Lichen ruber, also called lichen ruber planus or lichen planus (LP), is a noncontagious inflammatory skin disease. LP is the main representative and namesake of the group of lichenoid diseases, which are characterized by small papules often accompanied by severe itching. With 65% of cases, LP is primarily a disease of the mucous membranes. In 20% of the cases, the disease is found on the skin and mucous membranes; skin involvement alone is seen in only about 10% of cases. Cutaneous LP has a very favorable 1‑year prognosis of almost 80% healing as opposed to the mucosa and the adnexal organs. Histologically, keratinocytes with vacuolar degeneration, leaving behind apoptotic Kamino bodies and the characteristic band-shaped lymphocytic infiltrate at the dermatoepithelial junction, are common to lichenoid diseases. The horny layer is firm and compact and the stratum granulosum is thickened as a correlate of the Wickham stripes. The molecular pathogenesis, still partially hypothetical, assumes trigger factors leading to the presentation of intrinsic or foreign antigens. The triggered inflammation becomes independent in the sense of a classical cell-mediated autoimmune disease. Other autoimmune diseases are often associated with LP. Classical anti-inflammatory-immunosuppressive therapeutic concepts dominate with systemic retinoids ranking first in the highest evidence class for cutaneous LP with limitations in treatment of both mucosal and adnexal LP. More recently, interesting and new complementary phototherapeutics have been identified.
Keywords: Autoimmune diseases; Inflammation; Papules; Pruritus; Retinoids.