This study is a multicenter, prospective, observational research. It will register the basic demographic information, medical history characteristics, clinical features, auxiliary examinations, treatment, outcomes of tracheal intubation/ventilator related events, and clinical outcomes of Myasthenic Crisis patients. The objectives including:

1. Obtain epidemiological data of MC in China;
2. Establish a standardized registration system for MC patients in China;
3. Explore the epidemiology, clinical characteristics, serological characteristics, clinical characteristics of MC, predisposing and predictive factors, extubation process/time, weaning/extubation outcome and predictors of clinical outcome in Chinese MC patients.

Inclusion Criteria:

• clinical history and signs of fluctuating weakness and fatigability;
• seropositivity forAChR/MuSKantibodies;
• If negative or the tested antibodies, positive repetitive nerve stimulation(RNS) at low frequency(2-5Hz) is required;
• Crisis: a serious, life-threatening, rapid worsening of MG requiring intubation or noninvasive ventilation to avoid intubation.
• Impending crisis: rapid clinical worsening of MG that, in the opinion of the treating physician, could lead to crisis in the short term (days to weeks) with blood gases suggest hypoxia (oxygen saturation <95%) or elevated carbon dioxide (paco2>50mmHg).

Exclusion Criteria:

• the RNS had over 100% increase after high frequency stimulation or R2 repeats,to differentiate from lambert-Eaton syndrome and congenital MG.
• except when intubation or noninvasive ventilation are employed during routine postoperative management.

The study population will be recruited from multiple centers across China.