Author: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, 1997.
Dermatological diagnoses often have more than one name. DermNet NZ refers to various resources when naming conditions, including the World Health Organisation (WHO)'s International Classification of Diseases (see ICD11 coding tool), and the Systematized Nomenclature of Medicine Clinical Terms (SNOMED CT).
When examining the skin, a dermatologist assesses distribution, morphology and arrangement of skin lesions: 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:
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.
Epidermal appendages include:
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.
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?
Configuration refers to the shape or outline of the skin lesions. Skin lesions are often grouped. The pattern or shape may help in diagnosis as many skin conditions have a characteristic configuration.
Descriptive terms used to describe skin colour include:
Morphology is the form or structure of an individual skin lesion.
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.
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