The cause of oral lichen planus is unknown. However, some 40% of patients with symptomatic lichen planus of the mouth have relevant allergies, diagnosable by patch testing. These are usually to metals (especially gold and mercury) and flavourings such as cinnamon, pep-permint and spearmint. Lichen planus also results from drug reactions, liver disease and bone marrow transplantation.
When a lichen planus-like cutaneous eruption is pre-sent, finding lichen planus in the mouth confirms the diagnosis, and vice versa. In the mouth, typically, there is a lace-like whitening of the buccal mucosae (Fig. 6.4), but sometimes this laciness is not present. Oral lichen planus can also be red, and can ulcerate. A ‘desquamative gingivitis’ may occur, in which the mucosa shears off with friction, such as that from brushing the teeth or eating an apple. Desquamat-ive gingivitis can also result from pemphigus or pemphigoid . Often oral lichen planus is asymptomatic and more of a curiosity than a problem for the patient.
Oral lichen planus can last for yearsaeven for a life-time. Asymptomatic lichen planus does not usually progress to the symptomatic form.
In its classic lace-like state, the appearance of oral lichen planus is diagnostic.
Dysplastic leukoplakias are more likely to be focal, appearing on only a portion of the mucosae, gingivae or lips. They are also more likely to be red and symptomatic, and shown by those who have smoked cigarettes or chewed tobacco. Candidaalbicans infections may occasionally be considered,but their white patches scrape off.
A potassium hydroxide (KOH) examination and a culture will rule out candidasis. Biopsy will determine if a white patch is dysplastic or not. The histology of lichen planus, as seen in the skin, may be less typical in