Week 1 - G - Allergy and the skin - allergic reactions (IgE), symptoms, diagnosis, treatment, Type IV (contact dermatitis), irritant dermatitis Flashcards
Allergy is a hypersensitivity disorder of the immune system When do allergic reactions occur?
Allergic reactions occur when a person’s immune system reacts normally harmless substances in the environment - a substance that causes this reaction is called an allergic
How long do allergic reactions take to occur? What are the routes of exposure? If the person is allergic to an allergic, does it occur on every exposure?
Allergic reactions are immediate reactions typically occurring within minutes and up to 2 hours after exposure to the allergic Routes of exposure- skin contact, inhalation, ingestion and injection History is consistent reaction with every exposure
What is the clinical presentation of allergy?
Often can have urticaria - very itchy and lasts hours - aka hives, wheales, nettle rash Angiodema -localised swelling of subcutaneus tissue or mucous membranes Wheezing / asthma Anaphylaxis if severe
What investigations are carried out for diagnosing an allergy?
HISTORY IS THE MOST IMPORTANT Skin prick testing Specific IgE testing (RAST - radioallergosorbent testing) if skin prick fails Challenge testing
When is challenge testing carried out?
Challenge testing is only carried out if skin prick testing is negative - where the person is given the suspected allergen - do not carry out in primary care Also used in non-IgE mediated food allergy as no anaphylactic risk
What is the management of allergies?
ALLERGEN AVOIDANCE Anti-histamines (prevents effects of mast-cell activation) Anti-inflammatory agent (corticosteroids) Adrenaline autoinjector (for anaphylaxis)
What is type IV allergy mediated by? When is the onset of the reacton?
Type IIV allergy is delayed hypersensitivity It is mediated by Tcells - specifically Th1 cell mediated Onset of reaction is typically 24-48 hours after exposure
What are examples of type IV hypersensitivity?
Allergic contact dermatitis TB Graft rejection
How do we test patients with suspected allergic contact dermatitis? When are the readings carried out?
Gold standard test for allergic contact dermatitis is patch testing Allergens are put on special chamber and applied on the patients back for 48 hours Readings are taken at 48 hours and 96 hours
What are examples of allergic contact dermatitis?
Nickel in belt buckle Nitrile gloves Fragrance in deodarants PPD in black henna tattoes
Irritant contact dermatitis is not immune mediated What is the cause of this? Give examples
Cause is due to skin coming into contact with agents that abrade, irritate and traumatise the skin directly No prior sensitization necessary Nappy rash Lip lick dermatitis
