Dermatoscopy of "dysplastic nevi": a beacon in diagnostic darkness

The sequential progression model for melanocytic tumours from common nevus to malignant melanoma was proposed by Clark almost 30 years ago. The "dysplastic nevus" has frequently been considered a logical offspring of this concept and as a direct precursor of melanoma, analogous to the epithelial dysplasia-carcinoma sequence. Despite the use of modern molecular methods, there is no consensus as to if the dysplastic nevus represents a true precursor lesion of melanoma, a separate distinct type of nevus, or a diagnostic dilemma. Currently, the concept of melanocytic dysplasia remains subject to confusing definitions at all levels of the diagnostic process, i.e. clinical appearance, dermatohistopathology, and molecular biology. In this review, we collect evidence that nevi fulfilling Clark and Elder's classic histological criteria mostly represent "endpoints" of nevocytic evolution, whereas a minority of "dysplastic nevi" represent true melanoma precursors. The unsolved dilemma is that neither clinical, histopathological nor molecular criteria exist to make a distinction between dysplastic nevi and early melanomas. Our analysis of the current knowledge on dysplastic nevi shows that dermatoscopy remains the only quantifiable, easily applicable and reproducible diagnostic tool to approach the problem. Due to a "quantum leap" in optical resolution, objective scores can be established, e.g. the total dermatoscopy score (TDS) according to the ABCD rule, and documentation of changes over time are possible by digital image storage devices. Although dermatoscopy does not solve the dilemma of discriminating early, basically feature-less melanomas from dysplastic nevi, and it does not prove that dysplastic nevus is a distinct entity, it helps make melanocytic tumours with unclear malignant potential a manageable disease.