The goal of this clinical trial is to learn if ripertamab works to treat myasthenia gravis. It will also learn about the safety of ripertamab. The main questions it aims to answer are:Will ripertamab improve the symptoms of participants?What medical problems do participants have when using ripertamab?Researchers will compare ripertamab to a placebo (a look-alike substance that contains no drug) to see if ripertamab works to treat chronic inflammatory demyelinating polyneuropathy.Participants will:A single intravenous infusion of ripertamab.Visit the clinic for checkups and tests during W1, W2, W4, W8, W12. Keep a diary of their symptoms and the number of times they undergo rescue therapy.