# Open-label study of efgartigimod in seronegative myasthenia gravis

## TL;DR

Efgartigimod, a new treatment, significantly reduced symptoms in patients with myasthenia gravis who lack specific antibodies, though most side effects were mild.

## Contribution

First study to show efgartigimod's efficacy in seronegative myasthenia gravis patients.

## Key findings

- MG impairment index decreased by 11.92 points after 6 months of treatment.
- 72% of patients were responders, with 31% showing early improvement.
- Most adverse events were mild, with headache being the most common.

## Abstract

The ADAPT trial demonstrated the benefit of efgartigimod, a neonatal Fc receptor (FcRn) inhibitor, in acetylcholine receptor antibody (AChRAb) positive patients with generalized myasthenia gravis (MG). Information regarding the benefits in those lacking pathogenic antibodies is sparse.

We aimed to investigate the safety and efficacy of efgartigimod in patients with double-seronegative (SN) generalized MG.

An open-label 6-month prospective study, conducted at our center.

Patients aged at least 18 years with clinical and electrodiagnostic features of MG and negative results for AChRAb and muscle-specific tyrosine kinase antibodies were included. Efgartigimod was administered weekly for 4 weeks and then biweekly for 5 months followed by an observation period. The primary endpoint was the change in MG impairment index (MGII) at 6 months compared to baseline. Secondary endpoints include the change in MG activities of daily living (MG-ADL), other MG scores, overall responders, and early responders. The safety analysis included all patients who received at least one dose of efgartigimod.

We enrolled 30 patients with SN MG who were resistant to other treatments and had unacceptable MGII scores. The MGII decreased by 11.92 points (p < 0.01) with efgartigimod treatment. The MG-ADL also improved. Seventy-two percent of patients were responders with 31% being early responders. Adverse events were reported in 83.3% of patients, and in 90.6%, they were mild. Headache was the most common, reported in 26.7%, followed by flu/common cold in 20%, and urinary tract infection in 13.3%.

Efgartigimod was well tolerated and efficacious in patients with SN MG. Future randomized, placebo-controlled studies are needed.

This trial is registered at ClinicalTrials.gov (NCT 06587867), accessed via https://clinicaltrials.gov/study/NCT06587867?locStr=Toronto,%20ON,%20Canada&country=Canada&state=Ontario&city=Toronto&cond=Myasthenia%20Gravis&intr=efgartigimod&rank=1

The safety and efficacy of the novel treatment efgartigimod in myasthenia gravis with negative antibodies

We enrolled 30 patients with myasthenia gravis with negative antibodies. All patients received the new treatment Efgartigimod and we compared the severity of their myasthenia symptoms with the treatment, compared to the baseline (before giving it). The severity of the myasthenia was significantly reduced (observed in multiple clinical scores for myasthenia gravis). Adverse events were reported in 83.3% of patients, and in 90.6% they were mild. Headache was the most common, reported in 26.7%, followed by flu/common cold in 20%, and urinary symptoms in 13.3%. To conclude, in this study, we showed, for the first time that the novel treatment of Efgartigimod is well tolerated and efficacious in patients with Myasthenia gravis with no antibodies. Future prospective and placebo-controlled studies are needed.