Promising Results for Efgartigimod in Myasthenic Crisis

A new study, published in Case Reports in Neurological Medicine, highlights the case of a 57-year-old male patient with a first episode of generalized myasthenia gravis (MG) positive for acetylcholine-receptor antibodies (AchR+).¹ Myasthenic crises, characterized by profound muscle weakness, bulbar symptoms, and potential respiratory failure, pose significant treatment challenges. They are a rare but life-threatening complication of MG.²

Conventional therapies such as intravenous immunoglobulins (IVIG) and plasma exchange (PLEX) are typically employed to lower antibody levels and modulate immune responses in myasthenic crises, but they may not always suffice, especially in refractory cases. Recently, new therapeutic options, including efgartigimod (Vyvgart; Argenx), a neonatal Fc receptor (FcRn) antagonist, were approved for generalized AchR+ MG. Efgartigimod reduces the levels of pathogenic IgG antibodies, thereby mitigating the immune attack on acetylcholine receptors.³ Although the data show a quick and reliable treatment response, efgartigimod has not been studied as therapy for myasthenic crisis.

The patient in this case presented with worsening generalized weakness, dysphagia, and respiratory distress over the past 3 days, triggered by pneumonia due to dysphagia. Based on clinical presentation and serological markers, the patient was diagnosed with myasthenic crisis. His daily treatment regimen, when admitted, included oral pyridostigmine (600 mg/d) and prednisone (20 mg/d). Despite an initial improvement after treatment with IV pyridostigmine, 7 sessions of plasmapheresis, prednisone, and azathioprine, his condition deteriorated 2 weeks later, necessitating readmission and an additional 7 sessions of plasmapheresis.

Efgartigimod has been shown to reduce levels of pathogenic Immunoglobulin G antibodies, and it is approved to treat generalized AchR+ MG; however, it has not been studied as therapy for myasthenic crisis | Image Credit: mdaros-stock.adobe.com

The worsening of his symptoms led to the consideration of efgartigimod as an alternative treatment. He was administered efgartigimod at a dose of 10 mg/kg alongside IV pyridostigmine, oral prednisolone, and azathioprine. The patient completed 4 efgartigimod infusions. Remarkable clinical improvement was observed within 48 hours of the first efgartigimod infusion, with a significant reduction in Myasthenia Gravis Activities of Daily Living (MG-ADL) score from 20/24 to 5/24 and the Quantitative Myasthenia Gravis (QMG) score from 26/39 to 15/39.

Further improvements were noted after subsequent infusions, with the MG-ADL score reducing to 3/24 and the QMG score to 11/39 within 48 hours of the second efgartigimod infusion. The patient was eventually stable enough to be transferred to a rehabilitation facility.

"The patient's response to efgartigimod underscores its potential as a novel therapeutic option in the management of myasthenic crises, particularly in cases of refractory to conventional treatments," the authors state.

The report also discusses the general challenges in treating myasthenic crises and the need for continued exploration of new therapeutic avenues for managing myasthenic crises, particularly in refractory cases. Although IVIG and PLEX are common treatments, their limitations include delayed onset of action, high costs, and limited availability due to the need for volunteer blood donors. Efgartigimod, by targeting FcRns, presents a promising alternative by reducing the recycling of pathogenic autoantibodies.

This patient's rapid and significant improvement suggests that efgartigimod may offer a valuable therapeutic option for similar cases.

“This case report suggests that anti-FcRn monoclonal antibodies may offer a promising therapeutic option not only for the escalation treatment of generalized AchR+MG with high disease activity but also for severe, refractory cases of myasthenic crisis,” the authors note. However, the authors call for further studies and clinical trials to assess the long-term benefits and safety of this treatment.

References

1. Omar OA, Diel NJ, Gerner ST, Mück A, Huttner HB, Krämer-Best HH. Efgartigimod as rescue medication in a patient with therapy-refractory myasthenic crisis. Case Rep Neurol Med. 2024;2024:9455237. doi:10.1155/2024/9455237

2. Claytor B, Cho SM, Li Y. Myasthenic crisis. Muscle & Nerve. 2023;68(1):8-19. doi:10.1002/mus.27832

3. FDA approves new treatment for myasthenia gravis. News release. FDA. December 17, 2021. Accessed July 10, 2024. https://www.fda.gov/news-events/press-announcements/fda-approves-new-treatment-myasthenia-gravis