Category: Clinical Practice

Skin Diagnostic Aids Used in Clinical Practice

May 23, 2019

It is also known as dermoscopy. This technique refers to the examination of the skin using skin surface microscopy. A dermatoscope (or dermoscope) is a device used for the examination of cutaneous lesions. It has a hand-held device with a magnifier with either cross-polarized or non-polarized light or a liquid medium of oil between the instrument and the skin to illuminate a lesion without glare from reflected light. The device is useful for examining pigmented lesions such as naevi and potential malignant lesions such as melanomas. There are specific dermoscopic patterns that aid in the diagnosis of the following pigmented skin lesions such as melanomas, moles (benign melanocytic naevi), freckles (lentigos), atypical naevi, seborrhoeic keratosis and pigmented basal cell carcinomas. Evidence suggests that while dermatoscopy improves the diagnostic accuracy for melanoma compared to the unaided eye, it requires sufficient training and is not recommended for untrained users.

Wood’s light

Wood’s light is a lamp emitting long-wave UVA used to examine pigmentary changes in the skin and fluorescent infections. This ultraviolet light source is used to screen for the fungal infection, tinea capitis; however, only certain species fluoresce (green) (Microsporum canis and Μ. audouinii). Other uses include highlighting patches of pityriasis versicolor caused by Pityrosorum yeast which fluoresces yellow; erythrasma, a bacterial infection affecting the skin folds, caused by Corynebacterium fluoresces green and vitiligo which delineates patches which can be otherwise missed.

Mycology

Mycology can be used to identify superficial fungal infections including yeasts (candidiasis and pityriasis versicolor), dermatophytes (ringworm/ tinea – tinea unguium) or moulds (e.g. Scopulariopsis) using scales scraped from the edge of a scaly lesion, nails using a blunt instrument such as blunt scalpel blade or blunt edge of a stitch cutter. Scrapings of scale should be taken from the leading edge of the rash (as this is where active spores are most likely to be found) after the skin has been cleaned with alcohol, such as surgical spirit or 70% alcohol. This minimises contamination and is an aid to microscopy if greasy ointments or powders have been applied. Samples can be collected on kits providing black paper envelopes (e.g. Dermapak), which can be easily transferred to the lab. It is essential to have an adequate sample and provide full clinical details if the test is to be successful; whilst the precise quantity is difficult to quantify, as a general rule it is worth including as much material as possible so that full laboratory investigations can be carried out. It is always useful to have enough skin or nail to repeat the culture if necessary. Sample the discoloured, dystrophic or brittle parts of the nail only, gently digging as far back as possible from the distal part of the nail. For dermatophyte infections, samples should be taken from the distal nail and from debris under the nail (subungual debris). For superficial onychomycosis, the scraping should be from the nail surface and for Candida infections (e.g. a chronic paronychia) a swab should be taken from the proximal nail fold.

Hair can be plucked from the affected area with forceps; the infected hairs come out easily. The scalp may then be scraped with a blunt scalpel. Preferably, the sample should include hair stubs, the contents of plugged follicles and skin scales. Hair cut with a scissors is unsatisfactory as the focus of infection is usually below or near the surface of the scalp.

Biopsy

Where diagnosis is unclear but there is a differential diagnosis, an ellipse of skin can be taken through the edge of a lesion. There is a need to ensure that normal and abnormal skin (epidermis, dermis and fat) are included in the sample. Incisional, excisional and punch biopsies may be taken. Punch biopsies provide only limited sample, which may be inadequate for histological examination. Typically, the punch biopsy includes the full thickness skin and subcutaneous fat in the diagnosis of skin diseases. A round-shaped knife ranging in size from 1–8 mm is taken. The smaller size punch (1 mm) helps to minimise bleeding and assists in the vhealing of the wound without stitching. To diagnose many inflammatory skin conditions, the common punch size used is the 3.5- or 4-mm punch.

Bacteriology

The source of bacteria can be determined by swabbing a fluid sample pustules, vesicles, erosions and ulcers.

Patch testing

It is a technique used to diagnose contact allergic dermatitis based on the principle of delayed hypersensitivity (an immune response). Evidence of contact allergy is derived from a patient history (such as occupation), clinical examination and patch testing. The aim of the patch test is to ascertain allergic contact dermatitis by aiming to reproduce a rash on a small controlled area of skin using standardised batches or trays of allergens (termed batteries) or those commonly used at work or home. Standard batteries of substances (now often pre-prepared) are comprised of patches made up of Finn chambers and hypoallergenic tape that are applied to the patient’s upper back; they should incorporate probable (standard battery) and possible substances (e.g. occupational specific) based on their history. The results are read at two stages, 48 hours and 72 hours; this timing sequence is related to the type IV hypersensitivity reaction, which is a delayed immune response. Care is needed to avoid misleading results from contact irritants that are distinct from hypersensitivity reactions. Differentiation is not always easy, however, the use of standard allergens and rigorous technique are required.…