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

Abstract

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.

Paraproteinemic Neuropathies

“…12 Nerve ultrasound studies demonstrate significantly larger cervical nerve root cross-sectional area and regional nerve enlargements at the common entrapment sites of peripheral nerves in IgM anti-MAG neuropathy. 24,25 Pathologic studies of nerves show a mild loss of myelinated fibers, segmental demyelination, and deposits of IgM and complement in myelin sheets on immunofluorescence studies. Widening of myelin lamellae is noted in ultrastructural studies (FIGURE 9-1).…”

Value of Antibody Determinations in Chronic Dysimmune Neuropathies

“…Nerve ultrasound (US) studies confirm widespread nerve enlargement, not confined to the more distal parts of nerves, with the greatest enlargement at common entrapment sites [49][50][51]. However, the role of US in distinguishing anti-MAG neuropathy from CIDP remains debated.…”

Typical CIDP, distal variant CIDP, and anti-MAG antibody neuropathy: An ultra-high frequency ultrasound comparison of nerve structure

“…Concerning anti-MAG neuropathy, US features have not been well defined, with some authors describing a swelling of the nerve in its most distal portion 4 , while others reporting more widespread changes 5 or enlargement at entrapment sites. 6 Although nerve size is the main parameter described in most studies, more attention is increasingly paid to the internal structure of the nerve. Some data are available for fascicle CSA (f-CSA) in CIDP 7 but, to our knowledge, little is known about changes occurring at the level of the fascicle in d-CIDP and anti-MAG neuropathy.…”