To determine whether the quantitative myasthenia gravis score (QMGS) accurately represents disease severity in patients with myasthenia gravis (MG).
One hundred thirty-five patients with MG from 2 previous randomized studies were included. QMGS correlation with the Myasthenia Gravis Foundation of America (MGFA) score, quality of life scale, acetylcholine receptor antibodies (AChRAbs), and electrophysiological parameters was studied.
The QMGS showed a good correlation with the MGFA scale (r2 = 0.54, P < 0.0001), jitter (rs = 0.40, P < 0.0001), and 15-item quality of life scale (rs = 0.41, P = 0.007) and was less well correlated with the 60-item myasthenia gravis–specific quality of life survey and other electrophysiological markers. No correlation was demonstrated with AchRAb titers, but AchRAb-positive patients had higher QMGS (14.2 ± 4.5) than AchRAb-negative patients (12.0 ± 3.7, P = 0.008).
These results demonstrate that the QMGS is a valid marker for disease severity as shown by the MGFA scale, quality of life scale, and jitter, supporting the use of the QMGS as a primary outcome measure in clinical trials of MG.