title: Accuracy of the first step of the dermatoscopic 2-step algorithm for pigmented skin lesions.
abstract: OBJECTIVE
  To evaluate the frequency of misclassifications of equivocal pigmented lesions according to the first step of the dermatoscopic 2-step algorithm.
  
  
  METHODS
  707 consecutive cases from 553 patients of central Europe and Australia were included in the study. Dermatoscopic images were evaluated in a blinded fashion for the presence of features described in the 2-step algorithm to determine their melanocytic or non-melanocytic origin. Mucosal, genital and non-pigmented lesions were excluded.
  
  
  RESULTS
  The sensitivity of the first step was 97.1% for patients from Australia and 96.8% for patients from central Europe. The specificity was 33.6% for Australian patients and 67.9% for European patients. The most common reasons for misclassification were the presence of a pigmented network in a non-melanocytic lesion (n=68, 25.2%) and the absence of dermatoscopic features of melanocytic and non-melanocytic lesions in 69 (25.6%) non-melanocytic lesions.
  
  
  CONCLUSIONS
  The first step of the dermatoscopic 2-step algorithm, if applied consistently, has high sensitivity but low specificity. Many non-melanocytic lesions, especially solar lentigines and seborrheic keratoses, are wrongly classified as melanocytic. The worse performance of the first step algorithm in Australian patients is probably due to a higher rate of solar lentigines in patients with severely sun-damaged skin.
authors.affiliation: Department of Dermatology, Division of General Dermatology, Medical University of Vienna, Austria.
authors.forename: Philipp
authors.initials: P
authors.lastname: Tschandl
authors.forename: Cliff
authors.initials: C
authors.lastname: Rosendahl
authors.forename: Harald
authors.initials: H
authors.lastname: Kittler