Flashcards in MISC - Allergy diagnosis Deck (20)
What are allergens? Examples/
- generally PROTEINS that elicit an IgE response in allergic individuals
e.g. grass pollens, dust in rhinitis, asthma
e.g. peanuts, eggs in food allergy
How do you clinically Dx allergy?
Symptoms & demonstration of specific IgE (either by skin test or RAST)
Symptoms of allergy
dependent on route of exposure
- inhaled: rhinitis, asthma
- skin: acute contact urticaria
- mouth: oral allergy syndrome
- systemic: anaphylaxis
Within 1 hour usually seconds/min
(3) diagnostic tests of allergies
1. Skin prick test (>3mm wheal is considered positive).
- Highly sensitive
- but potential for anaphylaxis.
- May lack specificity
- only by specialists
2. Serology assays: RAST, EAST, CAP-FEIA (most commonly used)
- measure allergen-specific IgE
- available (GPs can do them), safe, good specificity
- false positive with elevated total IgE (e.g. eczema)
3. Challenge testing: gold standard
- usually only in specialised allergy clinics
- used when to disprove allergy. e.g. negative RAST/SPT but positive clinical Hx
- potentially risky
What is the dose of adrenaline for anaphylaxis?
0.5mg for adults
0.01mg/kg for children
Also give them hydrocortisone IV
Inappropriate/harmful immune response to foreign substances that are otherwise not harmful to the body, mediated largely, though not exclusively by IgE
Discuss allergy treatment
–Allergen specific immunotherapy
Non-specific treatments (medication)
–Antihistamines, corticosteroids, adrenaline, leukotriene antagonists, anti-IgE antibodies (omalizumab)
Discuss allergen immunotherapy
- Immunotherapy only current allergy therapy to provide prolonged improvement or cure
- Efficacy is limited by side effects – there is a small but important risk of anaphylaxis with subcutaneous immunotherapy
- Generally recommended to be initiated and/or supervised by an allergy specialist
Who are eligible for subcutaneous injection immunotherapy of allergy?
•Mainly indicated for venom allergy (bee and european wasp) and allergic rhinitis +/- mild, well controlled allergic asthma
•Level 1 evidence that it works in allergic rhinitis and allergic asthma, but risk of adverse reactions higher in asthmatics (must have stable symptoms and FEV1 > 70% predicted)
•Co-existent beta blockade a contraindication to immunotherapy
Discuss the proposed mechanism of allergen immunotherapy
Instead of Th2 pathway, immunotherapy leads to Th1 pathway which is the non-allergic response.
Allergen is picked up by APC -> presented to Th0.
Normally in allergy:
Th0 -> IL-4 -> Th2 -> IL-4, 5 -> B cell & makes IgE.
Th0 -> Th1 -> IFNgamma -> B cell & makes IgG
What are the practical aspects of injection allergen immunotherapy?
•ALWAYS wait at least 30min in surgery after injection
•Usually antihistamine prior advisable
•Always check the dose and extract
•Adrenaline and oxygen must be available for treatment of anaphylaxis if it occurs
Discuss sublingual immunotherapy
•Doses of allergen extract self-administered daily by patient sublingually, held for 2 minutes under the tongue and then swallowed
•Appears as effective as subcutaneous immunotherapy
•Minimal risk of anaphylaxis and no deaths reported with use
•Extracts are more expensive but can be administered at home by patient
•No clear consensus on definition
•“ Serious allergic reaction that may cause death”
•Generally implies IgE-mediated (as opposed to anaphylactoid which is non-IgE mediated)
•Is a generalised serious IgE-mediated allergic reaction which usually involves cardiovascular (hypotension) and/or respiratory tract (asthma/laryngeal oedema). Atypical presentations (eg without rash) are not uncommon, particularly in the very old or very young.
What is the mechanism of anaphylaxis?
•Massive mediator release primarily from mast cells and circulating basophils
•Vasodilation, fluid extravasation, bronchial smooth muscle contraction and mucosal oedema
•Death due to shock and/or hypoxaemia
What are the (6) Px of anaphylaxis?
•Pruritis - hand and groin
- lips, tongue
•Hypotension, Loss of consciousness
Discuss food allergy as a cause of anaphylaxis
•Food usually identified by patient/parent
•Common foods are peanuts, tree-nuts, eggs, milk, fish and crustaceans.
•Anaphylaxis is often life-long (except for egg and milk allergy which frequently remit, whereas only about 30% of children with peanut allergy will remit)
–Management of inadvertent exposure (adrenaline)
What are the risk factors for fatal food related anaphylaxis
•Lack of an self-injectable adrenaline (Epipen or Anapen)
How do you diagnose anaphylaxis?
•A clinical diagnosis
•A broad differential diagnosis including cardiovascular and other disorders
•Skin prick testing (when safe)
•Mast cell tryptase – an enzyme released during degranulation of mast cells. Peaks around 4-6 hours post anaphylaxis
What are the principles in long term therapy of allergy/anaphylaxis?
- Education on Action Plan
When to seek help
adrenaline injection: Epi-Pen or Anapen
Desensitisation if relevant
- Medical alert bracelet