Linear lichen planus (LLP), also referred to as Blaschkoid LP, is a rare type of lichen planus characterized by a linear distribution of lichenoid lesions along the lines of Blaschko, which are embryonic pathways of skin development.
The prevalence is unknown. Less than 0.5% of patients with LP present with Blaschkoid LP. Cases have been more commonly reported in children, however LLP does occur in adults.
Lesions appear as pruritic, violaceous papules in a linear distribution, usually on the limbs, but also anywhere on the body. It follows a Blaschkoid, not dermatomal, pattern of distribution. It can be superimposed on the more typical non-segmental and randomly-distributed lesions of classic LP. Histology is that of classical papulosquamous lichen planus. A very rare LLP variant, called zosteriform LP, has also been observed and is characterized by a segmental zosteriform distribution of lichenoid lesions. Zosteriform LP may appear as a Koebner phenomenon following herpes zoster infection.
Etiology of LLP is unknown, however it has been associated with metastatic carcinoma, HIV infection and hepatitis C infection. It is thought that LLP arises due to an abnormal keratinocyte clone that is only unmasked after the initiating event for lichen planus.
Last update: May 2011
- Dr Stephanie ARNOLD
- Dr Susan COOPER