Allergy and the skin Flashcards
What is the definition of hypersensitivity?
Immune response that causes collateral damage to self
What are the routes for a type 1 allergy?
Skin contact
Inhalation
Ingestion
Injection
What are the different types of allergens?
Ingestion - nuts, seafood
Inhalation - pollen, house dust mite
Skin contact - latex, animal dander
Injection - bee sting, medication
What is the pathophysiology of hypersensitivity type 1?
Sensitisation: dendritic cells match to peanut specific T cells. This activates Th2 cells that release IL-4, IL-5 and IL-13, this stimulates B cells to produce peanut-specific IgE which bind to mast cells releasing histamines, leukotrines, cytokines and prostglandins
What is urticaria?
Very itchy
Lesions appear within 1 hour
Last 2-6 hours
Described as hives, wheals and like a nettle rash
What is angiodema?
Localkised swelling of subcutaneous tissue or mucous membranes
Non pitting oedema
Not itchy
What are the investigations for allergy?
History Specific IgE Skin prick Challenge test Serum mast clls tryptase level during anaphylaxis
What is the sensitivity of a skin prick?
Specificity and sensitivity 90+%
How can you manage an allergy?
Avoidance Anti-histamines Corticosteroids Adrenaline for anaphylaxis Block mast cell activation via sodium cromoglycate Immunotherapy Medical alert bracelet Information and education
What are some examples of non allergic reactions?
Non IgE mediated - coeliacs, eosinophilic gastroenteritis
Direct mast cell degranulation - morphine, aspirin and NSAIDs
Metabolic - lactose intolerance
Toxic - scombroid fish toxin
What is an example of a type 4 hypersensitivity allergy?
Allergic contact dermatitis/ eczema
What are some examples of allergens that can cause type 4 hypersensitivity?
Direct skin contact
Airbourne contact
Injection
What impact does the acivation of CD8+ cytotoxic T cells have on the skin?
Induces apoptosis of keratinocytes and production of cytokines and chemokines by skin resident cells leading to the recruitment of leukocyes to the skin
What is the management for contact dermatitis?
Allergen/ irritat avoidance Emollients Topical steroids UV phototherapy Immunosuppressants
