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Approach to the Patient with a Skin Disorder
Thomas J. Lawley
Kim B. Yancey
The challenge of examining the skin lies in distinguishing normal from abnormal, significant findings from trivial ones, and in 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 malignant melanoma from a benign pigmented nevus can be difficult to recognize. To aid in the interpretation of skin lesions, a variety of descriptive terms have been developed to characterize cutaneous lesions and to formulate a differential diagnosis (Table 3).
For instance, the finding of large numbers of scaling papules, usually indicative of a primary skin disease, places the patient in a different diagnostic category than would hemorrhagic papules, which may indicate vasculitis or sepsis . It is important to differentiate primary skin lesions from secondary skin changes. 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 the redness and scale are secondary, while the correct interpretation would be that the patient has a pruritic eczematous dermatitis with erosions caused by scratching.
TABLE 1 Descriptions of Primary Skin Lesions
TABLE 2 Common Dermatologic Terms
TABLE 3 Selected Common Dermatologic Conditions
APPROACH TO THE PATIENT
In examining the skin it is usually advisable to assess the patient before taking an extensive history. This way, the entire cutaneous surface is sure to be evaluated, and objective findings can be integrated with relevant historic data. Four basic features of any cutaneous lesion must be noted and considered in the examination of
skin: the distribution of the eruption, the type(s) of primary lesion, the shape of individual lesions, and the arrangement of the lesions. In the initial examination it is important that the patient be disrobed as completely as possible. This will minimize chances of missing important individual skin lesions and make it possible to assess the distribution of the eruption accurately. The patient should first be viewed from a distance of about 1.5 to 2 m (4 to 6 ft) so that the general character of the skin and the distribution of lesions can be evaluated. Indeed, distribution of lesions often correlates highly with diagnosis . For example, a hospitalized patient with a generalized erythematous exanthem is more likely to have a drug eruption than is a patient with a similar rash limited to the sun-exposed portions of the face. The presence or absence of lesions on mucosal surfaces should also be determined. Once the distribution of the lesions has been established, the nature of the primary lesion must be determined. Thus, when lesions are distributed on elbows, knees, and scalp, the most likely possibility based solely on distribution is psoriasis or dermatitis herpetiformis The primary lesion in psoriasis is a scaly papule that soon forms erythematous plaques covered with a white scale, whereas that of dermatitis herpetiformis is an urticarial papule that quickly becomes a small vesicle. In this manner, identification of the primary lesion directs the examiner toward the proper diagnosis. Secondary changes in skin can also be quite helpful. For example, scale represents excessive epidermis, while crust is the result of a discontinuous epithelial cell layer. Palpation of skin lesions can also yield insight into the character of an eruption. Thus red papules on the lower extremities that blanch with pressure can be a manifestation of many different diseases, but hemorrhagic red papules that do not blanch with pressure indicate palpable purpura characteristic of necrotizing vasculitis
The shape of lesions is also an important feature. Flat, round, erythematous papules and plaques are common in many cutaneous diseases. However, target-shaped lesions that consist in part of erythematous plaques are specific for erythema multiforme In the same way, the arrangement of individual lesions is important. Erythematous papules and vesicles can occur in many conditions, but their arrangement in a specific linear array suggests an external etiology such as allergic contact
irritant dermatitis. In contrast, lesions with a generalized arrangement are common and suggest a systemic etiology.
As in other branches of medicine, a complete history should be obtained to emphasize the following features:
- Evolution of lesions
- Site of onset
- Manner in which the eruption progressed or spread
- Periods of resolution or improvement in chronic eruptions
- Symptoms associated with the eruption
- Itching, burning, pain, numbness
- What, if anything, has relieved symptoms
- Time of day when symptoms are most severe
- Current or recent medications (prescribed as well as over-the-counter)
- Associated systemic symptoms (e.g., malaise, fever, arthralgias)
- Ongoing or previous illnesses
- History of allergies
- Presence of photosensitivity
- Review of systems
Many skin diseases can be diagnosed on 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.
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 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.
A potassium hydroxide (KOH) preparation is performed on scaling skin lesions where a fungal etiology is a possibility. The edge of such a lesion is scraped gently with a scalpel blade, and the removed scale is collected on a glass microscope slide and treated with 1 to 2 drops of a solution of 10 to 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 will be seen more easily when the light intensity is reduced and the condenser is lowered. This technique can be utilized to identify hyphae in dermatophyte infections pseudohyphae and budding yeast in Candida infections and fragmented hyphae and spores in tinea versicolor. The same sampling technique can be used to obtain scale for culture of selected pathogenic organisms.
A Tzanck smear is a cytologic technique most often used in the diagnosis of herpesvirus infections [simplex or varicella-zoster. 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 herpes, but culture or immunofluorescence testing must be performed to identify the specific virus.
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. For instance, urticaria will blanch with pressure, whereas a purpuric lesion caused by necrotizing vasculitis 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 “apple jelly” appearance on diascopy.
A Wood's lamp generates 360-nm ultraviolet (or “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 red color, and wounds colonized by Pseudomonas to appear pale blue. Tinea capitis caused by certain dermatophytes such as Microsporum canis or M. audouini 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 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 and in recognition of ash leaf spots in patients with tuberous sclerosis.
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.