Unusual Dermoscopic Patterns of Seborrheic Keratosis

Seborrheic keratoses (SKs) may sometimes mimic benign and malignant skin tumors, and a biopsy can be necessary in order to rule out malignancy.

From the database of our pigmented lesion clinic, we evaluated the dermoscopic features of difficult-to-diagnose SKs that were biopsied between January 2010 and December 2014.

SKs represented 3.8% of all excised lesions (161/ 4,182). Specifically, 91 (56.5%) were excised to rule out melanoma, 63 (39.1%) to rule out squamous cell carcinoma and 7 (4.4%) to rule out basal cell carcinoma. The following 10 global dermoscopic patterns were identified: multicomponent (32; 19.9%); reticular (24; 14.9%), characterized by an irregular pigment network; bowenoid (21; 13.0%); hairpin (19; 11.8%); keratoacanthoma-like (16; 9.9%); blue-nevus-like (15; 9.3%); lichenoid (6; 3.7%); hyperkeratotic (6; 3.7%); clonal (5; 3.1%); spitzoid (5; 3.1%). Furthermore, 12 SKs (7.5%) were not included in any of such patterns (not classified).

Our results are in line with previous studies highlighting the dermoscopic variability of SKs. Although excised SKs may be classified into 1 of 10 repetitive dermoscopic patterns, a biopsy remains mandatory for those that cannot be clearly differentiated from common skin malignancies.