Dermoscopy and Reflectance Confocal Microscopy improves accuracy in differentiating atypical basal cell carcinoma from seborrheic keratosis and vice versa.

Background: To differentiate basal cell carcinomas (BCCs) and seborrheic keratoses (SKs) with reciprocal dermoscopic mimicking features is challenging. The aim of this study is to identify dermoscopic BCC and SK criteria predictive of diagnosis among reciprocal mimicking features, and to evaluate the impact of adjunctive reflectance confocal microscopy (RCM). Material and Methods: A multicenter study with retrospective evaluation of images was conducted by 3 dermatologists, blinded to histology. Histologically confirmed lesions with a complete set of clinical, dermoscopy and RCM images with ≥1 reciprocal dermoscopy feature were selected. Results: A total of 231 dermoscopy and RCM evaluations were included. No demographic differences between patients were observed. Independent dermoscopic diagnostic features revealed shiny white-red structureless areas (OR = 2.3, CI 1.1-4.8, P = .023), maple leaf-like areas (OR = 2.2, CI 1.0-4.9, P = .044), arborizing vessels (OR = 2.2, CI 1.0-4.7, P = .049), and blue-gray globules (OR = 2.0, CI 1.0–3.9, P = .041) for BCC and milia-like cysts (OR = 0.4, CI 0.2–0.9, P = .041), hairpin vessels (OR = 0.3, CI 0.1–0.5, P < .001), and coral-like pattern (OR = 0.2, CI 0.05–0.7, P = .018) for SK diagnoses. All reflectance confocal microscopy BCC-specific criteria were significantly more prevalent in BCCs (P < .001) and SK-specific criteria, with the exception of predominantly dilated loop vessels, were significantly more prevalent in SKs (P < .01). Conclusions: Despite the identification of independent dermoscopy criteria, diagnosis remains complex. Adjunctive RCM assists in the differential diagnosis.