Dermatology Test Questions - Canine & Feline Pruritis Flashcards
What is a papule?
Small solid elevation of skin less than 1 cm in diameter
Larger lesions are called plaques

Pustule (pimple)
Small circumscribed elevation of epidermis filled with pus
Crust (scab)
Adherence of dried exudate, serum, pus or blood to the skin surface
Epidermal collarette (scaly ring)
Peeling keratin arranged in a circle
Scale (flake, dandruff)
Cluster of corneocytes, which have retained a large degree of cohesion with one another and detach as such from the surface of the stratum corneum
4 goals of a skin biopsy
- Establishment of a definitive diagnosis
- Rule out other diseases
- Prioritize differential diagnoses
- Predict prognosis
Pathogenesis for Canine atopic (allergy) dermatitis (Type of reaction, route of exposure)
-> Older paradigm implied an immunological defect (inside-out theory)
• IgE-mediated, immediate hypersensitivity reaction (type I)
• Cell-mediated, delayed hypersensitivity reaction (type IV)
4 routes of exposure to environmental allergens
1. Percutaneous +++
2. Inhalation
3. Ingestion
4. conjunctival
(More recently, a primary defect in the skin barrier function has been recognized (outside-in theory))
Canine atopic dermatitis - typical lesion & distribution (11)
Face Ear pinnae, Front feet
Ventral neck, axillae, inguinae, ventral abdomen, perineum, ventral tail, flexural and medial aspects of extremities
Cutaneous adverse food reaction (CAFR) - pathogenesis (Type of reaction, route of exposure)
• Immune-mediated CAFR
IgE-mediated, immediate hypersensitivity reaction (type I)
Type III hypersensitivity reaction (immune-complex deposition)
Cell-mediated, delayed hypersensitivity reaction (type IV) 1
Route of exposure to trophallergen: ingestion
• Non immune-mediated (food intolerance)
Cutaneous adverse food reaction (CAFR) - typical lesion & distribution (4)
Face
Ear pinnae
Feet
Perianal area?
Cutaneous adverse food reaction (CAFR) - diagnosis
Relies primarily on the patient’s signalment, clinical signs and disease history and not on a laboratory test
Dietary restriction-provocation trial
Canine atopic dermatitis - diagnosis (2)
Relies primarily on the patient’s signalment, clinical signs and disease history and not on a laboratory test
Use most recent criteria for diagnosis of CAD (Favrot, 2010)
Flea allergy dermatitis - pathogenesis
Type of reaction, route of exposure
IgE-mediated, immediate hypersensitivity reaction (type I)
Cell-mediated, delayed hypersensitivity reaction (type IV)
Jones-Mote-type hypersensitivity (JMH, involves basophils)
1 route of exposure to flea salivary allergen: flea bite
Flea allergy dermatitis - distribution (3)
Dorso-lumbar area
Base of the tail
Medial and caudal thighs
Flea allergy dermatitis - diagnosis (6)
Signalment, clinical signs and disease history
Presence of fleas and/or flea dirt
Flea combing
Intradermal test (flea salivary allergen) Immunoglobulin E serum test (flea salivary allergen)
Parasiticidal therapeutic trial
Scabies - pathogenesis (type of reaction, method of infection)
Hypersensitivity reaction causes severe pruritus (sudden onset)
Puppy, kittens, young animals, poor hygiene Immunosuppression in adults
Exposure to wildlife (coyotes, red foxes, grey wolves, bears)
Exposure to other pets (breeding/boarding facilities, groomers, shows)
Contagion to owners (papular rash on forearms, abdomen)
Contagion to other dogs and cats in contact
Scabies - typical lesion & distribution (3)
Typical lesion: crust
Margin of the pinnae
Hock
Elbow
Scabies - diagnosis (4)
Positive pinnal-pedal reflex (Sensitivity 82%, specificity 94%, uncommon false positives: canine atopic dermatitis, otitis)
Positive superficial skin scrapings (parasites will NOT be found in 50-80-% of case, recovery of Sarcoptes eggs or fecal pellets is diagnostic)
Immunoglobulin G serum test (sensitivity 92%, specificity 96%, not available in Canada)
Parasiticidal therapeutic trial (« scabies incognito »)
Cheletielliosis - epidemiology
(mites) Puppies, kittens, young animals, poor hygiene
Immunosuppression in adults
Contagious
Potentually zoonotic
Cheletielliosis - typical lesion & distribution (1)
Typical lesion: scale
Dorsum
Cheletielliosis - diagnosis (3)
Superficial skin scraping
Acetate tape preparation
Parasiticidal therapeutic trial
Favrot`s criteria for CAD diagnosis (Canine Atopic Dermatitis)
Combination of any 5/8 criteria:
1. Onset of clinical signs under 3 years of age (>< food allergy, at any age)
2. Dog living mostly indoors
3. Glucocorticoid-responsive pruritus
4. Alesional pruritus at onset (pruritus without macroscopically visible clinical lesions)
5. Affected front feet
6. Affected ear pinnae
7. Non-affected ear margins (>< scabies)
8. Non-affected dorso-lumbar area (>< flea allergy dermatitis)
Miliary Dermatitis - description
(pattern) Small crusts, papules and erosions
Miliary means “like millet seeds”
Often localized to dorso-lumbar area and pre-aural region
May be generalized
Miliary Dermatitis - Differential diagnosis (5)
Allergy (flea allergy dermatitis (FAD) > feline atopic dermatitis, cutaneous adverse food reaction CAFR)
Ectoparasitic infestation
Dermatophytosis
Adverse drug reaction (face and head, methimazole, propanolol)
Idiopathic
Miliary Dermatitis - Diagnosis (8)
Skin scraping Acetate tape preparation Flea combing Wood's lamp examination Dermatophyte culture Parasiticidal therapeutic trial Dietary restriction-provocation trial Intradermal test, immunoglobulin E serum test
Symmetrical Alopecia - Description
Bilaterally symmetrical alopecia
Often localized to dorso-lumbar area and ventral abdomen, but can also affect limbs and flanks
Head and neck spared
Non-inflammatory (no other skin lesions)
Symmetrical Alopecia - Differentials (5)
Allergy (CAFR (Cutaneous adverse food reaction) > feline atopic dermatitis, FAD) Ectoparasitic infestation (e.g. Fleas)
Dermatophytosis
Psychogenic (psychological origin)
Paraneoplastic Endocrinopathy (rare) Idiopathic
Symmetrical Alopecia - Diagnosis (9 ways to help achieve)
Skin scraping Acetate tape preparation Flea combing Wood`s lamp examination Dermatophyte culture Parasiticidal therapeutic trial Dietary restriction-provocation trial Intradermal test, immunoglobulin E serum test Dermatohistopathology (lack of dermal inflammation is not a good indicator of psychogenic alopecia)
Eosinophilic Dermatoses - General Information/Using the term
Avoid using the name Eosinophilic granuloma complex clinically and histopathologically as it is an inconsitent mixture of clinical and histopathological terms
The 2 different forms of this cutaneous pattern: (1. Papule/ plaque / nodule / edema 2. Ulcer)
Have the same underlying causes
Have a common histoptahological feature: an eosinophilic cell infiltrate in the dermis
Can be observed in the same cat concurrently
Eosinophilic Dermatoses - Description (2 parts)
- Papule/ plaque / nodule / edema
Variable pruritus and pain
Papules or coalescing, firm, flat-topped erythematous and moist plaques, often localized to the ventral abdomen
Linear, vertical and firm lesions seen on caudal thighs, more rarely on the neck, lateral thorax and thoracic limbs
Firm nodule found in oral cavity (tongue, palate). May become ulcerated. May cause halitosis, partial anorexia, dysphagia and ptyalism
Pododermatitis with ulcerated or edematous footpads and interdigital erythema
Edema of lower lip or chin - Indolent ulcer
Non-pruritic and painless
Usually located on midline of upper lip or adjacent to canine upper teeth. May affect philtrum (between nose & upper lip)
Often unilateral, sometimes bilateral
Size varies from 2 mm - 5 cm, enlarges progressively
Eosinophilic Dermatoses - Differentials (5)
Allergy (Feline atopic dermatitis, CAFR, FAD)
Ectoparasitic infestation
Neoplasia (plaque = cutaneous lymphoma, mast cell tumor, mammary tumor metastases ; ulcer = squamous cell carcinoma)
Viral, fungal and bacterial dermatosis
Idiopathic
Eosinophilic Dermatoses - Diagnosis (8)
Skin scraping Acetate tape preparation Flea combing Parasiticidal therapeutic trial Dietary restriction-provocation trial Intradermal test, immunoglobulin E serum test Skin cytology Dermatohistopathology PCR (viral diseases)
ECDHN - Description
Erosive/crusting dermatosis of head/neck
Cat self-inflicts severe and spectacular lesions on the head and neck
Very pruritic and striking in appearance
Crusts, erosions, ulcers
ECDHN - Differentials (5)
Erosive/crusting dermatosis of head/neck
Allergy (CAFR, feline atopic dermatitis, FAD)
Ectoparasitic infestation
Viral dermatosis (herpesvirus , calicivirus, FeLV; a history of sneezing, ocular or nasal discharge may aid in providing a clue)
Néoplasia
Idiopathic
ECDHN - Diagnosis (9)
Erosive/crusting dermatosis of head/neck
Skin scraping Acetate tape preparation Flea combing Parasiticidal therapeutic trial Dietary restriction-provocation trial Intradermal test, immunoglobulin E serum test Skin cytology Dermatohistopathology PCR (viral diseases)
SOLC - Description
Spontaneously occurring large crusts
Large and thick crusts
Often localized to the face
SOLC - Differentials (5)
Spontaneously occurring large crusts
Allergy (Feline atopic dermatitis, CAFR, FAD) Ectoparasictic infestation
Dermatophytosis
Auto-immune skin disease (Pemphigus foliaceus)
Neoplasia
SOLC - Diagnosis (9)
Spontaneously occurring large crusts
Skin scraping Acetate tape preparation Flea combing Wood`s lamp examination Dermatophyte culture Parasiticidal therapeutic trial Dietary restriction-provocation trial Intradermal test, immunoglobulin E serum test Skin cytology (look for acantholytic cells) Dermatohistopathology (look for acantholytic cells)
Seasonality of pruritus - 1. Year-round pruritus
(4 differentials)
Scenario # 1 | Year-round pruritus
• Atopic dermatitis (involved environmental allergens: house dust and storage mites, epidermals, moulds)
• Atopic-like dermatitis
• Cutaneous adverse food reaction
• Non-seasonal ectoparasitic infestation (scabies, cheletiellosis, otoacariosis)
Seasonality of pruritus - 2. Warm weather seasonal pruritus (5 differentials)
- Atopic dermatitis (involved environmental allergens: pollens)
- Atopic-like dermatitis
- Flea allergy dermatitis
- Mosquito bite hypersensitivity
- Warm weather seasonal ectoparasitic infestation (flea infestation, trombiculosis, Pelodera dermatitis)
Seasonality of pruritus - 3. Year-round pruritus with warm weather exacerbation (5 differentials)
- Atopic dermatitis (involved environmental allergens: house dust and storage mites, epidermals, moulds, pollens)
- Atopic-like dermatitis
- Cutaneous adverse food reaction
- Flea allergy dermatitis
- Ectoparasitic infestation
Seasonality of pruritus - 4. Year-round pruritus with winter exacerbation (3 differentials)
- Atopic dermatitis (involved environmental allergens: house dust and storage mites, epidermals, moulds)
- Atopic-like dermatitis
- Winter seasonal ectoparasitic infestation (pediculosis - body lice)
Seasonality of pruritus - 5. Year-round pruritus, initially warm weather seasonal (3 differentials)
- Atopic dermatitis (involved environmental allergens: house dust and storage mites, epidermals, moulds, pollens)
- Atopic-like dermatitis
- Ectoparasitic infestation
Seasonality of pruritus - 6. Unknown seasonality (5 differentials)
- Atopic dermatitis (involved environmental allergens: ?)
- Atopic-like dermatitis
- Cutaneous adverse food reaction
- Flea allergy dermatitis
- Ectoparasitic infestation
Seasonality of pruritus - Practical implications
- In any pruritic patient, the first intervention should consist of ruling out parasitic causes
- Deep skin scrapings can rule out demodicosis
- However, some mite infestations (e.g. Sarcoptes) might be missed on superficial skin scrapings, trichograms and acetate tape preparations
- If a scabies is suspected, a parasiticidal therapeutic trial should be undertaken
- Fleas can be ruled in or out on the basis of a history of flea control, response to flea control or finding evidence of flea infestation via flea combing
- Flea control practices will also rule out louse infestations
Dietary restriction-provocation trial Step 1 – Restriction (describe 4 steps)
Step 1 – Restriction
1. Slowly introduce restriction diet!
• 1 meal of new food followed by 1 meal of old food
• Both types of food at the same time
2. Restriction diet is to be fed exclusively!
• No treats, rawhides
• No flavored medications/toothpaste
3. Duration of trial: 6-10 weeks
4. If pruritus is decreased by at least 50% during this time, a diagnosis of adverse food reaction can be presumed
Dietary restriction-provocation trial Step 2 – Provocation (describe 4 steps)
Step 2 – Provocation
- Reintroduce previous food
- If previous food contains offending allergen, pruritus should resume within 14 days
- May be unacceptable to some pet owners
- Does not differentiate between mechanisms of adverse food reaction (immunologic vs. non-immunologic adverse food reaction) but establishes a relationship between certain ingredients and observable clinical signs
Dietary restriction-provocation trial Step 3 – Sequential provocation (optional) - (describe 3 steps)
Step 3 – Sequential provocation (optional)
If pet owners want to identify exact offending allergen(s)
1. Feed restriction diet until pruritus resolves
2. Introduce 1 ingredient at a time for up to 14 days
Examples: Beef, chicken, lamb, fish, soybean, corn, wheat
3. Repeat sequence
- Environmental allergy tests General considerations - describe 2 types
Two types of environmental allergy tests are available:
- The intradermal test (skin test, IDT) screens for the presence of allergen-specific immunoglobulin E bound to the surface of dermal mast cells and their ability to degranulate upon exposure to an allergen (visualization of immediate wheal-and- flare reaction, type I hypersensitivity)
- The allergen-specific immunoglobulin E serum test (ASIST) screens for the presence of allergen-specific immunogobulin E circulating in the peripheral blood
Environmental allergy tests
Pros of Intradermal test: IDT In-vivo test (8)
Biological read-out (in-vivo test)
Gold standard (measures allergic response in skin = target of allergic reaction)
Quick results (15-25 minutes)
Allergen tested can be individualized for patient and geographic location
Use of positive (histamine), negative control (saline)
Higher percentage of dogs produce meaningful positive reactions compared to ASIST
More sensitive for Malassezia and flea saliva
What are the lesions and commonly affected sites in canine scabies?
Lesions are crusts in elbows, hocks and interface/margins of ears
Describe the pathogenesis of canine atopic dermatitis and cutaneous adverse food reaction
Canine Atopic Dermatitis: a genetically predisposed inflammatory and pruritic allergic skin disease with characteristic clinical features associated with IgE antibodies most commonly directed against environmental allergens. - Percutaneous +++, Inhalation, ingestion, conjunctival
Type I hypersensitivity reaction followed by a type IV hypersensitivity reaction
Canine Adverse food reaction: reactions involving a clearly demonstrated humoral response mediated by immunoglobulin E
Ingestion
A type I followed by a type III, followed by type IV
Environmental allergy tests
Pros of Serum test: ASIST In-vitro test (6)
Objective
Easy to perform
Simple blood draw No sedation, clipping Less effect of drugs No effect of stress
Good alternative to IDT for veterinarian Who chooses not to refer patients Who does not perform IDT
When pet owners decline referral When referral is impossible
Good alternative to IDT when a patient cannot be skin tested (drug withdrawal times not respected, patient cannot be sedated for medical reasons, very small dog)
Environmental allergy tests
Cons of Intradermal test: IDT In-vivo test (8)
Sedation (issue with certain breeds) Clipping
Healthy lateral thoracic skin
Effect of drugs (glucocorticoids, antihistamines, must be withdrawn days to weeks in advance) Effect of stress (endogenous steroids)
Skilled operator (subjective, effect of color- blindness)
Lack of standardization
Optimum concentrations are not validated
Expensive for veterinarian (> 40 allergens, cost- effective if multiple tests are performed within kit shelf life)
Suspect allergic patients may not react during peak of their allergic season (anergy, retest at more appropriate time?)
Environmental allergy tests
Cons of Serum test: ASIST In-vitro test (6)
Extrapolation (in-vitro test)
Presence and quantity of allergen-specific IgE do not correlate with severity of allergic disease
Serum samples need to be sent out (2-3 weeks)
No positive or negative control
Limitations due to laboratories
No interlaboratory standardization
Results not always reproducible in same patient between different samples
Variability of methods
Lack of information about specificity of reagents Allergen tested are those offered by laboratory Interference from other antibodies (IgG)
Arbitrary cut-off between positive an negative reaction Can be expensive for the owner
Higher percentage of false positive reactions
Patient may not have had recent exposure to allergen (retest at more appropriate time?)
What are commonly affected sites in canine flea allergy dermatitis?
Dorso-lumbar area, base of tail, medial & caudal thighs
How can you rule in or rule out canine scabies if superficial skin scrapings are negative?
Use the pinnal-pedal reflex
Look for IgG serum antibodies
Conduct an anti-parasitic trial & see if the clear it up
What is the classical lesion seen in a case of cheletiellosis ?
scales/flakes on dorsal body of young or immuno-compromised individual living in a dirty environment (skin scraping, tape, anti-parasitic trial)
Describe the 5 feline different cutaneous patterns
- Feline miliary dermatitis (FMD)
- Feline symmetrical alopecia (FSA)
- Feline eosinophilic dermatoses (ESD, ex-EGC)
- Erosive/crusting dermatosis of head/neck (ECDHN)
- Spontaneously occurring large crusts (SOLC)
Be able to formulate an adequate differential diagnosis based on seasonality of pruritus (6 scenarios)
atopic & atopic-like dermatitis are always on the table
add lice in winter, fleas & ectoparasites + mosquitoes in summer
List all the steps involved in doing a dietary restriction-provocation trial
- Take away food gradually (alternate old/new)
- Keep away for 6-10 weeks
- If pruritis is decreased by 50% -> sign!
- Re-introduce, possibly one ingredient at a time
- see if after 14 days the pruritis is back
Learn the 8 Favrot`s criteria for the diagnosis of canine atopic dermatitis
- > 3 years
- mostly indoor
- corticosteroids makes it go away
- originally no lesions
- on pinnae of ears
- not on margins of ears (scabies)
- on front paws
- not on dorso-lumbar area (fleas)
Describe the principles, advantages and disadvantages of the different ways allergy testing can be performed
intra-dermal -> fast, gold standard, good results, may have to refer, remove drugs if on them, stressful, clipping etc
IgE serum antibody –> cheaper, not as good results, may not need referral, less stressful
6 canine pruritic skin diseases
3 allergic skin diseases 1. Canine atopic dermatitis (CAD) 2. Cutaneous adverse food reaction (CAFR) 3. Flea allergy dermatitis (FAD) parasitic skin diseases 4. Scabies 5. Cheletiellosis (mites) 6. Pediculosis (lice)
