What is Lichen Planus?
This is a disease in which nerve fibers (under the skin) become thickened and scarred, causing chronic, itchy inflammation. The cause is not known but psychological factors are generally believed to play a role. Appears not to be allergic, affects more women than men, and is more common among Native Americans and Asians.

Symptoms
Itchy skin lesions
Lesions become dark, thick, and leathery with round scaly plaque underneath. The lesions may have well-defined rectangular borders, or present in oval, irregular, or angular shapes.
Exaggerated skin lines in the lesions
Usual locales -- nape of the neck, forearms, area on inside of elbows, wrists, inner thighs, behind the knees, and lower legs

Cause
Lichen planus may cause a small number of skin lesions or less often affect a wide area of the skin and mucous membranes. In 85% of cases it clears from skin surfaces within 18 months but it may persist longer especially when affecting the mouth or genitals.