Allergic disease

Question 1

Define allergy

Answer 1

Hypersensitivity reaction initiated by immune mechanisms

Question 2

Define atopy

Answer 2

Tendency to produce IgE in response to low doses of allergens

Question 3

Define anaphylaxis

Answer 3

Reaction initiated by exposure to a defined stimulus at a dose tolerated by normal subjects

Question 4

Describe hypersensitivity type 1

Answer 4

IgE in response to SOLUBLE ANTIGEN.

Degranulation of mast cells and eosinophils

e.g. allergic rhinitis, asthma, anaphylactic shock

Question 5

Describe hypersensitivity type 2

Answer 5

IgG or IgM in response to ANTIGEN ON SURFACE OF CELL

Tissue specific e.g. Graves, Myasthenia gravis

Cell destruction via formation of MAC (membrane attack complex) as part of complement system

Question 6

Describe hypersensitivity type 3

Answer 6

IgG in response to SOLUBLE ANTIGEN

Non tissue specific. Will get tissue damage where immune complex is.

e.g. SLE, RA

Question 7

Describe hypersensitivity type 4

Answer 7

T cell mediated.

Th1 and Th2: Macrophage activation in response to SOLUBLE ANTIGEN

CTL: Cytotoxicity in response to ANTIGEN ON SURFACE OF CELL

Response will be delayed due to time needed to recruit T lymphocytes

e.g. Coeliac, contact dermatitis, chronic asthma, chronic allergic rhinitis

Question 8

How to diagnose anaphylaxis in person with no known allergies

Answer 8

Hives/pruritis/flushing/swollen mouth

+ at least one of

• Reduced BP
• Respiratory compromise (dyspnoea, wheeze, stridor, etc)

Question 9

How to diagnose anaphylaxis in person with known allergies

Answer 9

Hives/pruritis/flushing/swollen mouth
+
-Reduced BP
-Respiratory compromise (dyspnoea, wheeze, stridor, etc)
-Persistent GI symptoms (vomiting, abdominal pain)

OR

-Reduced BP (>30% decrease from baseline systolic BP)

Question 10

Management of anaphylaxis

Answer 10

• Lie patient down or sit up
• Monitors and assess O2, assess ABC
• Adrenalin IM
• Salbutamol/Budenoside nebuliser
• Fluids IV
• Chlophenaramine and hydrocortisone IV
• Serum tryptase

Question 11

Given an example of a non-IgE mediated food allergy

Answer 11

Coeliacs.

T cell mediated, gluten interacts with T cells in gut lumen. Loss of normal villi, infiltration of T-cells into epithelial layer & lamina propria,

Question 12

Given an example of a mixed IgE and non-IgE mediated food allergy

Answer 12

Eosinophilic oesophagitis

Ingesting allergen provoke T cell mediated response. Eosinophils invade oesophagus mucosa.

May lead to narrowing/stricture of the oesophagus in severe cases.