Allergy

Question 1

How does an allergy develop?

Answer 1

Not born with it

Have to be exposed to allergen which causes sensitisation

Question 2

Describe mast cell degranulation

Answer 2

Causes onset of symptoms

Rapid release; histamine, tryptase and hydrolase

Later release; PGs, leukotrienes, cytokines

Question 3

What does histamine do?

Answer 3

Bronchial smooth muscle contraction; wheeze

Vasodilation; redness, flushing, faint

Separation endothelial cells; hives

Pain and itching

Question 4

Is it an allergy?

Answer 4

Rapid onset
Histamine mediated
Urticaria, angioedema, itching, pallor/sweating, wheeze
Improvement with antihistamine
Relatively quick resumption of symptoms

Question 5

Common food allergies

Answer 5

Milk
Hen's egg
Peanut
Tree nuts
Soya
Wheat
Fish
Sesame

Question 6

How severe was the reaction?

Answer 6

Not anaphylaxis; angioedema (not involving airway), urticaria and rash

Anaphylaxis; angioedema of airway, bronchospasm, hypotension

Question 7

What supporting evidence from allergy focussed Hx?

Answer 7

Previous reactions
Atopy; asthma, eczema, hayfever
FHx
Response to treatment
Co-existing asthma (anaphylaxis risk)

Question 8

What are allergy investigations?

Answer 8

Skin prick testing
Specific IgE
Oral food challenge

Question 9

Describe skin prick testing

Answer 9

Easy to perform
Non-invasive
Immediate results
Cheap

Negative SPT is excellent predictor of negative IgE mediated food reaction in patients with anaphylaxis

Question 10

What are pitfalls of skin prick testing?

Answer 10

Must stop antihistamines 48hrs prior

Broken skin

Theoretical risk of reactions

Dermatographism

Over-interpretation of positive results

Avoid random tests

Question 11

Describe specific IgE test

Answer 11

No need stop antihistamines

No risk reactions

Expensive and invasive

Delay in results

Less sensitive and specific than SPT

Highly unreliable results in eczema

Question 12

Describe the oral food challenge

Answer 12

day case procedure

Gold standard

What actually happens upon contact or ingestion

Question 13

Allergy POA

Answer 13

Clear Hx
Worst reaction
Supporting evidence from investigations
Advise on allergen avoidance

Question 14

What if allergen not identified?

Answer 14

Often none found

Idiopathic urticaria +/- angioedema

Chronic after 6months

prn non-sedating anti-histamines

regular non-sedating anti-histamines

leukotriene antagonist or H2 receptor antagonist

usually settles within 2-3yrs

Question 15

What happens in anaphylaxis?

Answer 15

Laryngeal oedema
Hypotension/collapse
Bronchospasm
Feeling of impending doom
Onset within minutes (invariably within 60)

Question 16

Biphasic reaction in anaphylaxis

Answer 16

20% have biphasic reaction 1-8hrs later therefore need steroids (to suppress biphasic reaction) and hospital admission

Question 17

Risk factors for anaphylaxis

Answer 17

asthma (poorly controlled)

Stress

Exercise

Viral infection

Alcohol

Question 18

Adrenaline pen

Answer 18

Adult/junior

Education on use home/school

1st line anaphylaxis treatment

Early use = better outcomes

Potential interaction with B-blockers and tricyclics

Question 19

Describe adrenaline

Answer 19

reverses peripheral vasodilation

Increases peripheral vascular resistance

Improves BP and coronary perfusion

Decreases angioedema

Causes bronchodilation

Decreases release inflammatory mediators

Question 20

Management options in allergy

Answer 20

Allergen avoidance
Anti-histamine
Adrenaline injections (asthma, anaphylaxis)
Dietary advice
Optimise asthma control

Question 21

Criteria for adrenaline

Answer 21

Co-existing asthma
Previous anaphylaxis
Parents want one