Skin Environmental - Pathology
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Chemical damage
Contact Dermatitis
Ergot Poisoning
Fescue Poisoning
Selenium Poisoning
Physical damage
Acral Lick Dermatitis
Callus
Feline Psychogenic Alopecia
Injection Site Reaction
Intertrigo
Pyotraumatic Dermatitis
Radiation Damage
Low Temperature Damage
=High Temperature Damage
Sunlight damage
- Transient erythema may develop into sunburn erythema (warmth, swelling, pain)
- Diffusion of inflammatory mediators (e.g. cytokines) from damaged keratinocytes and endothelial cells
- Photooxidation of existing melanin -> pigment darkening
- Melanogenesis
- Immune responses of skin are reduced by UV light
Solar dermatosis and neoplasia
- Caused by chronic sunlight damage
- Damaged tissue generates free radicals than may damage nucleis acids and proteins
- If damage repaired prior to mitosis - no lasting effect
- If mitosis occurs before repair, post-mitotic repair is prone to faults and DNA mutations may result in neoplasia
Solar dermatitis
- Particularly in white animals and where little or no hair is present
- Grossly:
- Erythema, scaling and crusting
- -> Wrinkled nand thickened skin
- Squamous cell carcinoma or haemangiosarcoma/haemangioma may develop
- Microscopically:
- Dyskeratotic cells
- Intercellular oedema
- Vacuolated keratinocytes
- Followed by hyperkeratosis, parakeratosis and acanthosis
- Endothelial swelling
- Haemorrhage
- Hyperplasia
- Dermal fibrosis
- Dogs may develop actinic comedones
Photosensitisation
Photoenhanced dermatoses
- Many immune-mediated cutaneous disease are made worse by sunlight
- Lupus erythematosus
- Dermatomyositis
- Pemphigus erythematosus
- Vasculitis in extremities, especially white-haired horses
- Grossly:
- Erythematous, well circumscribed crusted lesions or hyperkeratotic plaques
- Microscopically:
- Vasculitis of superficial dermal vessels
- Thrombi may be seen