Allergy and the Skin

Question 1

what are the general functions of the immune systems and what are the consequences of this?

Answer 1

defence against external (microbes) and external (cancer etc) antigens
causes intended destruction of antigen but also incidental collateral damage

Question 2

what is the definition of hypersensitivity?

Answer 2

exaggeration of normal immune response that causes collateral damage to self
basis for allergy and autoimmunity

Question 3

what is an allergy?

Answer 3

type 1 hypersensitivity disorder of the immune system which occurs when the immune system reacts to normally harmless substances

Question 4

how is the prevalence of allergy changing?

Answer 4

increasing

Question 5

describe the prevalence of allergy in the UK

Answer 5

V. high

30% children and 25% of adults suffer

Question 6

name 2 possible causes for the increase in allergy prevalence

Answer 6

increase in reporting of allergies

hygiene hypothesis

Question 7

describe type 1 hypersensitivity

Answer 7

immediate reaction within minutes, consistent with EVERY exposure to the antigen

Question 8

what routes of exposure can cause an allergy?

Answer 8

skin contact
inhalation
ingestion
injection

Question 9

what is the pathophysiology of type 1 hypersensitivity?

Answer 9

1st step = sensitisation (no reaction) creates antibodies against the allergen
2nd exposure = allergic reaction

Question 10

what is urticaria?

Answer 10

very itchy lesions
compressible dermal swellings that appear within 1 hour and last 2-6 hrs after exposure
“hives”

Question 11

what is angioedema?

Answer 11

localised soft tissue/mucous membrane swelling
no epidermis change
not itchy unless with urticaria

Question 12

name a mild and extreme allergic reaction

Answer 12

mild = wheezing/asthma
extreme = anaphylaxis

Question 13

what is anaphylaxis?

Answer 13

severe life threatening general or systemic allergic reaction
hives
flushing
facial swelling
runny nose
rapid breathing
dilation of vessels - hypotension
resp failure

Question 14

what is used for anaphylaxis?

Answer 14

adrenaline(epinepherine)

Question 15

what investigations are used to diagnose allergy?

Answer 15

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)

Question 16

what is the challenge test?

Answer 16

administer small amounts of the suspected allergen to measure response

Question 17

how is allergy managed?

Answer 17

avoidance is best
step 1 = antihistamine
step 2 = corticosteroid
step = arenaline autoinjector (EpiPen)
mast cell stabilisers also used
medic alert bracelets are useful

Question 18

how is adrenaline autoinjector prescribed?

Answer 18

for anaphylaxis
300µg in adults
150µg in kids
everyone gets 2 pens

Question 19

give some examples of non allergic reactions

Answer 19

coeliac, eosinophilic gastroenteritis(not IgE mediated)
aspirin, NSAIDs etc (cause direct mast cell degranulation)
lactose intolerance (metabolic issue)
fish toxins (directly toxic)

Question 20

describe type 4 hypersensitivity

Answer 20

delayed
antigen specific
onset usually 24-48 hrs after exposure
allergic contact dermatitis

Question 21

what mediated type 4 hypersensitivity?

Answer 21

T cells

Question 22

give an example of allergens that cause a type 4 reaction

Answer 22

cosmetic preservatives
fragrances, plants
tattoos

Question 23

what can cause variation in the clinical presentation of a type 4 hypersensitivity

Answer 23

the amount and site of exposure varies from person to person

Question 24

what are some reactions caused by type 4 hypersensitivity?

Answer 24

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)

Question 25

how can you differentiate an endogenous and exogenous disease?

Answer 25

well dermacted rash = exogenous as rash follows pattern/shape of what caused it (e.g plaster)
endogenous = general rash

Question 26

what is the gold standard test for allergic contact dermatitis?

Answer 26

Patch testing

allergens in special chambers are applied on the back for 48 hrs and readings then taken

Question 27

is allergy always the only cause for dermatitis? give an example

Answer 27

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

Question 28

what is the difference between allergy and irritation and how are they differentiated?

Answer 28

allergy requires sensitisation
irritation means skin is just sensitive, non-immunulogical
differentiated by patch test

Question 29

give 2 examples of irritation reactions

Answer 29

nappy rash

lip lick dermatitis

Question 30

give 2 examples of endogenous diseases

Answer 30

atopic eczema

psoriasis

Question 31

how is allergic contact dermatitis managed?

Answer 31

avoidance is best
emollients
topical steroids
UV phototherapy
immunosuppression