Tips for difficult to diagnose hypomelanotic melanomas on reflectance confocal microscopy

Amelanotic/hypomelanotic melanoma (AHM) represents a clinical diagnostic challenge. Dermoscopy improves AHM diagnosis thanks to visualization of little pigment and vascular pattern. Reflectance confocal microscopy (RCM) increases further the diagnostic accuracy of AHM but few and small studies have described in detail RCM features of AHM. We evaluated dermoscopic and RCM features of nine cases of difficult to diagnose hypomelanotic melanomas (HMs) to find clues for their diagnosis. The RCM score was suggestive of melanoma in all cases. The major criteria of nonedged papillae and/or cytological atypia at the dermo-epidermal junction were seen in all cases. Among the minor criteria, roundish pagetoid cells, including hyporeflective pagetoid cells, were found in four out of nine lesions. Dermoscopically, four out of nine HMs did not show prevalent suspicious criteria while revealing suspicious RCM features that were visible only after careful RCM examination by zooming mosaic images. RCM can improve HM diagnostic accuracy but only after extensive evaluation of images. Atypical cells were less reflective and the architectural irregularity was less visible than in pigmented melanoma and zooming was needed to identify both features.