Predictors of response to immunomodulation in patients with myasthenia gravis.

INTRODUCTION

Factors determining response to intravenous immunoglobulin (IVIg) and plasmapheresis in myasthenia gravis (MG) have not been evaluated systematically.

METHODS

This study included patients treated with IVIg (n = 63) or plasmapheresis (n = 42) from two trials evaluating IVIg vs. placebo or plasmapheresis in MG. Response was defined as improvement in the quantitative myasthenia gravis score (QMGS) of ≥3.5 points at day 14. Baseline clinical, electrophysiological, and immunological factors were analyzed as predictors.

RESULTS

Baseline QMGS, acetylcholine receptor antibody (AChRAb) positivity, single-fiber electromyography (SFEMG) jitter, and percent abnormal pairs and percent blocking pairs were higher in responders than in non-responders. Using multivariate logistic regression, the odds ratio for response was 13.0 (1.01-381.5) in QMGS 11-17 and 15.3 (1.34-414.3) in QMGS >17 compared with QMGS <11.

CONCLUSIONS

Baseline QMGS, AChRAb positivity, and SFEMG parameters were more abnormal in patients who responded to treatment. Using multivariate regression, baseline QMGS remained as the only significant independent predictor of response.