Lichen planus complicated with thymoma: Report of three Japanese cases and review of the published work.

Thymoma is recognized to be complicated with autoimmune diseases, such as myasthenia gravis, pemphigus vulgaris and bullous pemphigoid. Abnormal regulation of autoreactive lymphocytes may be involved in the pathogenesis of the autoimmune diseases. The association of thymoma and lichen planus (LP) is relatively rare. Among 50 patients with LP, we identified three patients with LP accompanied by thymoma (6%; 3/50) in our department from 2004 to 2014. This is the first report identifying the frequency of thymoma accompanied by LP among patients with LP. We herein report three cases of LP accompanied by thymoma along with clinical and histological features. In addition, we summarize 29 LP patients accompanied by thymoma previously reported in the English-language published works. Regarding the complications, hypogammaglobulinemia accompanied 58.6% (17/29) of patients diagnosed with Good's syndrome. Alopecia was present in 13.8% (4/29) of patients, and myasthenia gravis was present in 17.2% (5/29) of patients with LP and thymoma. Among the 27 patients with thymectomy, only 25.9% (7/27) experienced the improvement of LP, suggesting that thymectomy may not be effective for the lesions of LP. Treatment-resistant LP was reported in 54.2% (13/24) of patients. In all our cases, oral lesions were intractable to treatment with oral predonisone and topical steroids and/or tacrolimus. It is important for dermatologists to recognize the clinical characteristics of the patients with both LP and thymoma.