Allergy and Skin Flashcards
Main mediator in Type 1 hypersensitivity?
IgE
Main mediator in Type 2 hypersensitivity
IgG mediated cytotoxic hypersensitivity
Main mediator in Type 3 hypersensitivity
Immune complex
Main mediator in Type 4 hypersensitivity
Cell mediated
Skin example of type 4 hypersensitivity?
Allergic contact dermatitis, erythema, rash
Skin manifestations of type 1 hypersensitivity
urticaria, angioedema
Most common type of hypersensitivity associated with blood transfusions
Type 2
Most common conditions associated with type 3 hypersensitivity
necrotising vasculitis, glomerulonephritis,
rheumatoid arthritis,
SLE
What are the time limits for an allergic reaction to be classed as type 1?
seconds to 2 hours after allergen exposure
What makes the IgE that eventually binds to mast cells?
B cells
How long does urticaria typically last?
2-6 hours
Is angioedema pitting or non-pitting?
non-pitting
1st and 2nd line tests for type 1 hypersensitivity reactions
- IgE test
2. Prick test
1st line for type 4 hypersensitivity
Patch test
What to do if prick test is negative but you’re still convinced the patient has an allergy?
Challenge test
MoA of sodium cromoglycate?
Blocks mast cell activation thus stabilising them
1st, 2nd and 3rd line treatment for food allergy?
- antihistamine eg chlorphenamine
- prednisolone if antihistamine takes over 10min to work
- Adrenaline if still systematically unwell
How does adrenaline work?
Vasoconstricts blood vessels to bring blood pressure back to normal
Why is coeliac disease non-allergic?
Not mediated by IgE
Usual time frame of type 4 hypersensitivity?
24-48hrs
first line test for allergic contact dermatitis
patch test
Examples of irritant contact dermatitis?
Nappy rash, lip lick dermatitis, detergent, cosmetics, cement
Why is irritant contact dermatitis different to allergic contact dermatitis?
Not immune mediated, the irritants traumatise the skin directly and don’t require prior sensitisation
Best management for contact dermatitis?
AVOIDANCE, emollients, topical steroids, UV phototherapy, immunotherapy
How common is food allergy in children with moderate/severe eczema?
1 in 5
Main signs of anaphylaxis?
angiodema, colicky pain, tachycardia diarrhoea, vomiting, tachycardia, hypotension
Skin manifestations of type 3 hypersensitivity?
purpura, rash
Skin manifestations of type 2 hypersensitivity?
pemphigus/pemphygoid
