Subacute cutaneous lupus erythematosus starting as linear lupus erythematosus

Background Cutaneous lupus in childhood is usually associated with systemic lupus erythematosus (LE). Linear cutaneous LE (LCLE) is an unusual presentation mostly seen in children and young adults. Methods We report a rare case of cutaneous subacute LE with a segmentary pattern following the lines of Blaschko in an 18-month-old girl with a 2-month history of persistent, linear, asymptomatic, erythematous lesions along the right arm. The clinical diagnosis at presentation was lichen striatus. Results A biopsy showed an intense, band-like, inflammatory cell infiltrate with perivascular and periadnexal involvement associated with basal cell liquefactive degeneration. The lesions were treated with topical corticosteroids and healed without scarring. Two months later, new lesions manifested as multiple erythematous, edematous, polycyclic plaques. A new biopsy showed a periadnexal infiltrate, a large amount of mucin, and a thickened basement membrane. Direct immunofluorescence was negative. Our definitive diagnosis was subacute cutaneous LE starting as linear LE. The lesions responded slowly to oral corticosteroids. Six months later, only a mild livedoid skin pattern remained on the patient's legs. Conclusions Linear cutaneous LE usually presents with erythematous, atrophic, hyperkeratotic, dyschromic circular lesions arranged in a linear pattern; the main differential diagnosis is lichen striatum. In general, LCLE can be considered as discoid lupus following Blaschko's lines, which correspond to the direction of growth in clones of cutaneous cells that arise during embryogenesis. The present patient represents the first pediatric case of subacute cutaneous LE following Blaschko's lines, with posterior progression to a generalized form of subacute LE.