Allergy and the skin Flashcards
What is hypersensitivity?
An exaggerated immune response which causes collateral damage to oneself
Explain how hypersensitivity is classified (mediated, mechanism and common example)
What is an allergy reaction?
An immune system response to an environmental antigen which is normally harmless
Allergy incidence is increasing. What is thought to be the cause of this?
Hygiene hypothesis etc
What is the timeframe for a type 1 reaction?
Minutes up to two hours
What are the routes of exposure for a type 1 allergic reaction?
Direct skin contact, inhalation, ingestion & injection
What is the defining feature of type 1 allergic reaction history?
Consistant reaction with every exposure
How does type 1 allergic reaction present?
Urticaria, angioedema, wheezing/asthma, anaphylaxis
What are the features of urticaria?
Itchy, hive-like lesions which appear within an hour of exposure and last for several hours after
What are the features of angioedema?
Non-itchy, non-pitting localised swelling of subcutaneous tissue/mucous membrane
What is anaphylaxis?
Severe/life-threatening generalised/systemic hypersensitivity response involving the airways, breathing and circulation (most commonly with skin & mucosal involvement)
What investigations are indicated for suspected type 1 allergic reaction?
Specific IgE (RAST), skin prick testing, challenge test, serum mast cell tryptase level (during anaphylaxis)
What are the advantages of skin prick testing?
Very specific, cheap & easy, low chance of inducing anaphylaxis
How can type 1 allergic reaction be managed?
Avoidance, anti-histamines, corticosteroids, adrenaline autoinjector, sodium chromoglycate (mast cell stabiliser), immunotherapy, medic alert bracelet, education
When would an adrenaline autoinjector be given?
History of anaphylaxis or high risk patient with asthma
How many adrenaline autoinjectors should a patient be given?
Two
Name three drugs which cause non-immune mediated mast cell degranulation
NSAIDs, morphine & aspirin
What is the timeframe for a type 4 hypersensitivity reaction?
24-48 hours after exposure
What are the routes of exposure for type 4 allergic reaction?
Direct skin contact, airborne contact and injection
How do type 4 allergic reactions typically present?
Well defined rashes in areas exposed to allergen
Where do lichenoid allergic type 4 reactions typically present? Give an example of an allergen that might cause this
Mucous membranes (mouth most commonly). Amalgam fillings
Type 4 allergic reactions of the skin are usually called what?
Allergic contact dermatitis
What investigations are indicated for suspected type 4 allergic reaction?
Patch testing
What are the causes of dermatitis?
Allergens, endogenous (atopy), irritant & infectious
What is irritant contact dermatitis?
Non-immunologically mediated reaction caused by abrasive/irritating/directly traumatic agents
Irritant contact dermatitis and allergic contact dermatitis both require sensitization to the allergen/irritant before a visable reaction occurs. T/F
False - irritant contact dermatitis does not require prior sensitisation
What are the typical patterns of irritant contact dermatitis?
Dependant on exposure
Give 2 common examples of irritant contact dermatitis
Nappy rash & lip lick dermatitis
There is much overlap between irritant and allergic contact dermatitis. T/F
True
Give two examples of endogenous skin conditions. What are some differences between the two?
Atopic eczema (dry skin in flextural distribution) & psoriasis (scaly plaques on extensor surfaces)
How is contact dermatitis managed?
Avoidance/minimisation, emollients, topical steroids, UV phototherapy, immunosuppressants
Is prevelance of allergic reaction increasing or decreasing?
Increasing
