Allergy

Question 1

What is Allergy?

Answer 1

Type I Hypersensitivity Reaction (IgE Mediated) of the immune system to allergens.

Question 2

What is an Allergen?

Answer 2

A protein that the immune system recognises as foreign and potentially harmful, leading to an allergic immune response.

Question 3

What is Atopy?

Answer 3

A predisposition to having hypersensitivity reactions to Allergens - the tendency to develop conditions e.g. eczema, asthma, hay fever, allergic rhinitis and food allergies.

Question 4

Theory of Allergy.

Answer 4

Skin Sensitisation Theory -

1. Break in Infant’s Skin allows Allergens from environment to react with the immune system.
2. No contact from the GI tract - absence of GI exposure to the allergen.

Question 5

What inflammatory mediators are released during Mast Cell Degranulation? (3B)

Answer 5

A : Pre-Formed (Rapid Release) :

1. Histamine.
2. Tryptase.
3. Heparin.

B : Synthesised (Slow Release) :

1. Leukotrienes.
2. Prostaglandins.

Question 6

How are Hypersensitivities classified?

Answer 6

Coombs and Gell Classification.

Question 7

What is a Type I Hypersensitivity Reaction?

Answer 7

IgE antibodies to a specific allergen trigger mast cells (degranulation) and basophils to release Histamines and other Cytokines to cause an immediate reaction.

Question 8

What is a Type II Hypersensitivity Reaction?

Answer 8

IgG and IgM antibodies react to an allergen which causes activation of Complement System and direct damage to Local Cells.

Question 9

Examples of Type II Hypersensitivity Reactions (2).

Answer 9

1. Haemolytic Disease of the Newborn.

2. Transfusion Reactions.

Question 10

What is a Type III Hypersensitivity Reaction?

Answer 10

Immune complexes accumulate and damage local tissues.

Question 11

Examples of Type III Hypersensitivity Reactions (3).

Answer 11

1. SLE.
2. Rheumatoid Arthritis.
3. Henoch-Schonlein Purpur.

Question 12

What is a Type IV Hypersensitivity Reaction?

Answer 12

Cell-mediated hypersensitivity reaction caused by inappropriate activation of T-cells, causing inflammation and damage to local tissues.

Question 13

Examples of Type IV Hypersensitivity Reactions (2).

Answer 13

1. Organ Transplant Rejection.

2. Contact Dermatitis.

Question 14

What clinical features does Histamine cause?

Answer 14

1. Pruritus.
2. Vasodilation and Leakage - Hives, Angioedema, Hypotension.
3. Smooth Muscle Contraction - Bronchospasm, Wheezing.

Question 15

Investigations of Allergy (3).

Answer 15

1. Skin Prick Testing.
2. RAST (Radioallergosorbent Test). Testing.
3. Food Challenge Testing.

Question 16

Why are Skin Prick Tests and RAST Tests notoriously unreliable?

Answer 16

They assess sensitisation and not allergy.

Question 17

Which investigation is the gold-standard?

Answer 17

Food Challenge testing - but requires lot of time and resources.

Question 18

What is Skin Prick Testing? (4)

Answer 18

1. A patch of skin is selected, usually on forearm.
2. Select strategic allergen solutions e.g. peanuts, pollen and add a drop of each solution at marked points on the patch of skin with a water control and a histamine control.
3. Use a fresh needle to make a tiny break at the site of each allergen drop.
4. After 15 minutes, measure the size of the wheals.

Question 19

What is Patch Testing? (2)

Answer 19

1. A patch containing the allergen is placed on the patient’s skin.
2. Assess skin reaction 2-3 days later.

Question 20

What is Patch Testing most helpful in determining?

Answer 20

Allergic Contact Dermatitis in response to a specific allergen (not food allergies) e.g. latex, perfume, cosmetics, plants.

Question 21

What is RAST Testing?

Answer 21

Measure total and allergen-specific IgE quantities in the patient’s blood sample.

Question 22

What is the Food Challenge? (3)

Answer 22

1. Start with almost non-existent quantities diluted further in other foods.
2. Monitor kid very closely after exposure.
3. Specialist Unit.

Question 23

General Management of Allergy (3).

Answer 23

1. Establish Correct Allergen, Avoid and Prevent.
2. Prophylactic Antihistamines if Inevitable Contact.
3. Adrenaline Auto-Injector if Risk of Anaphylaxis.

Question 24

What is Immunotherapy?

Answer 24

Gradual exposure to allergens over months, with the aim of reducing reactions to certain foods/allergens.

Question 25

Medical Management of Allergen Exposure (4).

Answer 25

1. Antihistamines e.g. Cetirizine.
2. Steroids e.g. Prednisolone, Hydrocortisone.
3. IM Adrenaline in Anaphylaxis.
4. Close monitoring to ensure no progression to Anaphylaxis.