Seborrheic keratosis: reflectance confocal microscopy features and correlation with dermoscopy

Differentiation between seborrheic keratosis (SK) and skin cancers may be difficult. Reflectance confocal microscopy (RCM) enables noninvasive assessment of skin neoplasms at cellular-level resolution.

We sought to describe RCM features of SK and to correlate these RCM findings with dermoscopic structures.

Clinical, dermoscopic, and RCM images of 45 consecutive SK were obtained at a private and university dermatology clinic. Fourteen SK were biopsied because of equivocal clinical or dermoscopic features.

With RCM, all SK displayed a regular honeycomb pattern of the epidermis and densely packed, round to polymorphous, well-circumscribed dermal papillae at the dermoepidermal junction, features suggestive of a benign neoplasm. RCM features indicating the diagnosis of SK were also observed, including epidermal projections (43/45 SK; 96%) and keratin-filled invaginations (36/45 SK; 80%) at the lesion surface; corneal pseudocysts at epidermal layers (19/45 SK; 42%); and melanophages (21/45 SK; 47%) and dilated round and linear blood vessels (21/45 SK; 47%) in the papillary dermis. Of biopsied SK, 93% (13/14) displayed at least 3 characteristic RCM findings in the absence of RCM features suggestive of malignancy.

This was a limited study sample and retrospective study design.

SK display a distinct set of RCM criteria despite their variable clinical and dermoscopic appearances.