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Review Article

Role of the neuromuscular ultrasound in the

diagnostic of the multifocal motor neuropathy

Antonios Kerasnoudis , Kalliopi Pitarokoili , Min‑Suk Yoon 2
2
1
1 Department of Neuroimmunology, St. Luke Hospital, 55236 Panorama, Thessaloniki, Greece.
2 Department of Neurology, St. Josef Hospital, Ruhr‑University, 44791 Bochum, North Rhine‑Westphalia, Germany.

ABSTRA CT
Multifocal motor neuropathy (MMN) is the one of the most common acquired immune‑mediated inflammatory disorders of the peripheral
nervous system. The diagnosis is based on the distribution pattern of the neurological semiology and the pathological changes of
nerve conduction studies (NCS) in classical cases. However, in cases with subtle clinical presentation, an extended diagnostic workup
may be needed, such as cerebrospinal fluid examination, laboratory tests, and nerve biopsy. NCS remain nowadays fundamental
not only for the diagnosis, but also for the follow‑up and measurement of response to immune‑treatment in MMN. New challenges
arose though, on how best to acquire a static and dynamic imaging of the peripheral nerves, aiming to provide a holistic approach to
the nerve impairment. According to the literature, neuromuscular ultrasound is able to detect in MMN patients thickened or swollen
cervical roots, peripheral nerves or brachial plexus, findings that suggest ongoing inflammation. This review provides a timely update
on the nerve ultrasound findings in MMN.
Key words: Brachial plexus, conduction block, immune‑mediated neuropathies, multifocal motor neuropathy, nerve hypertrophy,
nerve ultrasound

INTRODUCTION CMAP duration did not exceed 15% greater than
normal. Computer modeling of conduction block
Μultifοcal motor neuropathy (MMN) is an intriguing and temporal dispersion in an animal model has
peripheral nerve disease with a prevalence of demonstrated that up to 50% area reduction of the
1-2/100,000 adults. Several diagnostic criteria have proximal to distal CMAP can be due entirely to
[1]
been proposed, mainly summarizing the slowly interphase cancellation. Similar studies in human
progressive, asymmetric weakness, with a striking have shown that distal CMAP duration and proximal
predilection for the upper extremities, whereas sensory CMAP duration prolongation are important factors
fibers and upper motor neuron involvement fail in the for the definition of conduction block in the median
[2]
disease course. Although the detection of conduction nerve segment over the forearm: the shorter the distal
block remains the electrophysiological hallmark of the duration and proximal duration prolongation the less
disease, it is important to recognize that it may not be CMAP amplitude reduction is needed to diagnose
[2]
possible to demonstrate this finding even after careful a conduction block. The association between
studies, because blocks may be activity-dependent, MMN and immunoglobulin M (IgM) antiganglioside
and the site of pathology may be very proximal in the GM1 (anti-GM1) antibodies have already been
brachial plexus or nerve root level. [2-5] suggested in the literature, however, the diagnostic
accuracy of anti-GM1 testing in diagnosing
The first papers defined conduction block as a MMN is unclear. The literature reports the presence
20-30% amplitude or area reduction in the distal of anti-GM1 IgM antibodies in between 30% and 80%
compound muscle action potential (CMAP) if the of MMN patients. [2]

Access this article online Meanwhile, neuromuscular ultrasound is an easily
Quick Response Code: applicable and safe method for studying structural
Website: changes in peripheral nerves. Various ultrasound
www.nnjournal.net
studies have reported pathological ultrasound
DOI: changes in MMN patients, reporting consistently an
10.4103/2347-8659.143657 asymmetric, inhomogenous increase of the nerve
cross-sectional area (CSA). [6-9] Three studies have

Corresponding Author: Dr. Antonios Kerasnoudis, Department of Neuroimmunology, St. Luke Hospital, 55236 Panorama,
Thessaloniki, Greece. E‑mail: antonis.kerasnoudis@gmail.com

Neuroimmunol Neuroinflammation | Volume 1 | Issue 3 | December 2014 103