Allergic Skin Disease Flashcards
How can you distinguish oedema from cellular swelling?
Oedema indents, cellular doesnt
Define hypersensitivity disease
> clinical HYPERSENSITIVITY =
- objectively reproducible signs
- exposure to a defined stimulus
- at a dose normally tolerated by other individuals
no assumption of allergic immunological mechanisms eg. lactose intolerance due to lack of lactose enzyme, only in white caucasians; drug intolerance.
BUT may be initiated by immunological hypersensitivty, with a known mechanism, which is therefore ALLERGY.
- state of heightened reactivity to antigen
- specific immunological mechanisms
- may be induced or aggravated by non-immunological factors but must be initiated by them
Which hypersensitivity/allergic skin diseases are seen?
- urticaria/angioedema syndrome
- food “allergy”
- contact allergy/dermatitis (rare)
- atopic dermatitis
Which species commonly affected by wheals, urticaria/angioedema?
Horses
What is urticaria?
multiple wheals or hives (sign, not disease)
= circumscribed raised lesions caused by dermal oedema
- mid-superficial vessels dilated
What is angioedema?
marked localised subcut oedema if deeper vessels affected
- will move ventrally following gravity
Mechanism od urticaria/angioedema?
> mast cell activation
- IgE dependent
- IgE Independent (eg. complement) or completely non-immunological (heat/cold/pressure induced) seen in some horses [dermatographism]
is urticaria/angioedema in horses always itchy?
No!
Triggers for urticaria/angioedema?
- iatrogenic substances
- infections: systemic/focal
- parasites/insects
- diet
- aeroallergens
- contact allergens
> other environmental/systemic disease/physical stimuli/hereditary/autoABs/idiopathic?
What types of urticaria/angioedema are recognised clinically?
- acute
- recurrent
- chronic
- seasonal or non-seasonal
- may progress to crusting/sloughing
What are allergy tests available for?
- mites
- insects
- pollens
- moulds
> though results may not be singificant!
What 2 forms of adverse reaction to food are possible? What subcategories exist and which are referred to as food hypersensitivity?
> IMmunological
- food allergy (IgE mediated or non-IgE mediated)
Non-Immunological
- food intolerance (idiosyncratic, pharmacological, metabolic, food poisoning)
^^^ both food hypersensitivity^^^
- Dietary indiscretion (scavenging, gluttony, pica)
- Food aversion (pysch avoidance or intolerance)
Is food allergy serology useful?
NO! No evidence that these tests work. Well marketed.
- no diagnositc value
How can food allergy be distinguished from atopic dermatitis?
Cant purely on PE - change diet and see what happens
Aetiology of atopic dermatitis?
- skin barrier
- IgE response and degree of allergen exposure
- Skin and immune system - early exposure
- environmental factors
What are the aspects of atopic dermatitis?
- self-trauma (pruritis)
- imparied skin barrier
- microbial overgrowth
- IgE sensitisation and response to allergen exposure
- inflammation
> viscous cycle!
Clinical sings in the history indicative of atopic dermatitis?
- age of onset 6m-3y
- breed predisposition (westies, sharpei, labretriever, boxer, english setters)
- no sex dispositions
- pruritis, rashes, ear infection
- time course
> exclusion of other diseases: food hypersesntivity etc.
Primary lesions of atopic dermatitis? Where is the worst itch and self-trauma?
None or erythema (diffuse or eyrthematous maculopapular rash)
- anything else = 2* lesions
> eyes, ears, jowls, ventral chest, feet, perianal, ventral abdomen (breed specific distributions)
What is lichenification?
Thickening of skin 2* to self trauma
Pathogenesis of ear infections with atopic dermatitis?
- immunological derangement/cutaneous abnormaltities (skin barrier)
- > 2* Staph pseudintermedius and malasezia pachydermatis infections (commensals)
- > skin lesions and exacerbation of pruritis
- > 2* trauma
Diagnosis of atopic dermatitis?
- hx
- clinical signs
- exclude r/o or resolve parasties, infections
- investigate atopic food hypersensitivity
> typical clinical signs, chronic pruritic skin disease, baseline itch present with infection r/o (Clinical Diagnosis)
What do allergy tests measure? What 2 are available? How cna these be used?
- Intradermal
- Allercept serology
> measures IgE levels, not necessarily indicative of clinical disease (normal dogs can be +)
> management - avoidance and immunotherapy [successful in 50% cases] rather than definitive diagnosis. Supportive.
Tx aim with atopic dermatitis?
- reduce pruritis to an acceptable level
- long term control as safely as possible
- address trigger factors
- individual treatment plan
Diagnosis of cause of urticaria/angioedema?
- avoidance and re-challenge
- for IgE mediated ONLY, demonstrate allergen specific IgE
8 criteria for distinguishing stopic dermatitis in practice?
- age of onset <3y
- mostly indoor
- corticosteroid responsive pruritis
- chronic/recurrent yeast infeection
- affected front feet
- affeted pinnae
- non-affected ear margins
- non-affected dorso-lumbar regions
