Chapter 52: Approach to the Patient with a Skin Disorder

The challenge of examining the skin lies in distinguishing normal from abnormal findings, distinguishing significant findings from trivial ones, and integrating pertinent signs and symptoms into an appropriate differential diagnosis. The fact that the largest organ in the body is visible is both an advantage and a disadvantage to those who examine it. It is advantageous because no special instrumentation is necessary and because the skin can be biopsied with little morbidity. However, the casual observer can be misled by a variety of stimuli and overlook important, subtle signs of skin or systemic disease. For instance, the sometimes minor differences in color and shape that distinguish a melanoma (Fig. 52-1) from a benign nevomelanocytic nevus (Fig. 52-2) can be difficult to recognize. A variety of descriptive terms have been developed that characterize cutaneous lesions (Tables 52-1, 52-2, and 52-3; Fig. 52-3), thereby aiding in their interpretation and in the formulation of a differential diagnosis (Table 52-4). For example, the finding of scaling papules, which are present in psoriasis or atopic dermatitis, places the patient in a different diagnostic category than would hemorrhagic papules, which may indicate vasculitis or sepsis (Figs. 52-4 and 52-5, respectively). It is also important to differentiate primary from secondary skin lesions. If the examiner focuses on linear erosions overlying an area of erythema and scaling, he or she may incorrectly assume that the erosion is the primary lesion and that the redness and scale are secondary, whereas the correct interpretation would be that the patient has a pruritic eczematous dermatitis with erosions caused by scratching.

Many skin diseases can be diagnosed on the basis of gross clinical appearance, but sometimes relatively simple diagnostic procedures can yield valuable information. In most instances, they can be performed at the bedside with a minimum of equipment.

Skin Biopsy

A skin biopsy is a straightforward minor surgical procedure; however, it is important to biopsy a lesion that is most likely to yield diagnostic findings. This decision may require expertise in skin diseases and knowledge of superficial anatomic structures in selected areas of the body. In this procedure, a small area of skin is anesthetized with 1% lidocaine with or without epinephrine. The skin lesion in question can be excised or saucerized with a scalpel or removed by punch biopsy. In the latter technique, a punch is pressed against the surface of the skin and rotated with downward pressure until it penetrates to the subcutaneous tissue. The circular biopsy is then lifted with forceps, and the bottom is cut with iris scissors. Biopsy sites may or may not need suture closure, depending on size and location.

KOH Preparation

A potassium hydroxide (KOH) preparation is performed on scaling skin lesions where a fungal infection is suspected. The edge of such a lesion is scraped gently with a no. 15 scalpel blade. The removed scale is collected on a glass microscope slide and then treated with 1 or 2 drops of a solution of 10–20% KOH. KOH dissolves keratin and allows easier visualization of fungal elements. Brief heating of the slide accelerates dissolution of keratin. When the preparation is viewed under the microscope, the refractile hyphae are seen more easily when the light intensity is reduced and the condenser is lowered. This technique can be used to identify hyphae in dermatophyte infections, pseudohyphae and budding yeasts in Candida infections, and “spaghetti and meatballs” yeast forms in tinea versicolor. The same sampling technique can be used to obtain scale for culture of selected pathogenic organisms.

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. 188-1 and 188-3). 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 Wright’s stain. Multinucleated epithelial giant cells suggest the presence of HSV or VZV; culture, immunofluorescence microscopy, or genetic testing must be performed to identify the specific virus.

Diascopy

Diascopy is designed to assess whether a skin lesion will blanch with pressure as, for example, in determining whether a red lesion is hemorrhagic or simply blood-filled. Urticaria (Fig. 52-11) will blanch with pressure, whereas a purpuric lesion caused by necrotizing vasculitis (Fig. 52-4) will not. Diascopy is performed by pressing a microscope slide or magnifying lens against a lesion and noting the amount of blanching that occurs. Granulomas often have an opaque to transparent, brown-pink “apple jelly” appearance on diascopy.

Wood’s Light

A Wood’s lamp generates 360-nm ultraviolet (“black”) light that can be used to aid the evaluation of certain skin disorders. For example, a Wood’s lamp will cause erythrasma (a superficial, intertriginous infection caused by Corynebacterium minutissimum) to show a characteristic coral pink color, and wounds colonized by Pseudomonas will appear pale blue. Tinea capitis caused by certain dermatophytes (e.g., Microsporum canis or M. audouinii) exhibits a yellow fluorescence. Pigmented lesions of the epidermis such as freckles are accentuated, while dermal pigment such as postinflammatory hyperpigmentation fades under a Wood’s light. Vitiligo (Fig. 52-12) appears totally white under a Wood’s lamp, and previously unsuspected areas of involvement often become apparent. A Wood’s lamp may also aid in the demonstration of tinea versicolor, sites of depigmentation within and/or surrounding melanomas, and in recognition of ash leaf spots in patients with tuberous sclerosis.

Patch Tests

Patch testing is designed to document sensitivity to a specific antigen. In this procedure, a battery of suspected allergens is applied to the patient’s back under 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 delayed hypersensitivity reactions (e.g., erythema, edema, or papulovesicles). This test is best performed by physicians with special expertise in patch testing and is often helpful in the evaluation of patients with chronic dermatitis.