thymectomy and myasthenia gravisnon thymomatous myasthenia gravissurgery for myasthenia gravisthymus surgery myasthenia gravisthymus operation myasthenia gravismyasthenia gravis thymus removaltranssternal thymectomyliving with myasthenia gravisseronegative myasthenia gravismyasthenia gravis thymomamyasthenia gravis prognosismyasthenia gravis pronunciation