- Lichen Planus is an idiopathic inflammatory skin disorder whose lesions are characterized by the 5 P's: Purplish, Planar, Pruritic, Polygonal Papules
- The etiology of lichen planus is unknown although a derangement of the immune system is suspected. In some cases, LP-like lesions can be induced by certain drugs.
- The lesions of LP are are classically well-demarcated flat-topped purplish papules with an angulated, polygonal shape. Their surface may be marked by a fine, lacy reticular pattern of white lines, termed "Wikham's Striae".
- Histologically, LP lesions show a saw-toothing of the epidermal rete ridges and degeneration of basal cells associated with a dense band-like lymphocytic infiltrate at a disrupted dermo-epidermal junction. Hyperkeratosis is also frequently seen.
- LP lesions are most bothersome to patients due to their pruritis. The lesions tend to occur on around the ankles and wrists as well as the oral mucosa.