Difference between revisions of "Skin Immunologic - Pathology"
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*Involves [[Skin Immunologic - Pathology#Type I reactions|Type I reaction]] | *Involves [[Skin Immunologic - Pathology#Type I reactions|Type I reaction]] | ||
*Mainly causes pruritus | *Mainly causes pruritus | ||
− | *Dogs - face rubbing and foot licking; secondary [[Bacterial skin infections - Pathology#Pyoderma|pyoderma]] or [[Skin Other#Secondary seborrhea|seborrhea]] | + | *Dogs - face rubbing and foot licking; secondary [[Bacterial skin infections - Pathology#Pyoderma|pyoderma]] or [[Skin Other - Pathology#Secondary seborrhea|seborrhea]] |
*Cats - facial, ear or generalised pruritus, miliary dermatitis, [[Skin Other - Pathology#Eosinophilic granuloma|eosinophilic granuloma complex]], symmetric alopecia | *Cats - facial, ear or generalised pruritus, miliary dermatitis, [[Skin Other - Pathology#Eosinophilic granuloma|eosinophilic granuloma complex]], symmetric alopecia | ||
*Horses - pruritic hea, pinnae, ventrum, legs, tailhead or recurrent [[Skin Glossary - Pathology|urticaria]] | *Horses - pruritic hea, pinnae, ventrum, legs, tailhead or recurrent [[Skin Glossary - Pathology|urticaria]] |
Revision as of 12:11, 30 October 2008
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General
- Classification:
- Hypersensitivity - response to normally harmless substances
- Auto-immune - antobodies or T-cells reactive against self-antigens
- Mostly involves mixture of types described below
Type I reactions
- Mediated by pharmacologically active substances from mast cells and basophils
- Due to antigen-antibody (usually IgE) binding to receptors on those cells
- Substances include histamine, serotonin, leukotriens, prostaglandins
- Can be systemic or local
- Skin becomes pruritic, raised erythematous borders of wheals
- Immediate reaction
- Includes:
- Atopic dermatitis
- Urticaria
- Angioedema
- Fly bite hypersensitivity
- Gastrointestinal parasites
- Food
- Microscopically:
- Capillary dilation, oedema, mast cell degranulation, eosinophil infiltration
Type II reactions
- Cytotoxic reaction
- IgG and IgM interaction with antigens bound to cellular membranes
- Often involves complement fixation -> cellular damage
- In skin - circulating antibody to proteins of desmosomes in intercellular areas along basement membranes at epidermal-dermal junction
- Includes:
Type III reactions
- Complement fixing immune complexes
- IgG or IgM
- Complexes deposit in tissue -> fix complement -> cytokines and othe factors attrack neutrophils -> release lysosomal enzymes, activation of complement and coagulation, platelet aggregation -> tissue damage
- Immune complex vasculitis -> purpura haemorrhagica
- Includes:
Type IV reactions
- Delayed hypersensitivity
- Haptens bind to carrier proteins (mainly epidermal)
- Mediated by sensitised T-cells -> release cytokines +/- recruit lymphocytes
- Used in diagnosis of tuberculosis, histoplasmosis and coccidiomycosis
- Perivascular mononuclear cell accumulation
Hypersensitivity reactions
Allergic contact dermatitis
- Usually involves Type IV reaction
- Pruritic lesions with self-inflicted trauma
- At areas in contact with allergen
- Grossly:
- Erythema, papules, +/- vesicles, exudation -> crusts
- If chronic, lichenification, hyperpigmentation, alopecia
- Microscopically:
- Spongiotic superficial perivascular dermatitis
- Mononuclear cells
- If chronic, epidermal hyperplasia
- May involve eosinophils
Atopy
- Involves Type I reaction
- Mainly causes pruritus
- Dogs - face rubbing and foot licking; secondary pyoderma or seborrhea
- Cats - facial, ear or generalised pruritus, miliary dermatitis, eosinophilic granuloma complex, symmetric alopecia
- Horses - pruritic hea, pinnae, ventrum, legs, tailhead or recurrent urticaria
- Lesions generally due to self-trauma
- Microscopically:
- Hyperplastic superficial perivascular dermatitis
- Mast cells, eosinophils, nonmetachromatic mononuclear cells
- Perivascular inflammation may be involved especially in horses
Culicoides hypersensitivity
- Usually involves Type I reaction and Type IV reaction due to salivary antigens of Culicoides sp.
- May be seasonally recurring or continuous depending on climate
- Grossly:
- Papules, crusts, alopecia, excoriations, lichenification
- Microscopically:
- Superficial and dep perivascular dermatitis
- Many eosinophils
- Epidermal hyperplasia
- Hyperkeratosis
- Dermal fibrosis
- Possibly eosinophilic folliculitis, intraepidermal pustules and eosinophilic granulomas
Flea bite hypersensitivity
- Usually involves Type I reaction and Type IV reaction and cutaneous basophil hypersensitivity
- Mainly dorsolumbosacral area involved, abdomen, caudomedial thighs, flanks, neck of cats
- Secondary trauma is self-inflicted
- Grossly:
- Papular dermatitis
- Secondary excoriations
- Alopecic nodule if chronic
- Microscopically:
- Hyperplastic superficial perivascular dermatitis
- Oedema, mast cells, basophils, eosinophils, lymphocytes, histiocytes
- Fibropruritic nodules covered by hyperplastic epidermis
Autoimmune reactions
Bullous pemphigoid
- Dogs and horses
- Involves oral cavity, mucocutaneous junctions, groin and axilla
- Subepidermal vesicles and bullae
- Antibodies bound to basement membrane
- Grossly:
- Similar to Pemphigus vulgaris
- Microscopically:
- Bullae containing fibrin, neutrophils or eosinophils
- Basement membrane forms floor of bullae and roof is lined with basal cells
- Bullae may rupture -> ulcers
Dermatomyositis
- See also Canine dermatomyositis
- Affects puppies of collies and shetland sheepdogs from 8 weeks of age
- Lesions - vesiculating dermatitis
- Face, lips, external ears, later distal extremities
- Microscopically: interface dermatitis and basal cell degeneration of epidermis and follicular wall, atrophy of follicles, epidermal vesicles and pustules, dermal scarring
Lupus erythematosus
- Systemic (SLE)
- Multiple organs involved
- Cats, dogs, horses
- Immune dysregulation:
- Damaged T-cell suppressor function, either primary deficiency or antibody mediated
- Cytokine dysregulation
- Resulting B-cell hyperactivity -> antibodies to self antigens -> antigen-antibody complexes deposited in various tissues -> Type III hypersensitivity
- Lesions localised or generalised
- Erythema, alopecia, depigmentation, crusting and scaling, ulceration
- Microscopically: lymphohistiocytic interface dermatitis, thickened basement membrane, vasculitis, subepidermal vesicles, basal cell degeneration
- Discoid
- Milder variant of systemic
- Depigmentation, erythema, scaling, erosions, ulceration, crusting
- Usually involves nasal planum, dorsum of muzzle, occasionally pinnae, lips, oral mucosa or periocular area
- Microscopically: lichenoid interface dermatitis, often with lymphocytes, plasma cells, basal cell degeneration, loss of pigment
Pemphigus
- Blistering diseases
- Autoantibodies bind to desmosomal proteins -> cell adhesion disrupted -> vesicles
- Types:
- Pemphigus vulgaris
- Rare, severe form
- Cats and dogs
- Vesicles or bullae -> erosions and ulcers
- Involves oral cavity, mucocutaneous junctions and skin
- Microscopically:
- Suprabasilar vesiculation and row of basal cells adhering to basement membrane
- Superficial perivascular dermatitis
- Pemphigus vegetans
- Rare
- Dogs
- Involves the trunk
- Mild version of P. vulgaris
- Vesicopustular dermatitis + epidermal hyperplasia -> papillomatous formations
- Pemphigus foliaceus
- More common
- Cats, dogs, horses, goats
- Localised lesions or generalised
- Symmetrical vesicular or pustular dermatitis, crusts, scales, alopecia
- Microscopically:
- Acantholytic cells
- Subcorneal or intragranular pustules
- In third of equine or canine cases eosinophils are predominant
- Pemphigus erythematosus
- Cats and dogs
- Mild form of P. foliaceus
- Usually involves only face and external ears
- Pemphigus vulgaris