Case Report: A Patient with Lambert-Eaton Myasthenic Syndrome Successfully Treated with Efgartigimod.

Background: Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular junction disorder which is frequently associated with tumors. Those patients generate pathogenic antibodies such as voltage-gated calcium channel (VGCC) antibodies. Existing studies have established the efficacy of efgartigimod in MG. This article reports the effect of efgartigimod following its administration to a patient with LEMS. Case Presentation: A 73-year-old male was diagnosed with small cell lung cancer two years ago. Gradually he developed difficulties in speaking, eating, and lifting his head, along with limb weakness. The neuroelectrophysiological examination findings were consistent with LEMS. Laboratory tests detected VGCC antibodies and SOX-1 antibodies in the serum. The patient's symptoms continued to worsen after one week of corticosteroids use. Consequently, efgartigimod at a dose of 10 mg/kg was added once a week. After three weeks of treatment, the patient's clinical manifestations had improved significantly. Laboratory tests revealed a decrease in serum VGCC antibody and IgG levels. Conclusion: This is the first report on the use of efgartigimod in LEMS. The patient demonstrated substantial clinical improvement following treatment. Nevertheless, more clinical studies are required to verify whether efgartigimod offers a novel treatment approach for patients with LEMS.