Examination

• Although a thorough examination of the whole skin is considered best practice there are occasions where it is not necessary, for example a patient presenting with a wart on the finger

• Patients found to have clinically important skin lesions (large numbers of melanocytic naevi, pre-cancerous lesions, skin cancer) or who have a relevant family history should have a full skin examination

• Patients with a rash should have a thorough skin examination along the following lines:
  • Note the general appearance of the patient for pointers of systemic disease such as thyroid disease or arthritis
  • Stand back and observe the distribution, symmetry and colour of the rash. Symmetrical rashes generally suggest an endogenous condition such as psoriasis or atopic eczema, whereas asymmetrical rashes are more likely to have an exogenous cause such as tinea. Is the rash more flexural such as with atopic eczema or does it mainly affect extensor surfaces such as psoriasis?
  • Then look closely at the skin to assess the morphology of the rash i.e. what do the individual ‘lesions/spots’ look like. Note the colour, shape, symmetry, elevation, edge (distinct or ill-defined) and if there is any scale or crust. Scratching or infection may modify the appearance of the lesions
  • Palpation of the skin to assess surface texture, site within the skin, and thickness of lesions. Disorders of the epidermis will often produce visible scale, but if this is not evident gentle scratching of the skin will often induce scale to become apparent. Removing crust from skin lesions is essential to see what lies underneath. Linear pressure may illicit a response in urticaria
  • The nails, scalp and oral mucosa may provide additional clues
  • Ask about involvement of the genitalia and examine if appropriate
• The use of a Woods light can aid in the diagnosis of a number of disorders:
  • Yellow fluorescence in pityriasis vesicolor
  • Coral pink fluorescence in erythrasma
  • The pale areas of vitiligo are exaggerated
• When formulating the differential diagnosis it is important to bear in mind the three following concepts:
  • Beware the sin of diagnostic greed – in other words you don’t need to have all the textbook features of a disease to make the diagnoses
  • Atypical presentations of common skin disease occur more frequently than typical presentations of rare skin disease - in other words an atypical presentation of psoriasis is more common than a typical presentation of a cutaneous t-cell lymphoma
  • The great mimickers - there are a number of dermatological disorders that can present in many different ways. These include amelanotic melanoma, lupus erythematoses, sarcoid, mycobacteria and cutaneous T-Cell lymphoma
• For more specific help in diagnosing skin conditions please refer to the diagnostic tables, which can be found on the main links