Clinical and morphological features and dermatoscopic diagnosis of seborrheic keratosis

Seborrheic keratosis (SK) is one of the most common benign skin neoplasms. Signs of SK are found in most adults over 60 years of age. The clinical manifestations of SK are characterized by marked heterogeneity and variability. Lesions may present with various morphological elements, including spots, papules, and plaques. The surface of the rash is typically dull, waxy, or verrucous, with possible comedo-like openings and keratotic crusts. The color of the lesions ranges from light whitish-pink, yellowish, gray-beige, and pale brown to intensely pigmented shades of gray, brown, grayish-brown, and even black. Skin lesions in SK are typically multiple and can be eruptive. In some cases, these lesions are regarded as a paraneoplastic manifestation (Leser-Trélat sign), indicating the presence of a malignant neoplasm of the internal organs. The main histological types of SK include acanthotic, hyperkeratotic, reticular, clonal, irritated, verrucous with features of keratoacanthoma variants, as well as melanocanthoma. Due to the diversity of clinical manifestations and morphological forms, the differential diagnosis of SK can be challenging and requires further evaluation, such as dermatoscopy and pathohistological examination. The classic dermatoscopic features of SK include comedo-like openings, brain-like and fern-like structures, milium-like cysts, hairpin vessels, and blue-gray globules.