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DERMATOLOGY > Allergy > Flashcards

Allergy Flashcards

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1
Q

What is the definition of hypersensitivity?

A

An immune response that causes collateral damage to self

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2
Q

What cell or antibody mediates Type I Hypersensitivity?

A

IgE

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3
Q

What cell or antibody mediates Type II Hypersensitivity?

A

IgG (mediates Cytotoxic hypersensitivity)

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4
Q

What cell or antibody mediates Type III Hypersensitivity?

A

Immune complex

antigen-antibody complex

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5
Q

What mediates Type IV Hypersensitivity?

A

T Cell-mediated

TH1 cells release cytokines to activate macrophages and Tc cells which cause direct cellular damage

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6
Q

How does IgE cause Type I Hypersensitivity?

A
  • Antigen induces crosslinking of IgE bound to mast cells and basophils
  • causes degranulation and releases vasoactive mediators
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7
Q

How does IgG cause Type II Hypersensitivity?

A
  • Antibody is directed against antigens on cell

- cell is destructed by either complement activation or ADCC

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8
Q

What is ADCC?

A

Antibody-dependent cell-mediated cytotoxicity

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9
Q

How does the immune complex cause Type III Hypersensitivity?

A
  • complex is deposited in various tissues
  • complement activation
  • massive neutrophil migration
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10
Q

Give an example of a typical manifestation of a Type I Hypersensitivity reaction?

A
  • Anaphylaxis
  • Local anaphylaxis
    e. g. hay fever, asthma, eczema, hives, food allergy
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11
Q

Give an example of a typical manifestation of a Type II Hypersensitivity reaction?

A
  • blood transfusion reaction

- autoimmune haemolytic anaemia

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12
Q

Give an example of a typical manifestation of a Type III Hypersensitivity reaction?

A
  • Localised e.g. Arthus reaction

- Generalised e.g. necrotising vasculitis, rheumatoid arthritis, Systemic lupus erythematosus

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13
Q

Give an example of a typical manifestation of a Type IV Hypersensitivity reaction?

A
  • Contact dermatitis
  • Graft rejection
  • Tubercular lesions
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14
Q

What causes an allergy?

A

An allergen

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15
Q

What is the “hygiene hypothesis”?

A

The thought that developing countries have less allergies as they are more exposed to an allergic environment.

Developed countries have higher levels of antibiotic use and better sanitation => develop more allergies.

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16
Q

How long after exposure does a Type I reaction occur?

A

Immediate reaction - occurs within minutes and up to 2 hours after exposure to allergen

17
Q

What routes of exposure can provoke a Type I reaction?

A

skin contact
inhalation
ingestion
injection

18
Q

Will a patient react the same way with every exposure to the allergen that provoked a Type I reaction?

A

Yes

reaction is consistent with every exposure

19
Q

Give examples of Type I allergens which can be ingested

A

Nuts

Seafood

20
Q

Give examples of Type I allergens which can be inhaled

A

Pollen

House dust mite

21
Q

Give examples of Type I allergens which come into contact with the skin

A

Latex

Animal Dander

22
Q

Give examples of Type I allergens which can be injected

A

Bee/wasp sting

Medication

23
Q

How does Urticaria usually present clinically?

A
  • Very itchy
  • Lesions appear within 1 hour
  • Lasts 2-6 hours, sometimes 24 hours

“hives”, “wheals”, “nettle rash”

24
Q

How does angioedema usually present clinically?

A
  • Localised swelling of subcutaneous tissue or mucous membranes
  • Non pitting oedema
  • Not itchy
25
Q

What investigations can be done in the case of a Type I reaction?

A
  • Specific IgE
  • Skin prick or prick-prick testing
  • Challenge test (only if SPT negative)
  • Serum mast cell tryptase level (during anaphylaxis)
26
Q

What is the risk of anaphylaxis during skin prick tests?

A

1:3000

27
Q

What medication can be used to manage Type I allergic reactions?

A
  • Anti-histamines
    Prevent effects of mast cell activation
  • Corticosteroids
    Anti-inflammatory
  • Adrenaline auto injector (for anaphylaxis)
  • Sodium Cromoglycate
    mast cell stabilisers => block mast cell activation
28
Q

Aside from medication, what other forms of management are there for Type I allergic reactions?

A
  • Allergen avoidance
  • Immunotherapy
  • Medic Alert bracelet
  • Information and Education
29
Q

What strength of adrenaline auto-injector should be prescribed for adults and for children?

A

300µg adults

150µg children

30
Q

How long after exposure does a Type IV reaction occur?

A

24-48 hrs

31
Q

Give examples of Type IV allergens which come into direct contact with the skin

A

preservatives in cosmetics

rubber accelerators

32
Q

Give examples of Type IV allergens which are responsible for airbourne contact

A

fragrances

plants

33
Q

Give examples of a Type IV allergen which is injected

A

Tattoo

34
Q

What are the chambers on patch testing called and where are they applied?

A

Finn chambers

applied on the back

35
Q

When are the patch tests removed and when are the readings taken?

A

Removed after 48 hours

Readings at 48 and 96 hours

36
Q

Other than allergy, what can be the cause of dermatitis?

A

Endogenous

Irritant

37
Q

What is irritant contact dermatitis?

A
  • Non-immunological process
  • Pattern depends on exposure
  • Contact with agents that irritate skin directly
38
Q

Give an example of an endogenous form of dermatitis?

A

Atopic eczema

  • Dry skin and flexural
  • Often associated with asthma and hayfever

DERMATOLOGY (18 decks)

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