Allergic skin disease Flashcards
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
What are the 2 main causes of skin (ear) infections?
- immunological derangement
- cutaneous abnormalities (skin barrier)
What are the 2 main pathogens implicated in ear infections?
- Staphylococcus pseudintermedius
- Malassezia pachydermatis
Dx - AD
- Hx
- CS
- Rule out/resolve other pruritic Dx (ectoparasites, skin infections)
- Investigate food hypersensitivity
What are criteria need to be met for an AD diagnosis?
5 CRITERIA OUT OF THE FOLLOWING TO BE MET:
- age at onset < 3 years
- mostly indoor
- corticosteroid-responsive pruritus
- chronic/recurrent yeast infections
- affected front feet
- affected pinnae
- non-affected ear margins
- non-affected dorso-lumbar area
When should you use allergy tests in the context of AD?
NOT FOR DIAGNOSIS. Use AFTER AD diagnosis has been made.
Use for MANAGEMENT (i.e. avoidance and immunotherapy) therefore has a supportive role.
Outline immunotherapy protocol
use extract from allergen, inject dog at increasing concentrations to hyposensitise them (i.e. move away from an IgE/Th2 response to a more tolerant response, works in 50% cases)
What is the treatment aim for CAD?
Reduce pruritus to an acceptable level long-term as safely as possible.
How is CAD tx best achieved? 3
- addressing as many trigger factors as possible
- combine tx modalities
- custom-tailored tx plan
