allergy Flashcards
Why does allergy matter?
12 million people in UK (1/5th of population) are now seeking treatment for allergy
estimated by 2025 half of entire EU population will be affected
List 5 common allergy diagnoses
hay fever
food allergies
atopic dematitis
allergic asthma
anaphylaxis
What are the 4 types of classifications of allergic reactions?
Type I - IgE–mediated release of histamine and other mediators
Type II - Cytotoxic hypersensitivity reactions
Type III - Immune-complex reactions
Type IV - Cell-mediated reactions
In practice we see mainly type 1 reactions
Hypersensitivity:
Can be broken down into which categories?
Hypersensitivity –> either non allergic hypersensitvity, allergic hypersensitivity –> either IgE mediated or not IgE mediated, or there is no hypersensitivity
What are the key features of an IgE mediated allergic reactions?
Timing –> rapid, seconds to 30 minutes
mechanism –> IgE mediated with mast cell degranulation
Classic clinical features –> wide spectrum, urticaria, vomiting, angioedema, anaphylaxis
common examples –> peanut, egg, CM, wheat
Systems involved –> resp/ GI/ skin
Relationship of dose to reaction –> can have severe response to minimal exposure
Investigations –> skin prick testings, specific IgE
What are key features of non IgE mediated allergic hypersensitivity?
Timing –> slow, up to a couple of days
mechanism –> diverse, includes T cell responses
Classic clinical features –> failure to thrive, chronic diarrhoea, eczema, rhinitis, rectal bleeding
common examples –> cows milk sensitivie enteropathy, trigger of eczema or asthma
Systems involved –> resp/ GI/ skin
Relationship of dose to reaction –> often a dose response relationship
Investigations –> dietary exclusion, under guidance of dietician
What are the key features of non allergic hypersensitivity?
Timing –> slow –> hours to days
mechanism –> multiple
Classic clinical features –> multiple
common examples –> lactose intolerance, caffiene
Systems involved –> multiple
Relationship of dose to reaction –> dose response relationship
Investigations –> reduced intake
Type 1 hypersensitivity –> describe the pathology
IgE coated resting mast cell, IgE binds the allergen epitope and causes degranulation –> release of histamine/ other infalmmatory mediators
Immediate hypersensitvity reaction and late phase reaction after repeat exposure
What are typical signs of IgE mediated allergy?
urticaria
swelling
oral symptoms
vomiting/ diarrhoea
wheeze
severe reactions –> resp/ circulatory
list some common triggers for allergy
cows milk
egg
legumes –> peanut and soya
tree nuts
fish
shellfish
cereals
fruits
drugs
How do you diagnose a hypersensitivity reaction?
- History is KEY –>what happens when they have an allergic reaction? what were they doing before? how quick was the reaction etc.
- Skin prcik tests
- Specific IgE blood tests –>
- (RAST)
- high background IgE
- Challenges –> bring individual to hospital, give a dose and watch for the response. Done if tests were negative, if we thought someone might have grown out of their allergy.
how do we manage allergies?
- Avoidance –> dietary education, dietician, substitutes
- Antihistamines
- adrenaline
- advice –> family, school ,management plan
- the future –> desensitization (small doses given over months regularly) , gene therapy?
What are the defining features of a slow type allergy?
hard to diagnose
often heterogeneous, blends with “normal” and there is often a dose/ respone
not dangerous per say
What is the best clinical approach to allergy?
mechanisms matter -> investigation and management
each trigger/ symptom complex can be by a separate mechansim
triggers by the same mechanism can be to a different specificity
each trigger/ sx complex is a separate presenting complaint
common foods can cause problems by each type of mechanism
