Define hypersensitivity disease
Objectively reproducible signs due to exposure to a defined stimulus at a dose tolerated by normal individuals with NO ALLERGIC IMMUNOLOGIC mechanism or UNKNOWN mechanism
Define allergic disease
Objectively reproducible signs due to exposure to a defined stimulus at a dose tolerated by normal individuals initiated by IMMUNOLOGIC HYPERSENSITIVITY due to a state of heightened reactivity to antigen or specific immunological mechanisms
What is allergic disease?
Reaction to a normally innocuous non-self antigen and the allergic inflammation produces a tissue injury and can be induced or aggravated by non-immunological factors
What are some examples of hypersensitivity/allergic skin disease?
Urticaria/angioedema (syndrome) 'Food allergy' Contact allergy/dermatitis Atopic dermatitis Insect sting/bite hypersensitivities
Define utricaria
Multiple wheals (hives) Circumscribed raised lesions caused by dermal oedema
Define angioedema
Marked localised subcutaneous oedema
What is the pathomechanism of urticaria/angioedema?
Mast cell is the principle effector cell
Mast cell activation can be IgE dependent (type 1 allergy) or IgE independent (complement activation/non-immunological)
What are the clinical characteristics of urticaria/angioedema?
Acute, recurrent, chronic, seasonalnon-seasonal, may progress to crusting/sloughing, variable pruritis
What are some possible triggers for urticaria/angioedema?
Administered/applied substances, infections, parasitis infestation, insect bites/stings, dietary components, aeroallergens, contact allergens, other environmental substances, systemic disease, physical stimuli, hereditary condistion, auto-antibodies, idiopathic
How is urticaria/angioedema diagnosed?
Avoidance and re-challenge ideally blinded and placebo controlled
For IgE mediated disease demonstration of allergen-specific IgE
What are the possible immunological adverse reactions to food?
IgE mediated food allergy
Non-IgE mediated food allergy
What are the possible non-immunological adverse reactions to food?
Idiosyncratic
Pharmacological
Metabolic
What are the possible clinical signs of food intolerance and allergy?
Gastroenteritis, enteropathy
Urticaria, angioedema, pruritic skin disease
How is food hypersensitivity/allergy diagnosed?
History and signs, response to restricted diet and relapse on old diet
Intra-dermal and serological tests of no benefit
How is food hypersensitivity managed?
Allergen avoidance, treat secondary complications, glucocorticoids if allergen avoidance isn’t possible
What is the aetiology of atopic dermatitis?
Genetics = skin barrier, IgE response, (skin) immune system
Environmental factors = reduced skin barrier, allergen exposure, typre of early immune stimulation (puppy/kitten), other factors?
What is the pathophysiology of atopic dermatitis?
IMAGE
What is the typical history of atopic dermatitis?
Age of onset 6mths- 3yrs, pruritis, rashes, ear infections
Time course can be seasonal, non-seasonal, non-seasonal with seasonal exacerbation, intermittent
What primary skin lesions are seen with atopic dermatitis?
None, erythema, erythematous maculopapular rash
What is the distribution of itch and lesions of atopic dermatitis?
Ears, face, armpits, feet, ventral abdomen, gluteals and hamstrings
Breed specific distributions
What is the pathology of skin and ear disease with atopic dermatitis?
Immunological derangement leads to cutaneous abnormalities in skin barrier so Staph pseudintermedius and Malassezia pachydermatis can infect causing skin lesions exacerbating pruritis
How is atopic dermatitis diagnosed?
Rule out/resolve other pruritic disease
5 of following criteria present = < 3 at onset, mostly indoor, corticosteroid responsive pruritis, chronic/recurrent yeast infections, affected front feet, affected pinnae, non-affected ear margins, non-affected dorso-lumbar area
What is the treatment aim of atopic dermatitis?
Reduce pruritis to acceptable level with long-term control as safely as possible
How is control of atopic dermatitis achieved quickest?
Addressing as many trigger factors as possible through combination of treatment modalities requiring a custom-tailored treatment plan