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Lichen planus
Primary lesion (early): Skin-colored to red, flat-topped papule with angulated border. White, reticulated surface lines are called Wickham striae.
Mineral oil accentuates the reticulated lines. Lesions become purple, thicker, and more numerous with time.
Papules appear most often on the flexor surfaces of wrists and forearms, ankles, and lumbar region. Lesions may be much more extensive.