DERMATOLOGY FOR THE USMLE BASICS OF DERMATOLOGY (7) DIAGNOSTIC PROCEDURES IN DERMATOLOGY

DERMATOLOGY FOR THE USMLE

BASICS OF DERMATOLOGY (7)

DIAGNOSTIC PROCEDURES IN DERMATOLOGY

10. DIAGNOSTIC PROCEDURES IN DERMATOLOGY

→	Dermoscopy (dermatoscopy): Noninvasive external examination of the skin using a handheld skin-surface microscope (dermatoscope), similar to a magnifying glass. Dermoscopy permits the physician to look into the epidermis and superficial dermis to see skin details not visible to the naked eye. Common uses for dermoscopy include: Pigmented lesions (aids in differentiating benign from malignant) Scabies and lice infestation Splinter injuries Psoriasis, warts and molluscum contagiosum Nail capillaries	DERMOSCOPY
→	Patch testing: Skin test used to identify offending allergens in chronic eczematous disorders (eg, allergic contact dermatitis) Most commonly the skin of the upper back is covered with a bandage that contains small disks of commonly encountered allergens. The bandage is left for 48 hours and subsequently removed to inspect the skin for irritation and allergy. The skin is reevaluated at 96 hours and often the following week. A positive result is erythema, papules and/or vesicles on the skin that was in contact with the specific allergen. A similar test called photopatch testing is used for photoallergic reactions
→	Diascopy: Mainly used to distinguish between inflammatory processes and hemorrhagic lesions. A glass slide is pressed against erythematous lesions to see if it blanches (whitens). If the lesion blanches, it is an inflammatory process (vasodilation or increased blood flow). If the lesion does not blanch, it is a hemorrhagic lesion (extravasated blood).
→	Skin, hair or nail scraping: Specimen obtained via scraping with a metal blade or glass slide. The sample can be used for any of the following procedures: »Potassium hydroxide preparation (Koh prep): Potassium hydroxide (KOH) solution is applied to the collected sample to dissolve keratin (eg, skin) allowing microscopic visualization of remaining fungus or yeast. Mainly used for diagnosing superficial fungal infections (eg, tinea versicolor, candidiasis and dermatophytosis). »Mineral oil preparation: Skin scrapings are obtained using an oildipped scalpel and placed on a glass slide with mineral oil. Microscopic examination of the sample allows detection of scabies mites, eggs and/or fecal matter »Tzanck smear: Nuclear stains (Giemsa, Wright’s or Hansel) are applied to scrapings obtained from the base of an ulcer or vesicle allowing microscopic detection of multinucleated giant cells or Tzanck cells. Mainly used for rapid detection of herpes simplex, varicella and zoster infections, although it cannot differentiate among them. »Dark field examination: Scrapings are usually obtained from the base and edge of an ulcer suspicious for syphilis and visualized under dark field microscopy for spirochetes.
→	Wood’s lamp examination: Noninvasive examination of skin, hair or urine under a black light emitted by the Wood’s lamp. Used to enhance variations is skin pigmentation and examine fluorescent color patterns not visible to the naked eye. Common uses include: Erythrasma (coral red fluorescence) Vitiligo and tuberous sclerosis “ash-leaf spots” (blue-white fluorescence) Porphyria cutanea tarda urine (red-pink fluorescence) Tinea capitis (differentiate among dermatophytes) »Microsporum canis or M. audouinii (blue-green fluorescence) »Trichophyton sp. (no fluorescence)
→	Skin biopsy: Procedure in which a sample of skin is removed for histopathological studies. Generally done to confirm or refute a clinical diagnosis (eg, suspicious malignant lesions) or as a treatment modality  Samples are routinely stained with hematoxylin and eosin (H&E) and analyzed under light microscopy. Additionally, samples can be used for cultures, direct immunofluorescence studies and electron microscopy  Special stains are available to aid in identification of specific cell types, tissue types and infectious organisms. Different types of biopsies are used for different skin disorders. Common examples include: √ Shave biopsy: A scalpel or blade is used to remove a thin layer of superficial skin. Usually, no stitches are required for wound closure and the skin heals in 1 to 2 weeks. Mainly used for skin diseases that affect only the epidermis and superficial dermis or as a treatment modality to remove small cutaneous lesions (eg, seborrheic or actinic keratoses, acrochordons, verrucae and superficial BCCs and SCCs). Shave biopsies are generally not useful to visualize processes deep in the dermis or subcutaneous tissue. √ Punch biopsy: A cylindrical, cookie cutter-like tool is used to quickly and conveniently obtain a round, full-thickness skin sample with minimal tissue damage. Punch biopsies range in size from 2 to 8 mm in diameter and usually require 1 to 2 stitches for wound closure. Mainly used for pathologies involving the epidermis and dermis (eg, eczema, psoriasis, drug eruption, vasculitis and autoimmune or blistering disorders). √ Incisional biopsy: A scalpel is used to remove a full thickness piece of skin lesion. Usually requires sutures for wound closure. Mainly used when larger samples are needed or when the suspected pathology involves deeper tissues, such as subcutaneous fat or fascia (eg, erythema nodosum). √ Excisional biopsy: A scalpel is used to remove the entire lesion including margins, most commonly using an elliptical excision. Sutures or more significant skin closure techniques (eg, skin grafting) are needed. Mainly used for dermal, subcutaneous and melanocytic neoplasms or as a treatment modality (eg, melanoma).
→	Direct immunofluorescence (DIF) studies: A known antibody is linked to a fluorescent agent that targets a specific antigen. When the antibody binds the target antigen, it fluoresces and can be seen under microscopy. The pattern and location of the fluorescence are used to diagnose specific skin diseases including blistering disorders (eg, bullous pemphigoid) and autoimmune skin diseases (eg, lupus erythematosus).