Background: In vivo epiluminescent light microscopy (ELM) of pigmented skin lesions reveals numerous elementary structures. Among them, the pigment network (PN), black dots (BD) and brown globules (BG) constitute important semiologic features. Based on histological extrapolations, it has been postulated that PN should reflect the presence of melanin in the epidermis and its honeycomb aspect should result from the dermoepidermal architecture.
Objective: To demonstrate this directly by analyzing separately by ELM the epidermal and dermal sides of melanocytic lesions.
Methods: We split the epidermis from the dermis of 10 pigmented lesions (6 lentigos, 4 nevocytic nevi) by incubation with dispase. ELM images were done in vivo before excision, then ex vivo on the whole specimen and separately on the split epidermis and dermis. Epidermal and dermal specimens were finally controlled by histology.
Results: PN was observed only on the epidermal side of the split. Its organization was remarkably conserved after the procedure as compared with prior in vivo images. In contrast, pigmentation observed on dermal sides of the splits showed no organized pattern and corresponded to melanophages. BG were found on the dermal side and BD on the epidermal side of the split lesions, which confirms previous hypotheses.
Conclusion: By subtracting the dermal pigmentation and vessels from the image, the split technique has thus established the epidermal origin of the PN and given a more detailed ELM analysis of network components.