Allergodermatitis Flashcards
Allergodermatitis definition
Aka Canine atopic dermatitis (allergic dermatitis, canine atopy) is an inherited predisposition to develop allergic symptoms following repeated exposure to some otherwise harmless substance, an “allergen”. Most dogs begin to show their allergic signs between 1 and 3 years of age.
Atopy - genetic predisp. To dev an allergy.
We see pruritis and skin lesions. Immunosuppression will decr. Flares as it is immune mediated. (GC etc)
Diff. diagnosis of pruritus
Must exclude others before we can diagnose alergoderm.
History (intensity, progression, skin lesions before/after pruritus, diet, environ.)
Physical examination (primary-secondary lesion, localization)
🔺 first we exclude infectious causes:
Skin scrape sample microscopical examination and culture (BOG, MOG, Malasseziaderm., pyoderma, dermatophytosis, ectoparasites scrape good except Sarcoptes, not in lesion run away!!)
+/- Blood examination: Sarcoptes-serology, mikrofilaria
And/or probe therapy (diagnosis ex juvantibus) (AB, AM,
antiworm th., acaricid th., dirofilaricid drug)
🔺 we start investigating allergens:
Elimination of contact allergens (contact allergy, eg metal dish)
8-12 weeks elimination monodiet (1 protein only, 2m) and provocation (2w, after monodiet no signs - can introduce new food to find spec. Allergen, OR just continue monodiet without provocation. (food allergy)
no response to monodiet -> Allergy-tests (IDT, IgE serology) (atopy, exclusion diagnosis + criteria fullfilled if doesnt respond to low dose predn. -> must be something else:)
🔺 other possiblities:
Skin biopsy (neoplastic/ hereditary/ congenital etc. food
diseases)
Why is it so important to be sure there is no sarcoptes invasion?
COMMON PROBLEM!
If Sarcoptosis or an other ectoparasitosis, and/or
if food allergy (FA) is treated by long term CS therapy without treating ectoparasites/FA !!!!
long Cs → Cushing, also incr the growth of mites
Hypersensitivity, allergy and atopy def
- Hypersensitivity: incr sensitivity to an allergen, reproducible signs (two or more times), no effect in normal induvidual
- allergy: hypersensitivtyof immunological origin (any immunological mechanism)
- atopy: (genetic) predisposition to develope allergic reaction (exaggerated igE mediated immune response)
Pseudoallergy, idiosyncrasia, allergen (food allergen) definition
PSEUDOALLERGY there is no specific
sensitivity / no immunological origin (stinging
nettle: formic acid, acetil-kolin, serotonin, histamin) but same symptoms
- IDIOSYNCRASIA there is no specific immunological reaction but increased sensitivity of mastocytes: opiats, radiological contrast- mass, colloidal plasma-inf., anaesthetica, complement-, kinin-, arachidonacid-syst., fibrinolysis, toxins, musclerelaxant, analgesics, salicilates, food-paints, preservings
- ALLERGEN: not infectious, not invasive, innocuous ANTIGEN,
- Food alllergen: 10-70 kD M, heat stabil, acid- and proteasestabil, waterdilutable glucoproteins
Hypersensitivity type 1 - reaction, antibody, antigen, reaction time, mediator and diseases causing it
(antigen bind antibody rec on cell causing degran)
Rection: Anaphylaxis
Antibody: IgE, IgGd, Ab receptor on cellsurface
Antigen: exogen (allergen) bind the ab receptor
Reaction time: 1-15-20 min
Mediator: histamin, biogenic amin (degran release, exocytosis)
Diseases: urticaria, angiodema, atopy
Hypersensitivity type 2 - reaction, antibody, antigen, reaction time, mediator and diseases causing it
(Cell with foreign ag bind cytotoxic cell ab receptor causing cell destruction -> tissue damage)
Reaction: cytotoxic (cell with ab receptor)
Antibody: IgG IgM on cytotoxic cell surface
Antigen: on cell surface
Reaction time: 4-8h
Mediator: complement
Disease: pemph., drug, AIHA, transf. fetal erythro-blastosis
Hypersensitivity type 3 - reaction, antibody, antigen, reaction time, mediator and diseases causing it
(Ab-Ag complex formation in blood deposit on endothel causing NG chemotaxis and degran -> vasculitis) Reaction: immune complex mediated Antibody: complement binding free IgG Antigen: extracellular Reaction time: 2-4-8h Mediator: complement Disease: SLE, GN vasculitis, drug
Hypersensitivity type 4 - reaction, antibody, antigen, reaction time, mediator and diseases causing it
(Ag recognized by T cell, t-cell mediated response (macroph activation, cytokine prod) forms days later causing tissue damage, inflammation)
Reaction: cell mediated/delayed (instead of ab mediated!)
Antibody: ab bind to T-lymphocyte
Antigen: extracellular or cellsurface
Reaction time: 24-72h
Mediator: heparinocytes
(Pro-inflamm Cytokine release)
Disease: allerg./autoim contact allerg, (tuberculosis)
Urticaria
Aka hives
- dog and cat uncommon
- Type 1 and 3 hypersensitivity reaction
- several possible causes: drugs, vaccines, insect bites, food allergy, environmental agent
- acute onset
- Localized or generalized wheals (circular hevelser), hairs stands up over the affected lesions, variable pruritus, mainly on the head
- Treatment: water-soluble CS systemic 2 mg/kg, antihistamines (+ Ca-prep.)
Angiooedema
(Aka angioneurotic edema)
- dog + cat
- Type 1. hypersensitivity
- Wasp and bee stings (as for urticaria)
- Extreme swelling of the face, head or feet ( +/- laryngeal oedema)
- Treatment.: epinephrine SC. (adrenalin) - we give bc laryngeal edema is life threatning!, CS IV, tracheotomy possibly
Atopic dermatitis (AD)
- most common dermatosis of dogs
- genetically predisposed inflammatoru and pruritis allergic skin disease
- associated with IgE antibodies (type 1), usually against environmental allergens
Atopic-like dermatitis (ALD)
Atopic-like dermatitis (ALD) is an inflammatory and pruritic skin disease with clinical features identical to
those seen in canine atopic dermatitis in which an IgE
response to environmental or other allergens CANNOT
be documented’ (intrinsic cause)
Describe how we can recognize atopic-like dermatitis
1.Familiar history (genetic predisp.)
2.Typical clinical signs
3. Typical histopathology
4. Decreased epidermal barrier function
(The typical layers of the skin is abnormal causing easier allergen penetration, dehydration, microbial proliferation —> cutaneus inflammation and pruritus)
5. NO POSITIVE ALLERGY TEST (IgE) !!!
Atopy (atopic disease)
- Any dog breeds but also breed predisposition
(rare in cats) - Symptoms begin between 1-3 years of age - allergens in contact with skin - not airborne!
- Clinical signs: seasonal(pollen)/nonseasonal (dust, mold)
- Pruritus is the main complaint
erythema > pyoderma, seborrhea, lichenification - Allergens: house dust, - mite, dander, pollens, fungi, moulds, feathers
- Causal allergen testing: ID skin testing, IgE testing
*CLINICAL DIAGNOSIS!! By exclusion, criteria! (We follow the newest)
