Oral erosive lichen planus associated with thymoma treated with etretinate

A 68-year-old Japanese woman was referred to our hospital with a 1-year history of multiple erosions on the oral mucosa and a few pruritic, bean-sized, reddish-blue plaques on the body. Based on physical examination, pathological findings, and immunofluorescence findings, a diagnosis of lichen planus (LP) was made. Computed tomography scan revealed a thymoma. After thymectomy, cutaneous LP lesions subsided spontaneously. Oral lesions responded well to oral etretinate therapy. We speculate that direct tissue injury by CD8+ T cells, activated by abnormal regulation of lymphocytes within the thymus, may cause LP.