Type 4 hypersensitivity reaction

Question 1

Type IV hypersensitivity

Answer 1

Delayed reaction

Onset typically after 24-48 hours

Question 2

Pathophysiology

Answer 2

T cell mediated

Generation of specific T cells and memory T cells

Question 3

Examples

Answer 3

Contact dermatitis
Graft rejection
Psoriasis
Poison ivy
Diabetes
Sarcoidosis
TB

Question 4

Direct skin contact allergens

Answer 4

Preservatives within cosmetics

Question 5

Airborne contact allergens

Answer 5

Fragrance, plants

Question 6

Injections allergens

Answer 6

Tattoo

Question 7

Clinical presentation

Answer 7

Very distinctive rash pattern

Think about where the external antigen is on the body e.g. an elastoplast

Question 8

Investigations

Answer 8

Patch test - gold standard, allergens placed on patients back for 48 hours. Readings done at 48 hours and 96 hours.

Question 9

Management

Answer 9

Allergen avoidance 
Emollients 
Topical steroids 
UV phototherapy 
Immunosuppressants