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Inter-relationship among myasthenia gravis, WHO histology, and Masaoka clinical stage and effect on surgical methods in patients with thymoma: a retrospective cohort study.

Background
The aim of study is to analyze the inter-relationship among WHO histology, myasthenia gravis (MG) and Masaoka stage and to assess the feasibility of thoracoscopic surgery in thymoma patients.


Methods
Data from 142 consecutive thymoma patients from January 2009 to March 2016 were retrospectively reviewed in our institution. Histological classification and clinical staging were assessed by WHO histology criteria and Masaoka stage. We investigated the clinical characteristics, inter-relationship among WHO histology, MG and Masaoka stage, and compared the feasibility and safety of thoracoscopic thymectomy by comparison of open thymectomy.


Results
Among 142 patients, the incidence of MG was 29.6%. Compared with A and AB-type thymomas, a higher prevalence of advance clinical stage was in B1 to C-type thymomas (37/63 vs. 9/43, P<0.001), and there was an increased trend of Masaoka stage from A to C-type thymomas (P<0.001). The incidence of MG was significantly higher in AB, B1 and B2-type thymomas than other type thymomas (23/63 vs. 6/44, P=0.009) and in early Masaoka clinical stage than advanced Masaoka clinical stage (29/80 vs. 12/59, P=0.042). Thoracoscopic surgery could significantly decrease blood loss in patients with (104.06±137.36 vs. 350.91±560.79 mL, P=0.001) or without MG (91.90±77.70 vs. 266.32±292.60 mL, P=0.02), with comparable complications. Additionally, thoracoscopic surgery could achieve an equal effect on the remission of MG with open surgery (7/11 vs. 10/14, P=1.000), and Masaoka stage was significantly associated with the remission of MG after thymectomy.


Conclusions
Our study suggests that WHO histology, MG, and Masaoka stage interrelate with one another, and Masaoka stage is an important prognostic factor in remission of MG after thymectomy in thymoma patients. Thoracoscopic thymectomy could achieve an equal efficacy to open thymectomy and should be recommended as a routine surgery for patients with early Masaoka stage.