Overview of canine atopic dermatitis Flashcards
(37 cards)
Define canine atopic dermatitis
Genetically predisposed inflammatory & pruritic allergic skin disease with characteristic clinical features, associated with IgE antibodies most commonly to environmental allergens
Which allergens might cause CAD?
Allergens include house dust mites, pollens and mould spores in the environment and food allergens fed to the dog
10-30% of cases have NO detectable allergen-specific IgE for environmental allergens, this is termed…?
Atopic like dermatitis
Describe the 4 main features in the pathogenesis of CAD
- Cutaneous inflammation and pruritis
- Defective skin barrier function
- Microbial colonisation
- Other flare factors
Which hypersensitivities are involved in CAD?
Type 1 = Immediate reactions
Type 4 = delayed reactions
Describe type 1 hypersensitivity reactions
- IgE bound to mast cells
- Allergen bound by IgE causes mast cell degranulation
- Products of mast cell degranulation cause tissue inflammation and pruritis
Describe type 4 hypersensitivity reactions
- TH2 bias
- Allergen peptides presented to T-cells by langerhans cells
- Induce clonal expansion
- T-cells produce pro-inflammatory cytokines which cause tissue inflammation and pruritis
- T-cells produce cytokines that direct B-cells to produce IgE
What are the presenting signs of CAD?
Most common clinical signs are pruritus, recurrent pyoderma, recurrent otitis, seborrhoea, alopecia and occasionally urticaria
Describe the defective barrier seen in CAD
- Leaky skin – water gets out – microbes and allergens can penetrate more easily
- Increased transepidermal water loss (TEWL)
- Wide intercellular spaces between corneocytes
- Disorganised & fragmented lipid matrix
- Decreased levels of certain proteins and lipids in some breeds
Dogs with cAD show increased carriage of which bacteria?
Staphylococcus spp
How does microbial colonisation affect CAD
- Increased binding sites (due to inflammation)
- Reduced lipids and other proteins (barrier function)
- Damage to skin surface (self trauma)
- Dysbiosis: changed patterns of bacterial colonisation on the skin - imbalance
What are Atopic flares?
VERY common to see secondary staphylococcal pyoderma and otitis and Malassezia dermatitis in cases of CAD
Bacteria and yeast induce further inflammation and pruritus that is often not alleviated by specific anti-pruritics (e.g., lokivetmab or oclacitinib)
Describe the ‘vicious cycle’ of CAD
Inflammation -> Skin thickening -> increased antigen penetration and presentation -> reduced barrier -> secondary infection ->
What are the common causes of flares in CAD?
- Bacteria and yeast 2˚ infection
- Increase in allergen through seasonal changes or changes in environment
- Fleas, scabies or other ectoparasite infestation
- Reduction of therapy by owner / vet
Clinical diagnosis of CAD is based on which factors?
Compatible history
Clinical signs
Exclusion of differential diagnoses
There are no pathognomonic signs!
Describe some typical features of a history that indicate CAD
- Pruritus seasonal or perennial or both
- Main clinical sign
- Pruritus precedes skin lesions
- 75% of dogs develop signs <3 years (up to 6 years)
- Food allergy more commonly starts <1 year - Certain breeds predisposed, but may occur in any breed or cross
- certain breeds may have certain distribution
- may have affected relatives
- no sex predilection - History is key: cannot rely on clinical signs
What are the main clinical signs of CAD?
- PRURITIS: includes scratching, rubbing, chewing, excessive grooming or licking, scooting, and/or head shaking
- Primary lesions may also include erythema +/-papules
List some secondary lesions seen in CAD
Otitis
Lesions due to pruritus
- Alopecia
- Excoriations
- Salivary staining
- Lichenification
- Pustules, epidermal collarettes and crusts
- Hyperpigmentation
Describe the distribution of CAD lesions
- Face and chin
- Periorbital areas
- Ears – pinnal and meatal skin (but not the pinnal margins)
- Elbow creases
- Feet: dorsal interdigital spaces and plantar/palmar surfaces
- Ventral abdomen (and axillae)
- Perianal area (anal gland disease only in some)
Is a bilaterally symmetrical disease and inside-out disease or an outside-in disease?
Inside out e.g. systemic diseases
Name an example of an outside-in disease
Infections and infestations
List the 7 of Favrot’s criteria for CAD
- Onset of signs under three years of age
- Dog living mostly indoors
- Glucocorticoid-responsive pruritus
- Pruritus sine materia at onset i.e. pruritis without lesions at onset
- Affected front feet and/ or ear pinnae
- Non-affected ear margins
- Non-affected dorso-lumbar area
List some DDx for pruritis
- Ectoparasites: sarcoptic mange, cheyletiellosis, flea infestation and hypersensitivity, trombiculiasis, pediculosis, otodectic mange & some cases of demodicosis
- Allergic skin disease e.g. contact dermatitis
- Microbial infection (2˚ to another problem): Bacterial pyoderma
- Malassezia dermatitis (rarely dermatophytosis)
- Pemphigus foliaceus
- Epitheliotropic lymphoma
How can you exclude ectoparasites as a DDx?
- Flea combing & Wet paper test
- Scale exam
- Acetate tape strips
- Hair plucks
- Skin scrapes
- Treatment trials
