Myasthenia Gravis

1. Neuromuscular Junction Dysfunction

•autoimmune MG example of a Type II hypersensitivity rxn

•immunoglobulin (Ig) G class autoantibodies target self-antigen expressed at the cell surface or in the extracelluar matrix and cause organ-specific damage

2. Subtypes of MG are broadly classified as follows [17]:

•early-onset MG: age at onset <50 years. Thymic hyperplasia, usually females,

• late-onset MG: age at onset >50 years. Thymic atrophy, mainly males,

•thymoma-associated MG (10%–15%)

•MG with anti-MUSK antibodies,

•ocular MG (oMG): symptoms only affecting extraocular muscles,

•MG with no detectable AChR and muscle-specific tyrosine kinase (MuSK) antibodies.

3. Myasthenia Gravis Foundation of America (MGFA) clinical classification:

Class I MG is characterized by the following:

any ocular muscle weakness.

may have weakness of eye closure.

all other muscle strengths are normal.

Class II MG is characterized by the following:

mild weakness affecting muscles other than ocular muscles,

may also have ocular muscle weakness of any severity.

Class IIa MG is characterized by the following:

predominantly affecting limb, axial muscles, or both

may also have lesser involvement of oropharyngeal muscles.

Class IIb MG is characterized by the following:

predominantly affecting oropharyngeal, respiratory muscles, or both,

may also have lesser or equal involvement of limb, axial muscles, or both.

Class III MG is characterized by the following:

moderate weakness affecting muscles other than ocular muscles,

may also have ocular muscle weakness of any severity.

Class IIIa MG is characterized by the following:

predominantly affecting limb, axial muscles, or both,

may also have lesser involvement of oropharyngeal muscles.

Class IIIb MG is characterized by the following:

predominantly affecting oropharyngeal, respiratory muscles, or both,

may also have lesser or equal involvement of limb, axial muscles, or both.

Class IV MG is characterized by the following:

severe weakness affecting muscles other than ocular muscles,

may also have ocular muscle weakness of any severity.

Class IVa MG is characterized by the following:

predominantly affecting limb, axial muscles, or both,

may also have lesser involvement of oropharyngeal muscles.

Class IVb MG is characterized by the following:

predominantly affecting oropharyngeal, respiratory muscles or both,

may also have lesser or equal involvement of limb, axial muscles, or both.

Class V MG is characterized by the following:

intubation with or without mechanical ventilation, except when employed during routine postoperative management,

the use of feeding tube without intubation places the patient in class IVb.