Allergy And Anaphylaxis Flashcards
Egs of paediatric allergy
Asthma, allergic rhinitis (hay fever), eczema, conjunctivitis, urticaria, hypersensitivity to drugs, food, bites/stings
Define hypersensitivity
Objectively reproducible symptoms/ signs following a defined stimulus (eg. Food/drug) at a dose tolerated by normal persons
Define allergy ? 2 types?
A hypersensitivity reaction initiated by specific immunological mechanisms. This can be IgE mediated (eg peanut) or non-IgE mediated (eg. Coeliac)
What is atopy ? What does it result in ?
A personal and/or familial tendency, usually in childhood or adolescence, to become sensitised and produce IgE antibodies in response to ordinary exposures to allergens, usually proteins.
Results in eczema, allergic rhinitis, conjunctivitis
Define anaphylaxis
A severe, life threatening, generalised / systemic hypersensitivity reaction
Approx how many children have a food allergy
6-8%
What percentage of children with atopic eczema have a reaction to certain foods
60%
What are the most common type of allergy in infancy?
How do they manifest?
Eczema and food allergy
Food reactions predominate with manifestations in skin, respiratory and GI tracts
What allergies are most common in childhood ?
What type of allergens predominate
Asthma and allergic rhinitis
Inhaled allergens - dust, pets, pollen, moulds
What is a cross reaction to allergens?
Egs of cross reaction?
Children sensitised to one allergen can develop reactions to others even though they have never encountered them.
Eg grass and peanut, latex and banana
Why do you get a cross reaction to allergens
Because they share the same IgE epitope and mimic each other
Basic mechanism of developing allergy (not cellular)
Early life infants exposed to wide variety of non specific environmental antigens which prime the immune system.
In allergy the priming is ABNORMAL (in genetically susceptible -> become atopic).
Cellular mechanism of allergy development?
What process makes an individual sensitised?
Exposure to specific antigen (eg. Peanut) –> allergic sensitisation.
Body identifies allergen and APC presents to Th2 cells
Th2 release cytokines which cause B cells to make IgE antibodies to allergen.
IgE present on mast cells = sensitised individual
What are the immediate and delayed reactions to allergen exposure? Key cells involved?
Immediate - degranulation of mast cells releasing histamine (also basophils)
Delayed - (4-6hrs) toxic chemicals at site of exposure (eosinophils)
Clinical aspects of respiratory allergy
Asthma/ wheeze, hoarseness, stridor/ angiooedema, rhino conjunctivitis
Clinical aspects of GI allergy
Nausea And vomiting, failure to thrive, abdominal distension
Cardiovascular clinical aspects of allergy
Hypotension and shock, dizziness
Clinical aspects of allergy in skin
Atopic dermatitis, angiooedema, urticaria, pruritus
What 3 investigations can be done for allergy
Skin prick, serum specific IgE (RAST) testing, food challenge
Benefits of skin prick testing
Cheap, quick, good safety
Drawback of skin prick testing
Positive test only gives 50% chance of true reaction (therefore need good Hx)
What is serum specific IgE (RAST) testing
Measures levels of IgE that are food specific (positive still meets positive Hx)
What is the gold standard for allergen testing ? Why?
Food challenge (if double blind placebo controlled) Only test to give true clinical reaction following food exposure
Management for allergies
MDT (specialist / nurse specialist, dietician, parent, school)
Avoid allergen
Antihistamines for mild reactions
Egs of antihistamines
Piriton (chlorphenamine).
Piriteze (cetirizene) - non drowsy
3 key pathophysiological features of anaphylaxis
Capillary leak
Mucosal oedema
Smooth muscle contraction
Features of anaphylaxis ? Results in
Respiratory - wheeze / upper airway obstruction , cough, angiooedema, stridor
And/or cardio - shock, hypotension , dizziness pallor, tachycardia
Vomiting / diarrhoea, floppiness, loss of conciousness
Who shouldn’t get flu vaccine
Children with egg allergy (risk of anaphylaxis)
Treatment of anaphylaxis
IM adrenaline
IV hydrocortisone and antihistamines
What is urticaria
Hives (pale red raised itchy bumps) see photo
How long does urticaria last
Chronic >6 weeks
Usual cause of urticaria
Idiopathic (usually non allergic )
Other causes of urticaria
Infection
IgE - foods, blood products, drugs (penicillins, cephlasporins)
Food containing histamine releasing (strawberries, egg white, cheese)
Aspirin and other NSAIDs
Heat, cold, pressure
