Skin Anatomy and Lesions: Epidermis, Dermis, and Skin Diseases, Lecture notes of Dermatology

Download Skin Anatomy and Lesions: Epidermis, Dermis, and Skin Diseases and more Lecture notes Dermatology in PDF only on Docsity!       S o a l a s   D e r m a t o l g o y   &   L a s e r   C l i n i c .   Page 1  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       S o a l a s   D e r m a t o l g o y   &   L a s e r   C l i n i c .   Page 2  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.       S o a l a s   D e r m a t o l g o y   &   L a s e r   C l i n i c .   Page 5  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).       S o a l a s   D e r m a t o l g o y   &   L a s e r   C l i n i c .   Page 6  Erythroderma  The skin condition affects the whole body or nearly the whole body, which  is red all over. Telangiectasia  Telangiectasia is the name given to prominent cutaneous blood vessels. Purpura  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).     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.       S o a l a s   D e r m a t o l g o y   &   L a s e r   C l i n i c .   Page 7  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 0.5  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)   • Flat‐topped   • Oval or round   • Pedunculated (with a stalk)   • Sessile (without a stalk)   • Umbilicated (with a central depression)   • Verrucous (warty)       S o a l a s   D e r m a t o l g o y   &   L a s e r   C l i n i c .   Page 10  • 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.       S o a l a s   D e r m a t o l g o y   &   L a s e r   C l i n i c .   Page 11  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.       S o a l a s   D e r m a t o l g o y   &   L a s e r   C l i n i c .   Page 12  Granuloma  A granuloma is 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.