Real-world outcomes after switching from standard therapy to efgartigimod in five patients with chronic inflammatory demyelinating polyradiculoneuropathy: a case series study in Japan.

Background: Efgartigimod, a neonatal Fc receptor blocker, has received regulatory approval for the treatment of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) in Japan in December 2024. Aims: To investigate the effectiveness and safety of efgartigimod in real-world clinical setting immediately after its approval. Methods: We conducted a prospective, single-center, case series study to evaluate the switch from standard therapy to efgartigimod in five patients with typical or variant CIDP in Japan. Effectiveness was assessed with clinical responses defined by changes in the Inflammatory Rasch-built Overall Disability Scale, Inflammatory Neuropathy Cause and Treatment, Medical Research Council sum scores, and grip strength. The occurrence of adverse events (AEs) was also monitored. Results: Three patients had typical CIDP, one had variant CIDP of the motor type, and one had distal type CIDP. All patients exhibited a clinical response evaluated using at least one effectiveness endpoint after switching to efgartigimod treatment. Especially, the three patients with typical CIDP experienced an significant effectiveness of efgartigimod, even in those with an inadequate response to intravenous or subcutaneous immunoglobulin. Conversely, one patient with distal CIDP did not exhibit a response to efgartigimod treatment. One patient experienced a severe headache after efgartigimod treatment; however, the AE was manageable. Conclusion: Efgartigimod is a useful treatment option for CIDP in real-world clinical practice. However, its effectiveness was different between the patients with typical CIDP and CIDP variant in our study, possibly due to variances in the immune pathophysiology of each disease subtype. Further validation is warranted in our exploratory findings.