Allergy and the Skin Flashcards
what are the general functions of the immune systems and what are the consequences of this?
defence against external (microbes) and external (cancer etc) antigens
causes intended destruction of antigen but also incidental collateral damage
what is the definition of hypersensitivity?
exaggeration of normal immune response that causes collateral damage to self
basis for allergy and autoimmunity
what is an allergy?
type 1 hypersensitivity disorder of the immune system which occurs when the immune system reacts to normally harmless substances
how is the prevalence of allergy changing?
increasing
describe the prevalence of allergy in the UK
V. high
30% children and 25% of adults suffer
name 2 possible causes for the increase in allergy prevalence
increase in reporting of allergies
hygiene hypothesis
describe type 1 hypersensitivity
immediate reaction within minutes, consistent with EVERY exposure to the antigen
what routes of exposure can cause an allergy?
skin contact
inhalation
ingestion
injection
what is the pathophysiology of type 1 hypersensitivity?
1st step = sensitisation (no reaction) creates antibodies against the allergen
2nd exposure = allergic reaction
what is urticaria?
very itchy lesions
compressible dermal swellings that appear within 1 hour and last 2-6 hrs after exposure
“hives”
what is angioedema?
localised soft tissue/mucous membrane swelling
no epidermis change
not itchy unless with urticaria
name a mild and extreme allergic reaction
mild = wheezing/asthma extreme = anaphylaxis
what is anaphylaxis?
severe life threatening general or systemic allergic reaction hives flushing facial swelling runny nose rapid breathing dilation of vessels - hypotension resp failure
what is used for anaphylaxis?
adrenaline(epinepherine)
what investigations are used to diagnose allergy?
1st line = RAST (specific IgE blood test)
2nd line = skin prick/prick prick test if RAST doesn’t pick up allergy
3rd line = challenge test
serum mast cell tryptase used to diagnose anaphylaxis (high in anaphylaxis)
what is the challenge test?
administer small amounts of the suspected allergen to measure response
how is allergy managed?
avoidance is best step 1 = antihistamine step 2 = corticosteroid step = arenaline autoinjector (EpiPen) mast cell stabilisers also used medic alert bracelets are useful
how is adrenaline autoinjector prescribed?
for anaphylaxis
300µg in adults
150µg in kids
everyone gets 2 pens
give some examples of non allergic reactions
coeliac, eosinophilic gastroenteritis(not IgE mediated)
aspirin, NSAIDs etc (cause direct mast cell degranulation)
lactose intolerance (metabolic issue)
fish toxins (directly toxic)
describe type 4 hypersensitivity
delayed
antigen specific
onset usually 24-48 hrs after exposure
allergic contact dermatitis
what mediated type 4 hypersensitivity?
T cells
give an example of allergens that cause a type 4 reaction
cosmetic preservatives
fragrances, plants
tattoos
what can cause variation in the clinical presentation of a type 4 hypersensitivity
the amount and site of exposure varies from person to person
what are some reactions caused by type 4 hypersensitivity?
nickel reaction from belt buckle thiuram (rubber accelerator) in gloves fragrance in deodorant chromate in leather garlic (first 3 fingers) PPD in henna surgical glue Ivy (linear rash/blisters)
how can you differentiate an endogenous and exogenous disease?
well dermacted rash = exogenous as rash follows pattern/shape of what caused it (e.g plaster)
endogenous = general rash
what is the gold standard test for allergic contact dermatitis?
Patch testing
allergens in special chambers are applied on the back for 48 hrs and readings then taken
is allergy always the only cause for dermatitis? give an example
no
usually a combination of allergy, irritation and endogenous disease (infection can also be involved)
e.g - hand eczema - combination of glover allergy, over washing hands and underlying disease
what is the difference between allergy and irritation and how are they differentiated?
allergy requires sensitisation
irritation means skin is just sensitive, non-immunulogical
differentiated by patch test
give 2 examples of irritation reactions
nappy rash
lip lick dermatitis
give 2 examples of endogenous diseases
atopic eczema
psoriasis
how is allergic contact dermatitis managed?
avoidance is best emollients topical steroids UV phototherapy immunosuppression
