Open-label study of efgartigimod in seronegative myasthenia gravis

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