What are the main classes of myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas Jowkar, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

The Myasthenia Gravis Foundation of America Clinical Classification divides MG into 5 main classes and several subclasses [3] :

  • Class I: Any ocular muscle weakness; may have weakness of eye closure; all other muscle strength is normal

  • Class II: Mild weakness affecting other than ocular muscles; may also have ocular muscle weakness of any severity

    • Class IIa: Predominantly affecting limb, axial muscles, or both; may also have lesser involvement of oropharyngeal muscles

    • Class 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 other than ocular muscles; may also have ocular muscle weakness of any severity

    • Class IIIa: Predominantly affecting limb, axial muscles, or both; may also have lesser involvement of oropharyngeal muscles

    • Class 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 other than ocular muscles; may also have ocular muscle weakness of any severity

    • Class IVa: Predominantly affecting limb, axial muscles, or both; may also have lesser involvement of oropharyngeal muscles

    • Class IVb: Predominantly affecting oropharyngeal, respiratory muscles, or both; may also have lesser or equal involvement of limb, axial muscles, or both

  • Class V: Defined by the need for intubation, with or without mechanical ventilation, except when used during routine postoperative management. The use of a feeding tube without intubation places the patient in class IVb.

See Clinical Presentation for more detail.


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