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

Abstract

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.

Thymoma and solid-organ transplantation

“…Some research favors this hypothesis. It turns out that thymoma has a higher incidence in China where EBV is endemic [5]. This could be related to the increased presence of the Epstein-Barr virus genome in thymoma, as suggested in one study [6].…”

Myasthenia gravis with thymoma is more common in the Maori and Pacific Island populations in New Zealand

“…Further study would be necessary to confirm this hypothesis; however, different associations of HLA and other T‐lymphocyte antigens have been demonstrated between thymomatous and non‐thymatous MG previously 31,32 . A role for EBV infection in the initiation of either specific tumour types or the autoimmune response in the Maori and Pacific Island populations also remains possible 17 . The investigation of thymoma tissue (with or without associated MG) in Maori and Pacific Island people for the presence of the EBV genome may also provide greater insights into the pathogenesis of this disorder.…”

“…Ethnic differences in the presentation of MG with thymoma have not been well described previously. Teoh et al have suggested that there is an increased incidence of thymoma among Hong Kong Chinese patients with MG compared with that described in other populations 17 . They have identified the Epstein–Barr virus (EBV) genome in two thymomas and have postulated an association with the increased rate of EBV‐related nasopharyngeal and salivary gland carcinoma in their population.…”

“…MG with thymoma tends to present at an older age, does not show the female sex preponderance seen in non‐thymomatous MG and carries a poorer prognosis, with more severe myasthenic symptoms, a poorer response to thymectomy and a higher mortality rate than MG without thymoma 5,6,9–16 . A higher than expected occurrence rate of thymoma with MG among the Chinese population in Hong Kong has been reported 17 . It has been our clinical impression in Auckland that thymoma associated with MG may be more common in patients of Polynesian descent than in other races.…”

Uncommon Thoracic Tumors

“…24,25 Defective viral genomes have been isolated in patients with lymphoepithelioma-like thymic carcinoma. There is a reported association between Epstein-Barr virus (EBV) infection and tumors of the thymus.…”