Allergy And Anaphylaxis

Question 1

Egs of paediatric allergy

Answer 1

Asthma, allergic rhinitis (hay fever), eczema, conjunctivitis, urticaria, hypersensitivity to drugs, food, bites/stings

Question 2

Define hypersensitivity

Answer 2

Objectively reproducible symptoms/ signs following a defined stimulus (eg. Food/drug) at a dose tolerated by normal persons

Question 3

Define allergy ? 2 types?

Answer 3

A hypersensitivity reaction initiated by specific immunological mechanisms. This can be IgE mediated (eg peanut) or non-IgE mediated (eg. Coeliac)

Question 4

What is atopy ? What does it result in ?

Answer 4

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

Question 5

Define anaphylaxis

Answer 5

A severe, life threatening, generalised / systemic hypersensitivity reaction

Question 6

Approx how many children have a food allergy

Answer 6

6-8%

Question 7

What percentage of children with atopic eczema have a reaction to certain foods

Answer 7

60%

Question 8

What are the most common type of allergy in infancy?

How do they manifest?

Answer 8

Eczema and food allergy

Food reactions predominate with manifestations in skin, respiratory and GI tracts

Question 9

What allergies are most common in childhood ?

What type of allergens predominate

Answer 9

Asthma and allergic rhinitis

Inhaled allergens - dust, pets, pollen, moulds

Question 10

What is a cross reaction to allergens?

Egs of cross reaction?

Answer 10

Children sensitised to one allergen can develop reactions to others even though they have never encountered them.
Eg grass and peanut, latex and banana

Question 11

Why do you get a cross reaction to allergens

Answer 11

Because they share the same IgE epitope and mimic each other

Question 12

Basic mechanism of developing allergy (not cellular)

Answer 12

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).

Question 13

Cellular mechanism of allergy development?

What process makes an individual sensitised?

Answer 13

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

Question 14

What are the immediate and delayed reactions to allergen exposure? Key cells involved?

Answer 14

Immediate - degranulation of mast cells releasing histamine (also basophils)
Delayed - (4-6hrs) toxic chemicals at site of exposure (eosinophils)

Question 15

Clinical aspects of respiratory allergy

Answer 15

Asthma/ wheeze, hoarseness, stridor/ angiooedema, rhino conjunctivitis

Question 16

Clinical aspects of GI allergy

Answer 16

Nausea And vomiting, failure to thrive, abdominal distension

Question 17

Cardiovascular clinical aspects of allergy

Answer 17

Hypotension and shock, dizziness

Question 18

Clinical aspects of allergy in skin

Answer 18

Atopic dermatitis, angiooedema, urticaria, pruritus

Question 19

What 3 investigations can be done for allergy

Answer 19

Skin prick, serum specific IgE (RAST) testing, food challenge

Question 20

Benefits of skin prick testing

Answer 20

Cheap, quick, good safety

Question 21

Drawback of skin prick testing

Answer 21

Positive test only gives 50% chance of true reaction (therefore need good Hx)

Question 22

What is serum specific IgE (RAST) testing

Answer 22

Measures levels of IgE that are food specific (positive still meets positive Hx)

Question 23

What is the gold standard for allergen testing ? Why?

Answer 23

Food challenge (if double blind placebo controlled)
Only test to give true clinical reaction following food exposure

Question 24

Management for allergies

Answer 24

MDT (specialist / nurse specialist, dietician, parent, school)
Avoid allergen
Antihistamines for mild reactions

Question 25

Egs of antihistamines

Answer 25

Piriton (chlorphenamine).

Piriteze (cetirizene) - non drowsy

Question 26

3 key pathophysiological features of anaphylaxis

Answer 26

Capillary leak
Mucosal oedema
Smooth muscle contraction

Question 27

Features of anaphylaxis ? Results in

Answer 27

Respiratory - wheeze / upper airway obstruction , cough, angiooedema, stridor
And/or cardio - shock, hypotension , dizziness pallor, tachycardia

Vomiting / diarrhoea, floppiness, loss of conciousness

Question 28

Who shouldn’t get flu vaccine

Answer 28

Children with egg allergy (risk of anaphylaxis)

Question 29

Treatment of anaphylaxis

Answer 29

IM adrenaline

IV hydrocortisone and antihistamines

Question 30

What is urticaria

Answer 30

Hives (pale red raised itchy bumps) see photo

Question 31

How long does urticaria last

Answer 31

Chronic >6 weeks

Question 32

Usual cause of urticaria

Answer 32

Idiopathic (usually non allergic )

Question 33

Other causes of urticaria

Answer 33

Infection
IgE - foods, blood products, drugs (penicillins, cephlasporins)
Food containing histamine releasing (strawberries, egg white, cheese)
Aspirin and other NSAIDs
Heat, cold, pressure