The causes of myasthenia gravis are divided into two major categories: 1. congenital genetic factors: very rare, not related to autoimmunity; 2. autoimmune diseases: more common, the cause is unclear, but generally believed to be related to infection, drugs, environmental factors, mainly autoimmune diseases caused by nerve-muscle junction transmission dysfunction. The main clinical manifestations are partial or generalized skeletal muscle weakness and easy fatigue, and the typical symptoms are light in the morning and heavy at night. Myasthenia gravis is associated with thymic hyperplasia in 65%-80% of patients and thymoma in 10%-20%. Therefore, when a patient suspects myasthenia gravis, it is necessary to have a chest CT to check for thymic changes.