Parallel pigmented network in lentigo maligna: a case series and correlation with in vivo reflectance confocal microscopy

Lentigo maligna (LM) often poses a diagnostic challenge due to its clinical and dermoscopic mimicry of benign lesions, leading to delayed diagnosis. Focal areas of reticular disruption have been described as one of the earliest dermoscopic signs observed. To describe a novel dermoscopic sign in LM, namely the presence of a parallel pigmented network. Case series of 22 histopathologically-proven LM and lentigo maligna melanoma (LMM), diagnosed between 2018 and 2023, at a tertiary centre. All lesions showed a parallel network upon dermoscopy, in the form of parallel reticular lines, light or dark brown in colour, not emanating from the follicle, with an asymmetrical distribution. Reflectance confocal microscopy (RCM) images were reviewed to correlate these areas. The median age of patients was 73 years old. The majority of lesions were in situ (91%) and extrafacial (82%). Lesions showed minimal signs of atypia other than a parallel network and mostly focal erased areas (100%), followed by perifollicular linear projections (18%) and asymmetrical follicular pigmentation (18%). On RCM, focally areas correlated with atypical junctional thickenings distributed in a parallel fashion (100%) and mitochondria-like structures (23%). Most cases (88%) showed atypical cells in the epidermis, mostly in the form of isolated dendritic cells (41%). Parallel network emerges as a potential dermoscopic sign associated with LM. We hypothesize that in early stages of LM transformation, disruption of the reticular network manifests as parallel lines and/or radial perifollicular lines. Validation with larger studies is warranted.