Dermatological descriptive terms

See also the separate Dermatological history and examination article.

Dermatological terminology

It is common for dermatologists to use specific words when describing a rash or a lesion. These are often of Latin or Greek derivation and are typically words that describe the appearance of the rash.

Understanding these words can help with diagnosis and with explanations to patients.

Basic dermatological terminology

• 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.

Structure of skin

The skin has three layers - the epidermis, the dermis, and the deep subcutaneous tissue, with a basement membrane between the epidermis and the dermis.

Epidermis

The epidermis has 5 layers:

• The stratum basale (basal layer): This consists of columnar cells at the base of the epidermis from which new cells are continuously produced. Melanocytes (pigment cells producing melanin) are normally scattered through this layer. Merkel's cells (which have a sensory function) are also found in this layer.

• The stratum spinosum: As keratinocytes mature, they move upwards towards the surface of the skin, developing into squamous cells, also known as spinous or prickle cells. Langerhans' cells (part of the immune system) are found in this layer as well.

• The stratum granulosum: Keratinocytes start to produce keratin in this layer, which has a protective and a water-proofing function.

• The stratum lucidum: Found only in the palms of the hand and the soles of the feet, this layer consists of a thin layer of dead cells.

• The stratum corneum (horny layer): In this layer, keratinocytes become corneocytes - dead keratinocytes which provide a protective function. The corneocytes eventually shed as new keratinocyte cells develop in the stratum basale layer and move through the other layers of skin.

Epidermal appendages
These include:

• Eccrine glands, which produce sweat.

• Apocrine glands, which are scent glands found in armpits and groins.

• Pilosebaceous structures containing hair and sebaceous glands.

• Nails.

Dermis

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.

Subcutaneous tissue

This is also called subcutis and is composed of adipose cells or lipocytes. These are surrounded by connective tissue, blood vessels, and nerves.

Dermatological terms for distribution of lesions

The distribution of lesions is often characteristic and hence of diagnostic importance.

• Acral (literally "topmost"): Used for lesions affecting the extremities - the feet and hands and, occasionally, the nose or ears.

• Blaschko's lines: Used to describe lesions which follow a segmental pattern described by Blaschko in 1901; they are thought to represent pathways of epidermal cell migration and proliferation during foetal development.¹

• Dermatomal: Corresponding with nerve root distribution, as with shingles.

• Flexural: Occurring on the flexor surfaces, such as the antecubital fossa and back of the knee.

• Extensor: Occurring on the extensor surfaces, such as over the tip of the elbow and usually just below the patella.

• Herpetiform: Grouped vesicles, as seen in herpes simplex and herpes zoster infections.

• Morbilliform (literally "like measles"): Pink or red flat macules which may coalesce. The rash tends to start on the trunk and spread to the limbs and neck. In children, the commonest cause is a virus. In adults, the commonest cause is a drug reaction.

• Seborrhoeic (literally "characterised by seborrhoea" - the oil produced by sweat glands): Refers to the areas generally containing these glands - the scalp, behind the ears, eyebrows, nasolabial folds, sternum, natal cleft, and interscapular region.

• Truncal: Affecting the trunk.

Dermatological terms for the shape of a lesion

• Annular (literally "in a ring") lesions are grouped in a circle.

• A gyrate rash appears to be whirling in a circle. The rash often has a typical wood-grain appearance and tends to spread outwards.

• A linear (literally "in a straight line") lesion, also known as striate, is relatively straight and often occurs from trauma such as scratching. (Perfectly straight lines are unusual and are often caused by artifacts or non-accidental injuries).

• Nummular (literally "like a coin") or discoid refers to round or coin-shaped lesions.

• Target lesions have concentric rings like an archery target.

Colour

• Erythro (literally "reddish"):

  • Erythema is red skin due to increased blood supply. It blanches on pressure.

  • Erythroderma is an inflammatory condition in which over 90% of the skin is affected. It is red all over.

• Purpura (literally "purple"):

  • Caused by bleeding into the skin.

  • Presents as petechiae (small red, purple or brown spots) or ecchymoses (bruises).

  • Does not blanch with pressure.

• Carotene (literally "carrot" and therefore refers to orange colouration):

  • 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.

• Leuko (literally "white"):

  • Leukoderma causes white skin.

  • It is also sometimes known as achromia (literally "absence of colour").

• Nigrans (literally "black"):

  • Acanthosis nigricans is a condition causing dry soft black or dark patches of skin, typically in the axillae, neck or groin.

  • Infarcts are black areas of necrotic tissue due to ischaemia.

• 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.

Discrete lesions

• A macule is an area of colour change that is less than 1 cm to 1.5 cm in diameter. The surface is smooth and cannot be felt by touch.

• 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.

  • Flat-topped.

  • 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.

Epidermal changes

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 bran-like 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.

Secondary changes

• 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.

Nails

• 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.

Mucocutaneous membranes

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.

Miscellaneous dermatological terms

• 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.