Accuracy of the first step of the dermatoscopic 2-step algorithm for pigmented skin lesions

Philipp Tschandl; Cliff Rosendahl; Harald Kittler

doi:10.5826/dpc.0203a08

Accuracy of the first step of the dermatoscopic 2-step algorithm for pigmented skin lesions

Authors

Philipp Tschandl Department of Dermatology, Division of General Dermatology, Medical University of Vienna, Austria
Cliff Rosendahl School of Medicine, University of Queensland, Brisbane, Australia
Harald Kittler Department of Dermatology, Division of General Dermatology, Medical University of Vienna, Austria

Abstract

Objectives: To evaluate the frequency of misclassifications of equivocal pigmented lesions according to the first step of the dermatoscopic 2-step algorithm.

Patients and 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.

Conclusion: 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.

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