Allergy and the skin Flashcards
What is hypersensitivity?
An exaggerated immune response which causes damaged to oneself
How can hypersensitivity be classified?
Type 1 - IgE mediated
Type 2 - IgG mediated cytotoxic
Type 3 - Immune complex mediated
Type 4 - Delayed cell mediated
What are allergic reactions?
Immune system response to a normally harmless substance
What is an allergen?
Substance which causes an immune reaction
What is the theory behind the increasing prevalence of allergy?
Hygiene hypothesis
What is the time frame of a type 1 allergic reaction?
Between minutes to two hours
What routes of exposure can cause a type 1 allergic reaction?
Inhalation
Ingestion
Skin contact
Injection
What is the main history feature of a type 1 allergic reaction?
Consistent reaction every time
What are the common ingested allergens?
Nuts
Seafood
What are the common inhaled allergens?
House dust mite
Pollen
What are the common skin contact allergens?
Animal dander
Latex
What are the common injected allergens?
Bee
Medication
How does a type 1 allergic reaction present?
Urticaria
Angioedema
Wheezing/asthma
Anaphylaxis
How does urticaria present?
Itchy
Wheals
Lasts 2-6 hours but less than 24 hours
What is angioedema?
Swelling of the subcutaneous tissues or mucous membranes
How does angioedema present?
Swelling
Not itchy
Non-pitting
What is anaphylaxis?
Life threatening general or systemic hypersensitivity reaction
How does anaphylaxis present?
Rapidly developing Airway (oedema) Breathing (tachypneoa) Circulation (hypotension) Associated skin/mucosal changes
How is suspected type 1 hypersensitivity investigated?
Specific IgE (RAST) Skin prick Challenge test (rare) Serum mast cell tryptase (during anaphylaxis)
What are the benefits and drawbacks of skin prick testing?
Cheap
Quick
Specific
Sensitive
Small anaphylaxis risk
When would challenge testing be undertaken?
Skin prick testing negative
Last resort
How is type 1 allergy managed?
Avoidance Anti-histamines Corticosteroids (anti-inflammatory) Adrenaline autoinjector (anaphylaxis) Sodium chromoglycate Immunotherapy
What is the dose of an adrenaline autoinjector in children and adults?
150ug
300ug
How many adrenaline autoinjector pens should a patient have at the one time?
2
Is coeliac an allergic condition?
No
Is lactose intolerance an allergic condition?
No
What is the timeframe for a type 4 hypersensitivity reaction?
Reaction occurs within 24-48 hours of exposure
Is type 4 hypersensitivity specific to a particular antigen?
Yes
Which type of cells are involved in type 4 hypersensitivity?
T cells
What type of skin reaction is mediated by type 4 hypersensitivity?
Allergic contact dermatitis
How do type 4 hypersensitivity skin reactions present?
Specific to allergen contact/exposure site/pattern
Mostly eczematous reaction
How are type 4 hypersensitivity skin reactions investigated?
Patch testing
How is a patch test carried out?
Allergens placed in wells
Wells applied to back and removed after 48 hours
Back is checked at 48 hours and 96 hours
If photo-allergens are suspected two wells must be done one exposed to UV and one not
What are the three main categories of dermatitis?
Atopic
Irritant
Allergic
Is irritant contact dermatitis an immunologically mediated process?
No
How does irritant contact dermatitis happen?
Skin comes into contact with something which directly irritates, abrades or traumatises it
How does irritant contact dermatitis present?
Depends on the pattern of exposure
Give two examples of irritant contact dermatitis
Lip lick dermatitis
Nappy rash
What is atopic eczema associated with?
Asthma
Hayfever/allergic rhinitis
How is atopic eczema distributed?
Flexural
How is psorisasis distributed?
Extensor
How is irritant dermatitis managed?
Avoidance or modification
How is dermatitis treated?
Emollients
Steroids
UV phototherapy
Immunosupressants
