Allergy and the Skin Flashcards

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1
Q

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

A

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

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2
Q

what is the definition of hypersensitivity?

A

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

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3
Q

what is an allergy?

A

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

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4
Q

how is the prevalence of allergy changing?

A

increasing

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5
Q

describe the prevalence of allergy in the UK

A

V. high

30% children and 25% of adults suffer

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6
Q

name 2 possible causes for the increase in allergy prevalence

A

increase in reporting of allergies

hygiene hypothesis

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7
Q

describe type 1 hypersensitivity

A

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

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8
Q

what routes of exposure can cause an allergy?

A

skin contact
inhalation
ingestion
injection

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9
Q

what is the pathophysiology of type 1 hypersensitivity?

A

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

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10
Q

what is urticaria?

A

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

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11
Q

what is angioedema?

A

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

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12
Q

name a mild and extreme allergic reaction

A
mild = wheezing/asthma
extreme = anaphylaxis
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13
Q

what is anaphylaxis?

A
severe life threatening general or systemic allergic reaction
hives
flushing
facial swelling
runny nose
rapid breathing
dilation of vessels - hypotension
resp failure
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14
Q

what is used for anaphylaxis?

A

adrenaline(epinepherine)

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15
Q

what investigations are used to diagnose allergy?

A

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)

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16
Q

what is the challenge test?

A

administer small amounts of the suspected allergen to measure response

17
Q

how is allergy managed?

A
avoidance is best
step 1 = antihistamine
step 2 = corticosteroid
step = arenaline autoinjector (EpiPen)
mast cell stabilisers also used
medic alert bracelets are useful
18
Q

how is adrenaline autoinjector prescribed?

A

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

19
Q

give some examples of non allergic reactions

A

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

20
Q

describe type 4 hypersensitivity

A

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

21
Q

what mediated type 4 hypersensitivity?

A

T cells

22
Q

give an example of allergens that cause a type 4 reaction

A

cosmetic preservatives
fragrances, plants
tattoos

23
Q

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

A

the amount and site of exposure varies from person to person

24
Q

what are some reactions caused by type 4 hypersensitivity?

A
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)
25
Q

how can you differentiate an endogenous and exogenous disease?

A

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

26
Q

what is the gold standard test for allergic contact dermatitis?

A

Patch testing

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

27
Q

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

A

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

28
Q

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

A

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

29
Q

give 2 examples of irritation reactions

A

nappy rash

lip lick dermatitis

30
Q

give 2 examples of endogenous diseases

A

atopic eczema

psoriasis

31
Q

how is allergic contact dermatitis managed?

A
avoidance is best
emollients
topical steroids
UV phototherapy
immunosuppression