OBJECTIVE: The objective was to describe the clinical and dermoscopic characteristics of difficult-to-diagnose melanomas (DDM). DESIGN: This study was a retrospective analysis of clinical data and dermoscopic images in a series of excised melanomas. SETTING: Cases were obtained from the database registers of three public hospitals in Barcelona (Spain), Naples (Italy), and Graz (Austria). PATIENTS: A total of 97 tumors with a main preoperative diagnosis different from melanoma and without sufficient criteria to be diagnosed clinically and dermoscopically as melanoma were studied. We studied clinical data from the patients and lesions, mean reason for excision, and consensus dermoscopic description of the lesions according to pattern analysis performed by a panel of four dermoscopists to obtain clues that allow these melanomas to be recognized. RESULTS: Ninety-three DDMs were evaluated. Three main dermoscopic categories of DDM have been identified: (1) DDMs lacking specific features (16/97), (2) DDMs simulating nonmelanocytic lesions (14/93), and (3) DDMs simulating benign melanocytic proliferations (67/93). The reasons for excision were (1) the subjective history of change referred by the patient (38% of cases), (2) the presence of clinical and/or dermoscopic "hints" for biopsy (33% of cases), and (3) the objective evidence of changes detected by digital dermoscopic follow-up (29% of cases). CONCLUSIONS: A diagnostic algorithm is proposed not to miss melanoma.
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