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FCP - Dermatology Week > Allergic Skin Disease > Flashcards

Allergic Skin Disease Flashcards

1
Q

What is an allergy?

A

Condition characterised by a hypersensitivity response to allergens
* Common cause of pruritus in small animals

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2
Q

Common triggers of allergy

A

Environmental allergens
Foods
Ectoparasites
Contact allergens
Micro-organisms (malassezia)
Drugs

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3
Q

Environmental allergen conditions

A

Environmental atopic dermatitis - dog
Feline atopic skin syndrome (FASS)
Equine atopic dermatitis

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4
Q

Food allergen conditions

A

Food-induced atopic dermatitis (FIAD) – dog
Feline food allergy (FFA) - cat
Equine food allergy

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5
Q

Ectoparasite allergen conditions

A

Flea allergic dermatitis
Insect bite hypersensitivity
Mite hypersensitivity

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6
Q

What is a hypersensitivity reaction?

A

Exaggerated immune system response to an antigen

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7
Q

Type I

A

Immediate
* Cross-linking of IgE molecules on mast cell surface by allergen
* Degranulation of mast cells
* Tissue inflammation

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8
Q

Type II

A

Antibody mediated cytotoxicity
* Destruction of target cell by effects of antibody and complement pathway

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9
Q

Type III

A

Imune-complex
* Antibody-antigen complexes
* Form locally in tissue when antibody in excess
* Circulate systemically if antigen in excess

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10
Q

Type IV

A

Delayed
* Cell mediated
* Sensitised mononuclear inflammatory cells release proinflammatory cytokines

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11
Q

What type of hypersensitivity is most common in allergic disease?

A

Type I - IgE
Causes mast cell degranulation

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12
Q

What is required fro allergic reaction?

A

Sensitisation of individual by repeated exposure to allergen
Subsequent exposure
* Immunologically excessive response
* Clinical disease

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13
Q

Environmental atopy dermatitis

A

Type I hypersensitivity involved in most cases
Acute lesions
* Lymphocytes classically follow Th2 pathway
* Produce IgE
Chronic lesions
* More complex pattern with Th1, Th2 and other T-cell responses

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14
Q

Causes of environmental atopic dermatitis

A

Aberrations in skin barrier
Dysregulation of microbiome

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15
Q

Mechanism of Sensitisation Phase

A
  1. Allergen crosses skin barrier
  2. Picked up by Langerhans cell
  3. Presented to T-helper cell
  4. Immunological response directed down Th2 route
  5. B cell produce IgE which is allergen specific
  6. Binds to mast cell ready for next exposure
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16
Q

Mechanism of Provocation Phase

A
  1. Allergen crosses skin barrier
  2. Picked up by Langerhans cell
  3. Triggers T-helper cell down Th2 route
  4. Tiggers production of IgE and cytokines
  5. Cytokine IL31 causes pruritus
    • Target for allergy therapy
  6. Allergen can also be met by IgE on mast cell
  7. Causes degranulation and release of inflammatory mediators
17
Q

cytokine IL31

A

Causes pruritus
Target for allergy therapy

18
Q

Clinical features of environmental atopic dermatitis

A

Very common
6mo-3yrs
Highly heritable
Chronic relapsing pruritus dermatitis - seasonal
Usually responsive to glucocorticoids

19
Q

Clinical signs of environmental atopic dermatitis

A

○ Initially erythema/papules
Self-induced alopecia/excoriations
Chronic changes
○ Affects esp ears/face, feet, carpi/tarsi, axillae/inguinum, ventrum, perineum

20
Q

Food-induced atopic dermatitis

A

Immunological reaction to dietary allergens
Pathogenesis is relatively unknown
Can occur at any age
Response to glucocorticoids is variable
Non-seasonal

21
Q

Feline Atopic Syndromes

A

Feline atopic skin disease (FASS)
Feline food allergy (FFA)

22
Q

Feline atopic skin disease (FASS)

A

Equivalent of environmental atopic dermatitis in dog
* Inflammatory/pruritic skin syndrome
* Likely associated with IgE to environmental allergens
* Usually young adult – 6mo-5y onset (occasionally older)
* Seasonal/ non-seasonal

23
Q

Feline food allergy (FFA)

A

Equivalent of food-induced atopic dermatitis in dog
* Can occur at any age (3mo+) but 27% cats <1yo
* Non-seasonal
* +/- GI/conjunctivitis/respiratory signs

24
Q

Cutaneous Reaction Patterns of cats

A
  1. Face, head, neck prurutius (FHN)
  2. Self-induced alopecia (SIA)
    Symmetrical
  3. Miliary dermatitis (MD)
  4. Eosinophilic granuloma couples (EGC)
25
Q

Equine atopic dermatitis

A

Horses suffer from a range of environmental allergens
* Type I hypersensitivity
* Less defined than in dogs/cats
Seasonal/non-seaosnal
Age of onset 1.5-6yrs
Often co-exist with insect-bite hypersensitivity

26
Q

Equine atopic dermatitis clinical signs

A

Pruritus
Urticaria - Oedematous wheals
Sometimes nodules (eosinophilic granulomas)
Lesion distribution poorly-defined
Generalised/localised lesions

27
Q

Ectoparasite allergies

A

Flea allergic dermatitis
Insect bite hypersensitivity
Mite hypersensitivity

28
Q

Flea allergic dermatitis

A

Common in dogs/cats
Type I & IV hypersensitivity to flea salivary antigens
Dogs
* Affects dorsal/caudal region of body
* Pruritus, self-trauma, chronic changes

Cats
* Any of the 4 cutaneous patterns

29
Q

Insect bite hypersensitivity

A
  • Culicoides in horses - ‘Sweet itch’
  • Culicoides in sheep - affects non-wooled areas
  • Mosquitoes in cats - affects face and pads
30
Q

‘Sweet itch’

A

Culicoides spp. hypersensitivity in horses
* Effects mane and tail
* Type I & IV hypersensitivity to midge salivary proteins

31
Q

Mite Hypersensitivity

A
  • In affected individuals -> increase pruritus from infestation
  • Potential reason for persistence of pruritus after parasite killed
  • E.g. Psoroptes (sheep), Sarcoptes (dog)
32
Q

Contact dermatitis

A

Uncommon
Type IV reaction
Sensitisation over a prolonged period of time
○ Plants, topical drugs/shampoos
○ Chemicals, cleaning products, rubber, plastic, leather, metal etc
Lesions only occur in contact areas

33
Q

Drug reactions

A

Any type of hypersensitivity
Variable pruritus
Common in antibiotics
* Potentiated sulphonamides

FCP - Dermatology Week (25 decks)

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