Dermatology: Immune- Mediated Disease Flashcards
What causes a primary and secondary immune mediated skin disease?
Primary
* no identifiable trigger present
Secondary
* Exogenous triggering antigen, most commonly drug, bacteria or virus
What diagnostic tests can be used for immune mediated disease?
- Skin scrapes and trichography
- Lesion cytology
- Bacterial/fungal culture and susceptibility testing
- Haematology, biochem
- Urinalysis
- Diagnostic imaging
- Blood smear cytology
- Coombs test
- Antinuclear antibody test
- Skin biopsy and histopath
Why are the following tests used for IMD?
1. Cytology
2. Skin biopsy/histopath
3. Baseline haem/biochem
4. Diagnostic imaging
- Differentiate sterile from infectious disease
- Rule out neoplasia, atypical infectious disease and determine skin path
- Prior to treatment
- Investigate internal triggering disease
How are diagnostic skin biopsy and histopathology samples obtained?
- Multiple biopsies
- Sample primary lesions
- Range of lesions- disease process
- Whole lesion where possible
- Avoid eroded/ulcerated lesions
What are the most common IMSD lesions?
- Pustules
- Plaques/nodules
- Eryhthematous macules
- Hypopigmented macules
Why are erosions, ulcers and crusts commonly seen with IMSD?
- Secondary lesions
- Erosions from keratinocyte death
- Crusts- dried exudate
- Ulcers- loss of full thickness of epidermis
What is a pustule?
Circumscribed elevation of skin containing pus
Formed from infiltrating neutrophils
What are differential diagnoses for pustules?
Which are sterile, immune mediated?
- Bacterial infection
- Pemiphigus foliaceus- S
- Superficial pustular drug reaction (rare)- S
- Superficial pustular dermatophytosis (rare)
What is the pathophysiology of canine pemiphigus foliaceous?
- Auto-antibodies target desmosomes that link keratinocytes
- Seperation of keratinocytes
- Neutrophilic response- superficial pustules with free floating acantholytic keratinocytes
What is the common signalment and history of pemphigus foliaceous?
- Middle aged
- Breeds- retriver, BBD, Shetland sheep dog
- Cats- face, claw fold, nipples
HX
* Variable pruritus
* UV exacerbation
* Guarded prognosis
What is a plaque and a nodule?
Plaque
* flat elevation in skin >1cm- infiltratoin of cells or coalition of papules
Nodule
* circumscribes solid elevation usually extending deeper into skin layers- masivie infiltration of cells
What is canine atopic (allergic) dermatitis?
An allergic skin condition causing pruritus- dog eczema
What is malassezia dermatitis?
A secondary skin diseases from Malassezia sp commensals (yeast)
What does this image show?
Eosinophilic furuncolosis of the face
(Hair follicle infection)
What does the following image show?
Sterile granulomatous dermatitis and lympadenitis (juvenile cellulitis)
What is the most common canine lupus eryhtmeatous?
Facial discoid lupus erythematous
What is the history of erythema multiforme?
What is the lesion morphology and distribution?
Hx
* Acute, non-pruritic
* Trigger- virus, drug, vaggine, infection, neoplasia
Lesion morphology- pleomorphic
* primary lesions- annular erythematous macule
* Target lesions
Distribution- ventral abdomen or mucosal
What is steven-johnsons syndrome?
Rare, life-threatening infection characterised by extensive necrosis and detachment of the epidermis
What is the lesion morhpology and distribution of uveodermatologic syndrome?
Bilateral uveitis, non pruritic
Lesion morphology
* hypopigmented macules
* patches, erosions, ulcers
Distribution- face, nose, lips, periocular skin
What causes alopecia areata?
Lymphocytic destruction of hair bulbs
