Allergic Skin Disease Flashcards

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1
Q

How can you distinguish oedema from cellular swelling?

A

Oedema indents, cellular doesnt

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2
Q

Define hypersensitivity disease

A

> clinical HYPERSENSITIVITY =
- objectively reproducible signs
- exposure to a defined stimulus
- at a dose normally tolerated by other individuals
no assumption of allergic immunological mechanisms eg. lactose intolerance due to lack of lactose enzyme, only in white caucasians; drug intolerance.
BUT may be initiated by immunological hypersensitivty, with a known mechanism, which is therefore ALLERGY.
- state of heightened reactivity to antigen
- specific immunological mechanisms
- may be induced or aggravated by non-immunological factors but must be initiated by them

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3
Q

Which hypersensitivity/allergic skin diseases are seen?

A
  • urticaria/angioedema syndrome
  • food “allergy”
  • contact allergy/dermatitis (rare)
  • atopic dermatitis
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4
Q

Which species commonly affected by wheals, urticaria/angioedema?

A

Horses

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5
Q

What is urticaria?

A

multiple wheals or hives (sign, not disease)
= circumscribed raised lesions caused by dermal oedema
- mid-superficial vessels dilated

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6
Q

What is angioedema?

A

marked localised subcut oedema if deeper vessels affected

- will move ventrally following gravity

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7
Q

Mechanism od urticaria/angioedema?

A

> mast cell activation

  • IgE dependent
  • IgE Independent (eg. complement) or completely non-immunological (heat/cold/pressure induced) seen in some horses [dermatographism]
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8
Q

is urticaria/angioedema in horses always itchy?

A

No!

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9
Q

Triggers for urticaria/angioedema?

A
  • iatrogenic substances
  • infections: systemic/focal
  • parasites/insects
  • diet
  • aeroallergens
  • contact allergens
    > other environmental/systemic disease/physical stimuli/hereditary/autoABs/idiopathic?
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10
Q

What types of urticaria/angioedema are recognised clinically?

A
  • acute
  • recurrent
  • chronic
  • seasonal or non-seasonal
  • may progress to crusting/sloughing
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11
Q

What are allergy tests available for?

A
  • mites
  • insects
  • pollens
  • moulds
    > though results may not be singificant!
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12
Q

What 2 forms of adverse reaction to food are possible? What subcategories exist and which are referred to as food hypersensitivity?

A

> IMmunological
- food allergy (IgE mediated or non-IgE mediated)
Non-Immunological
- food intolerance (idiosyncratic, pharmacological, metabolic, food poisoning)
^^^ both food hypersensitivity^^^
- Dietary indiscretion (scavenging, gluttony, pica)
- Food aversion (pysch avoidance or intolerance)

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13
Q

Is food allergy serology useful?

A

NO! No evidence that these tests work. Well marketed.

- no diagnositc value

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14
Q

How can food allergy be distinguished from atopic dermatitis?

A

Cant purely on PE - change diet and see what happens

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15
Q

Aetiology of atopic dermatitis?

A
  • skin barrier
  • IgE response and degree of allergen exposure
  • Skin and immune system - early exposure
  • environmental factors
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16
Q

What are the aspects of atopic dermatitis?

A
  • self-trauma (pruritis)
  • imparied skin barrier
  • microbial overgrowth
  • IgE sensitisation and response to allergen exposure
  • inflammation
    > viscous cycle!
17
Q

Clinical sings in the history indicative of atopic dermatitis?

A
  • age of onset 6m-3y
  • breed predisposition (westies, sharpei, labretriever, boxer, english setters)
  • no sex dispositions
  • pruritis, rashes, ear infection
  • time course
    > exclusion of other diseases: food hypersesntivity etc.
18
Q

Primary lesions of atopic dermatitis? Where is the worst itch and self-trauma?

A

None or erythema (diffuse or eyrthematous maculopapular rash)
- anything else = 2* lesions
> eyes, ears, jowls, ventral chest, feet, perianal, ventral abdomen (breed specific distributions)

19
Q

What is lichenification?

A

Thickening of skin 2* to self trauma

20
Q

Pathogenesis of ear infections with atopic dermatitis?

A
  • immunological derangement/cutaneous abnormaltities (skin barrier)
  • > 2* Staph pseudintermedius and malasezia pachydermatis infections (commensals)
  • > skin lesions and exacerbation of pruritis
  • > 2* trauma
21
Q

Diagnosis of atopic dermatitis?

A
  • hx
  • clinical signs
  • exclude r/o or resolve parasties, infections
  • investigate atopic food hypersensitivity
    > typical clinical signs, chronic pruritic skin disease, baseline itch present with infection r/o (Clinical Diagnosis)
22
Q

What do allergy tests measure? What 2 are available? How cna these be used?

A
  • Intradermal
  • Allercept serology
    > measures IgE levels, not necessarily indicative of clinical disease (normal dogs can be +)
    > management - avoidance and immunotherapy [successful in 50% cases] rather than definitive diagnosis. Supportive.
23
Q

Tx aim with atopic dermatitis?

A
  • reduce pruritis to an acceptable level
  • long term control as safely as possible
  • address trigger factors
  • individual treatment plan
24
Q

Diagnosis of cause of urticaria/angioedema?

A
  • avoidance and re-challenge

- for IgE mediated ONLY, demonstrate allergen specific IgE

25
Q

8 criteria for distinguishing stopic dermatitis in practice?

A
  1. age of onset <3y
  2. mostly indoor
  3. corticosteroid responsive pruritis
  4. chronic/recurrent yeast infeection
  5. affected front feet
  6. affeted pinnae
  7. non-affected ear margins
  8. non-affected dorso-lumbar regions