Nerve ultrasound characteristics of immunoglobulin M neuropathy associated with anti-myelin-associated glycoprotein antibodies

Introduction/Aims Immunoglobulin M neuropathy associated with anti-myelin-associated glycoprotein antibody (IgM/anti-MAG) neuropathy typically presents with chronic, distal-dominant symmetrical sensory or sensorimotor deficits. Ultrasonographic studies of IgM/anti-MAG neuropathy are limited, and were all performed on Western populations. We aimed to characterize the nerve ultrasonographic features of IgM/anti-MAG neuropathy in the Japanese population and evaluate whether they differ from the findings of the common subtypes of chronic inflammatory demyelinating polyneuropathy (CIDP). Methods In this cross-sectional study, we retrospectively reviewed medical records and extracted the cross-sectional areas (CSAs) of C5-C7 cervical nerve roots and median and ulnar nerves of 6 IgM/anti-MAG neuropathy patients, 10 typical CIDP (t-CIDP) patients, 5 multifocal CIDP (m-CIDP) patients, and 17 healthy controls (HCs). Results Cervical nerve root CSAs were significantly larger at every examined site on both sides in IgM/anti-MAG neuropathy than in m-CIDP and HCs but were comparable to those in t-CIDP. Peripheral nerve enlargements were greatest at common entrapment sites (ie, wrist and elbow) in IgM/anti-MAG neuropathy, a pattern shared with t-CIDP but not with m-CIDP. The degree of nerve enlargement at entrapment sites compared to non-entrapment sites was significantly higher in IgM/anti-MAG neuropathy than in t-CIDP. Discussion Our study delineated the ultrasonographic features of IgM/anti-MAG neuropathy in the Japanese population and observed similar characteristics to those of t-CIDP, with subtle differences. Further studies comparing results from various populations are required to optimize the use of nerve ultrasound worldwide.