The Classification of Myasthenia Gravis

Researchers and physicians use one of the two following classification systems to help categorize individual cases of Myasthenia Gravis, allowing them better understand if the patient may have a more mild or severe case, symptoms that may be associated alongside of the presentation and what may be prominently effected. This also helps tailor treatments and clinical trials while managing expectations and therapeutic outcomes. 

The four tier classification for Myasthenia Gravis, also known as Ossersman classification:

R = Remission 

I = Ocular only

IIA = Mild generalized 

IIB = Moderate generalized

III = Acute severe

 IV = Chronic severe

Advanced classification (1) is categorized as:

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 

While these two classification systems are the foundational premises for patient assessment academically, they do not allow for the possibility of hybrid or evolving symptom presentations over time and it does not define refractory cases (In medicine, refractory describes a disease or condition which does not respond to attempted forms of treatment), which requires aggressive therapy. Patients may begin in a less severe classification and advance as the disease progresses, while some will present with a more aggressive, sudden predominance earlier on to bulbar or respiratory weakness without showing strong exhibition of more mild manifestations, including ocular. 

Classification is a general guide. Not all patients will present with all symptoms as determined in these classification systems. This does not exclude or invalidate the disease presence.

Reference:

(1) MGFA Medical Advisory Board, 1997