Increased incidence of thymoma in Chinese myasthenia gravis: possible relationship with Epstein-Barr virus.

Thymectomy was carried out for treatment of myasthenia gravis in 27 unselected Chinese patients and thymoma was found in 13 of them. This 48% incidence of thymomas is two to three times greater than in Japanese and European patients, respectively. The reason for the higher incidence of thymomas observed in Chinese patients may be related to the presence of the Epstein-Barr virus genome in thymoma. Furthermore, all of the thymomas in our patients were lymphoepithelial and histologically resemble nasopharyngeal carcinoma and undifferentiated carcinoma of the salivary gland. Both these tumours are closely linked to the Epstein-Barr virus and in Hong Kong, nasopharyngeal carcinoma is the third commonest cause of death from malignancy. We recommend early thymectomy for patients with myasthenia gravis particularly in geographical areas where there is a high incidence of nasopharyngeal carcinoma and undifferentiated carcinoma of the salivary gland.