Dermatological diagnoses often have more than one name. The World Health Organisation (WHO) is undertaking a massive task to revise the International Classification of Diseases (ICD) to include preferred terminology for skin conditions, ICD11. Refer to the alpha draft of ICD11 for more information.
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 another name for skin disease.
When examining the skin, a dermatologist assesses distribution, morphology and arrangement of skin lesions, i.e. 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 light (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.
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: as the keratinocytes mature and move upwards towards the skin surface, they become flat in shape, or squamous (also called spinous or prickle cells). Langherhans cells are found in this layer.
- 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 (oil glands)
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: protein fibres arranged in bundles providing strength to the skin.
- Elastin: protein making up fibres that allow the skin to stretch
- Ground substance: gel containing hyaluronic acid and other polysaccharides.
- Fibroblasts: cells that produce collagen, elastin and ground substance.
- 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: extensive network of thin-walled vessels nourishing and draining the skin.
- Arector pili muscles: attached to hair follicles. Contraction results in goose bumps.
- 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.
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 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 – affects distal portions of limbs (hand, foot) and head (ears, nose).
- Blaschko lines – following a roughly linear, segmental pattern described by Blaschko and thought to be indicative of somatic mosaicism.
- 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
- Herpetiform – grouped umbilicated vesicles, as arise in Herpes simplex and Herpes zoster infections.
- Koebnerised – arising in a wound or scar. The Koebner phenomenon refers to the tendency of several skin conditions to affect areas subjected to injury.
- 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
- Seborrhoeic – the areas generally affected by seborrhoeic dermatitis, with a tendency to oily skin (seborrhoea). Scalp, behind ears, eyebrows, nasolabial folds, sternum and interscapular.
- 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
Configuration refers to the shape or outline of the skin lesions. Skin lesions are often grouped together. The pattern or shape may help in diagnosis as many skin conditions have 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 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.
Descriptive terms used to describe skin colour include:
- 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.
- 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.
- Leukoderma – white skin. Also known as achromia.
- Infarcts – black areas of necrotic tissue due to interrupted blood supply.
- Jaundice – excessive circulating bilirubin results in yellow/green skin colour, prominent in cornea.
- Erythema – red skin due to increased blood supply and blanch with pressure (“diascopy”).
- Erythroderma – the skin condition affects the whole body or nearly the whole body, which is red all over.
- Telangiectasia – prominent cutaneous blood vessels.
- Purpura – bleeding into the skin. This may be as petechiae (small red, purple or brown spots) or ecchymoses (bruises). Purpura does not blanch with pressure (diascopy).
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 – an area of colour change less than 1.5 cm diameter. The surface is smooth.
- Patch – a large area of colour change, with smooth surface.
- Papule – a small palpable lesion. The usual definition is that they 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. Papules may be:
- Acuminate (pointed)
- Dome-shaped (rounded)
- Filiform (thread-like)
- Oval or round
- Pedunculated (with a stalk)
- Sessile (without a stalk)
- Umbilicated (with a central depression)
- Verrucous (warty)
- Nodule – an enlargement of a papule in three dimensions (height, width, length). It is a solid lesion.
- Cyst – a papule or nodule that contains fluid, so is fluctuant.
- 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 – small fluid-filled blister less than 0.5cm diameter. They may be single or multiple.
- Pustule – a purulent vesicle. It is filled with neutrophils, and may be white, or yellow. Not all pustules are infected.
- Bulla – a large fluid-filled blister. It may be a single compartment or multiloculated.
- Abscess is a localised collection of pus.
- Weal – 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.
- 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 skin surface)
- Keratotic (horny scale)
- Exfoliation (peeling skin)
- Maceration (moist peeling skin)
- Verrucous (warty)
- 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 scratch mark. It may be linear or a picked scratch (prurigo). Excoriations may occur in the absence of a primary dermatosis.
- Erosion – caused by loss of the surface of a skin lesion; it is a shallow moist or crusted lesion.
- Fissure – a thin crack within epidermis or epithelium, and is due to excessive dryness.
- 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 – full thickness loss of epidermis or epithelium. It may be covered with a dark-coloured crust called an eschar.
- Granuloma – a histological (pathological) term refering to chronic inflammation in which there are several types of inflammatory cells including giant cells. Granulomas form in response to foreign bodies, certain infections (tuberculosis, leprosy) and inflammatory skin diseases (granuloma annulare, granuloma faciale, sarcoidosis).
- Hypertrophy – some component of the skin such as a scar is enlarged or has grown excessively. The opposite is atrophy or thinned skin.