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
How long should hyposensitization last?
Hyposensitization should be continued for at least 1 year before final evaluation of
efficacy.
If effective, the treatment will almost certainly need to be continued for the animal’s life.
How do you TREAT Atopic Dermatitis?
Systemic
◦Corticosteroids, antihistamines, EFAs,
cyclosporine, oclacitinib, lokivetmab,
maropitant (cats)
Topicals
◦Steroids, barrier aids
What CORTICOSTEROIDS do you use for DOGS and CATS with Atopic Dermatitis?
Dogs:
◦Prednisone, prednisolone,
methylprednisolone
◦ 1 mg/kg/d, then taper
Cats:
◦Prednisolone, methylprednisolone:
1.5 mg/kg q24h, then taper
◦Triamcinolone:
0.8 mg/kg q24h, then taper
What ANTIHISTAMINES do you use for DOGS and CATS with Atopic Dermatitis?
Dogs:
-Cetirizine 1mg/kg bid
–cetirizine is the active metabolite of hydroxyzine, so if one doesn’t work, the
other probably won’t either
–does not work in cats
-Diphenhydramine 2.2 mg/kg tid
-Hydroxyzine pamoate 2.2 mg/kg tid
-Chlorpheniramine 0.2-0.8 mg/kg bid-tid
*antihistamines not orally bioavailable or need large doses
Cats:
-Chlorpheniramine 2-4 mg/5 kg bid
-Clemastine 0.1 mg/kg bid
Which drug is helpful in reducing the amount of prednisone which must be given to atopic dogs?
trimeprazine 5mg and prednisolone 2 mg
(Temeril-P® [Vanectyl-P® in Canada], Zoetis)
What ESSENTIAL FATTY ACIDS do you use for DOGS and CATS with Atopic Dermatitis?
-nonsteroidal antipruritics
Dogs:
-Omega 3: fish oil, flax
◦Eicosapentaenoic Acid (EPA)
◦Docosahexaenoic Acid (DHA)
-Omega 6: EPO, borage
–25%- 40% AD dogs improve
–May take >3 months
–Steroid-sparing
◦Omega 3 dose: 66 mg per kg body
weight of combined
-No need to use omega 6!
-6-12 weeks for full effect
-These drugs interfere with the production and metabolization of arachidonic acid and other “pro-inflammatory” substances
Cats:
-Antihistamines + essential fatty acids may give relief from clinical signs in as high as 50% of atopic cats
How does Cyclosporine help treat Atopic Dermatitis?
-calcineurin inhibitor, mode of action: inhibit
T cell activation
-Atopica®, Elanco; CyclavanceTM , Virbac
SIDE EFFECTS:
Anorexia, vomiting, diarrhea
Papillomas, pyoderma
Hypertrichosis
Renal / hepatic disease (rare)
Gingival enlargement
to minimized vomiting:
-Keep in freezer and give frozen
-Give with food
-Give with maropitant citrate (Cerenia
®, Zoetis) for 3-5 days
-Ok to test (skin or serologic) for
allergies while receiving
-Ok to hyposensitize while receiving
Cats:
liquid preparation of Atopica have a similar
effective decrease in their pruritus
-Cats infected with T. gondii prior to CsA administration failed to develop clinical illness after administration of CsA
-Cats that have high CsA concentrations
when first exposed to T. gondii can develop
fatal infection
–Ideally test cats for both IgG and IgM
serology
–Keep treated cats indoors
What is Apoquel and how does it treat Atopic Dermatitis?
-only for dogs
-oclacitinib – Zoetis
-Janus-kinase-1 inhibitor interferes with interleukin effects especially IL 31 (mediator of pruritus at the nerve level)
-well-tolerated by dogs and suppresses
pruritus rapidly (within 24 hours)
-contraindications: a history of demodicosis or neoplasia
-Ok to test (skin or serologic) for allergies; ok
to hyposensitize concurrently
-Side effects: gastrointestinal upset and lethargy have been noted, and rare elevations of liver enzymes may occur. Rare cases of generalized demodicosis have been noted
What is Cytopoint and how does it treat Atopic Dermatitis?
-only for dogs
-Lokivetmab
-Caninized mouse antibody targeting interleukin 31
-monthly injection
-Good safety profile
-Somewhat expensive in large breed dogs
-Not to be used for cats (ineffective)
