Skin Other - Pathology

()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