Chapter 052. Approach to the Patient with a Skin Disorder (Part 8)

Tzanck Smear A Tzanck smear is a cytologic technique most often used in the diagnosis of herpesvirus infections [herpes simplex virus (HSV) or varicella zoster virus (VZV)] (see Figs. 173-1 and 173-3). An early vesicle, not a pustule or crusted lesion, is unroofed, and the base of the lesion is scraped gently with a scalpel blade. The material is placed on a glass slide, air-dried, and stained with Giemsa or Wrights stain. Multinucleated epithelial giant cells suggest the presence of HSV or VZV; culture or immunofluorescence testing must be performed to identify the specific virus.DiascopyDiascopy is designed to assess...
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Chapter 052. Approach to the Patient with a Skin Disorder (Part 8) Chapter 052. Approach to the Patient with a Skin Disorder (Part 8) Tzanck Smear A Tzanck smear is a cytologic technique most often used in the diagnosisof herpesvirus infections [herpes simplex virus (HSV) or varicella zoster virus(VZV)] (see Figs. 173-1 and 173-3). An early vesicle, not a pustule or crustedlesion, is unroofed, and the base of the lesion is scraped gently with a scalpelblade. The material is placed on a glass slide, air-dried, and stained with Giemsaor Wrights stain. Multinucleated epithelial giant cells suggest the presence ofHSV or VZV; culture or immunofluorescence testing must be performed toidentify the specific virus. Diascopy Diascopy is designed to assess whether a skin lesion will blanch withpressure as, for example, in determining whether a red lesion is hemorrhagic orsimply blood-filled. Urticaria (Fig. 52-11) will blanch with pressure, whereas apurpuric lesion caused by necrotizing vasculitis (Fig. 52-4) will not. Diascopy isperformed by pressing a microscope slide or magnifying lens against a lesion andnoting the amount of blanching that occurs. Granulomas often have an opaque totransparent, brown-pink apple jelly appearance on diascopy. Figure 52-11 Urticaria. Discrete and confluent, edematous, erythematous papules andplaques are characteristic of this whealing eruption. Woods Light A Woods lamp generates 360-nm ultraviolet (or black) light that can beused to aid the evaluation of certain skin disorders. For example, a Woods lampwill cause erythrasma (a superficial, intertriginous infection caused byCorynebacterium minutissimum) to show a characteristic coral pink color, andwounds colonized by Pseudomonas to appear pale blue. Tinea capitis caused bycertain dermatophytes such as Microsporum canis or M. audouini exhibits ayellow fluorescence. Pigmented lesions of the epidermis such as freckles areaccentuated, while dermal pigment such as postinflammatory hyperpigmentationfades under a Woods light. Vitiligo (Fig. 52-12) appears totally white under aWoods lamp, and previously unsuspected areas of involvement often becomeapparent. A Woods lamp may also aid in the demonstration of tinea versicolor andin recognition of ash leaf spots in patients with tuberous sclerosis. Figure 52-12 Vitiligo. Characteristic lesions display an acral distribution and strikingdepigmentation as a result of loss of melanocytes. Patch Tests Patch testing is designed to document sensitivity to a specific antigen. Inthis procedure, a battery of suspected allergens is applied to the patients backunder occlusive dressings and allowed to remain in contact with the skin for 48 h.The dressings are removed, and the area is examined for evidence of delayedhypersensitivity reactions (e.g., erythema, edema, or papulovesicles). This test isbest performed by physicians with special expertise in patch testing and is oftenhelpful in the evaluation of patients with chronic dermatitis. FURTHER READINGS Dermatology Lexicon Project: www.futurehealth.rochester.edu/dlp2/ James WD et al: Andrews Diseases of the Skin: Clinical Dermatology,10th ed. Philadelphia, Elsevier, 2006 Wolff K et al (eds): Fitzpatricks Dermatology in General Medicine, 7th ed.New York, McGraw-Hill, 2008