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 melanoma (Fig. 51-1) from a benign nevomelanocytic nevus (Fig. 51-2) 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 (Tables 51-1, 51-2, and 51-3 as well as Fig. 51-3) and to formulate a differential diagnosis (Table 51-4). For instance, the finding of scaling papules (present in patients with psoriasis or atopic dermatitis) places the patient in a different diagnostic category than would hemorrhagic papules, which may indicate vasculitis or sepsis (Figs. 51-4 and 51-5, 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 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.
Superficial spreading melanoma. This is the most common type of melanoma. Such lesions usually demonstrate asymmetry, border irregularity, color variegation (black, blue, brown, pink, and white), a diameter >6 mm, and a history of change (e.g., an increase in size or development of associated symptoms such as pruritus or pain).
Nevomelanocytic nevus. Nevi are benign proliferations of nevomelanocytes characterized by regularly shaped hyperpigmented macules or papules of a uniform color.
A schematic representation of several common primary skin lesions (see Table 51-1).
Necrotizing vasculitis. Palpable purpuric papules on the lower legs are seen in this patient with cutaneous small vessel vasculitis. (Courtesy of Robert Swerlick, MD; with permission.)
Meningococcemia. An example of fulminant meningococcemia with extensive angular purpuric patches. (Courtesy of Stephen E. Gellis, MD; with permission.)
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