Special tools and techniques
A magnifying lens is a helpful aid to diagnosis because subtle changes in the skin become more apparent when enlarged. One attached to spectacles will leave your hand free.
A Wood’s light, emitting long wavelength ultraviolet radiation, will help with the examination of some skin conditions. Fluorescence is seen in some fungal infections , erythrasma and pseudomonas infections. Some subtle disorders of pigmentation can be seen more clearly under Wood’s light, e.g. the pale patches of tuberous sclerosis, low-grade vitiligo and pityriasis versicolor, and the darker café-au-lait patches of neurofibromatosis. The urine inhepatic cutaneous porphyria often fluoresces coral pink, even without solvent extraction of the porphyrins (see Fig. 19.10).
Diascopy is the name given to the technique in whicha glass slide or clear plastic spoon is used to blanch vascular lesions and so to unmask their underlying colour.
Photography, conventional or digital, helps to recordthe baseline appearance of a lesion or rash, so that change can be assessed objectively at later visits. Small changes in pigmented lesions can be detected by ana-lysing sequential digital images stored in computerized systems.
This non-invasive technique for diagnosing pigmented lesions in vivo has come of age in the last few years. It is particularly useful in the diagnosis of malignant melanomas. The lesion is covered with mineral oil, alcohol or water and then illuminated and observed at 10 × magnification with a hand-held dermatoscope (Fig. 3.4).
The fluid eliminates surface reflection and makes the horny layer translucent so that pigmented structures in the epidermis and superficial dermis and the superficial vascular plexus can be assessed. The dermatoscopic appearance of many pigmented lesions, including seborrhoeic warts, haemangiomas, basal cell carcinomas and most naevi and malignant melanomas is characteristic (Fig. 3.5). Images can be recorded by conventional or digital photography and sequential changes assessed. With formal training and practice, the use of dermatoscopy improves the accur-acy with which pigmented lesions are diagnosed.
A dermatoscope can also be used to identify scabies mites in their burrows.