Allergic skin disease Flashcards
(32 cards)
What are the 4 main allergic diseases which affect the skin?
- Urticaria/angioedema
- Atopic Dermatitis (AD)
- Food Hypersensitivity
- Insect Hypersensitivity
- (Contact Allergy)
What mechanism underlies urticaria and angioedema?
Commonly involves IgE mediated type 1 immediate hypersensitivity leading to focal oedema. Common problem in the horse
What mechanisms underlies atopic dermatitis (AD)?
chronic inflammatory skin disease with features of both cell-mediated and IgE-mediated hypersensitivity and characterised by pruritus. Common in dogs, less common in cats and horses.
What are the similarities between hypersensitivity disease and allergic disease? 3
- objectively reproducible signs
- exposure to a defined stimulus
- at a dose tolerated by normal individuals
What are the differences between hypersensitivity disease and allergic disease? 3
- HYPERSENSITIVITY = no allergic immunologic mechanisms (e.g. idiosyncratic metabolic or pharmacologic mechansim) OR unknown mechanism
- ALLERGY = initiated by immunologic hypersensitivity (state of heightened reactivity to Ag), known allergic mechanism
T/F: allergic inflammation produces tissue injury
True
T/F allergic disease can be induced/aggravated by non-immunological factors (infection, exercise etc)
True
Define Urticaria
Multiple wheals (hives). Circumscribed raised lesions caused by dermal oedema
Define Angioedema
marked localised SC oedema. Strictly a sign, not a disease
What is the principal effector cell in urticaria and angioedema?
Mast cell. MC activation can be:
- IgE dependent (classical type 1 allergy)
- IgE independent - other immunologiccal mechanisms such as complement or non-immunological mechanism
Features of urticaria/angioedema
- Possibly all animals, principally horses
- Acute
- Recurrent
- Chronic
- Seasonal/non-seasonal
- May progress to crusting/sloughing
- Variable pruritus
What are the main triggers for uritcaria and angioedema? 6
- administered/applied substances
- infections, systemic/focal
- parasitic infestation, insect bites/stings
- dietary components
- aeroallergens
- contact allergenss
What are less important triggers for urticaria and angioedema?
- other environmental substances
- systemic disease
- physical stimuli
- hereditary conditions
- autoAbs
- idiopathic
How can urticaria and angioedema be diagnosed?
- Avoidance and re-challenge
- For IgE-mediated (immediate) allergies –> demonstrate allergen-specific IgE. Mites, insects and pollens only
What type of reaction is a food hypersensitivity? 2
FOOD ALLERGY and FOOD INTOLERANCE have IMMUNOLOGICAL components:
ALLERGY - IgE mediated OR non-IgE mediated
INTOLERANCE - idiosyncratic, pharmacological, metabolic
What are the CS of food hypersensitivity?
GIT: gastroenteritis, enteropathy
SKIN: urticaria, angioedema, pruritic skin disease, trigger of AD?, possible in dog, cat and horse.
Tx - cutaneous adverse food reaction/food hypersensitivity 3
- allergen avoidance
- treat secondary complications
- GCs if allergen avoidance is not possible
Dx - cutaneous adverse food reaction/ food hypersensitivity
- Hx and Cs
- response to restricted diet + relapse on old diet
- (intradermal and serological tests of no benefit)
What is CAD
Canine Atopic Dermatitis
Outline the aetiology of CAD
GENETICS - skin barrier, IgE response, (skin) immune system
ENVIRONMENTAL FACTORS - decreased skin barrier, allergen exposure, type of early immune stimulation
What is a typical Hx for AD?
- age at onset typically 6m-3 years
- breed, (WHWT, Shar Pei, Boxer, Retriever, English Setter)
- Family
- Pruritus, rash, ear infection
- Timing - seasonal, non-seasonal, non-seasonal with seasonal exacerbation, intermittent
What primary lesions are associated with AD? 3
(Pruritis +…)
- none
- erythema
- eryhtematous maculopapular rash
What is important to remember about breeds and AD?
- Some breeds affected earlier (French Bull, Shar Pei)
- Accuracy of diagnostic criteria variable
What are the 2 main causes of allergic skin disease?
- AD
- Food allergy
