Allergy

Question 1

What is the difference between a type 1 and type 4 reaction?

Answer 1

Type 1:

• IgE mediated and occurs w/i minutes of exposure
• resolves w/i hours
• life-threatening

Type 4:

• delayed hypersensitivity reaction= 1-2 days post-exposure
• lasts >4 hrs

Question 2

What allergies would be included in the type 1 allergy spectrum?

Answer 2

Hay fever 
Allergic asthma 
Atopic dermatitis 
Food allergy 
Drug allergy 
Venom allergy

Question 3

What is the process of developing a type 1 allergy?

Answer 3

SENSITISATION EVENT via exposure to allergen

Specific IgE production

Re-exposure to allergen leads to acute allergic response due to IgE binding the antigen and cross-linking with high affinity receptors on mast cell

Question 4

What mast cell mediators are released during mast cell degranulation and why does it lead to such a rapid response?
What actions do mast cell mediators have?

Answer 4

Histamine
Prostaglandins 
Leukotrienes 
Platelet activating factor (PAF)
Tryptase (longer half like of 4-6hrs)
Rapid reaction due to the mediators being preformed 

Action:

• vasodilation
• increased vascular permeability
• increase HR and cardiac contraction
• glandular secretion
• Bronchoconstriction-> leads to wheeze

Question 5

What causes hay fever/allergic rhinitis?
How might someone present?
What tests can be done to try and confirm?

Answer 5

Allergic response to aeroallergens 
Presentation:
-Itching in nose or eyes 
-rhinorrhea 
-sneezing
-allergic conjunctivitis 
-tears 

Tests:

• serum specific IgE (confirm HX of allergy)
• total IgE= helps to interpret ssIgE
• skin prick test= purified protein on skin= induces IgE mediated response (20mins for results)

Question 6

What are the management options for allergic rhinitis?

Answer 6

STEP1:

• allergen avoidance
• douching
• nasal/oral antihistamine

STEP2a:

• nasal steroids + nasal antihistamine
• pre-medicate before season if hay fever

STEP2b: (special circumstances)

• Ipratropium bromide= decreases secretions
• LTRA- seasonal asthma
• increase antihistamine dose
• short course of oral steroids if in atopic crisis

STEP3:

• need to confirm failure on maximal medical therapy i.e. persistent poor control after checking compliance/SE/technique
• needs immunotherapy

Question 7

What is allergic asthma?

Answer 7

Exposure to allergen causes reversible bronchial hyper-reactivity (SM contraction) leading to worsening of symptoms
-exacerbates and causes disorder airway movement in small airways = WHEEZE
(Can have complex late phase response due to inflammation)

Question 8

How can allergic asthma be treated?

Answer 8

Allergen avoidance
Stabilise mast cells via sodium chromoglycate
Treat inflammation= steroids or ILTRA
Relieve bronchospasm= beta-agonists

Question 9

What is atopic dermatitis?

Answer 9

(Eczema)
Combination of:
-allergic skin disease= very high IgE but not usually in response to specific allergen
-immunodeficiency= often associated with genetic defect in barrier defence
-chronic inflammation

Question 10

What genetic defect of the skin is associated with eczema?

Answer 10

Disruption of filaggrin (structural protein in keratinocyte layer) which leads allergens being able to penetrate the skin
Allergens come into contact with APC-> generates Th2 immune response

Question 11

Why is eczema associated with dry skin?

Answer 11

Disruption of keratinocyte skin layer enables fluid to leave due to damage to skin barrier

Question 12

What is the treatment of eczema?

Answer 12

Avoid allergen (if known) 
Prevent itch-scratch cycle by using emoliants to lessen itch 
Prevent barrier defence breakdown= moisturisers overnight 
Treat any infection= antibiotic creams 
Treat chronic inflammation= steroids

Question 13

What is the difference between food allergy and food intolerance?

Answer 13

Allergy:
-symptoms associated with type 1 hypersensitivity
I.e. mouth itching/swelling/hives/angioedema
-life-threatening
-onset in 30 mins
-resolves quickly with treatment
-no tolerance

Intolerance:

• not IgE mediated
• not life-threatening
• onset >1hr
• longer lasting symptoms (abdo pain/discomfort/N+V/bloating/diarrhoea/headache)
• unpredictable
• can tolerate different amounts but usually threshold

Question 14

How do you manage food allergies?

Answer 14

Strict avoidance
Antihistamine if have mild symptoms
Andrenalin with significant symptoms
Medical alert

Question 15

How do you manage food intolerance?

Answer 15

Avoidance
Reintroduce slowly
-might be due to recent shedding of bowel brush border if had infection and can take time to regrow
-no medication