Paediatric Allergy Flashcards
what is the pathophysiology of allergy?
The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body’s immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine
IgE bind to mast cells and that’s where out develop sensitisation to an allergen
what is mast cell degranulation?
- Rapid release and onset of symptoms: Histamine , Tryptase, Hydrolase
- Later release with subsequent effects (Biphasic reaction):
Secreted inflammatory mediators – Prostaglandins, Leukotrienes, PAF, Cytokines
what are the effects of histamine?
- Bronchial smooth muscle contraction
- Vasodilation
- Separation of endothelial cells (responsible for hives) (also oedema)
- Pain and itching
Is it allergy? - what features point towards allergy?
Do I think it is IgE mediated allergy
Want to see immediate development of the reactions within minutes and certainly within an hour
Longer it takes for a reaction to manifest itself, less likely it will be IgE meidated
what are Common Food Allergens (>90%)?
How severe was the reaction? :
what would oyu see in mild/moderate reacitons and what would you see in severe reacitons?
Cardiovascular or respiratory involvement is real danger signs
what is Supporting evidence that the reaction is an allergy?
preivous reactions
atopy
family history
response to treatment
co-exisitng asthma
what are the 3 main investigaitons?
- Skin Prick Testing
- Specific IgE (blood test)
- Oral Food Challenge
what is Skin-prick testing?
- Easy to perform
- Non-invasive
- Immediate results (within 20 minutes)
- Cheap
- Negative SPT is an excellent predictor for a negative IgE mediated food reaction in patients with anaphylaxis (>95%)
what are the pitfalls of skin prick tesitng?
- Must stop antihistamines 48hrs prior
- Broken skin
- Theoretical risk of reactions
- Dermatographism
- Over-interpretation of positive results
- Avoid random tests
what are the features of Specific IGE?
- No-need to stop antihistamines
- No risk of reactions
- Expensive and invasive
- Delay in obtaining results
- Less sensitive and specific than SPT
- Highly unreliable results in eczema
what are the +ve and -vs of SPT and specific IgE?
how should Oral Food Challenge be done?
- Day case procedure
- Gold standard
- What actually happens upon contact or ingestion
what is needed to make a diagnosis?
how common is Urticaria and Angioedema?
- Lifetime Prevalence of 8.8%
- Chronic (>6 weeks) in 30-45%
- Urticaria alone 50%
- Urticaria + Angioedema 40% (Sabre et Al 85%)
- Angioedema alone 10%
- Up to 20% of those referred to hospital remain symptomatic after 10 years
how do you invesitgate urticaria and angiodema?
- Urticaria only with no trigger (none)
- Consider SPT / IgE if suspected food or environmental trigger
- Angioedema only (most commonly in teenagers with new presentation) look for Hereditary Angioedema C4 and C1 Esterase Inhibitor
- Rarely: FBC, Urinalysis, ESR, LFT, Coeliac Screen, TFT and antithyroid Ab, ANA (auto-immune)
how do you treat urticaria and angiodema?
- Avoidance of triggers
- H1- Antihistamine (2nd or 3rd generation)
- High Dose Antihistamines +/- second antihistamine
- Leukotriene Antagonist
- Corticosteroids (3-5 days)
- Tranexamic Acid
- Anti IgE Monoclonal antibody (Omalizumab) in children over 7 years of age
what effects does anaphylaxis cause?
- Laryngeal Oedema
- Hypotension/collapse
- Bronchospasm
- Feeling of impending doom
- Onset usually in minutes
what is the onset of anaphylaxis?
- Almost invariably symptoms begin within 60 mins
- The later the onset the less severe the attack
what are the Risk Factors for Anaphylaxis?
- Asthma (poorly controlled)
- Stress (emotional or physical)
- Exercise
- Viral infection
- Alcohol
what is 1st line treatment of anaphylaxis?
Adrenaline Pen
•Early use is associated with better outcomes
what are the effects of adrenaline?
Counter the physiological manifestations of histamine
Good for treating anaphylaxis
who should have an adrenaline pen?
Management and specific food allergies:
What management do I give?
- Allergen avoidance
- Anti-histamine
- Adrenaline Injectors (Asthma, Anaphylaxis)
- Dietary advice
- Optimise Asthma control
(All children who have IgE allergy will have one of these)
