Skin Environmental - Pathology

From WikiVet English
Jump to navigation Jump to search
This article has been peer reviewed but is awaiting expert review. If you would like to help with this, please see more information about expert reviewing.


WikiPathWikiPath Banner.png
()Map INTEGUMENTARY SYSTEM (Map)



Chemical damage

Contact dermatitis

  • Results due to exposure to chemicals (not immunologic reaction)
    • Acids, alkali, detergents, irritant plants etc.
  • In cats and dogs lesions usually on skin of abdomen, feet, chest, eyelids, axillae
  • In horses lesions on muzzle, lower limbs, under tack
  • Grossly:
  • Microscopically:
    • Hyperplastic, spongiotic dermatitis
    • Superficial perivascular inflammation
    • Necrosis may be caused by corrosive substances

Ergot poisoning

  • Caused by ingestion of grains or grass contaminated by fungus Claviceps purpurae
  • Affects especially cattle
  • Toxic alkaloids damage capillary endothelium, peripheral arterial and venous constriction -> thrombosis and possible tissue ischaemia
  • Clinical signs develop about a week after consumption
  • Grossly:
    • Red and swollen extremities
    • Dry gangrene may develop on pinnae and tail

Fescue poisoning

  • Caused by excessive consumption of Festuca arudinacea
  • Clinical signs develop about two weeks after consumption
  • Grossly:

Selenium poisoning

  • Caused by ingestion of plants that have accummulated excessive amounts of selenium
  • May affect any herbivore, possibly also pigs
  • Acute poisoning:
    • Multiple organ systems are involved
  • Chronic poisoning
    • Poor hair quality, partial alopecia
    • Horses - loss of mane and tail hair, deformed hooves that may be shed

Physical damage

Acral lick dermatitis

  • Also called lick granuloma or neurodermatitis
  • Mostly occurs in dogs due to constant licking or chewing
  • Areas most affected are carpal, metacarpal, metatarsal, radial or tibial areas
  • Usually a single lesion
  • Grossly:
    • Circumscribed hairless areas that may ulcerate
  • Microscopically:
    • Compact hyperkeratosis
    • Hyperplasia of follicular and epidermal epithelium and sebaceous glands
    • Collagenous fibres causing dermal thickening
    • Perivascular and periadnexal plasma cell accumulation
    • May be associated with mild snsory polyneuropathy

Callus

  • Hypertrophy of epidermis, particularly at pressure points
  • Usually affects giant breed dogs and pigs kept on hard floor
  • May be followed by folliculitis, furunculosis and ulceration
  • Microscopically:
    • Hyperkeratosis and acanthosis or epidermis and follicular epithelium
    • Comedones and follicular cysts may be present, potentially rupture and cause secondary pyoderma
    • Excessive keratin widening follicular openings

Feline psychogenic alopecia

  • Occurs in cats
  • Broken hairs cused by persistent licking -> partial alopecia
  • Areas mostly affected: dorsal midline, perineal, genital, medial thigh, abdomen
  • Microscopically:
    • Usually normal skin
    • Possibly increased telogen follicles

Injection site reaction

  • May be caused by subcutaneous injections
  • Granulomatous nodules form with central necrotic and foreign material
  • Macrophages and multinucleated giant cells around the centre
  • Surrounded by granulation tissue, perivascular lymphocytes that may form lymphoid follicles, eosinophils
  • Cats may develop fibrosarcomas secondary to vaccination
  • Dogs, especially poodles, may develop lymphoplasmacytic panniculitis and perivasculitis, vasculitis and follicular atrophy secondary to killed rabies vaccine

Intertrigo

  • Also called skin fold dermatitis
  • Develops due to irritation and bacteria in areas of skin friction and moisture (tears, saliva, glandular secretions, urine)
  • Areas affected are commonly facial fold in brachycephalic breeds, lip fold, body fold, vulvular fold (obese females), tail fold (corkscrew tails)
  • Cows with large, pendolous udder may become affected in area between thigh and udder
    • In severe cases, skin and subcutis may slough

Pyotraumatic dermatitis

  • Also called acute moist dermatitis or 'hot spot'
  • Common in dogs, especially self-inflicted due to pain and itching
  • Usual causes: allergies, irritants, matted hair, parasites
  • Lesions tend to be worse in hot and humid weather
  • Grossly:
    • Hairless, red and moist lesion
    • Fluid exudate
    • Edges are circumscribed and red
  • Microscopically:
    • Superficial erosive to ulcerative exudative dermatitis
    • May be deeper suppurative folliculitis

Radiation damage

  • Cells sensitive to radiation include anagen hair follicles, germinal basal cells, melanocytes and endothelial cells
  • Early changes:
    • Erythema, epidermal blisters and oedema, erosions and ulceration
    • Healed by scarring, hyperpigmentation with lower doses and hypopigmentation with higher doses
    • Temporary or permanent alopecia
  • Chronic changes:
    • Scarring, altered pigmentation, alopecia
    • Epidermal and adnexal atrophy
    • Degeneration of vascular and elastic tissue
    • Fibrosis of dermal and subcutaneous tissue
    • Ulceration
    • In severe damage, squamous cell carcinoma may develop

Low temperature damage

  • Prolonged cold can cause ice crystal formation and vascular injury resultic in damage to tissue due to increased intracellular salt concentration
  • Slow chilling can cause vasoconstriction, cellular damage -> secondary vasodilation and increased permeability -> oedema
  • Severe and persistent cold causes vasoconstriction, increase in blood viscosity and tissue anoxia
  • Lesions may occur in wet or hypoglycaemic neonates or animals recently moved from warm to cold environment
  • Areas affected are extremities
  • Lesions consist of gangrene and necrotic tissue

High temperature damage

  • May result from excessive heat, liquids, flames, friction, lightning, electricity
  • Partial or full thickness burns (first, second and third degree burns)
  • Full thickness burns:
    • Total destruction of skin and adnexa
    • Has to be repaired by grafting
    • Life threatening
  • Partial thickness burns:
    • Some structures preserved -> regeneration may occur
    • Grossly:
      • Erythema (capillary dilation)
      • Oedema (increased permeability of capillaries)
      • Vesicles
    • Microscopically:
      • Coagulation necrosis of epidermis
      • Subepidermal vesiculation
      • Necrosis of adnexa
      • Degenerated subepidermal collagen
      • May involve large numbers of neutrophils if secondary ifection is present

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:
  • Microscopically:

Photosensitisation

  • Primary
    • Ingestion of photodynamic substance from plants (Hypericum perforatum and Fagopyrum sagittatum - buckwheat) or fungal contaminants
    • Induced by drug administration - phenothiazines, tetracyclines, thiazides, sulphonamides
  • Abnormal porphyrin metabolism
    • Bovine congenital porphyria
    • Bovine erythropoeitic protoporphyria
  • Hepatogenous
    • Impaired excretion of phylloerythrin (chlorophyl metabolism product) due to hepatic disease
    • Biliary obstruction
    • Inherited defects
    • Hepatic injury due to toxic plants or fungal contaminants, chemicals or some infectious agents
  • Grossly:
    • In areas lacking hair or pigment
    • Erythema, oedema -> blisters, exudation, necrosis, sloughing or keratitis
  • Microscopically:
    • Subepidermal vesicles
    • Ulceration
    • Secondary infection

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
Retrieved from "https://en.wikivet.net/index.php?title=Skin_Environmental_-_Pathology&oldid=48737"