Derm Path 1

• Components of normal skin


  • Epidermis
  • Dermis
  • Adnexa (hair follicles, sebaceous glands, apocrine glands)

  
• Non-keratinocyte components of the epidermis

  • Melanocytes
  • Langerhans cells
  • Merkel cells
• Dermis


  The layer of skin beneath the epidermis, containing extracellular matrix, blood vessels, lymphatics, nerves, and arrector pili muscles

  
• Arrector pili muscle


  Smooth muscle that contracts in response to sympathetic stimulation, pulling hair follicles vertical (piloerection)
• Adnexa


  Structures associated with the skin, including hair follicles, sebaceous glands, and sweat glands

  
• Hair follicle cycle


  • Anagen (growth stage)
  • Catagen (development of pointed club hair)
  • Telogen (resting/quiescent stage)
  • Exogen (shedding of hair shaft)
  • Kenogen (prolonged empty telogen)

  
• Hair follicle types


  • Simple (single primary hair shaft)
  • Compound (primary hair shaft with multiple secondary shafts)
• Hair follicle components


  • Dermal papilla
  • Outer root sheath
  • Inner root sheath
  • Hair shaft

  
• Sebaceous glands


  Holocrine glands that produce sebum, a physical and chemical barrier
• Sweat glands


  Apocrine glands (open into hair follicles) and eccrine glands (open directly onto the skin surface)
• Subcutis


  The layer of skin beneath the dermis, containing connective tissue and adipose tissue

  
• Outcomes of acute epidermal injury

  • Intracellular edema
  • Intercellular edema
  • Keratinocyte apoptosis or necrosis
• Outcomes of chronic epidermal injury

  • Epidermal hyperplasia
  • Epidermal and follicular hyperkeratosis
  • Hyperpigmentation
• Outcomes of acute dermal injury

  • Dermal edema
• Outcomes of chronic dermal injury


  • Dermal fibrosis
  • Dermal atrophy
• Congenital


  Lesions present at birth
• Hereditary


  Inherited (genetic) lesions that may be congenital or develop later in life
• Hereditary and congenital skin diseases

  • Epidermis: Ichthyosis, Hereditary zinc deficiency, Epidermolysis bullosa, Congenital hypotrichosis
  • Pigmentation: Hypopigmentation (Albinism, Vitiligo), Hyperpigmentation (Acanthosis nigricans, Lentigo simplex)
  • Epidermal differentiation: Seborrhea, Acne, Schnauzer comedo syndrome
  • Connective tissue: Collagen dysplasia
  • Dermis and epidermis: Canine dermatomyositis, Dermatosis vegetans, Porcine juvenile pustular psoriasiform dermatitis
• Ichthyosis


  Generalized scaling caused by congenital or hereditary cornification disorders
• Ichthyosis in dogs


  • Epidermolytic (defect in keratin formation, vacuolation and lysis of keratinocytes, hyperkeratosis)
  • Non-epidermolytic (mild scaling, often with secondary yeast infections)
• Ichthyosis in cattle


  • Ichthyosis fetalis (severe, fatal)
  • Ichthyosis congenita (less severe)
• Hereditary zinc deficiency


  Dry, flaky/scaly/crusting skin lesions, often with thymic hypoplasia and diarrhea
• Hereditary zinc deficiency in cattle and bull terriers

  • Cattle: Caused by intestinal malabsorption, usually fatal within 4-8 weeks without treatment
  • Bull terriers: Lethal acrodermatitis, fail to respond to zinc supplementation, usually fatal by 18 months
• Epidermolysis bullosa


  Group of mechanobullous hereditary skin diseases characterized by minor mechanical trauma causing blistering and ulceration
• Epidermolysis bullosa subtypes


  • Epidermolysis bullosa simplex
  • Junctional epidermolysis bullosa
  • Dystrophic epidermolysis bullosa
• "Epitheliogenesis imperfecta" was the old name for epidermolysis bullosa
• Albinism


  Hereditary hypopigmentation disorder
• Vitiligo


  Hereditary hypopigmentation disorder with a different pathogenesis than albinism
• Uveodermatologic syndrome


  Hereditary disorder with common signalment and clinical signs
• Seborrhea


  Hereditary disorder characterized by excessive scaling and greasy skin
• Collagen dysplasia


  Hereditary disorder with clinical lesions affecting the connective tissue
• Dermatosis vegetans


  Hereditary disorder with clinical lesions affecting the dermis and epidermis
• Porcine juvenile pustular psoriasiform dermatitis


  Hereditary disorder with clinical lesions affecting the dermis and epidermis
• nc


  Usually die within 4-8 weeks of clinical onset (w/o tx) - FATAL
• This condition is responsive to oral zinc supplementation
• Bull Terriers


  Lethal acrodermatitis
• Fail to respond to zinc supplementation - pathogenesis not well-understood
• Epidermolysis bullosa


  Group of mechanobullous hereditary skin diseases
• Epidermolysis bullosa


  • Primary feature: minor mechanical trauma → blistering and ulceration of skin
• Epidermolysis bullosa subgroups


  • Epidermolysis bullosa simplex
  • Junctional epidermolysis bullosa
  • Dystrophic epidermolysis bullosa