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Introduction to dermatology

Terminology in dermatology

Objectives

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.

Distribution

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?

Acral
Affects distal portions of limbs (hand, foot) and head (ears, nose).
Dermatomal
Corresponding with nerve root distribution.
Extensor
Involving extensor surfaces of limbs. Contrast with "flexor" surfaces.
Flexural
Involving skin flexures (body folds); also known as "intertriginous"
Follicular
Individual lesions arise from hair follicles. These may be grouped into confluent plaques.
Generalised universal distribution
May be mild or severe, "scattered" or "diffuse"
Koebnerised
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).
Photosensitive

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

Symmetrical
In the same regions, the left side is affected in a similar way to the right side.
Truncal
Favours trunk and rarely affects limbs.
Unilateral
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.

Annular
Lesions grouped in a circle. Multiple rings are "polycyclic"
Discoid
Round (coin-shaped) lesions. Also known as "nummular".
Gyrate
A rash that appears to be whirling in a circle or spiral.
Linear
A linear shape to a lesion often occurs for some external reason such as scratching. Also "striate"
Reticulated
Resembling a net.
Target lesion
Concentric rings like a dartboard. Also known as "iris" lesion.

Colour

Skin colour can range from white to black, including shades of red, yellow, blue and green. Terms relating to skin colour include:

Achromia
White skin (absence of pigment). Also known as "leucoderma".
Carotenaemia
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.
Erythema
Red skin due to increased blood supply. Blanches with pressure.
Erythroderma
The skin condition affects the whole body or nearly the whole body, which is red all over.
Hyperpigmentation
Hypermelanosis or haemosiderin deposits result in skin colour that is darker than normal.
Hypopigmentation
Loss of melanin results in skin colour that is paler than normal but not completely white.
Infarcts
Infarcts are initially purple then black areas of necrotic tissue due to interrupted blood supply.
Jaundice
Excessive circulating bilirubin results in yellow/green skin colour, prominent in cornea.
Purpura
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
Telangiectasia is the name given to prominent cutaneous blood vessels.

Morphology

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

Abscess
Localised collection of pus within a nodule, more than 1 cm in diameter.
Bulla
Large fluid-filled blister. It may be a single compartment or multiloculated.
Cyst
A papule or nodule that contains fluid so is fluctuant.
Macule
An area of colour change less than 1.5 cm diameter. The surface is smooth.
Nodule
An enlargement of a papule in three dimensions (height, width, length). It is a solid lesion.
Papule
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.
Patch
A large area of colour change, with smooth surface.
Plaque
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.
Pustule
A purulent vesicle. Filled with neutrophils. May be white or yellow. Not all pustules are infected.
Vesicle
A small blister less than 0.5cm diameter. Fluid-filled papule. May be single or multiple.
Weal
An oedematous papule or plaque caused by swelling in the dermis. Wealing often indicates urticaria.

Skin surface

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.

Scaling
Flaking skin due to an increase in the dead cells on the surface of the skin (stratum corneum).

Secondary changes

Secondary changes are seen in older skin lesions and result from progression of the disease process, trauma or healing processes.

Atrophy
Thinned. Reflects shrinkage or reduced growth of some component of the skin, for example atrophic scars due to chickenpox.
Crusting
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.
Erosion
A shallow moist lesion caused by loss of the surface of a skin lesion.
Eschar
Dark-coloured adherent crust over longstanding ulceration.
Excoriation
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.
Fissure
A thin crack within epidermis or epithelium due to excessive dryness.
Hypertrophy
Thickened. Reflects enlargement or excessive growth of some component of the skin, for example a hypertrophic scar in which there is excessive collagen.
Lichenification
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.
Scar
Permanent mark, where skin healing has involved fibrous connective tissue with collagen deposition. Commonly hypopigmented, sometimes hyperpigmented. May be atrophic or hypertrophic.
Ulcer
Full thickness loss of epidermis or epithelium. Slow-healing tendency (>4 weeks). May be covered with eschar. Heals with a scar.