Dermatoscopy for facial pigmented skin lesions

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On the face, the important differential diagnosis of pigmented skin lesion is between lentigo maligna, lentigo maligna melanoma, and flat seborrheic keratosis or lentigo seniles (synonymous with flat seborrheic keratosis in our terminology). In this article, we have summarized our experience in this field. Numerous examples for the criteria mentioned are given in the second edition of the Color Atlas of Dermatoscopy.1 Table 1 and Figure 1 are also adopted from that atlas with permission. A conventional pigment network is rarely found on adult facial skin. The rete ridges are flat to absent, so they produce no pigmented pattern. Instead, a pseudonetwork with a broad mesh and holes is created by the numerous pigment-free terminal and vellus hair follicles, as well as the openings of sweat glands. This pseudonetwork is location dependent and therefore present in both melanocytic lesions and nonmelanocytic lesions, such as seborrheic keratoses, on the face. On the face, therefore, the pseudonetwork does not distinguish between melanocytic and nonmelanocytic lesions, making it necessary to employ appropriate primary criteria.2–4 We compared the dermatoscopic features of lentigo maligna and lentigo senilis on the face by using logistic regression analysis.5 In this analysis, horn pseudocysts, yellow opaque areas, and fingerprint-like structures were most suggestive of lentigo senilis. In equivocal lesions, the presence of a moth-eaten border and the jelly sign can indicate lentigo senilis. A biopsy or close observation is necessary if asymmetric pigmented follicles occur. The pigmented rete ridges can produce grouped circular structures resembling grape clusters; these, along with horn pseudocysts, also indicate lentigo senilis. Sometimes at the periphery of seborrheic keratosis, streaklike areas are identified, which look very similar to branched streaks of a melanocytic lesion. The differential diagnosis is then extremely difficult. In thicker lesions, pseudofollicular openings and broad, blue-gray areas can occur. In our same analysis, features favoring lentigo maligna were dark, rhomboidal structures, slate-gray dots and globules, and asymmetric, pigmented, follicular openings forming an annulargranular pattern (Cognetta sign). In lentigo maligna and lentigo maligna melanoma, the hypopigmented follicular openings are frequently surrounded by a rim of hyperpigmentation. When the follicles lie close together, a second pseudonetwork appears, which, in contrast to the location-dependent pseudonetwork that has broad mesh and holes, is characterized by a thin mesh and holes. Both of these networklike structures are seen only with a dermatoscope and are pseudonetworks because they are not due to pigmentation of rete ridges, but rather the openings of skin appendages superimposed on pigmented facial skin in one instance and the close association of hair follicles in the other. In both pseudonetworks, the central holes often exhibit hair follicles. These should not be confused with horny pseudocysts or pseudofollicular openings, which could lead to the misdiagnosis of seborrheic keratosis. On the other hand, in some initial From the Department of Dermatology, University of Regensburg, Regensburg, Germany, and Traubingerstr. 45a, 82327 Tutzing, Germany. Address correspondence to Wilhelm Stolz, MD, Oberarzt Dermatologische Klinik der Universitat Regensburg, Franz-Josef-Strau -Allee 11 D-93042, Regensburg, Germany. E-mail address: wilhelm.stolz@klinik.uni-regensburg.de Table 1: Diagnostic criteria for lentigo maligna (LM) and lentigo maligna melanoma (LMM) on the face