Skin Other - Pathology


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()Map INTEGUMENTARY SYSTEM (Map)



Epidermal growth or differentiation disorders

Seborrheic disease complex

  • Abnormal cornification or function of sebaceous glands
  • Large amounts of free fatty acids and cholesterol
  • Decreased amounts of diester waxes in surface lipids
  • Bacterial population changes to pathogenic coagulase positive staphylococci
  • Chronic disease affecting mainly dogs, sometimes cats and horses
  • Dry form - white to grey scales
  • Greasy form - scaly, excess brown to yellow lipids sticking to skin and hair

Primary idiopathic seborrhea

  • Abnormal cornification
  • Epidermal turnover reduced to about 2/3 of normal
  • Microscopically:
    • Hyperkeratosis distending follicular ostia causing papillary appearance
    • Parakeratosis at edges of follicular ostia
    • Congested, oedematous dermal papillae
    • Spongiotic epidermis with leukocytes

Secondary seborrhea

  • Develops secondarily to many types of disease (e.g. ectoparasites, fungal infections, endocrine disease, internal disease or allergy)
  • Microscopically:
    • Hyperkeratosis and/or parakeratosis of follicles and epidermis
    • Lesions relevant to the other disease

Sebaceous adenitis

  • Inflammation of sebaceous glands, alopecia, hyperkeratosis
  • Possibly immune-mediated
  • Mainly affects dogs
    • Long haired show multifocal, serpiginous and annular lesions
  • Microscopically:
    • Inflammation of sebaceous glands
    • Possibly orthokeratotic hyperkeratosis
    • Chronic lesions are deprived of sebaceous glands and contain mild inflammation and fibrosis at follicular isthmus

Pigmentation disorders

Hypopigmentation

  • Leukoderma or vitiligo - loss of pigment in the skin
  • Leukotrichia - loss of pigment of the hair
  • Hypopigmentation or incomplete albinism - generalised reduction of pigment in skin or hair
  • Albinism - inherited lack of pigment
  • Dilution - reduced pigmentation
  • Can be localised or generalised, idiopathic or asociated with other diseases
  • Examples of hereditary conditions: Maltese dilution of cats, Chediak-Higashi syndrome, leukoderma and leukotrichia of Dobermans, Arabian fading syndrome
  • Asociated with some immune-mediated disorders, e.g. discoid lupus erythematosus

Hyperpigmentation

Image of endocrine hyperpigmentation from Cornell Veterinary Medicine

  • Results from irritation or inflammation, pigmented neoplasms or metabolic diseases
  • Lentigo - circumscribed macular or slightly raised plaque with epidermal hyperplasia and hyperpigmentation

Eosinophilic infiltration

Eosinophilic plaques

  • Common in cats
  • Medial thighs and abdomen mostly involved
  • Often associated with hypersensitivity
  • Grossly:raised plaques, erythematous, pruritic, erosed or ulcerated
  • Microscopically: acanthosis, spongiosis, erosions or ulceration, predominantly eosinophilic dermatitis, possibly areas of collagen degeneration

Eosinophilic granulomas

  • Involves cats, dogs, horses
  • Collagen degeneration in lesions os eosinophil degranulation
  • Often involved in reaction to parasites, foreigh bodies or mas cell tumours
  • Grossly:
    • Papules, nodules, plaques, ulcers in skin
    • Nodules or ulcers in oral mucosa of cats and dogs or on foot pads of cats
  • Microscopically:
    • Nodular dermatitis or stomatitis
    • Fragments of degenerated collagen surrounded by eosinophils and macrophages

Eosinophilic folliculitis and furunculosis

  • Rare in cats, dogs, cattle and horses
  • Possibly due to arthropod bites
  • May be multifocal in horses

Sterile granulomatous disorders

Juvenile pyoderma

  • Also known as Juvenile sterile granulomatous dermatitis and lymphadenitis, juveline cellulitis, puppy strangles
  • Involves dogs of less then 4 months of age
  • Grossly: pustular and nodular dermatitis with oedema involving the face, ears, mucocutaneous junctions
  • Microscopically: granulomatous or pyogranulomatous perifolliculitis, paniculitis and dermatitis

Equine generalised granulomatous disease

  • Also known as Sarcoidosis
  • In horses
  • Rare
  • Involves cutaneous lesions and systemic disease causing anorexia and weight loss
  • Grossly: alopecia, scales, crusts, sometimes nodules and masses
  • Microscopically: multifocal granulomas, multinucleated giant cells