Presentation of a Case and Proposal of a Novel Hypothesis about the Pathogenesis of Lichen Striatus

Abstract

A 60-year-old man was treated for herpes zoster on his right lower leg by a local physician. Four weeks later, he noticed asymptomatic eruptions on different sites from the herpetic lesions and visited us. Physical examination revealed linearly arranged lesions that were located from the left chest to the left upper arm, from the middle of the lower abdomen to the left side of the abdomen, and from the left thigh to the left lower leg. Each lesion consisted of pink flat papules distributed continuously or discontinuously along Blaschko’s lines. Histopathological findings included exocytosis and individual cell necrosis of the epidermis, liquefaction degeneration of basal layer, and lymphocytic infiltrations in the upper dermis and around the sweat gland in the mid-dermis. Based on the above findings, we made a diagnosis of lichen striatus and administered 0.1% tacrolimus ointment. After 15 weeks, skin lesions had subsided well leaving only mild pigmentation. Blaschko’s lines are thought to represent the migration pathway of ectodermal cells in the process of embryogenesis of skin. According to the conventional view, postzygotic mutation may lead to cutaneous mosaicism, and some immunological responses to these abnormal clones along the Blaschko’s lines may play a role in the pathogenesis of lichen striatus. However, one of the lesions in our case developed along the ventral median line, which corresponds to the junction of multiple Blaschko’s lines but does not belong to any specific keratinocyte clones. Therefore, we would like to propose a hypothesis that lichen striatus initially develops on the junctional area between the adjoining different keratinocytes clones, not on the same clonal area of keratinocytes. This “junction”theory could also explain some other features of lichen striatus. Skin Research, 21 : 175-180, 2022