Allergy and the Skin

Question 1

What is the function of the immune system?

Answer 1

Defence against external and internal antigens

Question 2

What are some consequences of the immune system?

Answer 2

Intended destruction of antigens, incidental collateral damage of tissue

Question 3

What is hypersensitivity?

Answer 3

Immune response that causes collateral damage to self due to exaggeration of normal immune mechanisms

Question 4

What conditions is hypersensitivity the pathophysiological basis for?

Answer 4

Allergy, autoimmunity

Question 5

Why do allergies occur?

Answer 5

A person’s immune system reacts to normally harmless substances in the environment

Question 6

What are allergens?

Answer 6

A substance that causes an allergic reaction

Question 7

What two factors interact to cause allergies?

Answer 7

Genetics and the environment

Question 8

What are some factors that predispose to allergy?

Answer 8

Westernised countries, small family size, affluent urban homes, stable intestinal flora, high antibiotic use, low/absent helminth burden, good sanitation

Question 9

What kind of reaction occurs in a type 1 allergy?

Answer 9

Immediate reaction within minutes up to 2hrs after exposure

Question 10

What are some routes of exposure to allergens?

Answer 10

Skin contact, inhalation, ingestion, injection

Question 11

What is the history of a patient with a type 1 allergy?

Answer 11

Consistent reaction with every exposure to allergen

Question 12

What is the clinical presentation of an allergic reaction?

Answer 12

Urticaria, angioedema, wheezing/asthma, anaphylaxis

Question 13

What are some features of urticaria?

Answer 13

Very itchy, lesions appear within 1hr, last 2-6 hrs, also called hives/wheals/nettle rash

Question 14

What is angioedema?

Answer 14

Localised swelling of subcutaneous tissue/mucous membranes, non-pitting oedema, not itchy (unless associated with urticaria)

Question 15

What is anaphylaxis?

Answer 15

Severe, life threatening generalised or systemic hypersensitivity reaction

Question 16

What is anaphylaxis characterised by?

Answer 16

Rapidly developing life threatening problems with the airway (pharyngeal/laryngeal oedema), breathing (bronchospasm with tachypnoea) and circulation (hypotension and tachycardia)

Question 17

When should serum mast cell tryptase levels be measured?

Answer 17

During anaphylaxis

Question 18

What are some investigations that can be done for allergies?

Answer 18

Specific IgE (RAST), Challenge testing, Serum mast cell tryptase level, skin prick testing

Question 19

What are the benefits of skin prick testing?

Answer 19

Cheap and quick, results in 15-20 mins, specificity and sensitivity of 90+%

Question 20

Is there a risk of anaphylaxis with skin prick testing?

Answer 20

Yes- 1:3000

Question 21

When should challenge testing be done?

Answer 21

Only if skin prick test is negative

Question 22

What is the sensitivity and specificity of specific IgE (RAST) testing?

Answer 22

70-75%

Question 23

How can allergies be managed?

Answer 23

Allergen avoidance, block mast cell activation and its effects, anti-inflammatory agents, adrenaline autoinjectors, immunotherapy, medic alert bracelet

Question 24

What kind of drugs are used to prevent the effects of mast cell activation?

Answer 24

Anti-histamines

Question 25

How many adrenaline autoinjectors should patients be prescribed?

Answer 25

2 pens

Question 26

What are some anti-inflammatory agents used to treat allergies?

Answer 26

Corticosteroids

Question 27

What condition are adrenaline autoinjectors used to prevent?

Answer 27

Anaphylaxis

Question 28

How much adrenaline is pre-loaded in autoinjector pens?

Answer 28

300 micrograms for adults, 150 micrograms for children (new brand of injector has 500 micrograms for adults which is better dose)

Question 29

What is an example of a drug which blocks mast cell activation?

Answer 29

Sodium cromoglicate-mast cell stabiliser

Question 30

Are non-allergic reactions mediated by IgE?

Answer 30

No

Question 31

What are some forms of non-allergic reaction?

Answer 31

Direct mass cell degranulation (morphine, aspirin, NSAIDS), metabolic (lactose intolerance), toxic (scombroid fish toxin), Type IV hypersensitivity

Question 32

What are the features of type IV hypersensitivity?

Answer 32

Delayed hypersensitivity, antigen specific, T cell mediated, onset of reaction typically after 24-48hrs

Question 33

What is an example of a skin condition caused by type IV hypersensitivity?

Answer 33

Allergic contact dermatitis

Question 34

What are some routes of contact of substances that trigger non-allergic reactions?

Answer 34

Direct skin contact (preservatives within cosmetics), airborne contact (fragrance), injection (tattoos)

Question 35

What does the presentation of a non-allergic reaction depend on?

Answer 35

Contact and exposure

Question 36

What occurs in Patch testing?

Answer 36

Allergens prepared on Finn chambers, Finn chambers applied on the back and removed after 48hrs, readings taken at 48hrs and 96hrs

Question 37

What is the sensitivity and specificity of patch testing?

Answer 37

70-80%

Question 38

What is Irritant contact dermatitis?

Answer 38

Non-immunological process in which contact with agents abrades, irritates and traumatises the skin directly

Question 39

Does Irritant contact dermatitis require previous sensitisation?

Answer 39

No

Question 40

What are some examples of endogenous reactions?

Answer 40

Atopic eczema and psoriasis

Question 41

Are endogenous reactions an allergic response?

Answer 41

No

Question 42

What are some features of atopic asthma?

Answer 42

Dry skin and flexural, often associated with asthma and hayfever

Question 43

What occurs in psoriasis?

Answer 43

Scaly plaques on extensor surfaces of skin

Question 44

What are some ways to manage endogenous reaction and irritant contact dermatitis?

Answer 44

Irritant avoidance and minimisation, emollients, topical steroids, UV phototherapy, immunosuppressants