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reported controversial findings on the correlation Using the intranerve CSA variability, the sonographer
between sonographic and electrophysiological results may differentiate a focal (higher values) from diffuse
in MMN patients. [6,8,10] In view of the severe functional (lower values) nerve hypertrophy while the internerve
disability of MMN patients, it remains unknown that of CSA variability may reveal possible distribution patterns
these two methods could better highlight the functional of peripheral nerve impairment. On the other hand,
[7]
and clinical status of these patients. [11] the side to side difference ratio of the intranerve CSA
variability may be useful in detecting any lateralization
The aim of this review is to provide a timely update of pathologic changes and the intraplexus CSA
on the role of the neuromuscular ultrasound in the variability in differentiating focal (higher values) from
diagnostic of the MMN. diffuse (lower values) brachial plexus hypertrophy. [9,13]

QUANTIFICATION OF NERVE ULTRASOUND RESULTS
FINDINGS
Currently, 6 studies (evaluating a total of 55 cases)
Cross-sectional area reference values for peripheral of nerve sonography in MMN patients have been
nerves and brachial plexus have been already reported published [Table 2]. [6-10,14] The first description of
in the literature. [7,12,13] The difficulty, however, to pathological ultrasound findings in MMN was
differentiate normal from a pathologic heterogeneity of published by Beekman et al. In this report, the
[6]
CSA changes in peripheral nerves, especially in cases of authors documented at least one anatomical site with
immune-mediated neuropathies, remains an important pathological hypertrophy of the median or ulnar or
limitation of the neuromuscular ultrasound in clinical radial nerves and/or brachial plexus in 90% of the
application. CSA enlargement can be the result either cases. The authors concluded that the neuromuscular
of edema (usually accompanied by disturbed fascicular ultrasound may allow the detection of pathological
echostructure) or hypertrophy (usually accompanied signs to a greater extent than nerve conduction tests
by preserved fascisular echostructure). in MMN. In a later study of 12 MMN patients, nerve
hypertrophy was documented in the median (forearm),
Novel ultrasound measures, aiming to quantify ulnar (Guyons’ canal, forearm, elbow, upper arm) and
pathologic ultrasound changes of peripheral nerves tibial nerve (ankle), but not in brachial plexus, when
in immune-mediated polyneuropathies, have compared to controls [Figures 1 and 2].
been recently introduced in the literature: [7,9,11-13]
(1) the intranerve CSA variability (for each nerve), Considering the morphology of peripheral nerve
defined as maximal CSA/minimal CSA; (2) the internerve hypertrophy (focal vs. diffuse), Padua et al. have
[7]
CSA variability (for each patient), defined as nerve reported the inhomogenous CSA enlargement, mainly
with maximal intranerve CSA variability/nerve with of the median, ulnar and fibular nerve in a small group
minimal intranerve CSA variability; (3) the side to side of MMN patients. A second study on two MMN patients
difference ratio of the intranerve CSA variability (for not only confirmed the focal type of CSA enlargement,
each nerve), defined as side with maximal intranerve but also documented the significant lateralization
CSA variability/side with minimal intranerve CSA of ultrasound findings. Another MMN study has
[8]
variability; and (4) the intraplexus CSA variability documented a focal type of CSA enlargement in the
defined as maximal CSA of the brachial plexus/minimal median nerve, when compared with controls. In addition,
CSA of the brachial plexus [Table 1]. the higher values of the internerve CSA variability and
“side to side difference ratio of the intranerve CSA
Table 1: Equations for calculating the intranerve‑, variability’’ of the median, ulnar and fibular nerve,
internerve‑, intraplexus CSA variability and side to side were attributed by the authors to the possible striking
difference ratio of the intranerve CSA variability predilection of MMN to certain peripheral nerves and
Variability Calculating equation the asymmetry of findings respectively. [10]
Intranerve CSA variability Maximal CSA/minimal CSA
(for each nerve)
Intranerve CSA variability Peripheral nerve with the maximal A possible explanation for the CSA enlargement in
(for each subject) intranerve CSA variability/ MMN cases could derive from pathological studies at
peripheral nerve with the minimal sites of conduction blocks. According to these studies,
intranerve CSA variability
Side to side difference ratio of Side with the maximal intranerve perivascular areas contain scattered demyelinated
the intranerve CSA variability CSA variability/side with the axons, which are often surrounded by small onion bulb
(for each nerve) minimal intranerve CSA variability formations. These onion bulb formation may lead to a
[15]
Intraplexus CSA variability Maximal CSA of brachial plexus/
(for each brachial plexus) minimal CSA of brachial plexus consecutive CSA enlargement of the nerve. In addition,
CSA: Cross sectional area pathological CSA changes are usually detected at

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