Belimumab Nonsuperior to Placebo for Reducing Symptoms of Myasthenia Gravis

As assessed by changes in the Quantitative Myasthenia Gravis (QMG) scale, belimumab does not significantly reduce signs of generalized myasthenia gravis compared with placebo, according to a phase 3, randomized study published in Neurology.

Investigators randomly assigned 40 patients with MG to either 10 mg/kg intravenous belimumab (n=18) or placebo (n=22). During the 24-week treatment and the 12-week follow-up periods, patients received standard of care therapy in addition to either belimumab or placebo. The average change from baseline in the QMG scale at the end of the treatment phase comprised the primary outcome. Additionally, the investigators assessed changes in MG Composite Score (MGC) and MG Activities of Daily Living (MG-ADL) scores during follow-up. The frequency and severity of adverse events were also assessed.

At baseline, MG severities were similar between the belimumab and placebo arms as measured by median QMG scores (12.00 [range 8.0, 19.5] and 12.50 [6.50, 23.0], respectively). By week 24, the mean change (standard error) in the QMG scale score was greater in the belimumab vs placebo group (-4.21 ([standard error, 1.14] vs -2.37 [1.10], respectively), yet there was no statistically significant treatment difference (1.84 points) between the 2 arms (P =.256).

A greater proportion of patients receiving belimumab experienced a nonsignificant change of ≥3 points in QMG score compared with those receiving placebo (61% vs 29%, respectively; P =.082), yet fewer patients sustained this change (44% vs 24%, respectively; P =.184). Similar changes in MG-ADL (-2.32 [0.60] vs -2.01 [0.59]) and MGC (-3.81 [1.06] vs -3.86 [1.04]) scores were observed between the treatment and placebo groups at 24 weeks. There were no significant differences between those receiving belimumab or placebo in terms of adverse events (78% vs 91%, respectively). 

The investigators hypothesized that the recruited participants may have reached a plateau in symptoms, which may have decreased the chances of additional improvement with belimumab treatment. In addition, the small sample size and the potential for significant variability among patients may limit the findings.

Because the QMG scale “is entirely physician-assessed and scores all symptoms on the same scale,” compared with the MGC and MG-ADL scales, the investigators suggested that differences in scales “may explain the slight improvement observed in the QMG score compared with either MGC or MG-ADL.”

Reference

Hewett K, Sanders DB, Grove RA, et al. Randomized study of adjunctive belimumab in participants with generalized myasthenia gravis [published online March 21, 2018]. Neurology. doi: 10.1212/WNL.0000000000005323