Melanomas difficult to diagnose via dermoscopy

Due to the potentially lethal nature of melanoma, prompt diagnosis and timely excision are of paramount importance. The clinical ABCD mnemonic (asymmetry, boarder irregularity, color variegation and diameter greater than 6mm) is one of the first and most widely used methods introduced to teach early melanoma recognition. Unfortunately, some melanomas can evade the clinical ABCD rule and mimic benign melanocytic nevi or mimic benign and/or malignant variants of non-melanocytic lesions. Over the last two decades, knowledge and insight have been gained into the dermoscopic primary morphology of melanocytic and non-melanocytic lesions. This has allowed for the use of dermoscopy to substantially increase the diagnostic accuracy for melanoma over clinical naked-eye examination alone. Unfortunately, even with dermoscopy, some melanomas remain difficult to diagnose. However, these difficult to diagnose melanomas often reveal subtle dermoscopic clues that allow for their correct identification. In this review, we focus on five variants of melanoma that are challenging to identify and discuss the dermoscopic features that can assist in their diagnosis.