A Study to Assess the Efficacy and Safety of Empasiprubart Versus IVIg in Adults With Multifocal Motor Neuropathy

The main purpose of this study is to compare empasiprubart and IVIg in adult patients with MMN. The study consists of a double-blinded part A (empasiprubart, IVIg) and an open-label part B (empasiprubart). The maximum study duration for participants is up to 49 months. More information can be found here: https://clinicaltrials.argenx.com/empassion

Inclusion Criteria: * Is at least 18 years of age and the local legal age of consent for clinical studies * Has a confirmed diagnosis of definite or probable MMN at screening according to the EFNS/PNS 2010 guidelines * Has responded to IVIg in the past 5 years. * Is receiving IVIg at a treatment interval of once every 2, 3, 4, or 5 weeks, and a dose of 0.4 to 2.0 g/kg body weight per cycle * Is receiving a maintenance regimen (no change in frequency, and no change in dose \>10%) of IVIg for at least 8 weeks before screening (or at least 10 weeks for participants receiving IVIg once every 5 weeks) * Minimum converted weekly IVIg dose of ≥0.125 g/kg * Has documented immunization against encapsulated bacterial pathogens (N meningitidis and S pneumoniae) within 5 years of screening or is willing to receive immunization at least 14 days before first study drug administration Exclusion Criteria: * Besides the indication under study, known autoimmune disease (eg, SLE) or any other medical condition that would confound the study results or put the participant at undue risk * Clinical signs or symptoms suggestive of neuropathies other than MMN, such as motor neuron disease (eg, bulbar signs, brisk reflexes) or other inflammatory neuropathies (eg, sensory neuropathy)