Superimposed segmental dermatitis with chronic prurigo.

Common acquired skin diseases with a polygenic background, such as lichen planus, may show linear or segmental manifestations of underlying systemic skin disease. The linear arrangement in such cases is usually consistent with the lines of Blaschko. Happle summarized the various types of segmental arrangement of common polygenic diseases and proposed a novel designation of superimposed segmental dermatosis. Here, we report a unilateral linear dermatitis distributed along the lines of Blaschko on the leg, which was not self-healing and persisted for at least 6 years without complete remission, and was accompanied by preceding chronic prurigo on the extremities. Histological examination showed subacute spongiotic dermatitis and epidermal infiltration of CD4-positive cells. This case report presents a superimposed segmental dermatitis that arose based on systemic eczematous conditions, such as chronic prurigo.