Reflectance confocal microscopy correlates of dermoscopic patterns of facial lesions help to discriminate lentigo maligna from pigmented nonmelanocytic macules

Background The clinical recognition of lentigo maligna (LM) and LM melanoma can be very challenging due to the overlapping features it shares with other pigmented macules of the skin. Noninvasive diagnostic techniques can assist in the differential diagnosis. Objectives To identify reflectance confocal microscopy (RCM) indicators for LM through the identification of in vivo microscopic substrates of the main dermoscopic features seen in flat pigmented lesions of the face. Methods Retrospective analysis of 60 pigmented lesions (LM, invasive melanoma, solar lentigo/flat seborrhoeic keratosis, lichen planus-like keratosis, pigmented actinic keratosis) was carried out. The main dermoscopic patterns and RCM features were described. A new method for correlating RCM with dermoscopic patterns was developed. Results Pseudonetwork (37 of 60 lesions) and annular granular structures (37 of 60 lesions) were the most frequent dermoscopic patterns, followed by pigmented blotches (27 of 60 lesions). Upon RCM examination, pseudonetwork and blotches differed in melanomas and other nonmelanocytic lesions. These differences included the intraepidermal proliferation of atypical cells (predominantly dendritic-shaped with adnexal tropism) and the presence of a meshwork pattern at the junction. Also, annular granular structures exhibited dendritic cells almost exclusively in melanoma, with no difference between melanomas and nonmelanocytic lesions for the junctional and upper dermal pattern (characterized by dermal inflammation). Fingerprinting was mostly present in nonmelanocytic lesions or corresponded to an overlap with solar lentigo in melanomas. Conclusions RCM is useful for identifying the histological substrate of dermoscopic features in pigmented lesions of the face. It can provide a better definition of the lesion areas, enabling an improved diagnostic approach. What's already known about this topic? The clinical diagnosis of facial pigmented lesions can be challenging because of the overlapping features of benign and malignant entities. Dermoscopy and reflectance confocal microscopy (RCM) can assist in the diagnostic process. What does this study add? This article provides an original perspective regarding the role of dermoscopy and RCM in the diagnosis of facial malignant lesions. RCM can be used to assess appropriate treatment options and follow-up protocols for facial lesions.