Myasthenia Gravis Classification | Medical Algorithm

The Myasthenia Gravis Foundation of America (MGFA) has developed a clinical classification for patients with myasthenia gravis.

Class	Features
I	any ocular muscle weakness; may have weakness of eye closure; all other muscles are normal
II	mild weakness affecting muscles other than the ocular muscles; may also have ocular muscle weakness of any severity
III	moderate weakness affecting muscles other than the ocular muscles; may also have ocular muscle weakness of any severity
IV	severe weakness affecting muscles other than the ocular muscles; may also have ocular muscle weakness of any severity
V	intubation with or without mechanical ventilation (exception: intubation for routine perioperative management)

Subclass	Features
A	predominantly affects the limb muscles, axial muscles or both; may have lesser involvement of the oropharyngeal or respiratory muscles
B	predominantly affects the oropharyngeal muscles, respiratory muscles or both; may have lesser or equal involvement of the limb or axial muscles

Patient designation = (class designation) + (subclass designation)

Special category: feeding tube = Class IVB

For weakness graded 0 = none, 1 = mild, 2 = moderate, 3 = severe:

Class	Ocular	Limb and/or Axial	Oropharyngeal and/or Respiratory
0	0	0	0
I	1 - 3	0	0
IIA	0 - 3	1	0
IIB	0 - 3	0 - 1	1
IIIA	0 - 3	2	0 - 1
IIIB	0 - 3	0 - 2	2
IVA	0 - 3	3	0 - 2
IVB	0 - 3	0 - 3	3
IVB	NA	NA	feeding tube
V	NA	NA	intubation

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Clinical Classification of Myasthenia Gravis