A case of seborrheic keratosis distributed along skin cleavage lines

A 65-year-old woman with seborrheic keratosis following skin cleavage lines is reported. The mostly brownish-yellow lesions were located on the back. The round, oval, spindle, comet, and slightly raised papules varied from 1 mm to 2 cm in diameter. The distribution of lesions was unusual; they tended to follow skin cleavage lines on her lower back and waist. The arrangement of lesions was streamlined. The skin biopsy specimen revealed hyperkeratosis, acanthosis, and papillomatosis. The acanthosis was caused by proliferation of squamous and basaloid cells.