Reflectance confocal microscopy criteria of lichen planus-like keratosis

Background Lichen planus-like keratosis (LPLK) may be difficult to differentiate from melanoma and other skin cancers on sun-damaged skin based on clinical and dermoscopic examination. Reflectance confocal microscopy (RCM) allows evaluation of skin lesions at high resolution. Objectives The aim of this study was to identify criteria for specific diagnosis of LPLK using in vivo RCM. Methods Lesions included in the study were derived from patients presenting for skin examination at a private dermatology practice specializing in skin cancer. We retrospectively analysed RCM features of 28 biopsy-proven LPLK and compared them to RCM findings in skin cancers on sun-damaged skin, including five in situ squamous cell carcinomas, six actinic keratoses, seven superficial basal cell carcinomas and eight melanomas. Results The main RCM features of LPLK and their relative frequencies were: (i) typical honeycomb pattern of the spinous layer (78.6%); (ii) elongated cords and/or bulbous projections at the dermal-epidermal junction (75%); and (iii) numerous plump-bright cells and/or bright stellate spots in the superficial dermis (92.9%). These RCM features correlated with the following histopathological findings respectively: (i) spinous-granular layers without significant atypia of keratinocytes; (ii) elongated, bulbous rete ridges; and (iii) dense infiltration of melanophages and lymphocytes in superficial dermis. We propose diagnostic criteria that classify correctly 71.4% of LPLK, while avoiding misclassification of any of the skin cancers in the present series as LPLK. Conclusions We identified RCM criteria for diagnosis of LPLK that correlate well with histopathological findings and that allow differentiation of LPLK from skin cancer.