Lichen planus on the arm

The cause of lichen planus is unknown. It appears as raised, many-sided purple bumps (violaceous polygonal papules) with overlying white lines (Wickham's striae). It commonly involves the wrists (flexor surface), lower back (lumbar region), shins, and ankles. The lesions often itch. Females are more frequently affected than males and the age range is approximately 30 to 60 years of age.