Pigmented linear discoid lupus erythematosus following the lines of Blaschko: A retrospective study of a Chinese series

Background: Linear cutaneous lupus erythematosus is a rare subtype of lupus erythematosus (LE) that develops linear lesions following the lines of Blaschko. Linear cutaneous lupus erythematosus may present as various subtypes of LE, including linear discoid lupus erythematosus. There are few reports about pigmentedlinear discoid lupus erythematosus in the literature. Aims: We aimed to summarize the clinical and pathological features of patients with pigmented linear discoid lupus erythematosus following the lines of Blaschko. Methods: Eighteen patients with pigmented linear discoid lupus erythematosus attending the outpatient department of the Dermatology, Peking Union Medical College Hospital, China, were enrolled in the study. We recorded clinical data including sex, age at onset, disease duration, location and distribution of the lesions, symptoms, trigger factors, antinuclear antibody (ANA) testing, therapy, and therapeutic responses. Histopathological features were also summarized. Results: All 18 patients presented with well-defined brownish pigmented linear or segmental macules or plaques, following the lines of Blaschko. All the lesions were located on the head or neck. Unilaterally distributed lesions were found in 94.4% of patients. Two patients showed low titers of ANA in a speckled pattern. No systemic involvement or progression to systemic LE was noted. The patients were clinically diagnosed as pigmented lichen planus (55.6%), pigmented linear discoid lupus erythematosus (33.3%), and linear morphea (11.1%) before histopathological examination. Limitations: The study was retrospective and direct immunofluorescence was not performed. Not all patients' information was available and 4 patients were lost to follow-up because their contact information was changed. Conclusion: Pigmented linear discoid lupus erythematosus mostly occurs on the head and neck. It manifests as brownish macules along the lines of Blaschko. Differentiation between pigmented linear discoid lupus erythematosus and other dermatoses that have a linear distribution can be difficult both clinically and pathologically, but histological details can help distinguish them.