Terminology in dermatology

Introduction

If you don't find what you are looking for on this page, try DermNet's Glossary of Dermatology Terms or Dermatological diagnoses often have more than one name. DermNet refers to various resources when naming conditions, including the World Health Organisation (WHO)'s International Classification of Diseases (see ICD11 coding tool), and the Systematized Nomenclature of Medicine Clinical Terms (SNOMED CT).

Describing skin conditions

• A lesion is any single area of altered skin. It may be solitary or multiple.
• A rash is a widespread eruption of lesions.
• Dermatosis is a generic term for a disease of the skin.

When examining the skin, a dermatologist assesses distribution, morphology and arrangement of skin lesions: their number, size, and colour, which sites are involved, their symmetry, shape, and arrangement.

The dermatologist will carefully feel individual lesions, noting surface and deep characteristics. Which layer(s) of the skin are involved? If scaly, does the surface flake off easily? If crusted, what is underneath?

Specialised techniques include:

• Wood's lamp (long wave UVA) examination for pigmentary changes and fluorescent infections
• Dermoscopy for pigmented lesions to diagnose melanoma.

Structure of the skin

The skin is considered to have three parts: the outer epidermis, middle dermis and deep subcutaneous tissue. There is a basement membrane that separates the epidermis from the dermis and acts as a communication channel between the two layers.

Epidermis

The epidermis is a complex ‘brick wall’ made of cells called keratinocytes, which produce a protein called keratin. The epidermis also contains pigment cells called melanocytes, which produce melanin, Langerhans cells, which present antigens to the immune system, and Merkel cells, which have a sensory function.

• Basal layer — the columnar or rectangular cells at the bottom of the epidermis from which new cells are continuously produced. Scattered melanocytes are normally found in this layer.
• Squamous cells — flat epithelial cells found on the skin surface. The structure of the skin is described as a stratified squamous epithelium, referring to the way the cells are built up in layers.
• Granular layer — flattened cells filled with dark granules containing keratohyaline protein.
• Horny layer — stacks of dead cells without nuclei make up the dry or keratinised stratum corneum. The top layer of cells loosens and falls off.
• Desmosomes — the structures that stick adjacent keratinocytes tightly together, rather like cement between bricks.

Epidermal appendages include:

• Eccrine glands, which produce sweat
• Apocrine glands, scent glands found in armpits and groins
• Pilosebaceous structures containing hair and sebaceous glands
• Nails.

Dermis

The dermis is made up of connective tissue that supports the epidermis, providing nutrients and protecting it. The papillary dermis is the upper portion beneath the epidermis, and the lower portion is the reticular dermis.

• Collagen — a structural protein making up the bulk of the dermis. It is produced by fibroblasts. It is composed of a triple helix of strong fibres.
• Elastin — the protein that makes up thin elastic fibres. These are produced by fibroblasts. They return deformed skin to its resting position.
• Ground substance — the gel component of the dermis. It contains hyaluronic acid, dermatan sulphate, and chondroitin-6-sulphate (these are anionic polysaccharides or glycosaminoglycans).
• Fibroblasts — cells found in the dermis that produce collagen, elastin, ground substance and fibronectin (a glycoprotein).
• Nerves — sensory and autonomic fibres with distinct nerve endings for touch, heat, cold, pressure and pain.
• Blood vessels — arteries, arterioles, capillaries, venules and veins carrying blood to and from the skin.
• Lymphatics — an extensive network of thin-walled vessels that nourish and drain the skin.
• Arrector pili muscles — these are attached to hair follicles. Contraction results in goosebumps.
• Cellular infiltrations — immune cells around blood vessels, and recruited in great numbers to heal wounds and fight infection. Many skin diseases are characterised by specific patterns of these cells.

Subcutaneous tissue

The subcutaneous tissue, also called subcutis, is made up of adipose cells or lipocytes (fat cells). These are surrounded by connective tissue, blood vessels, and nerves.

Distribution

Distribution refers to how the skin lesions are scattered or spread out. 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 — relating to or affecting the distal extremities (eg, ears, fingers, toes, nose, penis and nipples).
• Blaschko lines — following the roughly linear, segmental pattern described by Blaschko. Many birthmarks appear to be distributed within these segments.
• Dermatomal — lesions confined to one or more segments of skin innervated by a single spinal nerve (dermatomes).
• Extensor — involving extensor surfaces of limbs. Contrast with flexor surfaces.
• Flexural — related to flexion, or skin folds, such as the backs of knees, the armpits, the elbow creases and the groin.
• Follicular — lesions located within or around hair follicles.
• Generalised — lesions distributed randomly over most of the body surface area (widespread) or within an anatomical region.
• Herpetiform — solid papules within a cluster.
• Koebnerised — the appearance of new lesions of skin disease, such as psoriasis, at the site of a trauma.
• Photosensitive — increase in the reactivity of the skin to sunlight.
• Head and neck — spares eyelids, depth of wrinkles and furrows, areas shadowed by hair, nose and chin. Typically involves “V” of the 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 flexor surfaces
• Trunk — dorsal and ventral surfaces (back and front of the torso)
• Pressure areas — affecting areas regularly prone to injury from pressure at rest
  • Tops of the ears when sleeping
  • Buttocks when sitting
  • Heels when lying.
• Seborrhoeic — relating to seborrhoea (US English: seborrhea) where there is abnormally increased secretion and discharge of sebum (fatty lubricant matter secreted by sebaceous glands), producing an oily appearance to the skin and the formation of greasy scales.
  • Seborrhoeic keratosis — a common, harmless warty growth.
• Symmetrical – both sides are the same or similar.
• Truncal — favours trunk and rarely affects limbs.
• Unilateral — the rash affects one side of the bod only.

Configuration of lesions

Configuration refers to the shape or outline of the skin lesions. Skin lesions are often grouped. The pattern or shape may help in diagnosis as many skin conditions have a characteristic configuration.

• Nummular lesion — round (coin-shaped) lesions; also known as discoid.
• Linear lesion — a linear shape to a lesion often occurs for some external reason, such as scratching; also known as striate.
• Target lesion — concentric rings like a dartboard; also known as iris lesion.
• Gyrate rash — a rash that appears to be whirling in a circle.
• Annular — lesions grouped in a circle.

Colour

Descriptive terms used to describe skin colour include:

• Carotenoderma — yellow/orange skin hue due to excessive circulating beta-carotene (vitamin a precursor derived from yellow/orange coloured vegetables and fruit); tends to be pronounced on palms and soles, and does not affect the sclera.
• Hyperpigmentation — darkened skin compared to normal; it can be localised or generalised.
• Hypopigmentation — skin colour that is paler than normal.
• Leukoderma — white skin; also known as achromia.
• Infarcts — black areas of necrotic tissue due to an interrupted blood supply.
• Jaundice — yellowing of the skin and the whites of the eye and is due to a buildup of bile pigments in the blood; this is usually due to biliary or liver disease.
• Erythema — red skin due to an increased blood supply; may be applied to any red coloured dermatosis.
• Erythroderma — the skin condition affects the whole body or nearly the whole body, which is red all over.
• Telangiectasia — prominent cutaneous blood vessels; they are red or purple.
• Purpura — bleeding into the skin, either as petechiae (small red, purple or brown spots) or ecchymoses (bruises); purpura does not blanch with pressure (diascopy).

Morphology

Morphology is the form or structure of an individual skin lesion.

• 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.
• Macule — a small patch of skin that is altered in colour, but is not elevated.
• Patch — a large area of colour change, with a smooth surface.
• Papule — elevated, solid, palpable lesion that is ≤ 1 cm in diameter. They may be solitary or multiple. Papules may be:
  • Acuminate (pointed)
  • Dome-shaped (rounded)
  • Filiform (thread-like)
  • Flat-topped
  • Oval or round
  • Pedunculated (with a stalk)
  • Sessile (without a stalk)
  • Umbilicated (with a central depression)
  • Verrucous (warty)
• Nodule — elevated, solid, palpable lesion > 1 cm usually located primarily in the dermis and subcutis (deeper layers of the skin). The greatest portion of the lesion may be above or beneath the skin surface.
• Cyst — papule or nodule that contains fluid or semi-fluid material so is fluctuant.
• Plaque — a circumscribed, palpable lesion more than 1 cm in diameter; most plaques are elevated. Plaques may result from a coalescence of papules. 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. The name 'plaque' is derived from the French word for a plate. Plaques may be:
  • Annular (ring-shaped)
  • Arcuate (half-moon)
  • Polygonal (varied non-geometric shape)
  • Polymorphic (varied shape)
  • Serpiginous (in the shape of a snake)
  • Poikilodermatous (variegated appearance, usually mixed pallor, telangiectasia and pigmentation)
• Vesicle — a small blister. It is a circumscribed lesion ≤ 1 cm in diameter that contains liquid (clear, serous or haemorrhagic). They may be single or multiple. The adjective is "vesicular".
• Pustule — a circumscribed lesion that contains pus. It is filled with neutrophils and may be white, or yellow. Not all pustules are infected.
• Bulla — a large blister. A circumscribed lesion more than 1 cm in diameter that contains liquid (clear, serous or haemorrhagic).
• An abscess is a localised collection of pus.
• Weal — also spelt ‘wheal’, is a transient elevation of the skin due to dermal oedema, often pale centrally with an erythematous rim and without surface change. Wealing indicates urticaria or an urticaria-like condition.

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 or hyperkeratosis — an increase in the dead cells on the surface of the skin (stratum corneum). Descriptive terms for scale include:
  • Desquamation (skin coming off in scales)
  • Psoriasiform (large white or silver flakes)
  • Pityriasiform (branny powdery scale)
  • Lichenoid (apparent scale is tightly adherent to the skin surface)
  • Keratotic (horny scale)
  • Exfoliation (peeling skin)
  • Maceration (moist peeling skin)
  • Verrucous (warty).

Secondary changes

• 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.
• Crusting — the result of plasma exuding through an eroded epidermis. It is rough on the surface and is yellow or brown in colour. Bloody crust appears red, purple or black.
• Dystrophy — degeneration or abnormal formation of the skin. It is often used to refer to nail diseases.
• Excoriation — a loss of the epidermis and a portion of the dermis due to scratching or an exogenous injury. It may be linear or punctate.
• Erosion — a sore due to the superficial or partial destruction of surface tissue such as the skin.
• Fissure — a split, crack, erosion or narrow ulceration of the skin.
• Fungating — refers to a large malignant tumour that is erupting like a mushroom or fungus.
• Granulation tissue — made of a mass of new capillaries and fibrous tissue in a healing wound.
• Ulcer — the full-thickness loss of the epidermis plus at least a portion of the dermis; it may extend into the subcutaneous tissue. An ulcer heals with a scar.
• Granuloma — a type of inflammation characterised by histiocytes.
• Hypertrophy — explains that some component of the skin such as a scar is enlarged or has grown excessively.