Abstract: Objective To explore the clinical characteristics and outcome in myathenia gravisac companied with thymoma or thymic hyperplasia. Methods From January, 2007 to December, 2016, 118 myathenia gravis patients with thymoma, and 42 myathenia gravis patients with thymic hyperplasia were enrolled. Their age of onset, gender, initial symptom, osserman classification, muscles involved, myasthenia crisis, low-frequency repetitive nerve stimulation and complete stable remission rate data were retrospectively analyzed. Results Compared with myathenia gravis patients with thymic hyperplasia, myathenia gravis patients with thymoma showed older age in onset, higher proportion in type III and lower rate in complete stable remission rate (P<0.05), and more respiratory muscle involved (χ²=6.364, P=0.011) and myasthenia crisis (χ²=5.455, P=0.022). There were significant differences in respiratory muscle involved (χ²=8.532, P=0.036) and the incidence rate of myasthenia crisis (χ²=8.956, P=0.030) among thymoma with different pathological types, in which type B3 was the highest, and type A+AB was the lowest. The low-frequency repetitive nerve stimulation positive rate was higher in myathenia gravis patients with thymoma than with thymic hyperplasia, however, there was no significant difference (χ²<1.357, P>0.05). There was a rising trend with pathological classification altered in the low-frequency repetitive nerve stimulation positive rate with no significant difference (χ²<6.623, P>0.05). Conclusion Myathenia gravis patients with thymoma were common in middle-aged to old people, who were serious in clinical symptom, particularly respiratory muscle involved and myasthenia crisis. Myathenia gravis patients with thymic hyperplasia were more benefit from thymectomy. The low-frequency repetitive nerve stimulation positive rate of myathenia gravis patients does not correlate with thymic lesion type. Respiratory muscle involved and myasthenia crisis are relevant with pathological types of thymoma.

Key words: thymoma, thymic hyperplasia, myathenia gravis, respiratory involved, myasthenia crisis