Skin Congenital and Hereditary - Pathology

()Map INTEGUMENTARY SYSTEM (Map)

Acanthosis Nigricans

• Occurs in Dachshunds
• Bilateral axillary hyperpigmentation, lichenification, alopecia
• May be followed by secondary pyoderma or seborrhea
• Microscopically:
  • Thickened epidermis by mainly acanthosis
  • Hyperkeratosis
  • Increased melanin in epidermis

Alopecia and Hypotrichosis

• Occurs in most species
• Bred for in some breeds, e.g. Mexican hairless dog, Sphinx cat
• May be due to decreased number of hair follicles, failure of hair growth or follicular dysplasia
• Also associated with maternal deficiency of iodine

Collagen Dysplasia

Collagen dysplasia - dog tail (Courtesy of Bristol BioMed Image Archive)

• Occurs in many species
• Very stretchy and loose skin that tears easily
• Due to variety of defects of enzyme necessary for collagen synthesis or processing
• Histologically:
  • Varies depending on cause
  • May appear normal
  • Collagen bundles varied in shape, size and their organisation

Epidermolysis Bullosa

Epidermolysis bullosa in a lamb (Courtesy of Bristol BioMed Image Archive)

• Also called Red Foot Disease
• Occurs in sheep, dogs, cattle and horses
• Development of cutaneous blisters
• Varies depending on hereditary cause
• Affected animals tend not to survive
• Lesions appear at surfaces that are easily damaged, e.g. oral mucosa, feet
• Microscopically:
  • Epidermal vesicular disease
  • Healing displaces lesions more dorsally
  • May become infected and form pustules

Epitheliogenesis Imperfecta

• Also called Aplasia Cutis
• Incomplete development of squamous epithelium and adnexa of skin and epithelium of oral mucosa
• Occurs in most species
• Grossly:
  • Circumscribed areas of missing squamous epithelium
• Unprotected underlying tissue gets easily damaged and infected, possibly resulting in bacteraemia

Hypertrichosis

• Increased hair growth
• Both congenital or hereditary
• In sheep may be caused by Border Disease virus
• Microscopically:
  • Enlarged primary follicles and wool fibres
• Also accociated with maternal hyperthermia

Ichthyosis

• Inherited cutaneous disease
• Occurs in dogs and cattle
• Grossly:
  • Thickened skin due to hyperkeratosis
  • May crack resembling fish scales
• Increased adherence of keratocytes preventing normal desquamation
• In cattle occurs in two forms:
  • Ichthiosis fetalis - fatal, stillborn calves or die within days of birth
  • Ichthiosis congenita - folded and thickened skin, fissures and partial alopecia

Photosensitisation

• May be due to inherited defects
• See HERE

Porcine Juvenile Pustular Psoriasiform Dermatitis

• Also called Pityriasis Rosea
• Occurs in pigs
• Symmetric lesions on the abdomen, loin and medial thigh
• Start as small papules covered by brown crusts
• -> lesions join and spread -> umbilicated plaques containing white centres with erythematous and scaly borders
• Similar to dermatophytosis
• Histologically:
  • Epidermal hyperplasia, parakeratosis, epidermal pustules and superficial perivascular dermatitis
• For more detail see Porcine Juvenile Pustular Psoriasiform Dermatitis

Zinc-related disorders

• Occurs in Bullterriers and calves
• Resolves with zinc supplementation in calves but not dogs
• In dogs:
  • Fatal acrodermatitis
  • Lesions start between digits and on foot pads -> severe interdigital pyoderma -> paronychia and hyperkeratosis of pads
  • May also occur on pinnae, elbows, muzzle, hocks or become generalised with crusting, ulceration and secondary pyoderma
  • Histologically:
    • Hyperkeratosis and bacterial pustular dermatitis