ABSTRACT
This chapter discusses different types of linear hyperpigmentation, such as pigmentary demarcation lines (PDLs), linear and whorled nevoid hypermelanosis (LWNH), linear morphea or en coup de sabre, acquired blaschkoid dermatitis, linear epidermal nevus, Becker's nevus and linear lichen planus. PDL occur in all races and skin types. The separation of zones corresponds to the lines of Blaschko, indicating that they are a common manifestation of cutaneous mosaicism. PDLs are physiological, abrupt transitions from darker-colored skin to lighter-colored skin. Patients with facial PDLs often seek treatment for cosmetic reasons. Sun avoidance and regular use of broad-spectrum sunscreen may minimize the colour contrast of the lighter and darker skin areas. LWNH is a sporadic pigmentary disorder appearing within the first weeks of life with characteristic swirls and streaks of macular hyperpigmentation following the lines of Blaschko. Histopathology examination shows diffuse increased pigmentation in the basal layer and a prominence of melanocytes without incontinence of pigment in the dermis.
