Lichen planus and lichenoid reactions as a systemic disease.

Lichen planus (LP) is a chronic disease that involves the skin, scalp, mucous membranes, and nails. The etiology of LP is still unknown; however, some external and internal factors (eg. drugs, stress, hepatitis C virus) have been suggested to trigger the disease. Many studies have investigated an immunologic pathogenesis that is probably related to T-cell autoimmunity with the keratinocyte as the target cell. Altered self-antigens on the surface of basal keratinocytes modified by viruses or by drugs are believed to be the targets of the T-cell response. Various drugs and contact allergens like amalgam may cause lichenoid reactions, which are the main differential diagnoses of LP. Clinically and histologically, LP and lichenoid reactions cannot be distinguished with certainty in many cases. Treatment is mainly symptomatic and can be difficult. The first-line therapies for LP are topical or systemic corticosteroids; however, some studies have mentioned acitretin leading to similar improvement. Medical treatment, together with patient education and psychosocial support, can significantly benefit patients' quality of life.