MG Composite Scale Interpretation
The MG Composite is a 10-item weighted scale (0-50 points) designed to assess myasthenia gravis disease severity, where lower scores indicate better disease control and higher scores reflect more severe impairment. 1
Scale Structure and Administration
The MG Composite was constructed by selecting 10 items from existing MG assessment tools (QMG, MMT, and MG-ADL scales) that are:
- Relevant to MG manifestations 1
- Meaningful to both physicians and patients 1
- Responsive to clinical change 1
Key practical features:
- Takes less than 5 minutes to complete 1
- Requires no equipment 1
- Items are weighted based on expert consensus considering quality of life, disease severity, risk, prognosis, validity, and reliability 1
Score Interpretation Framework
Understanding the Numerical Range
The scale produces ordinal scores from 0-50 that represent MG status, with weighting designed to better capture meaningful clinical change 1. However, like all composite measures, the MG Composite score should never be interpreted in isolation—individual component performance must also be examined 2.
Clinical Context Considerations
A provider with an intermediate MG Composite score could represent either:
- Intermediate performance across all domains, OR
- Excellent control in some areas with poor control in others 2
This distinction is critical because aggregate scores may obscure specific areas requiring targeted intervention 2.
Relationship to Other MG Measures
The MG Composite correlates with other validated MG outcomes:
- Shows associations with MG-ADL scores 3
- Correlates with QMG scores 3
- Relates to MGFA classification 3
- Demonstrates concurrent validity with disease severity measures 4
Important caveat: The MG Composite is considered a more objective measure of disease severity, while patient-reported outcomes like the MG-QOL15 capture the patient's perception and tolerance of dysfunction 5. Both types of measures should be used together in clinical practice 5.
Detecting Meaningful Change
Individual Patient Level
When following individual patients, interpretation requires caution because not all components necessarily trend in the same direction with treatment or disease progression 2. A change in composite score driven predominantly by only one component may have limited clinical validity 2.
Reliability Considerations
The scale demonstrates good measurement properties including:
- Good to excellent test-retest reliability 3
- Internal consistency reliability 3
- Responsiveness to clinical change 1
Common Pitfalls in Interpretation
Critical warnings:
The "black box" problem: Composite measures can obscure which specific aspects of disease are improving or worsening 2. Always review individual item scores alongside the total 2.
Weighting assumptions: The weighting of items reflects expert consensus but has not been extensively tested across all treatment contexts 2. Different clinical scenarios may warrant different emphasis on specific components 2.
Missing data impact: If individual items are missing, the composite score's validity may be compromised 2. Document which components were assessed 2.
Group vs. individual interpretation: Group mean changes may not reflect individual patient experiences 2. A population showing improvement on average may still contain individuals who are deteriorating 2.
Clinical Application Algorithm
When interpreting an MG Composite score:
Record the total score (0-50 range) 1
Examine each of the 10 individual components to identify specific areas of weakness or strength 2
Compare to previous scores if available, noting which components changed 2
Consider clinical context:
Integrate with other measures:
Document which components drive any observed change in the total score 2
The MG Composite provides valuable objective data about disease severity, but clinical decisions should incorporate both the composite score and its individual components, alongside patient-reported outcomes and clinical judgment 2, 5.