Inclusion Criteria:  (1)clinical history and signs of fluctuating weakness and fatigability; (2)seropositivityforAChR/MuSKantibodies; (3)If negative or the tested antibodies, positive repetitive nerve stimulation(RNS) at low frequency(2-5Hz) is required; (4)A serious, life-threatening, rapid worsening of MG and potential airway compromise from ventilatory or bulbar dysfunction.  Exclusion Criteria:  the RNS had over 100% increase after high frequency stimulation or R2 repeats,to differentiate from lambert-Eaton syndrome and congenital MG.