Dermoscopy and Reflectance Confocal Microscopy Improves Accuracy in Differentiating Atypical Basal Cell Carcinoma from Seborrheic Keratosis and Vice Versa

Introduction: To differentiate basal cell carcinomas (BCCs) and seborrheic keratoses (SKs) with reciprocal dermoscopic mimicking features is challenging. The aim of this study was 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). 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 features 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 = 0.023), maple leaf-like areas (OR = 2.2, CI: 1.0-4.9, p = 0.044), arborizing vessels (OR = 2.2, CI: 1.0-4.7, p = 0.049), and blue-gray globules (OR = 2.0, CI: 1.0-3.9, p = 0.041) for BCC and milia-like cysts (OR = 0.4, CI 0.2-0.9, p = 0.041), hairpin vessels (OR = 0.3, CI: 0.1-0.5, p < 0.001), and coral-like pattern (OR = 0.2, CI: 0.05-0.7, p = 0.018) for SK diagnoses. All BCC-specific RCM criteria were more prevalent in BCCs (p < 0.001) and all SK-specific RCM criteria were more prevalent in SKs (p < 0.001), with the exception of dilated loop vessels. Conclusion: Despite the identification of independent dermoscopy criteria, diagnosis remains complex. Adjunctive RCM assists in the differential diagnosis.