Both multifocal motor neuropathy (MMN) and chronic inflammatory demyelinating polyneuropathy (CIDP) are chronic progressive immune-mediated peripheral neuropathies without sensory loss. We aimed to explore the different features of ultrasonographic and electrophysiological changes among MMN, motor CIDP and typical CIDP patients.

Nerve ultrasonographic studies were performed in 19 patients with MMN, 15 patients with motor CIDP and 117 patients with typical CIDP. Cross-sectional areas (CSAs) were measured on the bilateral median and ulnar nerves and brachial plexus. Nerve conduction studies (NCSs) were performed on the median and ulnar nerves.

In patients with MMN and typical CIDP, the percentage enlargement in the brachial plexus (MMN 45.7%, typical CIDP 78%) was similar to that in the arm (MMN 42.9%, typical CIDP 76.8%) and forearm (MMN 42.9%, typical CIDP 79.4%). However, in patients with motor CIDP, the percentage enlargement in the brachial plexus (74.1%) was more pronounced than in the arm (65.5%) and forearm (58.6%). The CMAPerb/CMAPaxilla in MMN was significantly higher than in motor CIDP (median nerve, 0.82 ± 0.28 for MMN and 0.60 ± 0.37 for motor CIDP, P = 0.017). The CSA decreased in the order of typical CIDP, motor predominant CIDP (MPred-CIDP), pure motor CIDP (PM-CIDP) and MMN. The motor nerve conduction velocity increased in the order of typical CIDP, MPred-CIDP, PM-CIDP and MMN. A total of 3/6 PM-CIDP and 3/3 MPred-CIDP patients responded to steroid treatment.

Treatment response, nerve ultrasonography and NCS in MMN, PM-CIDP, MPred-CIDP and typical CIDP constitute a spectrum.