Somatic Mosaicism in Blaschkolinear Inflammatory Disorders

Linear lichen planus (LP) is a rare dermatologic disease in which lichenoid lesions conform to a blaschkolinear distribution, most commonly on the extremities. Linear discoid lupus erythematosus (DLE) is a cutaneous manifestation of lupus that also conforms to Blaschko’s lines. Blaschkolinear disorders have been shown to result from somatic mosaicism, most recently in nevus sebaceus, epidermal nevi, and syringocystadenoma papilliferum. In linear LP and DLE, presentation of papules along Blaschko’s lines suggests that these disorders can result from keratinocytic genetic mosaicism. Their onset later in life suggests that a secondary trigger is necessary to drive inflammatory reactions to these linear lesions. To date causative mutations have not be identified. We report 2 cases of linear lichen planus and 1 case of linear discoid lupus erythematosus, all histologically confirmed. Both LP patients have experienced episodic regression and recurrence of their lesions in precisely the same distribution, with moderate symptomatic benefit from topical steroids and non-steroidal anti-inflammatories. The DLE patient showed gradual response to hydroxychloroquine over the course of 14 months. These cases highlight linear inflammatory diseases which represent localized variants of disorders for which there are few efficacious therapies. Their linear presentations suggest that they result from somatic mosaicism and genetic investigation of such disorders may reveal relevant therapeutic targets.