Diagnosing gMG
Mike, a patient living with gMG. Mike has received compensation from Alexion Pharmaceuticals, Inc. and has a relative who works for Alexion.
About generalized myasthenia gravis (gMG)
Diagnosing gMG1-3
gMG diagnosis begins with a review of the patient’s medical history and physical examination, but clinicians must be careful as signs and symptoms of gMG can look similar to other conditions. Once gMG is suspected, several tests are used to confirm the diagnosis.
If gMG is suspected, testing for anti-acetylcholine receptor (AChR) antibodies is a key step toward confirming diagnosis
- Blood tests are used to detect the presence of anti-AChR and other antibodies. However, the absence of anti-AChR does not exclude gMG
- Additional tests can include ice pack tests, especially if ptosis is a key symptom (ice packs are placed over the eye for 2 to 5 minutes to assess ptosis improvement). There may be benefit in testing the recovery of muscle strength after rest and the ability to look upward for a sustained period
- Diagnostic testing is preferred to help confirm diagnosis, as unofficial measures/additional testing options may not yield the most accurate results
All patients with confirmed gMG should undergo diagnostic imaging to exclude the presence of a thymoma, as thymomas have been reported in up to 30% of patients with MG.
gMG symptoms in patients are commonly measured by the MG-ADL and QMG scales
The Myasthenia Gravis Activities of Daily Living scale (MG-ADL scale) is a categorical scale that assesses the impact on daily function of 8 signs or symptoms that are typically affected in gMG. Each item is assessed on a 4-point scale where a score of 0 represents normal function and a score of 3 represents loss of ability to perform that function. The total score ranges from 0 to 24, with the higher scores indicating more impairment.4
The Quantitative Myasthenia Gravis scale (QMG scale) is a 13-item categorical scale assessing muscle weakness. Each item is assessed on a 4-point scale where a score of 0 represents no weakness and a score of 3 represents severe weakness. The total score ranges from 0 to 39, where higher scores indicate more severe impairment.5
Alexion has compiled a variety of assessment tools that are available for download below.
Download the Assessment Tool BookletReview a common classification method utilized to group MG patients based on symptom severity6
Per the MGFA Clinical Classification, symptoms are divided into different classes based on severity:
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. Prominently affecting limb, axial muscles, or both. May also have lesser involvement of oropharyngeal muscles.
IIb. Primarily affecting oropharyngeal, respiratory muscles, or both; and potentially 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. Mainly affecting limb, axial muscles, or both; with potentially less impact of oropharyngeal muscles.
IIIb. Mainly affecting oropharyngeal, respiratory muscles, or both; with 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. Primarily affecting limb, axial muscles, or both; with lesser impact of oropharyngeal muscles.
IVb. Predominantly affecting oropharyngeal, respiratory muscles, or both; with potentially lesser or equal impact of limb, axial muscles, or both.
Class V: Defined as intubation, with or without mechanical ventilation, except when employed during routine postoperative management. Using a feeding tube without intubation classifies a patient as IVb.
MG, myasthenia gravis; MGFA, Myasthenia Gravis Foundation of America.
