Background Lichenoid keratosis (LK) is a well-described entity which has been proposed to represent an immunological or regressive response to pre-existing epidermal lesions such as solar lentigines or seborrhoeic keratoses.
Objectives To evaluate the dermoscopic criteria of a series of cases of LK with remaining areas of seborrhoeic keratosis which were both dermoscopically and histologically diagnosed.
Methods Pigmented lesions with dermoscopic areas of seborrhoeic keratosis and LK in the same tumour were consecutively diagnosed and prospectively included in the study. All pigmented lesions were examined and registered using DermLite Foto equipment (3Gen, LLC, Dana Point, CA, U.S.A.), at 10-fold magnification, at the Dermatology Department of Hospital de Sant Pau i Santa Tecla (Tarragona, Spain), between 1 January 2003 and 31 December 2005.
Results In total, 24 cases of lesions with dermoscopic areas of seborrhoeic keratosis and LK were collected. In four lesions (17%), the clinical differential diagnosis without dermoscopy included malignant melanoma and in seven lesions (29%), basal cell carcinoma. The diagnosis of LK was clinically considered without dermoscopy in only six cases (25%). A granular pattern was observed to be distributed throughout the LK areas of the lesions. This pattern consisted of the presence of brownish-grey, bluish-grey or whitish-grey coarse granules that formed, in 11 cases (46%), globules and/or short lines. In one lesion, located on the face, these short lines produced annular or rhomboid structures as seen in lentigo maligna melanoma.
Conclusions Dermoscopy is a useful tool which assists in the correct clinical recognition of LK, which may also potentially illuminate the pathogenesis of these tumours, showing the intermediate stage of regressing epidermal lesions in an LK.