MINIMAL CLINICALLY IMPORTANT DIFFERENCE IN MYASTHENIA GRAVIS: OUTCOMES FROM A RANDOMIZED TRIAL

Introduction: The minimal clinically important difference (MCID) is the smallest outcome change that has clinical significance. Its use has not been established in the study of myasthenia gravis (MG). Methods: Patients from a published intravenous immunoglobulin (IVIg) vs. placebo study were studied. One anchor-based and 3 distribution-based techniques were used to identify quantitative myasthenia gravis score (QMGS), repetitive nerve stimulation (RNS), and single-fiber electromyography (SFEMG) MCID cut-offs. Patients with a change-score exceeding MCID cut-offs were compared. Results: MCID cut-offs were below a QMGS change of 3.0. Anchor-based and 1 x SEM cut-offs showed 58.3% vs. 30.7% responders (P=0.017), 1/2 SD 54.2% vs. 19.2% responders (P=0.018), and effect size 0.519 vs. 0.164 (P=0.011) in IVIg vs. placebo. Anchor-based (P=0.73) and effect-size (P=0.41) MCID cut-offs did not show a difference between IVIg and placebo. MCID methods did not produce meaningful RNS cut-offs. Conclusions: QMGS MCID values provide clinically relevant information and are recommended in MG trials. MCID analysis shows that improvement in MG patients treated with IVIg reflects clinically meaningful changes. Muscle Nerve49: 661-665, 2014