Atopic Dermatitis (Marsella) Flashcards
Atopic dermatitis (AD)
- Inherited
- Relapsing
- Pruritic dermatitis
- Commonly associated w/ IgE against environmental allergens
Possible AD pathogenesis (general)
- Type I hypersensivity (IgE, allergy)
- T cell imbalances
- 1º skin barrier defect
AD pathogenesis via inhalantion of allergens
Allergen is inhaled & systematically absorbed → IgE migrates to tissue & binds to mast cells
AD pathogenisis via percutaneous absorption
Allergen is captures by Langerhans cells in the skin → local produciton of IgE
Clinical signs of AD in dogs
- Familial hx
- Breed predilection (terriers, shar peis, setters, retrievers, beagles, dalmatians, cockers)
- Onset 1-3 yrs old
- Season signs at 1st
- Progressive worsenig w/ time
- Pruritis & erythema (face, feet, ears, groin, axillae)
- Front feet 1st, then progresses to all
- Chronic: excoriations, lichenification, hyperpigmentation
- 2º ear & skin infections (pyoderma, malassezia)
AD in cats
- Young adults
- Progressive
- Pruritis
- Symmetrical alopecia
- Miliary dermatitis
- Eosinophilic granuloma complex
AD diagnosis
- History
- Clinical signs
- Exclusion of other pruritic dz
Willemse’s MAJOR criteria for diagnosis of AD
At least 3 major and 3 minor criteria
- Major
- Pruritis
- Facial and/or digital involvement
- Lichenification of flexor surfaces
- Chronicaly relapsing dermatitis
- Familial hx
- Breed predilection
Willemse’ MINOR criterial for diagnosis of AD
At least 3 major and 3 minor criteria
- Minor
- Onset of clinical signs before 3 yrs old
- Facial erythema
- Bacterial conjunctivitis
- Superficial pyoderma
- Hyperhydrosis
- Positive skin test
- Elevated allergen specific IgE
Why do we do allergy testing?
To select allergens to use for immunotherapy
Intradermal skin testing (IDST) - general info
- Evaluate presence of IgE in the skin
- Small amounts of allergen are injected in the skin
- Evaluate mast cell degranulation
- Treat all concurrent diesases before testing
- Off steroids & antihistamines for 2 mos
Intradermal skin test (IDST) process
- Sedate (xylazine)
- Inject
- Negative control (saline)
- Positive control (histamine)
- Allergens
- Wait 15 minutes
- Evaluate
Intradermal skin test (IDST) evaluation
- Subjective - visualization
- Erythema
- Induration
- Size
- Objective
- measurement of wheal (hive)
False positive on IDST
- Irritant allergens
- Contaminated allergens
- Skin sensitizing antibodies
- Poor technique
- Substances that trigger mast cell degranulation
False negative on IDST
- Subcutaneous injection
- Too little allergen
- Outdated allergen
- Steroids
- Antihistamines
- Tranquilizers
- Progestational compound
- Anergy (peak of the season)
- Off season testing
- Estrus, pseudopregnancy
- Severe stress
In vitro allergy testing - Serology
- Measurement of circulated allergen specific IgE
- Radioallergosorbent test (RAST)
- ELISA
- Usually poor correlation w/ IDST
Advantages of serology
- No need to clip
- No need to discontnue drugs (steroids & antihistamines)
- No need to keep in stock allergens
Disadvantages of serology
- Poor correlation w/ IDST
- False positives (non specific binding)
- Not reproducible results
AD therapy
- Treat concurrent dz
- other allergies
- skin infections
- Allergen avoidance
- Hyposensitization (allergy vax)
- Systemic therapy
- Topical therapy
Hyposensitization
- 60-80% efficacy
- Good option if prolonged season of pruritis
- No results for first 3 mos
- Life long therapy
- Based on positive rxns
- No more than 12 allergens/vax
Adverse effects of hyposensitization
- Rare
- Incr. pruritis
- Anaphylaxis
- Urtiaria
Systemic therapy - Glucocorticoids
- Low dose, oral
- Decr. efficacy over time
- Long term side effects
- Palliative
- Indicated only w/
- short season
- no concurrent pyoderma
- no concurrent demodicosis
Systemic therapy - Cyclosporins
- Immunomodulant (suppresses T cells & cytokine production)
- Life long therapy
- Monitor for infections
- Adverse effects
- drug interactions, GI, papillomatous dermatitis
Oclacitinip (Apoquel)
- Targets pruritis of various causes
- JAK inhibitor
- Extremely effective & fast acting
- May precipitate demodicosis
IL-31 monoclonal antibody
- Inject once a month
- Blocks IL-31 (important in transmission of pruritis)
- Not as effective as other therapies
- Considered adjunctive
Antihistamines
- Effective 40-50%
- Better for prevention rather than tx of pruritis
- Side effects
Essential fatty acids
- Anti-inflammatory (modulate leukotrienes)
- Improve barrier function
- Restoration of normal lipid composition
Topical therapy
- Frequent, cold baths
- Oatmeal
- Topical anesthetic (pramoxine)
- Topical anthistamine
- Lime sulfur
- Topical steroids
- Capsaicin
- Topical calcineurin inhibitors
Topical steroids
- Triamcinolone spray
- Leave on hydrocortisone
Capsaicin
- Active ingredient of chili pepper
- Used for localized pruritis (lick granuloma)
- Initial worsening
- Prolonged relief
Tacrolimus
- Topical calcineurin inhibitor
- Minimally absorbed (safe)
- Effective esp. for localized cases
- Initial burning sensation
Treatments to restore barrier function
- Phytosphingosine
- Ceramides
- Essential fatty acids
- Emollients
