Professional Reference articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
See also separate Dermatological History and Examination article.
The need for terminology
Dermatologists can sound erudite when they use the abundance of descriptive terms at their disposal. These terms are often simply describing the rash in Latin. Sometimes the words are of Greek derivation such as ichthyosis (meaning scales like a fish). Latin or Greek terminology may be used but the two should not be mixed.
The skin is affected by a vast number of insults and diseases, including genetic and metabolic abnormalities as well as infections and yet there is a limited number of ways in which it can respond. History and examination involve making an assessment of the condition, including describing it. Simply understanding dermatological terminology will facilitate diagnosis.
- A lesion is any single area of altered skin. It may be solitary or multiple.
- A rash is a widespread eruption of lesions (greater than 20 lesions).
- Dermatosis simply means skin disease.
- Dermatitis means inflammation of the skin. It is not a final diagnosis.
Structure of skin
The skin has three layers called epidermis, dermis and deep subcutaneous tissue with a basement membrane between the epidermis and the dermis.
The epidermis has an outer layer of cells called keratinocytes, which produce keratin. The epidermis also contains pigment cells called melanocytes, which produce melanin, Langerhans' cells, which are part of the immune system, and Merkel's cells, which have a sensory function.
- The basal layer is the columnar cells at the base of the epidermis from which new cells are continuously produced. Melanocytes are normally scattered through this layer.
- Squamous cells are produced as the keratinocytes mature and move upwards towards the surface of the skin. They become flat in shape, or squamous and are also called spinous or prickle cells. Langherhans' cells are found in this layer.
- The granular layer contains flattened cells filled with dark granules containing keratohyaline protein.
- The horny layer is stacks of dead cells without nuclei and they make up the dry or keratinised stratum corneum. The top layer of cells loosens and falls off.
- Desmosomes are the structures that produce adherence of keratinocytes and they bind them together.
- Eccrine glands, which produce sweat.
- Apocrine glands, which are scent glands found in armpits and groins.
- Pilosebaceous structures containing hair and sebaceous glands.
The dermis is composed of connective tissue that supports the epidermis, providing nutrients and protection. The papillary dermis is the upper portion beneath the epidermis and the lower portion is the reticular dermis.
- Collagen is protein fibres arranged in bundles to give strength to the skin.
- Elastin is a protein that allows the skin to stretch.
- Ground substance is gel containing hyaluronic acid and other polysaccharides.
- Fibroblasts produce collagen, elastin and ground substance.
- The dermis also contains sensory and autonomic nerves, blood vessels as arteries, arterioles, capillaries, venules and veins, and an extensive network of lymphatics.
- Erector pili muscles are attached to hair follicles.
- There may be a cellular infiltration of immune cells around blood vessels in infection, allergy and trauma.
This is also called subcutis and is composed of adipose cells or lipocytes. These are surrounded by connective tissue, blood vessels and nerves.
Distribution of lesions
This is important, as the distribution of lesions is often characteristic and hence of diagnostic importance:
- Acral means affecting the distal portions of limbs (hand, foot) and head (ears, nose).
- Blaschko's lines means that lesions follow a segmental pattern described by Blaschko and this is thought to suggest somatic mosaicism.
- Dermatomal means corresponding with nerve root distribution, as with shingles.
- Flexural means occurring in the flexor surfaces, such as the antecubital fossa and back of the knee, whilst extensor is occurring on the extensor surfaces, such as over the tip of the elbow and usually just below the patella.
- Herpetiform means grouped umbilicated vesicles, as seen in herpes simplex and herpes zoster infections.
- Morbilliform means that the patient has a rash that looks like measles.
- Seborrhoeic refers to the areas generally affected by seborrhoeic dermatitis, with a tendency to oily skin or seborrhoea. They include the scalp, behind the ears, eyebrows, nasolabial folds, sternum, natal cleft and interscapular region.
- Truncal means affecting the trunk and (rarely) the limbs.
Shape of lesions
- Annular lesions are grouped in a circle.
- A gyrate rash appears to be whirling in a circle.
- A linear lesion, also known as striate, is like a line and often occurs from trauma such as scratching.
- Nummular or discoid means round or coin-shaped lesions.
- Target lesions, also known as iris lesions, have concentric rings like an archery target.
- Erythroderma is a skin condition in which the whole body or nearly the whole body is affected. It is red all over.
- Erythema is red skin due to increased blood supply and it will blanch on pressure.
- Purpura is 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, is the 'glass test' that is publicised for meningococcal septicaemia.
- In carotenaemia, excessive circulating beta-carotene results in yellow-to-orange skin colouration. It is most pronounced on palms and soles and, unlike jaundice, it does not affect the cornea.
- Hyperpigmentation may be caused by excess of melanin or haemosiderin deposits which result in skin colour that is darker than normal. Hypopigmentation is loss of normal melanin and results in skin colour which is paler than normal but not completely white.
- In leukoderma, also known as achromia, the skin is white.
- Infarcts are black areas of necrotic tissue due to ischaemia.
- A macule is an area of colour change less than 1 to 1.5 cm in diameter. The surface is smooth.
- A papule is a small palpable lesion. The usual definition is that they are less than 0.5 cm in 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 (means pointed).
- Dome-shaped or hemispherical.
- Filiform or thread-like.
- Oval or round.
- Pedunculated (have a stalk).
- Sessile (have no stalk).
- Umbilicated (have a central depression).
- Verrucous (like warts).
- A patch is a large area of colour change (bigger than a macule) with a smooth surface.
- A nodule is an enlargement of a papule in three dimensions (height, width and length). It is a solid lesion.
- A cyst is a papule or nodule that contains fluid and so is fluctuant although it may be tense.
- A plaque is a palpable flat lesion greater than 0.5 cm in 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. Plaques may be:
- Annular - ring-shaped.
- Arcuate - like a half-moon.
- Polygonal - have varied non-geometrical shapes.
- Polymorphic - being of varied shape.
- Serpiginous - in the shape of a snake or serpent.
- Poikilodermatous - have a variegated appearance, usually mixed pallor, telangiectasia and pigmentation.
- Vesicles are small fluid-filled blisters less than 0.5 cm in diameter. They may be single or multiple.
- A pustule is a purulent vesicle. It is filled with neutrophils and may be white or yellow. Not all pustules are infected.
- A bulla is a large fluid-filled blister. It may be a single compartment or multiloculated.
- An abscess is a localised collection of pus.
- A wheal is an oedematous papule or plaque caused by swelling in the dermis. Wheals often indicate urticaria.
Scaling or hyperkeratosis is an increase in the dead cells on the surface of the skin called the stratum corneum. Descriptive terms for scale include:
- Desquamation - skin coming off in scales.
- Psoriasiform - large white or silver flakes, as in psoriasis.
- Pityriasiform - a branny powdery scale.
- Lichenoid - when scale is tightly adherent to the surface of the skin.
- Keratotic - horny scale with plenty of keratin.
- Exfoliation - peeling off of skin.
- Maceration - moist peeling skin.
- Verrucous - resembling a wart.
- Lichenification is 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.
- Crust occurs when plasma exudes 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 refers to degeneration or abnormal formation of the skin. It is often used to refer to nail diseases.
- An excoriation is a scratch mark. It may be linear or a picked scratch called prurigo.
- An ulcer is full-thickness loss of epidermis or epithelium. It may be covered with a dark-coloured crust called an eschar.
- Erosion is caused by loss of the surface of a skin lesion. It is a shallow moist or crusted lesion. These terms are not confined to the skin but may be used to differentiate gastric erosions and ulcers.
- A fissure is a thin crack within the epidermis or epithelium and is due to excessive dryness.
- Fungating describes a large, usually malignant tumour, which is erupting like a mushroom or fungus.
- Granulation tissue is a mass of new capillaries and fibrous tissue in a healing wound.
- A granuloma is a histological term referring to chronic inflammation in which there are several types of inflammatory cells including giant cells. Granulomas form in response to foreign bodies, certain infections including tuberculosis and leprosy, and with inflammatory skin diseases including granuloma annulare, granuloma faciale and sarcoidosis.
- In hypertrophy, some component of the skin such as a scar is enlarged or has grown excessively. The opposite is atrophy or thinned skin.
- Onychodystrophy is any abnormality of nails.
- Nails may show pitting, including thimble pitting, as in psoriasis when they have numerous tiny indentations like a thimble.
- Onychomadesis is loosening and shedding of nails.
- Onychogryphosis is an abnormal condition of the nails characterised by marked hypertrophy and increased curvature.
- Onychoschizia is a condition of the nails marked by lamination in two or more layers and by scaling away in thin flakes.
- Koilonychia is spoon nails and is a feature of iron deficiency.
- Clubbing involves increased curvature in both directions. It may be congenital or indicate other diseases.
- Subungual means under the nails.
- Pterygium is a forward growth of the cuticle over the nail. It is also a triangular fleshy mass of thickened conjunctiva at the inner side of the eyeball, covering part of the cornea, and causing a disturbance of vision.
It is important in dermatology to examine the mucocutaneous areas of the body, particularly the mouth and lips. Most oral involvement in the mucocutaneous diseases is associated with an immunological component to the disease. When an eruption is on a mucous membrane, it is called an enanthem. Examples include:
- Strawberry tongue (eg, with scarlet fever and with Kawasaki's disease).
- Leukoplakia - a thick, whitish-colour patch that forms on the inside of the cheeks, gums or tongue.
- Gingivitis - a form of periodontal disease that affects the gums.
- In Köbner's phenomenon, lesions arise in an area of trauma. This is typical of psoriasis and lichen planus.
- Dermatographism (dermatographia) is the ability to write on skin. It occurs with urticaria. If a firm instrument, like an orange stick, is used to make lines or letters on the skin then, shortly afterwards, the wheal will form and the pattern of marks will be very obvious.
- In Nikolsky's sign, the skin of a bulla is lightly rubbed and it separates, showing failure of the adhesive process.
- Telangiectasia is prominent cutaneous blood vessels, the size of tiny red hairs.
- Exanthem is another term for a rash.
- Excoriation is an area of the skin covered by a crust, or scab, usually caused by scratching.
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Further reading & references
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