) to ‘stick’ to the stratum corneum
◦Water loss
What is the DOG SIGNALMENT for Atopic Dermatitis?
Age at onset: 1-7 years; mean at UC Davis: 1.66 yrs
Breed: Retrievers, Terriers, Dalmatians, Shar-peis, Shiba inus, French bulldogs
No sex predilection
What are the DOG CS for Atopic Dermatitis?
Pruritus
Erythema
Rarely, small papules
Feet, face, axilla, ears, conjunctivitis
What is CAT SIGNALMENT for Atopic Dermatitis?
Etiology: presumed to be similar to
dogs
No age or sex predilection
Himalayans, Persians, Abyssinians at greater risk
What are the CAT CS for Atopic Dermatitis?
Facial / head / neck pruritus
Miliary dermatitis
Eosinophilic granuloma complex
Self-induced alopecia
How do you DIAGNOSE Atopic Dermatitis?
history
physical examination
and (except in the “classic” case of recurrent, strictly seasonal “typical” clinical signs, erythema/pruritus of face, etc.) ruling out other causes of pruritus, especially food allergy, ectoparasites, etc
History
◦seasonal, < 7 years old at onset
Clinical Signs
◦pruritus feet, face, axilla, ears
Rule outs
◦food allergy, ectoparasites, etc
-Classic: seasonal, typical lesion distribution
-Semi-classic: non-seasonal or non-typical lesion distribution
-Not classic: rule outs fail
What Secondary Infections can mainly dogs, some cats, get from atopic dermatitis?
Staphylococcus pseudintermedius
Malassezia pachydermatis
If owners are interested in HYPOSENSITIZATION from atopic dermatitis, what testing would you do?
looking for allergen-specific IgE –>
- Intradermal testing (IDT)
- Serologic testing
◦ELISA
◦VARL-EIA
◦RAST
because of high incidence of “false positive” (or, at least, clinically non-relevant) findings, these
tests should only be performed if other diagnoses have been ruled out.
What is hyposensitization?
-therapy to try and get rid of allergies
What % of dogs improve with hyposensitization?
70% of dogs that improve, do so within 4-6 months