Table 1. MGFA clinical classification.

Classification	Definition
Class I	Any ocular muscle weakness; may have weakness of eye closure. All other muscle strength is normal
Class II	Mild weakness affecting muscles other than ocular muscles; may also have ocular muscle weakness of any severity: IIa—predominantly affecting limb, axial muscles, or both. May also have lesser involvement of oropharyngeal muscles; IIb—predominantly affecting oropharyngeal, respiratory muscles, or both. May also have lesser or equal involvement of limb, axial muscles, or both
Class III	Moderate weakness affecting muscles other than ocular muscles; may also have ocular muscle weakness of any severity: IIIa—predominantly affecting limb, axial muscles, or both. May also have lesser involvement of oropharyngeal muscles; IIIb—predominantly affecting oropharyngeal, respiratory muscles, or both. May also have lesser or equal involvement of limb, axial muscles, or both
Class IV	Severe weakness affecting muscles other than ocular muscles; may also have ocular muscle weakness of any severity: IVa—predominantly affecting limb, axial muscles, or both. May also have lesser involvement of oropharyngeal muscles; IVb—predominantly affecting oropharyngeal, respiratory muscles, or both. May also have lesser or equal involvement of limb, axial muscles, or both
Class V	Defined as intubation, with or without mechanical ventilation, except when employed during routine postoperative management. The use of a feeding tube without intubation places the patient in class IVb

MGFA, Myasthenia Gravis Foundation of America.