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Terminology in dermatology
Lesion A lesion is any single area of altered skin. It may be solitary or multiple. Rash A rash is a widespread eruption of lesions. Dermatosis Dermatosis is another name for for skin disease. Whan 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.
Structure of the skin
Images provided by University of Auckland 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 : 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.
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 & neck: spares eyelids, depth of wrinkles & furrows, areas shadowed by hair, nose & 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.
Colour
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 Infarcts are 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).
Macule A macule is an area of colour change less than 1.5 cm diameter. The surface is smooth. Patch A patch refers to a large area of colour change, with smooth surface. Papule Papules are small palpable lesions. The usual definition is that they are less than 0. 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)
- Flat‐topped
- Oval or round
- Pedunculated (with a stalk)
- Sessile (without a stalk)
- Umbilicated (with a central depression)
- Verrucous (warty)
Nodule A nodule is an enlargement of a papule in three dimensions (height, width, length). It is a solid lesion. Cyst A cyst is a papule or nodule that contains fluid so is fluctuant. Plaque A plaque is 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. 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 & pigmentation) Vesicle Vesicles are small fluid‐filled blisters less than 0.5cm diameter. They may be single or multiple.
- Maceration (moist peeling skin)
- Verrucous (warty) Psoriasiform scale Pityriasiform scale Exfoliation Verrucous scale
Secondary changes
Lichenification 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. Crusting 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 Dystrophy refers to degeneration or abnormal formation of the skin. It is often used to refer to nail diseases.
Excoriation An excoriation is a scratch mark. It may be linear or a picked scratch ( prurigo ). Excoriations may occur in the absence of a primary dermatosis. Erosion Erosion is caused by loss of the surface of a skin lesion; it is a shallow moist or crusted lesion. Fissure A fissure is 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 Granulation tissue is a made of a mass of new capillaries and fibrous tissue in a healing wound. Ulcer An ulcer is full thickness loss of epidermis or epithelium. It may be covered with a dark‐coloured crust called an eschar.
