Skin

Introduction to Dermatology

• Presenter: Vanessa Paddon, Dermatologist at St Vincent's Hospital.

What is Dermatology?

• Definition: The branch of medicine concerned with the diagnosis and treatment of skin disorders, including diseases of hair and nails.

• Objectives:

  • Understand the functions of the skin at a basic level.

  • Observe and describe common skin lesions.

  • Understand skin phototypes.

• Practice in Australia:

  • Skin conditions account for about 15% of patient encounters at GP visits.

  • Skin cancer is the second most common reason for referral to a specialist.

Structure of the Skin

• Largest Organ: Weighs over 5 kg in a 70 kg person.

• Components:

  • Epidermis: Stratified cellular layer.

  • Dermis: Connective tissue layer.

  • Subcutaneous fat layer.

  • Appendages: Includes hair follicles, sweat glands, and sebaceous glands.

Epidermis

• Description:

  • Mainly composed of keratinocytes that are layered.

  • Basal layer divides and migrates upwards approximately every 30 days.

  • Top layer (stratum corneum) is highly insoluble.

• Cell Types:

  • Melanocytes: Produce melanin pigment.

  • Langerhan’s cells: Immune function.

  • Merkel cells: Mechanosensors.

Dermis

• Function: Supportive matrix made of proteins and polysaccharides.

• Components:

  • Collagen (85% of dry weight): Provides tensile strength.

  • Elastic fibers (2-4%): Provide elasticity and resilience.

  • Contains blood supply, lymphatics, nerves, and ground substance, which holds water in the skin.

Functions of the Skin

• Primary Roles:

  • Mechanical barrier.

  • Immune defense.

  • Protection from UV radiation.

  • Thermoregulation.

  • Synthesis of vitamin D.

• Appendage Functions:

  • Nails: Protect ends of fingers/toes, assist in pinching and prising.

  • Hair: Offers social and psychological value.

Skin Lesion Terminology

• Lesion: An area of altered skin (could be solitary or multiple).

• Eruption: Widespread multiple lesions.

• Dermatosis: General term for skin disease.

Morphology of Skin Lesions

Macule

• Definition: A small non-palpable area of color change, less than 1.5 cm in diameter.

Papule

• Definition: A small palpable lesion, less than 0.5 cm in diameter.

Nodule

• Definition: A solid mass in the skin, elevated or palpable, more than 0.5 cm in diameter.

Patch

• Definition: A large non-palpable area of color change.

Plaque

• Definition: A palpable flat lesion greater than 1 cm in diameter.

Vesicle

• Definition: A small fluid-filled blister less than 0.5 cm in diameter.

Bulla

• Definition: A large fluid-filled blister.

Cyst

• Definition: A closed cavity or sac containing fluid or semisolid material.

Pustule

• Definition: A purulent vesicle (contains pus).

Abscess

• Definition: A localized collection of pus.

Erosion

• Definition: Loss of epidermis that heals without scarring (often follows a blister).

Ulceration

• Definition: Loss of epidermis and dermis which heals with scarring.

Secondary Descriptions of Morphology

Color

• Variations: Erythematous (red), Hyperpigmented, Yellow, Orange, Blue, Black, Green, Pink, and more.

Texture

Texture Variations:

• Scaly: Thin flakes of skin that are often dry, appearing as raised areas or spots on the skin surface.

• Crusted: A hardened layer of dried exudate or serum that forms a protective covering over damaged skin, often associated with healing lesions.

• Fissured: Thin, linear breaks in the skin that can occur in areas of dryness or irritation, sometimes painful or bleeding.

• Lichenified (thickened): Thickened skin that has developed as a result of prolonged scratching or irritation; often has a leathery appearance.

• Atrophic (thinned): Skin that appears thinner and fragile, often resulting from aging, certain diseases, or long-term use of topical steroids.

• Indurated: Hardened or thickened skin, often due to chronic inflammation or the presence of underlying lesions.

• Seborrhoeic: Associated with seborrheic dermatitis; characterized by oily, flaky, and often greasy patches on the skin.

• Verrucous: Rough and warty in texture, resembling a wart; often elevated with a bumpy surface.

Pattern

• Descriptions:

  • Grouped: Lesions that are clustered together.

  • Linear: Lesions that appear in a line or band-like formation.

  • Annular (ring-shaped): Lesions that form a circular or ring-like appearance.

  • Round/discoid: Lesions that are round and coin-shaped.

  • Reticular: Lesions that have a lace-like or net-like pattern.

  • Serpiginous: Lesions that have a wavy, snake-like appearance.

Distribution

• Descriptions:

  • Localized: Lesions that are confined to a specific area of the skin.

  • Generalized: Lesions that are widespread across the body.

  • Unilateral: Lesions that are present on one side of the body.

  • Bilateral: Lesions that are present on both sides of the body.

  • Trunk vs Limbs: Lesions may be located primarily on the torso (trunk) or on the arms and legs (limbs).

  • Acral: Lesions found on the extremities, such as hands and feet.

  • Sun exposed: Lesions that typically occur on areas of the skin that are frequently exposed to sunlight.

  • Intertriginous: Lesions located in skin folds where two skin surfaces touch, such as underarms and groin.

Skin Photocarcinogenesis

• Definition: Ultraviolet radiation is a known carcinogen.

• Types of UV Radiation:

  • UVC: Completely absorbed by the atmosphere.

  • UVB: Effective for causing sunburn.

  • UVA: Penetrates deeply, causes photoaging.

• Impact: Both UVA and UVB contribute to skin cancer development.

UV Index

• Definition: International standard measurement of sunburn-inducing UV radiation.

• Factors Influencing UV Index:

  • Time of day, year, cloud cover, altitude, and surrounding surfaces.

Fitzpatrick Skin Phototypes

• Overview: Numerical classification of human skin color based on response to UV light and basic color:

  1. Type I: Pale white, burns easily, no tan.

  2. Type II: Fair skin, tans with difficulty, burns easily.

  3. Type III: Darker white skin, tans after initial sunburn.

  4. Type IV: Light brown/olive skin, tans easily, minimal burning.

  5. Type V: Brown skin, tans easily, rare burning.

  6. Type VI: Dark brown/black skin, tans very easily, does not burn.

Summary

• Key Learnings:

  • Basic understanding of skin anatomy and functions.

  • Ability to describe different skin lesions.

  • Recognition of Fitzpatrick skin phototypes for appropriate assessment and treatment.