[Thymoma Showing Elevating Anti-acetylcholine Receptor Antibody without Clinical Symptoms of Myasthenia Gravis;Report of a Case].

: A 46-year-old man was referred to our hospital with a suspicion of pericardial cyst. Chest computed tomography (CT) revealed an anterior mediastinal tumor. He had no symptoms, but laboratory data showed positive titer to acetylcholine receptor antibody (Anti-AchR Ab). Under a clinical diagnosis of thymoma, extended thymectomy was performed. This case may represent subclinical myasthenia gravis, so we suggest extended thymectomy is crucial for thymoma with elevated level of Anti-AchR Ab without any symptoms.