Immune mediated skin disease Flashcards
What is an immune mediated skin disease?
The immune system fails to tolerate self antigens and it mounts a response against normal skin components
What is a primary immune mediated skin disease?
No identifiable trigger factor present = idiopathic
What is a secondary immune mediated skin disease?
Exogenous trigger antigen, most commonly drug, bacteria or virus
How you should patients with potential immune mediated skin disease be clinically assessed?
- Consider signalment (particularly breed) & key historical features
- Look for primary lesions
- Look at distribution of lesions
- Make differential diagnosis list
- Run tests according to differentials
- Interpret results in line with clinical findings
List some diagnostic tests that can be used to diagnose immune mediated skin disease
- Skin scrapes & trichography
- Lesion cytology
- Bacterial/fungal culture and susceptibility testing
- Haematology, biochemistry: to give a general picture of the animal’s heath before treatment
- Urinalysis
- Diagnostic imaging: radiography, ultrasonography
- Blood smear cytology
- Coombs test
- Antinuclear antibody (ANA) test
- Skin biopsy & histopathology
How is cytology used to narrow down the DDX
Cytology to differentiate sterile from infectious disease (and rule out secondary bacterial infection)
How is skin biopsy and histopathy used to narrow down the DDX
Rule out neoplasia, atypical infectious diseases and determine skin pathology (definitive diagnosis)
What are the advantages of cytology
Easy, cheap, rapid (in house) results
Differentiate sterile from septic (infectious) disease
Determine type of inflammation
May inform management prior to histopath results
Mixed neutrophils and macrophages indicate what type of inflammation?
Sterile pyogranulomatous inflammation
Neutrophils with cocci bacteria indicate what type of inflammation?
Coccoid bacterial inflammation
Direct impression smears can be used for which lesion types?
Pustules, exudative lesions (erosions, ulcers), draining tracts
FNA can be used for what types of lesions?
Nodules, plaques, tumours, lymph nodes
When in the diagnostic process in skin biopsy and histopathology used?
Test often comes after cytology once the differential list has been narrowed down
Where are samples taken when doing skin biopsies?
- Take multiple biopsies +3
- Sample primary lesions
- Sample range of lesions to represent disease process
- Sample whole lesion where possible
- Avoid eroded / ulcerated lesions (or sample from margin to include epidermis) - If only these lesions are present you need to sample from the lesion margins
Name the 4 most common primary lesions seen in immune mediated skin disease
- Pustules
- Plaques/nodules
- Erythematous macules/patches
- Hypopigmented macules/patches
List some other lesions seen in immune mediated skin disease
Alopecia
Vesicles
Erosions/ulcers
Crusts
Purpura
Scale
Define an erosion
Loss of the surface layer of the epidermis
Define an ulcer
Loss of full thickness of the epidermis
Are ulcers and erosions primary or secondary lesions?
Secondary
- less helpful in making DDx
What are the most common causes of ulcers and erosions?
Keratinocyte death, loss of KC adhesion, self trauma (pruritus), secondary bacterial infections
What are crusts?
Dried exudate on skin surface
- Pus from pustules
- Exudate from erosions/ulcers
- Blood
Define a pustule
A circumscribed elevation of skin containing pus
Pus is formed from infiltrating neutrophils
Case 1:
- Physical examination = General WNL except pyrexia 40oC and mild peripheral lymphadenomegaly
- Lesion morphology = Rare pustule, thick, adherent crusts, pus, erosions
- Lesion distribution = Multifocal - Dorsal muzzle, periocular, medial pinnae, footpads
What are the 4 DDx?
- Bacterial infection (pyoderma/folliculitis)
- Pemphigus foliaceus
- Superficial pustular drug reaction (rare)
- Superficial pustular dermatophytosis (rare)
What are acantholytic keratinocytes?
Large epithelial cells (larger than neutrophils) – rounded (normal keratinocytes are normally anuclear and angular)
Describe the pathophysiology of canine pemphigus foliaceous
- Auto-antibodies (mainly IgG) target components of desmosomes that link keratinocytes in superficial epidermis
- Separation of KCs > acantholytic ‘rounded up’ KCs
- Neutrophilic inflammatory response > superficial pustules with free floating acantholytic KCs
Describe the appearance of pemphigus foliaceous on histopathology
Subcorneal (superficial) pustular dermatitis with acantholytic keratinocytes
Name the most common autoimmune skin disease of dogs
Pemphigus foliaceus
Describe the signalment of pemphigus foliaceus
Middle aged (any), predisposed breeds akita, chow chow, cocker spaniel, dachshund, Labrador retriever, British bulldog & Shetland sheep dog (affects many breeds)
Describe feline pemphigus foliaceous
- Less common than dog PF
- Signalment: X
- Lesion distribution: face, claw fold (paronychia) and nipples
- Prognosis fair
Define a plaque
Flat elevation of skin more than 1cm in diameter. Cause by infiltration of cells of coalition of papules
Define a nodule
Circumscribed solid elevation > 1cm diameter, usually extending into deeper skin layers. Caused by massive infiltration of cells
Describe the signalment of Eosinophilic furunculosis of the face
Young adults
How does Eosinophilic furunculosis of the face present?
History: rapid onset, intense pruritus
Lesion morphology: eroded/ulcerated plaques and nodules
Distribution: face
Cytology: eosinophilic inflammation
Histopathology: eosinophilic folliculitis & furunculosis
Describe the signalment of Sterile granulomatous dermatitis and lymphadenitis (juvenile cellulitis)
Puppies (sporadic cases in adults)
How does Sterile granulomatous dermatitis and lymphadenitis (juvenile cellulitis) present?
History: acute onset, non-pruritic (painful), pyrexia, lethargy
Lesion morphology: follicular nodules (furuncules) & plaques (often eroded & crusted), diffuse swelling, alopecia (check for Demodex), lymphadenomegaly
Distribution: face (muzzle, periocular, pinnae), lymph nodes
Describe the cytology and histology of Sterile granulomatous dermatitis and lymphadenitis (juvenile cellulitis)
FNA cytology: sterile pyogranulomatous inflammation
Histopath: sterile perifollicular granulomatous-pyogranulomatous inflammation & furunculosis
Define a macule
flat area of skin discolouration < 1cm diameter
Define a patch
flat area of discolouration > 1cm diameter
List 3 DDx of Hypopigmented or erythematous macules & patches
Hypopigmentation, erythematous macules/patches, erosions/ulcers
Describe the clinical presentation of facial discoid lupus erythematous
- Loss of cobblestone surface
- Hypopigmented macules and patches
- Erosions, ulcers and crusting
- Black to blue to pink pigmentary change
- Note biopsies taken from blue pigmentary change rather than ulcers or crusting
- Hypopigmentation, erosion, crusting periocular skin and lips
- Severe ulceration and crusting
Describe the history of an animal with Erythema multiforme (major/minor)
Acute onset, non-pruritic, +/- systemic signs (pyrexia, lethargy, inappetence)
Trigger: virus, drug, vaccine, microbial infection, neoplasia, systemic disease, food (can be idiopathic)
Describe the lesions seen in cases of Erythema multiforme (major/minor)
- Primary lesion = annular erythematous macule (may be targetoid)
- Can see vesicles, bullae, wheals, ulceration, crusts
- Distribution: ventral abdomen > generalised, mucosae (often oral cavity)
Describe the ‘target lesions’ seen in erythema multiforme major/minor
Erythematous macules spread peripherally producing annular or arciform pattern
- Central erythema/pupura, ring of clear oedema (may be raised), ring of erythema = target lesion
- Centre may be a vesicle/bulla resulting in ulcers and crusts
Describe the cytology and histopathology of erythema multiforme major/minor
Cytology: sterile non-specific inflammation (NB ulcers may be secondarily infected!)
Histopathology: keratinocyte apoptosis (death), lymphocyte satellitosis, interface (epidermis/dermis) dermatitis
The degree of apoptosis in erythema multiforme determines?
Severity of epithelial loss i.e. EM vs SJS vs TEN
Describe the main features of hyperkeratotic erythema multiforme
Chronic, persistent
Older dogs
Idiopathic
Lesions more exudative and crusting
Often face and ears but can be generalised
Describe Stevens-Johnson syndrome
Erythema multiforme
No target lesions
More ulcerative – lose large sections of skin
Guarded prognosis
What is the signalment of Uveodermatologic syndrome
young to middle aged, Akita predisposed
Describe the history and clinical presentation of Uveodermatologic syndrome
History: acute bilateral uveitis, non-pruritic
Lesion morphology: hypopigmented macules > patches, erythematous macules, erosions, ulcers, crusts
Distribution: face; nose, lips, periocular skin (occasionally footpads, scrotum, perineum)
List the DDx for immune mediated alopecia
Sebaceous adenitis
Alopecia areata
Dermatomyositis
Ischaemic dermatopathy
Post-injection alopecias
Which test is used to rule out demodicosis and dermatophytosis?
Trichography +/- skin scrapes
Describe the signalment of sebaceous adenitis
Standard poodle, Akita, vizsla, *autosomal recessive mode of inheritance
How does sebaceous adenitis present?
History: non-pruritic unless SBI
Lesion morphology: partial alopecia and poor coat quality, follicular casts and scale
Distribution: generalised
Describe the cytology and histopathology of sebaceous adenitis
Cytology: no significant findings unless SBI
Histopath: pyogranulomatous inflammation targeting sebaceous glands > destruction of sebaceous glands and hair follicle atrophy
Describe how cases of alopecia areata present
History: non pruritic, chronic onset
Lesion morphology: focal to multifocal, partial to complete patches of alopecia +/- erythema and hyperpigmentation
Distribution: head/face
Describe the histological appearance of alopecia areata
Lymphocytic destruction of hair bulbs
Describe the signalment of Dermatomyositis/ischaemic dermatopathy
Young collies, SSD, Beauceron shepherd, Belgian shepherd, PWD predisposed to dermatomyositis (familial)
Describe the clinical presentation of Dermatomyositis/ischaemic dermatopathy
History: non-pruritic, chronic course +/- myositis
Quite a rare disease
Lesion morphology: focal to multifocal alopecia with variable hyperpigmentation, hypopigmentation, scaling, erosion/ulceration & crusting
Distribution: face and extremities (dorsal digits, pinnae & tail tips, nails)
Describe the histological appearance of Dermatomyositis/ischaemic dermatopathy
Chronic dermal & vascular inflammation > follicular atrophy (include muscle in biopsy to check myositis)
How is immune mediated disease managed?
- Removal/treatment of any external triggers e.g. Drugs, UV light: sunscreen, food
- Control of inappropriate immune response: Immunosuppressive/immunomodulatory drugs
