Atopic Dermatitis Flashcards
What are 3 parts to the pathogenesis of atopic dermatitis?
- damage/dysfunction of epidermal barrier allows increased exposure to allergens and secondary infections
- genetic predisposition to Type I hypersensitivities (allergen access body via skin)
- aberrant immune response - shift in cytokines that regulate immune responses to increased Th2 cells over Th1 and lymphocytes
What cytokines and cells are increased in dogs with atopic dermatitis?
- IL-31
- IL-17
- Treg cells
- IL-4 (in skin)
- IL-34
- Th2 cells
Why are secondary infections commonly seen with atopic dermatitis?
damage to the epidermal barrier allows increased adherence of bacteria and yeast, resulting in increased carriage of bacteria (S. pseudintermedius)
In what 3 conditions is atopy considered the primary factor?
- pyoderma - all forms, acral lick dermatitis, other regional pyoderma
- Malassezia dermatitis
- otitis externa
What does relevance of allergens depend on? What are the 4 major categories?
volume, buoyancy, allergenicity, geographic distribution
- pollens - grass, trees, weeds
- molds
- epidermal - human, horse, cat
- misc - house dust mite, feathers, wool, tobacco, kapok (tree pod), cotton liners, insects (chitin)
What is the top allergen of humans and dogs?
house dust mite
How can seasons be used to differentiate possible causes of atopy?
- SPRING - tree pollen, molds
- SUMMER - grass pollen, weed pollen, mold
- FALL - weed pollen, mold
- WINTER - indoor allergens, mold
What are the major clinical causes of itch?
- parasites - mange
- infectious - pyoderma
- allergy
- inflammation
use database for rule out other causes –> left with atopic dermatitis if they are negative
When do clinical signs of atopic dermatitis typically occur? What are 2 key clinical features?
1-3 y/o
- pruritus PRECEDES lesion - mild to moderate, responds to glucocorticoids if secondary infection is not present
- seasonality progresses to year-round signs
What differentials are associated with severe/mild itch?
SEVERE - sarcoptic mange, flea allergy, Malasseazia, seborrhea
MILD - allergies
What factors typically lower the itch threshold?
increases itch
- breed
- heat
- dry skin
- inflammation
What factors typically increase the itch threshold?
decrease itch
- breed
- cool temperature
- hydrated skin
What 3 physical exam findings are commonly associated with atopic dermatitis?
- erythema, excoriation, and scale in thin-skinned areas
- chronic - hyperpigmentation, lichenification
- secondary infection - S. pseudintermedius, M. pachydermatis
What breeds have a predilection for developing atopic dermatits?
- Terriers
- Golden Retriever
- Lab
- English Bulldog
- French Bulldog
- Chinese Shar-Pei
What is the hallmark of atopic dermatitis?
pruritus preceding lesion development
- licking
- rubbing
- scratching
- chewing
What distribution of lesions are characteristic of atopic dermatitis? What are 3 concurrent clinical features seen?
thin-skinned areas –> peri-ocular, interdigital, axilla, ventral abdomen (depends on breed!)
- perianal pruritus - can lead to recurrent anal sac inflation and infection
- recurring otitis externa
- recurring pyoderma - superficial, acral lick dermatitis
Atopic dermatitis:
characteristic abdomen, periocular skin, interdigital areas, perianal
Atopic dermatitis:
dorsal AND ventral interdigital skin
Atopic dermatitis:
traumatic conjunctivitis due to rubbing face on ground to itch periorbital skin
What is the main manifestation of atopic dermatitis in cats? What 2 other clinical features are commonly seen?
licking of ventral abdomen and extremities
- feline reaction patterns - eosinophilic granuloma complex –> eosinophilc plaques, collagenolytic granuloma, indolen ulcers + military, chin, and exfoliative (scale) dermatitis
- otitis externa
Atopic dermatitis, cat:
patchy, thin skin due to licking
Atopic dermatitis, cat:
reaction pattern - miliary dermatitis
How is atopic dermatitis diagnosed?
- signalment, history, PE, response to treatment
- dermatologic database
- allergy testing - intradermal, in-vitro allergy tests
What are 7 clinical criteria indicative of atopic dermatitis? What 2 criteria can rule it out?
- onset <3 y/o
- dog living mostly indoors
- glucocorticoid responsive
- pruritus without lesions at onset
- affected front feet and ear pinnae
- non-affected ear margins (sarcoptic mange)
- non-affected dorsolumbar area (flea allergy dermatitis)
What is the purpose of performing intradermal skin testing? What are the 4 keys to success?
confirm diagnosis and provide information about hyposensitization
- patient selection
- patient preparation
- quality of antigens
- technique and interpretation
What occurs if an intradermal injection for allergy testing is done too deep?
goes into superficial dermis, where mast cells are –> no reaction seen even if allergic
What confirms intradermal location for skin allergy testing? When should reactions be read?
wheal development –> wheal + flare = +
in about 10 mins
What positive and negative controls are used for skin allergy testing?
POSITIVE = histamine
NEGATIVE = saline
What can help when assessing intradermal skin allergy tests?
indirect light = easier to see wheal and inflammation
What are in-vitro allergy tests? What are 3 advantages? Disadvantage?
detection of circulating antigen-specific IgE
- minimal drug withdrawal
- rapid, easy - blood collection
- no special supplies needed
higher tendency to give false positive results - increased background IgE (parasitism)
Intradermal vs. serologic allergy testing:
How is allergy testing interpreted?
- fitting the clinical picture - seasonality, geographical area, severity of pruritus
- determining therapy - if unclear, consider symptomatic treatment first
What are 3 parts to managing atopic dermatitis?
- support epidermal barrier
- control infections - Malassezia pachydermatis, S. pseudintermedius
- decrease itch
What ingredients in topicals are best for supporting epidermal barriers?
lipids - ceramides, fatty acids, essential oils, ophytrium
- omega 6 > omega 3
When is maintenance therapy began for cases of atopic dermatitis? What is done? How long?
after infections are cleared
- weekly baths
- wipes, mousses, or sprays on predisposed areas
FOREVER or until underlying allergy is fully controlled
What are 4 options for controlling pruritus in cases of atopic dermatitis? What is commonly added?
- glucocorticoides
- cyclosporine
- IL-31 blockers - Oclacitinib, Lokivetmab
- allergen-specific immunotherapy (hyposensitization)
steroid-sparing agents - antihistamines, fatty acids, topicals
When are topical therapies for itch associated with atopic dermatitis especially useful? What are 3 shampoo options?
withdrawal period of glucocorticoids prior to allergy testing
- colloidal oatmeal - keratinolytic, hydrates skin, 24 hours
- pramoxine - topical anesthetic, 2 days
- glucocorticoids - hydrocortisone only, much longer, $$$
How are wipes used for controlling itch associated with atopic dermatitis?
clean feet and other problem areas once daily to remove allergens from the skin
What supportive therapy is recommended when treating pruritus associated with atopic dermatitis? What 2 functions do they have?
fatty acids and antihistamines –> ineffective by themselves, synergistic together, highly recommended for dogs on steroids
- reduce anxiety
- support skin barrier
What 3 glucocorticoids are used to treat pruritus associated with atopic dermatitis?
- prednisolone - cat
- prednisone - dog
- methylprednisolone
good potency long-term
What is the protocol for Prednisone/Prednisolone treatment for atopy?
- 1.1 mg/kg SID, PO for 5-7 days
- 1.1 mg/kg EOD, PO for 14-21 days
- slowly decrease dose by 10-20% every 10-21 days (5-10 doses)
- end maintenance dose of 0.5-1.1 mg/kg EOD
(if there is no itch control, secondary infection is still likely there)
What are some advantages and disadvantages to glucocorticoid therapy for pruritus in cases of atopy?
ADVANTAGES - highly effective, inexpensive, easy to dose
DISADVANTAGES - Cushing’s like adverse effects (PU/PD, nocturia, polyphagia, panting, personality changes), easy to mess up dosing
When are higher doses commonly needed for glucocorticoid therapy? What should owners be warned about?
severe allergy seasons
avoid daily dosage after initial induction period –> affects HPA axis daily, EOD still necessary but dose can be increased
What is another glucocorticoid that may be effective for cases of atopy?
Temaril-P –> 2 mg prednisolone + 5 mg trimeprazine tartrate
- appears to allow lower doses, but same side effects are associated and $$$
What forms of glucocorticoids are contraindicated for atopy treatment?
injectables –> HPA axis!
Glucocorticoids, adverse effects:
Cushingoid - calcinosis cutis, alopecia
What are 2 options for topical glucocorticoids? How often are they given? How are they best used?
- Triamcinolone
- Betamethasone - readily absorbed, hair loss common (strong!)
BID for a week –> SID for a week –> twice weekly
spot treatment or occasional adjunct (will affect HPA axis!)
What 3 situations may result in prednisolone-resistant pruritus?
- true resistance - possible, but not confirmed
- non-prednisone responsive disease - food allergy
- secondary infection - Staph, Malassezia
When is Cyclosporine recommended for treating atopy? How long/often? What can reduce dose?
control pruritus
plan for SID dosage for 3-6 weeks –> full effect often takes 6 weeks, then reduce
add Ketoconazole
What 5 adverse effects are associated with Cyclosporine therapy?
- vomiting
- glucose metabolism disturbance
- papillomatosis, cutaneous neoplasm - immunosuppression
- gingival hyperplasia
- infections - UTI, opportunistic
+ expensive, compounded not recommended
What IL-31 blockers are available for cases of pruritus seen in atopy?
APOQUEL (oclacitinib) - oral, blocks JAKSTAT receptors
CYTOPOINT (IL-31 monoclonal antibody) - canine IgG against IL-31, SQ
How does Apoquel (oclacitinib) work? In what dogs is it contraindicated?
JAK inhibitor selective for JAK1 pathway, which downregulates IL-2, 4, 6, 13, and 31
dogs <12 months of age –> immune dysfunction can cause demodicosis
What are 3 advantages to using Apoquel in cases of atopy? 2 disadvantages?
ADVANTAGES - highly effective, works fast, few adverse effects at label doses short-term
DISADVANTAGES - not as selective, no residual activity into the night when given in the morning (try for noon SID)
What adverse effects have been reported with Apoquel?
- GI upset
- demodicosis (<1 y/o)
- hematologic abnormalities
- increased cutaneous masses
- seizures
- weight gain
more common in high doses and chronic administration
What are the 2 main indications for Apoquel?
- rapid response to pruritus when CS is not an option
- induction period of immunotherapy (up to 9 months)
price point is variable depending on size
How long is Cytopoint typically effective for? How does it compare to Apoquel?
4-6 weeks
- more consistent
- reduces client compliance
- price point variable
How does immunotherapy work? What 4 things does this result in?
gradual exposure to increasing doses of allergen and reduces mast cell and basophil triggering
- increases Treg cells, which represses immune response and produces IL-10 and TGF-b to reduce B cell production of IgE and inhibit inflammation
- increases Th1 over Th2
- higher IFN-y/IL-4 ratio
- forms IgG as a blocking antibody
Why consider immunotherapy?
What are the 4 major advantages to immunotherapy?
- several options available - traditional, rush, regional-specific, sublingual
- alters immunologic pathways - possible cure
- more effective when primary manifestation of allergy is infection
- overall pretty successful (35-70%)
What are 5 disadvantages to immunotherapy?
- price point is variable - great cost/benefit ratio for larger dogs
- injectable options require training
- sublingual options difficult
- adverse effects - increased itch, urticaria, anaphylaxis
- requires knowledge of allergens - testing is important
What is the normal immunotherapy protocol?
- weekly injections until maximum efficacy (4-9 months)
- reduce to every 10-14 days
- continue reduction every 2-4 months
seasonal variation - more frequent injections during allergy season
What are 2 major problems with commercial allergy testing and hyposensitization?
- allergens selected are based on numbers, which can be misleading with no consideration of geography, pet, or environment
- standard schedule and reduction of frequency of injections, not based on patient response
How does sublingual immunotherapy work? How often is it given?
absorption by lymphoid tissues located in the oral cavity
BID, under the tongue
What are some options of combination therapy used for atopy?
- glucocorticoids and antihistamines
- antihistamines and EFAs
- glucocorticoids and EFAs
- Apoquel/Cytopoint and antihistamines/glucocorticoids
- topicals
- immunotherapy
combo therapy is always superior to a single-drug treatment
In what patients do glucocorticoids work best? Less likely?
- need of rapid response
- need anti-inflammatory effects
- seasonal, short-term
- cost
concurrent health issues, patient can not tolerate, plan to allergy test
In what patients do cyclosporine work best? Less likely?
- small dogs and cats
- some anti-inflammatory effect desired (GC not an option)
concurrent infections, DM, cost is a factor
In what patients do Apoquel work best? Less likely?
- need rapid response
- prior to allergy testing
- while waiting for immunotherapy
- cost
long-term use, does not provide 24 hrs of relief
In what patients do Cytopoint work best? Less likely?
- client compliance
- convenience
- adverse effects to other options
clients are not mobile, large dogs (cost)
In what patients do immunotherapy work best? Less likely?
- younger dogs
- infections, otitis main manifestations
- owners prefer to treat disease vs masking symptoms
client compliance/ability to administer treatment, owners want short-term gratification
