Overview
Dermatology can be defined as the study of both normal and abnormal skin, and associated structures such as hair, nails, and oral and genital mucous membranes.
- Functions of skin
- Protective barrier to physical agents
- Protection from mechanical injury
- Controls loss of body fluids, proteins and minerals
- Protects against UV radiation
- Temperature regulation
- Sensation
- Affords surface for grip
- Vitamin D synthesis
- Immunosurveillance
- Appearance/cosmesis
- Structure of skin
- Epidermis
- 4 major cell types
- Keratinocytes – produce protective barrier of keratin
- Langerhans’ cells – present antigens and activate T-cells (immunosurveillance)
- Melanocytes – produce pigment melanin that protects cell nuclei against radiation-induced DNA damage
- Merkel cells – specialized nerve endings for sensation
- 5 layers (each representing a different stage of keratinocyte maturation)
- Stratum basale (basal cell layer) – actively dividing cells; deepest layer
- Stratum spinosum ( prickle cell layer) – differentiating cells
- Stratum granulosum (granular cell layer) – with kerato-hyaline granules that secrete lipids into the intracellular spaces
- Stratum lucidum – paler compact keratin; in areas of thick skin like the soles
- Stratum corneum (horny layer) – layer of keratin; most superficial layer
- Pathology principles:
- Change in epidermal turnover time – e.g. reduced in psoriasis
- Change in surface if skin/ loss of epidermis – e.g. scales, crusting, exudate, ulcer
- Change in skin pigmentation – e.g. hypo or hyperpigmentation
- 4 major cell types
- Dermis
- Made up of collagen (70%), elastin, glycosaminoglycans; contains skin appendages, nerves, lymphatic and blood vessels, immune cells
- Pathology principles:
- Change in skin contour or loss of dermis – e.g. pustules, nodules, skin atrophy, ulcers
- Disorders of skin appendages (see below)
- Changes related to blood and lymphatic vessels – e.g. erythema (vasodilation), purpura (capillary leakage), urticaria (increased capillary and small venule permeability)
- Subcutaneous layer: loose connective tissue and fat
- Skin appendages
- Hair
- Found on all globous skin except palms, soles, glans penis and vulva
- 3 types of hair
- Lanugo hair – fine long hair in in utero from 20 weeks and in premature babies
- Vellus hair – short, fine, light-coloured hair on all body surfaces
- Terminal hair – coarse long hair on scalp, eyebrows, eyelashes, pubic area. Stimulated at puberty by androgen
- Each hair consists of
- Hair shaft – tube of modified keratin
- Hair bulb – actively dividing cells + melanocytes which give pigment to hair
- 3 phases of hair follicle growth cycle
- Anagen – long growing phase (approx. 2-6 years)
- Catagen – short regressing phase (approx. 3 weeks)
- Telogen – resting/shedding phase (approx. 3 months)
- Pathology principles:
- Reduced/absent melanin production – e.g. in grey or white hair
- Changes in growth cycle duration – e.g. hair loss caused by premature entry of hair follicles into telogen phase
- Shaft abnormalities
- Nails
- Each nail made up of:
- Nail matrix: is the source of dividing nail cells, which mature to become keratinised and move to become the nail plate
- Nail plate: lies on the nail bed and adheres to it
- Hyponychium: Thick epidermis (thickened layer of stratum corneum) underneath the free edge of the nail (section that extends beyond the skin)
- Eponychium: Live skin at the base of the nail. May be referred to as the nail fold. Differs from cuticle, which consists of dead cells.
- Perionychium: Skin surrounding nail
- Lunula – whitened half-moon at base of nail, outlining the nail matrix. If damaged, leads to permanent nail deformity.
- Note: Fingernails grow faster than toenails: this affects the duration of treatment in nail diseases; Fingernails are treated for 3 months vs. toenails which are treated for 6 months.
- Each nail made up of:
- Sebaceous glands
- An exocrine (holocrine) gland in the dermis that excretes sebum, an oily, waxy substance that provides lubrication and water-proofing to hair skin. Also has antimicrobial, antioxidant and photoprotective properties.
- Associated with hair structure and are androgen-sensitive (inactive between ages 6 months and puberty therefore cannot get infected at this time). Inhibited by estrogens.
- Pilosebaceous unit = sebaceous gland + arrector pili muscle + hair follicle
- Sweat glands
- Tube-like coiled structures within the dermis that produce watery secretions
- There are 2 types:
- Eccrine: universally found in the skin, they are profuse on the palms, soles, axilla, and forehead. They have thermal and psychological control and are innervated by sympathetic cholinergic nerves
- Apocrine: open into hair follicles, are larger than eccrine glands and are mostly found in the axilla, perineum and areolae. They are innervated by sympathetic adrenergic nerves
- Nerve supply
- The hands, face and genitalia have the highest supply
- All skin nerves have their cell body in the dorsal root ganglia.
- Free nerve endings end as Merkel cells and detect pain, temperature and itch
- Meissner corpuscles are located in the palms and soles.
- Hair
- Epidermis
Dermatological History
- Biodata
- Age
- Race
- Sex
- Presenting complaint
- Nature, site, and duration of the problem
- History of presenting complaint
- Description of the initial appearance of the lesion
- Evolution of lesion: describe how it spread as well as any change in the appearance of individual lesions (Where did it first appear? How did it look? Where is it now? How does it look now?)
- Associated symptoms, particularly itch and pain
- Any relieving or aggravating factors (triggers may include heat/cold, sun, exercise, recent contact, travel, drug ingestion, pregnancy, illness, or stressful events)
- Any previous history of similar complaints
- Previous and current treatments (effective or not)
- Patient’s current skincare regimen (soaps, lotions, creams, oils, makeup, etc..)
- Skin phototype/ Fitzpatrick skin type (studies are questioning the efficacy of this classification)
Fitzpatrick skin type and scoring
| Skin type and score | Typical features | Tanning ability |
|---|---|---|
| I (0-6) | Pale white skin, blue/green eyes, blonde/red hair | Always burns, does not tan |
| II (7-13) | Fair skin, blue eyes | Burns easily, tans poorly |
| III (14-20) | Darker white skin | Tans after the initial burn |
| IV (21-27) | Light brown skin | Burns minimally, tans easily |
| V (28-34) | Brown skin | Rarely burns, tans darkly easily |
| VI (35-36) | Dark brown or black skin | Never burns, always tans darkly |
- Past medical history
- History of atopy (asthma, eczema, allergic rhinitis, etc.)
- Known food or drug allergies
- Known chronic diseases (diabetes, hypertension, etc.)
- History of immunosuppression (RVD status, steroid use, nutrition status, chemotherapy etc..)
- History of skin malignancy or suspicious skin lesions
- Habits ( smoking, alcohol intake, drug abuse)
- Family and social history
- Family history of skin disease
- Occupation: Do lesions disappear or improve when away from work?
- Impact of skin condition on daily life and psychological state
- Review of systems
- Constitutional symptoms
- “Acute illness” syndrome – headache, chills, fever, weakness
- “Chronic illness” syndrome – fatigue, anorexia, weight loss, malaise
Examining the Skin
Preferably done in natural light. A magnifying lens or dermatoscope may be used.
4 important principles:
- INSPECT (in general)
- General observation of site and number of lesions
- Pattern of distribution and configuration if multiple
- DESCRIBE (individual lesions) SSCAMM:
- Size (widest diameter)
- Shape
- Color
- Associated secondary change
- Morphology
- Margin
- Asymmetry
- Border irregular
- Colors within lesion are two or more
- Diameter >6mm
- PALPATE (individual lesions)
- Surface
- Consistency
- Mobility
- Tenderness
- Temperature
- Estimated depth
- SYSTEMATIC CHECK
- Examine nails, scalp, hair and mucous membranes (very important!)
- General examination of all systems
Terms Used in Dermatology
These terms are used to describe, record, and communicate examination findings accurately.
General Terms
- General terms used in dermatology
- Pruritus: itching
- Lesion: an area of altered skin, a general term for an area of disease and is usually small
- Can either be primary pathology or secondary to factors like infection
- Primary lesion unit is 0.5 cm. Examples: macules, papules, nodule, bulla, vesicles, pustules and plaque
- Secondary lesions: scale, ulcer, fissure, crust
- Rash/ eruption: more widespread skin involvement
- Naevus: a localized malformation of tissue structures e.g. pigmented melanocytic naevus (mole)
- Comedone: a plug in sebaceous follicles that contains altered sebum, bacteria, and cellular debris. Can present as either open (blackheads) or closed (whiteheads)
Distribution
- Terms used to describe distribution (pattern of spread of lesion)
- Isolated- single lesions
- Localised – restricted to one area of skin only
- Generalised – all over the body
- Widespread – extensive
- Flexural – body folds, e.g. groin, neck, popliteal and antecubital fossae, behind ears
- Extensor – elbows, knees, shins
- Pressure areas – sacrum, buttocks, ankles, heels
- Dermatome – area of skin supplied by a single spinal nerve
- Photosensitive – affecting sun-exposed areas e.g. face, neck, back of hands (as seen in sunburn)
- Köebner phenomenon – a linear eruption arising at site of trauma (as seen in psoriasis)
Configuration
- Terms used to describe configuration (pattern or shape of grouped lesion)
- Discrete – individual lesions; separated from each other
- Confluent – lesions merging together
- Linear – in a line
- Target – concentric rings
- Centrifugal – radiating from the centre (as seen in erythema multiforme, erythema nodosum, smallpox)
- Centripetal – radiating to centre (as seen in pitiyriasis rosea, chicken pox)
- Annular – circular or ring-like (as seen in tinea corporis)
- Discoid / nummular – round or coin-shaped (as seen in discoid eczema)
Color
- Terms used to describe color
- Erythema – redness due to inflammation and vasodilation which blanches on pressure
- Purpura – red, purple or darkened coloration due to bleeding into skin or mucus membranes, which does not blanch on pressure
- Petechiae – small pinpoint macules <4mm
- Purpura – 4-10mm
- Ecchymoses – larger bruise-like patches >10mm
- Hypopigmentation – area(s) of paler skin (as seen in pityriasis versicolor)
- Depigmentation – white skin due to absence of melanin (as seen in vitiligo)
- Hyperpigmentation – area(s) of darker skin due to various causes e.g. post-inflammatory, pregnancy (as seen in melasma)
- Pallor
- Jaundice
- Cyanosis
Morphology
- Primary lesion (initial structure of lesion)
- Macule – a flat area of altered skin colour <0.5cm (as seen in freckles)
- Patch – a flat area of altered colour or texture >0.5cm (as seen in naevus flammeus)
- Papule – a solid raised lesion <0.5cm diameter (as seen in xanthomata)
- Nodule – a solid raised lesion >0.5cm with a deeper component (as seen in pyogenic granuloma)
- Plaque – palpable scaling raised lesion >0.5cm diameter (as seen in psoriasis)
- Vesicle – raised, clear, fluid-filled lesion <0.5cm diameter (small blister)
- Bulla– raised, clear, fluid-filled lesion >0.5cm diameter (large blister)
- Pustule – pus-containing lesion <0.5cm diameter (as seen in acne)
- Abscess – localized accumulation of pus in the dermis or subcutaneous tissues
- Wheal – transient raised lesion due to dermal edema (as seen in urticaria)
- Furuncle – staphylococcal infection around or within a hair follicle
- Carbuncle – staphylococcal infection of adjacent hair follicles (furuncles)
- Secondary lesion (lesion that evolves from primary lesion)
- Excoriation – loss of epidermis following trauma causing a raw linear area; often self inflicted
- Lichenification – well-defined roughening of skin with accentuation of skin markings
- Scales – dry flakes of stratum corneum
- Large, loose scales signify an acute condition compared to smaller adherent scales
- Crust – rough surface consisting of dried serum, blood, bacteria, and cellular debris that has exuded through an eroded epidermis (dried exudate)
- Scar – new fibrous tissue which occurs post-wound healing, and may be:
- Atrophic – thinning
- Hypertrophic – hyperproliferation within wound boundary
- Keloidal – hyperproliferation beyond wound boundary
- Erosion: area of loss of the epidermis
- Ulcer – area of loss of epidermis and dermis which heals with scarring
- Fissure – an epidermal crack, often due to excess dryness, that is longer than it is wide
- Striae – linear areas that progress from purple to pink to white, with the histopathological appearance of a scar, associated with excessive steroid usage, glucocorticoid production, growth spurts, and pregnancy
Hair
- Terms used to describe hair
- Alopecia – loss of hair
- Hirsutism – androgen-dependent hair growth in a female
- Hypertrichosis – non-androgen dependent pattern of excessive hair growth
Nails
- Terms used to describe nails
- Clubbing – loss of angle between the posterior nail fold and nail plate
- Koilonychia – spoon-shaped depression of nail plates
- Onycholysis – separation of the distal end of the nail plate from the nail bed (can be seen in psoriasis)
- Pitting – punctate depression of the nail plate (can be seen in psoriasis, eczema, alopecia areata)
