This clinical trial is focused on studying the long-term effects of a treatment called ARGX-117 in adults with a condition known as Multifocal Motor Neuropathy (MMN). MMN is a rare disorder that affects the nerves, leading to muscle weakness, primarily in the arms and hands. The treatment being tested, ARGX-117, is a type of medication known as a monoclonal antibody, which is a protein designed to target specific parts of the immune system. In this study, ARGX-117 is given as an infusion, which means it is administered directly into the bloodstream through a vein.

The purpose of this study is to evaluate the long-term safety and tolerability of ARGX-117 in people with MMN. Participants in the study will receive either the ARGX-117 treatment or a placebo. The study will monitor various aspects of health, including any side effects, changes in muscle strength, and overall well-being over time. Participants will have regular visits to assess their condition and the effects of the treatment.

This study is an extension of a previous trial, meaning it continues to follow participants who have already been involved in earlier research with ARGX-117. The trial aims to gather more information on how the treatment works over a longer period and to ensure it is safe for continued use. The study will help researchers understand the potential benefits and risks of using ARGX-117 for treating MMN, contributing to the development of effective therapies for this condition.