Old lines tell new tales: Blaschko linear lupus erythematosis.

Patients with lupus erythematosus (LE) specific cutaneous manifestations distributed along the lines of Blaschko are seldom encountered in clinic. In this paper, we reported 5 new cases and perform a systematic review of all the published cases in the English and Chinese literature. We provide a comprehensive summary of the clinical manifestations and explore potential etiology and pathogenesis. Sixty-eight published papers (53 English and 15 Chinese) and 93 cases (including 5 cases reported by us) were included in the analysis. In contrast to classical cutaneous LE, these cases have a series of distinctive clinical features and also have a potentially unique pathogenesis. The pathogenesis of this condition may involve the presence of mosaic abnormal skin cells, possessing crucial pathogenic gene(s)/epigenetic modification(s), located along the lines of Blaschko during embryogenesis. A comparison of the mosaic cells and surrounding "wild-type" cells and in-depth exploration of the interaction between susceptive gene(s)/epigenetic modification(s) and the immune system may potentially bring to light the secrets hidden in LE. Thus, we consider this condition to be a distinct subtype of LE and "Blaschko-linear lupus erythematosus" would be a more appropriate designation. The clues provided in the study of the pathogenesis of this form of LE may potentially unlock the mysteries of the various forms of LE as a whole.