Clinicopathological spectrum of lichen planus

The term „lichenoid“ was first established as a clinical definition for diseases characterized by flat, dull red papules with smooth surface. Over time, a second definition of lichenoid became commonly used as well, the histopathological one, which refers to a dense, bandlike inflammatory infiltrate obscuring the dermo-epidermal junction. Today, the term lichenoid is used interchangeably in its clinical and histopathological meanings to define the so-called lichenoid dermatoses. Lichenoid dermatoses represent a group of unrelated inflammatory conditions that share some clinical and/or histopathological features; some of these are clinically but not histopathologically lichenoid, while others are histopathologically but not clinically lichenoid. Lichen planus (LP) represents the prototype of a cutaneous inflammatory disease that presents with both clinical and histopathological lichenoid features. Besides the skin, the disease commonly affects the oral mucosa and the nails. Involvement of the hairs (lichen planopilaris) can result in a form of scarring alopecia. Several clinical and/or histopathological variants of LP have been described over the years, including such disparate forms as linear, atrophic, hypertrophic, and ulcerative LP among others. In some cases, association with other diseases (e.g., LP pemphigoides, LP/lupus erythematosus overlap syndrome) is well described. It is important to understand that the variants of LP are not specific entities; for example, an atrophic LP is commonly pigmented, often located at sites of inverse LP, and may present with an annular configuration. In this article we briefly review the protean clinicopathological spectrum of LP.