Introduction to dermatology
Terminology in dermatology
To develop skills in describing dermatological signs including:
- Site and size of a skin lesion.
- Distribution of skin eruption.
- Configuration (shape) of skin lesions.
- Morphology of primary skin lesion.
- Secondary changes.
This section provides a glossary of dermatological terms to enable students to describe dermatoses. A lesion is any single area of altered skin. It may be solitary or multiple. A rash is a widespread eruption of lesions.
Skin lesions may be isolated (solitary or single) or multiple. The localisation of multiple lesions in certain regions helps diagnosis, as skin diseases tend to have characteristic distributions. What is the extent of the eruption and its pattern?
Affects distal portions of limbs (hand, foot) and head (ears, nose).
Corresponding with nerve root distribution.
Involving extensor surfaces of limbs. Contrast with "flexor" surfaces.
Involving skin flexures (body folds); also known as "intertriginous"
Individual lesions arise from hair follicles. These may be grouped into confluent plaques.
- Generalised universal distribution
- May be mild or severe, "scattered" or "diffuse"
Arising in a wound or scar. The Koebner phenomenon refers to the tendency of several skin conditions to affect areas subjected to injury (particularly psoriasis, lichen planus and vitiligo).
Favouring sun exposed areas. Does not affect skin that is always covered by clothing.
- Head and neck: spares eyelids, depth of wrinkles and furrows, areas shadowed by hair, nose and chin. Typically involves "v" of neck.
- Backs of hands: spares finger webs. More severe on proximal than distal phalanges.
- Forearms: extensor rather than flexor.
- Feet: dorsal surface, sparing areas covered by footwear.
- Lower legs: may affect extensor and/or flexor surfaces
- Trunk: rarely affected
- Pressure areas
Affecting areas regularly prone to injury from pressure at rest.
- Tops of the ears when sleeping
- Buttocks when sitting
- Heels when lying
In the same regions, the left side is affected in a similar way to the right side.
Favours trunk and rarely affects limbs.
Wholly or predominantly on one side of the affected region.
Configuration of Lesions
Skin lesions are often grouped together. The pattern or shape may help in diagnosis as many skin conditions have characteristic configuration.
Lesions grouped in a circle. Multiple rings are "polycyclic"
Round (coin-shaped) lesions. Also known as "nummular".
A rash that appears to be whirling in a circle or spiral.
A linear shape to a lesion often occurs for some external reason such as scratching. Also "striate"
Resembling a net.
- Target lesion
Concentric rings like a dartboard. Also known as "iris" lesion.
Skin colour can range from white to black, including shades of red, yellow, blue and green. Terms relating to skin colour include:
White skin (absence of pigment). Also known as "leucoderma".
Excessive circulating beta-carotene (vitamin-a precursor derived from yellow/orange coloured vegetables and fruit) results in yellow/orange skin colouration. Tends to be pronounced on palms and soles. Does not affect cornea.
Red skin due to increased blood supply. Blanches with pressure.
The skin condition affects the whole body or nearly the whole body, which is red all over.
Hypermelanosis or haemosiderin deposits result in skin colour that is darker than normal.
Loss of melanin results in skin colour that is paler than normal but not completely white.
Infarcts are initially purple then black areas of necrotic tissue due to interrupted blood supply.
- Excessive circulating bilirubin results in yellow/green skin colour, prominent in cornea.
Bleeding into the skin. This may be as petechiae (small red, purple or brown spots) or ecchymoses (bruises). It does not blanch with pressure.
Telangiectasia is the name given to prominent cutaneous blood vessels.
Skin lesions may be flat, elevated above the plane of the skin or depressed below the plane of the skin. They may be skin coloured or red, pink, violaceous, brown, black, grey, blue, orange, yellow.
Consistency may be soft, firm, hard, fluctuant or sclerosed (scarred or board-like). The lesions may be hotter or cooler than surrounding skin. They may be mobile or immobile
- Localised collection of pus within a nodule, more than 1 cm in diameter.
Large fluid-filled blister. It may be a single compartment or multiloculated.
A papule or nodule that contains fluid so is fluctuant.
An area of colour change less than 1.5 cm diameter. The surface is smooth.
An enlargement of a papule in three dimensions (height, width, length). It is a solid lesion.
A small palpable lesion. The usual definition is that papules are less than 0.5 cm diameter, although some authors allow up to 1.5 cm. They are raised above the skin surface, and may be solitary or multiple.
A large area of colour change, with smooth surface.
A palpable flat lesion greater than 0.5 cm diameter. Most plaques are elevated, but a plaque can also be a thickened area without being visibly raised above the skin surface. They may have well-defined or ill-defined borders.
A purulent vesicle. Filled with neutrophils. May be white or yellow. Not all pustules are infected.
A small blister less than 0.5cm diameter. Fluid-filled papule. May be single or multiple.
An oedematous papule or plaque caused by swelling in the dermis. Wealing often indicates urticaria.
The skin surface of a skin lesion may be normal or smooth because the pathological process is below the surface, either dermal or subcutaneous.
Surface changes indicate epidermal changes are present.
Flaking skin due to an increase in the dead cells on the surface of the skin (stratum corneum).
Secondary changes are seen in older skin lesions and result from progression of the disease process, trauma or healing processes.
Thinned. Reflects shrinkage or reduced growth of some component of the skin, for example atrophic scars due to chickenpox.
Hard surface deposit. Occurs when plasma exudes through an eroded epidermis. It is rough on the surface and is yellow or brown in colour. Bloody or haemorrhagic crust appears red, purple or black.
A shallow moist lesion caused by loss of the surface of a skin lesion.
Dark-coloured adherent crust over longstanding ulceration.
A scratch mark. It may be a linear scratch or a picked lesion (as in prurigo). Excoriations may occur in the absence of a primary skin lesion.
A thin crack within epidermis or epithelium due to excessive dryness.
Thickened. Reflects enlargement or excessive growth of some component of the skin, for example a hypertrophic scar in which there is excessive collagen.
Caused by chronic rubbing, which results in palpably thickened skin with increased skin markings and lichenoid scale. It occurs in chronic atopic eczema and lichen simplex.
Permanent mark, where skin healing has involved fibrous connective tissue with collagen deposition. Commonly hypopigmented, sometimes hyperpigmented. May be atrophic or hypertrophic.
Full thickness loss of epidermis or epithelium. Slow-healing tendency (>4 weeks). May be covered with eschar. Heals with a scar.