allergy and the skin Flashcards

1
Q

what is the function of the immune system

A

defence against external (micro-organisms) and internal antigens (cancer)

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2
Q

what is the consequence of the immune system

A

intended destruction of antigen and incidental collateral tissue damage

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3
Q

what is hypersensitivity

A

immune response that causes collateral damage to itself

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4
Q

what is type 1 hypersensitivity

A
  • IgE mediated
  • Ag induces cross linking of IgE bound to mast cells and basophils with release of vasoactive mediators
  • typical manifestations include systemic anaphylaxis and localised anaphylaxis such as hay fever, asthma, hives, food allergies
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5
Q

what is type 2 hypersensitivity

A
  • IgG mediated cytotoxic hypersensitivity
  • Ab directed against cell surface antigens mediates cell destruction via complement activation of ADCC
  • typical manifestations include blood transfusion reactions, erythroblastosis fettles and autoimmune haemolytic anaemia
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6
Q

what is type 3 hypersensitivity

A
  • immune complex mediated hypersensitivity
  • Ag-Ab complexes deposited in various tissue induce complement activation and ensuing inflammatory response mediated by massive infiltration by neutrophils
  • typical manifestations include localised Arthus reaction and generalised reactions such as serum sickness, necrotising vasculitis, glomerulonephritis, rheumatoid arthritis and systemic lupus erythematosis
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7
Q

what is type 4 hypersensitivity

A
  • cell mediated hypersensitivity
  • sensitised TH1 cells release cytokines that activate macrophages or Tc cells which mediate direct cellular damage
  • typical manifestations include contact dermatitis, tubercular lesions and graft rejection
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8
Q

what is an allergy

A

hypersensitivty disorder of the immune system. Allergic reactions occur when a persons immune system react to normally harmless substances in the environment.

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9
Q

what is the hygiene hypothesis

A

the immune system is no longer getting challenged and hence exaggerated reactions yo normal substances

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10
Q

what is a type 1 allergy

A
  • IgE mediated
  • Immune reaction - occurs within minutes to hours
  • Reproducable reaction
  • routes of exposure - skin contact, inhalation, ingestion and injection
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11
Q

what is the clinical presentation of a type 1 allergy

A

Urticaria

  • very itchy
  • lesions appear within one hour
  • lasts 2-6 spurs
  • ‘hives’, ‘wheals’

Angioedema

  • localised swelling of subcutaneous tissue or mucous membranes
  • non pitting oedema
  • not itchy
Nausea 
Vomitting
Diarrhoea 
Colicky abdominal pain 
Nasal itching 
Sneezing 
Rhinorrhoea 
Wheezing 

Anaphylaxis
- severe or life threatening hypersensitivity reaction

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12
Q

what investigations are done for a type 1 allergic reaction

A
  • history
  • skin prick
  • specific IgE
  • challenge test
  • serum mast cell tryptase level
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13
Q

how do you manage an type 1 allergic reaction

A
  • allergen avoidance
  • prevent effects of mast cell activation (anti histamines)
  • anti-inflammatory agent (corticosteroids)
  • adrenaline auto injector
  • block mast cell activation (mast cell stabilisers - sodium cromoglycate)
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14
Q

what is an adrenaline auto injector used for and what are its doses

A

its used for anaphylaxis and is preloaded adernaline syringe

adult = 300ug 
children = 150ug
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15
Q

what is a type 4 allergy

A
  • delayed hypersensitivity
  • antigen specific
  • T cell mediated
  • allergic contact dermatitis
  • onset of reaction typically after 12-24 hours
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16
Q

what is the pathophysiology of type 4 allergy

A
  1. sensitisation - allergens penetrate the epidermis and are taken up by APCs of the skin (langerhans). B cells migrate to draining lymph nodes where they present the allergens to bot CD8 and CD4 T cells. Recirculate through the blood
  2. elicitation - some pathogens applied to the skin and is taken up APC and present allergens to specific T cells. The T cells activated and recruits more T cells from the draining lymph nodes and produce cytokines and chemokines which leads to
17
Q

what is irritant contact dermatitis

A
  • non immunological process
  • contact with agents that abrade, irritate and traumatise the skin directly
  • doesn’t require prior sensitisation
  • pattern depends on exposure
18
Q

how do you manage irritant contact dermatitis

A
  • allergen/irritant avoidance
  • allergen/irritant minimisation
  • emollients
  • topical steroids
  • UV phototherapy
  • immunosuppressants