Oral lichen planus is an inflammatory disease that occurs inside the mouth. The condition affects the mucous membrane, and results in swollen tissues, sores and patches in the mouth, which can be quite painful and uncomfortable. The sores can appear in the inside of the cheeks, as well as on the gums, palate, tongue and inner areas of the lips. To diagnose the condition, Dr Patterson may conduct some lab tests, such as a biopsy and blood tests. If the condition is severe, treatment options may include topical medicines such as a mouthwash or ointment; or an oral or injected corticosteroid.