Allergy Flashcards
(21 cards)
How does an allergy develop?
Not born with it
Have to be exposed to allergen which causes sensitisation
Describe mast cell degranulation
Causes onset of symptoms
Rapid release; histamine, tryptase and hydrolase
Later release; PGs, leukotrienes, cytokines
What does histamine do?
Bronchial smooth muscle contraction; wheeze
Vasodilation; redness, flushing, faint
Separation endothelial cells; hives
Pain and itching
Is it an allergy?
Rapid onset Histamine mediated Urticaria, angioedema, itching, pallor/sweating, wheeze Improvement with antihistamine Relatively quick resumption of symptoms
Common food allergies
Milk Hen's egg Peanut Tree nuts Soya Wheat Fish Sesame
How severe was the reaction?
Not anaphylaxis; angioedema (not involving airway), urticaria and rash
Anaphylaxis; angioedema of airway, bronchospasm, hypotension
What supporting evidence from allergy focussed Hx?
Previous reactions Atopy; asthma, eczema, hayfever FHx Response to treatment Co-existing asthma (anaphylaxis risk)
What are allergy investigations?
Skin prick testing
Specific IgE
Oral food challenge
Describe skin prick testing
Easy to perform
Non-invasive
Immediate results
Cheap
Negative SPT is excellent predictor of negative IgE mediated food reaction in patients with anaphylaxis
What are pitfalls of skin prick testing?
Must stop antihistamines 48hrs prior
Broken skin
Theoretical risk of reactions
Dermatographism
Over-interpretation of positive results
Avoid random tests
Describe specific IgE test
No need stop antihistamines
No risk reactions
Expensive and invasive
Delay in results
Less sensitive and specific than SPT
Highly unreliable results in eczema
Describe the oral food challenge
day case procedure
Gold standard
What actually happens upon contact or ingestion
Allergy POA
Clear Hx
Worst reaction
Supporting evidence from investigations
Advise on allergen avoidance
What if allergen not identified?
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
What happens in anaphylaxis?
Laryngeal oedema Hypotension/collapse Bronchospasm Feeling of impending doom Onset within minutes (invariably within 60)
Biphasic reaction in anaphylaxis
20% have biphasic reaction 1-8hrs later therefore need steroids (to suppress biphasic reaction) and hospital admission
Risk factors for anaphylaxis
asthma (poorly controlled)
Stress
Exercise
Viral infection
Alcohol
Adrenaline pen
Adult/junior
Education on use home/school
1st line anaphylaxis treatment
Early use = better outcomes
Potential interaction with B-blockers and tricyclics
Describe adrenaline
reverses peripheral vasodilation
Increases peripheral vascular resistance
Improves BP and coronary perfusion
Decreases angioedema
Causes bronchodilation
Decreases release inflammatory mediators
Management options in allergy
Allergen avoidance Anti-histamine Adrenaline injections (asthma, anaphylaxis) Dietary advice Optimise asthma control
Criteria for adrenaline
Co-existing asthma
Previous anaphylaxis
Parents want one
