Skin Immunologic - Pathology

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

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

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

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