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Basics of Dermatology

Fitzpatrick scale of skin phototypes
  • Skin phototype I: White skin color that always burns, and does not tan
  • Skin phototype II: White skin color that burns easily, and tans with difficulty
  • Skin phototype III: Beige skin color that burns mildly, and tans gradually
  • Skin phototype IV: Brown skin color that rarely burns, and tans easily
  • Skin phototype V: Dark brown skin color that rarely burns, and tans very easily
  • Skin phototype VI: Black skin color that never burns, and tans very easily
Types of melanin:
  1. Eumelanin (brown-black)
  2. Pheomelanin (yellow-red)

Inflammatory
  • Infectious: bacterial, viral, fungal, protozoal
  • Non-infectious: Autoimmune connective tissue diseases, urticaria and erythema, papulosquamous dermatoses, eczematous dermatoses, autoimmune bullous diseases
Neoplastic
  • Benign
  • Malignant
Other
  • Metabolic and toxic trauma
  • Genodermatoses and developmental anomalies

  • Native language of dermatologists to describe the appearance of skin lesions irrespective of etiology
  • Primary skin lesions: most characteristic skin lesion
  • Secondary skin lesions: effects of exogenous factors or temporal changes that evolve during the course of a skin disease
Primary lesions
  1. Macule
    • < 1 cm, non- palpable, circumscribed, discolored area of skin, hypo/hyperpigmented or other colors such as pink, red or violet
  2. Patch
    • > 1 cm, non- palpable, circumscribed, discolored area of skin, hypo/hyperpigmented or other colors such as pink, red or violet
  3. Papule
    • < 1 cm, palpable, circumscribed, elevation that results from increased thickness of epidermis or cells/ deposits within the dermis
    • Surface: Flat-topped (lichenoid), dome-shaped, umbilicated, verrucous
  4. Plaque
    • >1 cm palpable, circumscribed, elevation that results from increased thickness of epidermis or cells/ deposits within the dermis
    • May be palpable without being elevated e.g. morphea
  5. Nodule
    • Greater volume than papule, often >1 cm palpable, circumscribed, elevation that results from increased thickness of epidermis or cells/ deposits within the dermis
    • Involves the dermis and/or the subcutis
    • Can be exophytic or beneath the skin surface
  6. Wheal
    • Dermal edema leads to transient skin elevation
    • Pale center with an erythematous rim
  7. Vesicle
    • < 1 cm in diameter, elevated, circumscribed lesion filled with clear, serous or hemorrhagic fluid
    • May become pustular, umbilicated or have a secondary erosion
  8. Bulla
    • >1 cm in diameter, elevated, circumscribed lesion filled with clear, serous or hemorrhagic fluid
    • May become pustular, umbilicated or have a secondary erosion
  9. Pustule
    • < 1 cm in diameter, elevated, circumscribed lesion filled with purulent fluid
  10. Burrow
    • Tunnel (primary lesion seen in scabies)
Secondary lesions
  1. Crust
    • Dried serum, blood or pus on the skin
    • May include bacteria e.g. staphylococcus
  2. Scale
    • Hyperkeratosis
    • Increased proliferation and/or delayed desquamation leading to accumulation of stratum corneum
  3. Fissure
    • Linear split in skin
    • Painful
    • 2° to drying, thickening of the skin, and decreased elasticity
  4. Excoriation
    • Injury of all or part of the epidermis
    • Linear or punctate
  5. Erosion
    • Loss of part of the epidermis
  6. Ulcer
    • Complete loss of the epidermis
    • Possible loss of the dermis or subcutis
  7. Infarct
    • Tissue ischemia due to vascular compromise, thrombosis, emboli, vasculitis or vasospasm
    • Gray-white to purple to black
  8. Atrophy
    • Epidermal atrophy: thinning of the epidermis, wrinkling, and shiny appearance e.g. lichen sclerosis
    • Dermal atrophy: loss of dermal collagen and/or elastin leading to skin depression e.g. striae
    • Subcutaneous e.g. lipoatrophy
  9. Lichenification
    • Thickening (acanthosis) of the epidermis with resultant accentuation of skin lines
    • Commonly caused by rubbing
Configuration
  1. Annular e.g. tinea corporis
  2. Serpenginous e.g. cutaneous larva migrans
  3. Clustered/grouped e.g. herpetiform vesicles
  4. Reticulated e.g. Erythema ab igne
  5. Retiform e.g. Purpura fulminans
  6. Linear
    • Trauma/exposure e.g. contact dermatitis to poison ivy
    • Sporotrichoid pattern: Infectious agents can lead to papulonodules aligning along lymphatic vessels
    • Koebner phenomenon e.g. lichen planus
      • Formation of new lesions of a pre-existing dermatosis secondary to trauma
      • Pseudokoebner (autoinoculation): infection arising in damaged skin
      • Wolf isotopic response: Formation of a new dermatoses in the site of previously healed dermatoses e.g. granuloma annulare at a site of healed zoster)
    • Lines of Blaschko: Pathways of epidermal cell migration and proliferation during embryogenesis e.g. epidermal nevi
    • Dermatomal: Area of skin innervated by a spinal nerve e.g. herpes zoster
Distribution
  1. Extensor surfaces: Elbows and knees e.g. psoriasis
  2. Flexural surfaces: Antecubital and popliteal fossae e.g. Atopic dermatitis
  3. Inverse: Skin folds e.g. psoriasis
  4. Langer cleavage lines: Natural skin tension lines e.g. pityriasis rosea
  5. Seborrheic distribution: Areas rich in sebaceous glands; includes head and neck + upper trunk e.g. seborrheic dermatitis
  6. Photodistributed: Lesions emphasized in areas exposed to ultraviolet irradiation as well as photodermatoses e.g. polymorphic light eruption
Temporal course
  • Acute presentation: urticaria, morbilliform drug eruption, viral exanthem, allergic or irritant contact dermatitis, pityriasis rosea
  • Emergencies: Often present with fever and rash e.g. Stevens-Johnson syndrome, toxic epidermal necrolysis
  • Cephalocaudal progression: measles, pityriasis rubra pilaris
  • Scale: reflection of parakeratosis which needs 2 weeks to develop
  • Intact tense bullae: Rarely present for more than a week
  • Lichenification: develops in weeks or months

Erythema
  • (e.g. Dermatitis, Psoriasis, Morbiliform drug eruption, Viral exanthems, Insult that leads to vasodilation)
  • Palpation: helps determine whether erythema is blanchable; if erythema disappears with pressure suggests the color is 2° to vasodilation, but if erythema does not blanch, it is 2° to extravasation of red blood cells into the tissue i.e. purpura
Black
  • e.g. Skin necrosis due to: vascular compromise, vasculitis, Eschar e.g. anthrax, Cutaneous melanoma, Traumatic tattoos)
Blue (ceruloderma)
  • e.g. Cyanosis, Ecchymoses, Dermal melanocytosis e.g. Mongolian spot, Dermal melanocytomas e.g. blue nevi, Venous congestion, Drugs/deposits e.g. minocycline
Brown
  • can be seen in pigmented lesions e.g. Lentigines, nevi, or others e.g. postinflammatory hyperpigmentation, Melasma
Gray
  • e.g. Postinflammatory hyperpigmentation, Drugs/deposits e.g. argyria
Purpura
  • Non-palpable purpura e.g. solar purpura
  • Palpable purpura e.g. small vessel vasculitis
  • Vascular neoplasms e.g. angiosarcoma
White
  • Absence of melanocytes or melanin production e.g. vitiligo
  • Scarring e.g. discoid lupus erythematosus
  • Vasospasm e.g. Raynaud phenomenon
  • Deposits e.g. gouty tophi
  • Macerated stratum corneum or mucosal surfaces e.g. leukoplakia
Green
  • e.g. Pseudomonas infection, Tattoo, Chloroma
Orange-red/salmon
  • e.g. Pityriasis rubra pilaris
Yellow
  • e.g. Xanthomas, Carotenoderma, Deposits/drugs (e.g. quinacrine)