Objectives: To describe morphological features of seborrheic keratosis as seen by dermoscopy and to investigate their prevalence. Design: Prospective cohort study using macrophotography and dermoscopy for the documentation of seborrheic keratosis. Settings: Seborrheic keratoses were prospectively collected in 2 sites: a private practice in Plantation, Fla (site 1), and the Department of Dermatology at the University Hospital Geneva in Switzerland (site 2). Patients: A total of 203 pigmented seborrheic keratoses (from 192 patients) with complete documentation were collected (111 from site 1 and 93 from site 2). Interventions: Screening for new morphological features of seborrheic keratosis and evaluation of all lesions for the prevalence of these criteria. Main Outcome Measures: Identification of new morphological criteria and evaluation of frequency. Results: A total of 15 morphological dermoscopic criteria were identified. Standard criteria such as milialike cysts and comedolike openings were found in a high number of cases (135 and 144, respectively). We found network and networklike structures to be present in 94 lesions (46%). Using standard diagnostic criteria for seborrheic keratosis, 30 lesions would not have been diagnosed as such. Conclusions: The classic dermoscopic criteria for seborrheic keratosis (milialike cysts and comedolike openings) have a high prevalence but the use of additional dermoscopic criteria such as fissures, hairpin blood vessels, sharp demarcation, and moth-eaten borders improves the diagnostic accuracy. The proper identification of pigment network and networklike structures is important for the correct diagnosis.
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