Intravenous immunoglobulin maintenance treatment in myasthenia gravis: A randomized, controlled trial sample size simulation

Abstract

In cases of exacerbation or crisis, myasthenia gravis (MG) patients can be treated with intravenous immunoglobulin (IVIg), plasmapheresis, or immunoadsorption. However, IVIg efficacy data in maintenance treatment are sparse. We prospectively observed 16 index patients with chronic and insufficiently controlled MG under standard immunosuppressant therapy and symptomatic treatment. The IVIg treatment response was measured using changes in quantitative myasthenia gravis (QMG) score and surrogates. Based on these results, a sample size calculation for a future randomized, controlled trial (RCT) was simulated. There was an enduring decline in QMG score and other parameters of about 50% under IVIg maintenance treatment. RCT sample size calculation results in 73 or 33 patients per arm to detect at least a 20% vs. 30% clinical difference in QMG score. We recommend using the QMG score as a primary endpoint for an RCT of IVIg maintenance for chronic MG.