DERMAT

• Embryonic development and fetal maturation of the skin


  • 4 weeks gestation: fetal skin has two distinct layers - the basal cell layer and outer layer (i.e. periderm)
  • 9 weeks gestation: keratinization begins
  • 14 weeks gestation: stratification of epidermal layer; primordial hair follicle forms from the basal cell bud
  • 16 weeks gestation: local proliferation of mesenchymal cells associated with the epidermal buds as hair follicles develop and elongate
  • 18 weeks gestation: sebaceous gland develops; hair follicle elongates
  • 23 weeks gestation: continuous elongation of the hair follicle; primordial eccrine gland forms from the basal cell bud
  • 30 weeks gestation: continuous elongation and foiling coiling of the eccrine glands
• Neonatal changes


  • Full-term infants have skin with all five layers, similar to adults
  • Epidermal cells mature from columnar stratum basale to squamous keratinocytes of the stratum corneum
  • Maturation occurs more rapidly in facial skin than trunk or limb skin
  • Neonatal skin is more coarse and develops into a more smooth texture homogeneously during the first 30 days of life
  • Infants have smaller corneocytes and thinner stratum corneum until two years old
  • From infancy to puberty, dermal thickness increases
• Skin repair, regeneration, and changes associated with stages of life

  • Regeneration relies on tissue-specific stem cells and restricted progenitor cells
  • Regenerative abilities decline with age as both cell types undergo a loss of self-renewing capacities, altered proliferative activity, and functional decline
  • With age, the skin becomes thinner and less able to withstand external stress due to epidermal attenuation, keratinocyte proliferative loss, dermal volume loss, and hyaluronic acid diminishment
  • This leads to conditions such as senile purpura and male pattern baldness
  • The decline in regenerative ability can also be seen as postmenopausal hair changes
• Senile purpura

  Typically arise spontaneously; characterized by non-blanchable red-to-purple patches that resolve over 1 to 3 weeks, leaving residual brown-yellow discolouration secondary to hemosiderin deposition
• Layers of the epidermis


  • Stratum basale (germinativum)
  • Stratum spinosum (prickle cells)
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum
• Keratinocytes


  Located in all layers of the epidermis except the stratum corneum; connected to each other by desmosomes
• Melanocytes


  Located in the stratum basale; keratinocyte:melanocyte ratio in the basal layer is 10:1; melanocyte number is equal among races; produce melanosomes containing melanin, which are transferred to keratinocytes
• Langerhans cells


  Dendritic cells which are important for immune surveillance
• Merkel cells


  Located in the stratum basale; involved in touch sensation
• Cells of the dermis


  • Fibroblasts
  • Mast cells
• Components of the dermis


  • Blood vessels
  • Nerves
  • Pilosebaceous units
  • Sweat glands
• Subcutaneous tissue (hypodermis)


  Consists primarily of adipose cells, larger calibre vessels, nerves, and fascia
• Epidermal appendages


  • Hair
  • Nails
  • Cutaneous glands
• Pilosebaceous unit


  Hair + hair follicle + sebaceous gland + arrector pili muscle
• Sebaceous gland


  Part of pilosebaceous unit; produces sebum which is secreted into the hair follicle via the sebaceous duct, where it covers the skin surface (protective function); sebum has some antifungal properties; these glands cover entire skin surface and are absent only in non-hair bearing areas
• Apocrine sweat gland


  Apocrine duct empties into hair follicle above sebaceous gland; not part of pilosebaceous unit; found concentrated in axillae and perineum; likely a vestigial structure, functions in other species to produce scent (e.g. pheromones)
• Eccrine sweat gland


  Not part of pilosebaceous unit; found over entire skin surface except lips, nail beds, and glans penis; important in temperature regulation via secretion of sweat to cool skin surface
• Skin functions


  • Protection
  • Thermal regulation
  • Sensation
  • Metabolic function
• Primary lesions


  De-novo initial lesions that have not been altered by trauma or manipulation, and have not regressed
• Types of primary morphological lesions


  • Macule (e.g. freckle)
  • Patch (e.g. vitiligo)
  • Papule (e.g. wart)
  • Plaque (e.g. psoriasis)
  • Nodule (e.g. dermatofibroma)
  • Tumour (e.g. lipoma)
  • Vesicle (e.g. HSV)
  • Bulla (e.g. bullous pemphigoid)
• Secondary lesions


  Develop during the evolutionary process of skin disease, created by manipulation, or due to complication of primary lesion (e.g. rubbing, scratching, infection)
• Types of secondary morphological lesions


  • Crust
  • Scale
  • Lichenification
  • Fissure
  • Excoriation
  • Erosion
  • Ulcer
  • Xerosis
  • Atrophy
• SCALDA


  • Size and Surface area
  • Colour
  • Arrangement
  • Lesion morphology
  • Distribution
  • Always check hair, nails, mucous membranes, and intertriginous areas
• Other morphological terms


  • Cyst
  • Pustule
  • Scar
  • Wheal
  • Open comedone (blackhead)
  • Closed comedone (whitehead)
  • Petechiae
  • Purpura
  • Ecchymosis (bruise)
  • Telangiectasia
• Patterns and distribution of morphological lesions


  • Acral
  • Annular
  • Follicular
  • Guttate
  • Koebner phenomenon
  • Morbilliform
  • Reticular
  • Satellite
  • Serpiginous
  • Target/targetoid
• Differential diagnoses for common presentations


  • Brown macule
  • Discrete red papule
  • Red scales
  • Vesicle
  • Bulla
  • Pustule
  • Oral ulcer
• Immune


  • lichen planus
• Vascular


  • hemangioma
  • pyogenic granuloma
• Other


  • dermatofibroma
  • miliaria rubra
• Pityriasis rosea


  Red Scales
• Secondary syphilis
• Dermatitis


  • atopic
  • contact
  • nummular
  • seborrheic
• Discoid lupus
• Autoimmune


  • lichen planus
• Neoplastic


  • mycosis fungoides
• Viral


  • HSV
  • HZV
  • VZV
  • Molluscum
  • Coxsackie
• Acute contact dermatitis
• Dyshidrotic eczema
• Other


  • dermatitis herpetiformis
  • porphyria cutanea tarda
• Acute dermatitis


  • EM
  • SLE
  • SJS/TEN