Allergy and the skin

Question 1

Briefly outline the immunopathology of Type 1 hypersensitivity.

Answer 1

Antigen is presented by dendritic cells to specific T cells; these T cells undergo differentiation to Th2 cells and “help” B cells to make antibody against the antigen; antibody becomes bound to mast cell receptors; on subsequent encounter with antigen, receptor cross-linking leads to mast cell degranulation and release of mediators

Question 2

Define anaphylaxis. What are the manifestations?

Answer 2

Severe, life-threatening, systemic allergic reaction.

Airway oedema, bronchospasm, hypotension, tachycardia, skin/mucosal changes

Question 3

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

Answer 3

70-75%

Question 4

If a skin-prick test is negative, what should be carried out?

Answer 4

Challenge test (under close supervision)

Question 5

What is the volume of adrenaline contained within an autoinjector for adults and children respectively?

Answer 5

300ug

150ug

Question 6

What is the gold standard in testing for allergic contact dermatitis?

Answer 6

Patch testing

Question 7

How does irritant contact dermatitis differ from allergic?

Answer 7

Non immune-mediated; caused by (repeated) exposure to agents which directly traumatize the skin

Question 8

How is allergic/irritant skin disease managed?

Answer 8

Allergy avoidance/minimisation 
Emollients
Topical steroids
(phototherapy)
(immunosuppressants)