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Table 3 Myasthenia gravis foundation of America (MGFA) Clinical Classification. The sclae divides MG into 5 classes and several subclasses to identify subgroups of patients with MG who share distinct clinical features or severity of disease that may indicate different prognoses or responses to therapy, (https://myasthenia.org/What-is-MG)

From: Myasthenia gravis exacerbation after melatonin administration: case series from a tertiary referral centre

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.
A. IIa. Predominantly affecting limb, axial muscles, or both. May also have lesser involvement of oropharyngeal muscles.
B. 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.
A. IIIa. Predominantly affecting limb, axial muscles, or both. May also have lesser involvement of oropharyngeal muscles.
B. 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.
A. IVa. Predominantly affecting limb, axial muscles, or both. May also have lesser involvement of oropharyngeal muscles.
B. 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.