Allergic Skin Disease

Question 1

How can you distinguish oedema from cellular swelling?

Answer 1

Oedema indents, cellular doesnt

Question 2

Define hypersensitivity disease

Answer 2

> 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

Question 3

Which hypersensitivity/allergic skin diseases are seen?

Answer 3

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

Question 4

Which species commonly affected by wheals, urticaria/angioedema?

Answer 4

Horses

Question 5

What is urticaria?

Answer 5

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

Question 6

What is angioedema?

Answer 6

marked localised subcut oedema if deeper vessels affected

- will move ventrally following gravity

Question 7

Mechanism od urticaria/angioedema?

Answer 7

> mast cell activation

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

Question 8

is urticaria/angioedema in horses always itchy?

Answer 8

No!

Question 9

Triggers for urticaria/angioedema?

Answer 9

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

Question 10

What types of urticaria/angioedema are recognised clinically?

Answer 10

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

Question 11

What are allergy tests available for?

Answer 11

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

Question 12

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

Answer 12

> 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)

Question 13

Is food allergy serology useful?

Answer 13

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

- no diagnositc value

Question 14

How can food allergy be distinguished from atopic dermatitis?

Answer 14

Cant purely on PE - change diet and see what happens

Question 15

Aetiology of atopic dermatitis?

Answer 15

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

Question 16

What are the aspects of atopic dermatitis?

Answer 16

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

Question 17

Clinical sings in the history indicative of atopic dermatitis?

Answer 17

• 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.

Question 18

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

Answer 18

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

Question 19

What is lichenification?

Answer 19

Thickening of skin 2* to self trauma

Question 20

Pathogenesis of ear infections with atopic dermatitis?

Answer 20

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

Question 21

Diagnosis of atopic dermatitis?

Answer 21

• 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)

Question 22

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

Answer 22

• 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.

Question 23

Tx aim with atopic dermatitis?

Answer 23

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

Question 24

Diagnosis of cause of urticaria/angioedema?

Answer 24

• avoidance and re-challenge

- for IgE mediated ONLY, demonstrate allergen specific IgE

Question 25

8 criteria for distinguishing stopic dermatitis in practice?

Answer 25

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