Allergy

Question 1

What is the process of developing an allergy?

Answer 1

Sensitisation

IgE specific to the allergen activated on the primed mast cells

Question 2

What happens when an allergen contacts the mast cell?

Answer 2

Degranulation

Question 3

What happens in mast cell degranulation?

Answer 3

Histamine
Typtase
Hydrolases

Question 4

What does histamine do?

Answer 4

Bronchial smooth muscle contraction
Vasodilation
Separation of endothelial cells
Pain and itching

Question 5

Is there a genetic influence to allergies?

Answer 5

Yes

Parental atopy

Question 6

Is it an allergy?

Answer 6

Rapid onset
Histamine mediated reactions
Urticaria, itching, angioedema, pallor and wheeze
Better with anti-histamines?
Quick resumption of  symptoms?

Question 7

What cause the reaction?

Answer 7

Food
Contact
Environmental agent
No cause?

Question 8

How severe was the reaction?

Answer 8

Mild/moderate = angioedema, urticaria and rash

Severe = angioedema of airway, bronchospasm and hypotension

Question 9

What are the investigations for an allergy?

Answer 9

Skin prick testing
Specific IgE
Oral food challenge

Question 10

What is skin prick testing?

Answer 10

Easy and quick
Immediate results
Negative SPT is an excellent predictor for a negative IgE mediated food reaction in patients with anaphylaxis

Question 11

What are the pitfalls of the skin prick test?

Answer 11

Must stop antihistamines 48hrs before
Not on broken skin
Theoretical risk of reactions
Dermatographism
Over-interpretation of positive results 
Avoid random tests

Question 12

What is specific IgE test?

Answer 12

No risk of reaction
Expensive
Delay in results - 2 weeks
Invasive 
Less sensitive and specific than SPT
Highly unreliable results in eczema

Question 13

What happens in oral food challenge?

Answer 13

Gold standard
Its a day case procedure
Shows what actually happens upon contact or ingestion

Question 14

How to make the diganosis?

Answer 14

Clear history
Worst reaction
Supporting evidence
ID and advise on avoidance

Question 15

What if the allergen cant be found

Answer 15

Often there is nothing found
Idiopathic urticaria +/- angioedema
Chronic after 6 months

Non-sedating anti-histamines
Leukotriene antagonist or H2 receptor antagonist

Question 16

What happens in anaphylaxis?

Answer 16

Laryngeal oedema
Hypotension
Bronchospasm
Onset in minutes - later the onset, the less severe the attack

Question 17

What is the biphasic reaction

Answer 17

20% 1-8 hrs later therefore need steroids and hospital admission

Question 18

What are the RF’s for anaphylaxis?

Answer 18

Asthma
Stress
Exercise
Viral infection
Alcohol

Question 19

What is an adrenaline pen?

Answer 19

Education
1st line treatment
Early use associated with better outcomes
Potential interaction with b blockers and tricyclics

Question 20

What does adrenaline do?

Answer 20

Reverses vasodilation
Increases peripheral vascular resistance
Improves BP and coronary perfusion
Decreases angiooedema
Causes bronchodilation
Decreases release of inflammatory mediators

Question 21

What management is given?

Answer 21

Allergen avoidance
Anti-histamine
Adrenaline injection (co-existing asthma, previous anaphylaxis and if parents want one)
Dietary advice
Optimise asthma control

Question 22

What are emerging therapies?

Answer 22

Immunotherapy