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Kobylarz et al. Plast Aesthet Res 2023;10:2 https://dx.doi.org/10.20517/2347-9264.2022.38 Page 17 of 20

[8]
from the first dorsal interosseous (FDI) muscle . Some of these electrodiagnostic tests can be time-
consuming or technically challenging to perform. Even if these challenges are overcome, it may remain
impossible to precisely localize the ulnar neuropathy with electrodiagnostic testing. Neuromuscular
[30]
ultrasound is emerging as an adjunctive technique in this setting but is outside the scope of this review .

In addition to localization value for the surgeon, there is prognostic value provided by outpatient
electrodiagnostic studies. For example, the existence of a conduction block across the elbow to the FDI with
a normal CMAP amplitude from the abductor digiti minimi is strongly associated with significant or
[31]
complete recovery . In another series, a reduced FDI CMAP amplitude predicted pre-operative weakness,
while isolated slowing across the elbow did not, leading the authors to conclude that CMAP amplitude is a
[32]
sensitive indicator of axonal loss . In addition to confirming or at least supporting a diagnosis of UNE, the
[33]
degree of severity can be graded based on electrodiagnostic studies . This can be invaluable in counseling
patients about outcomes and consideration of surgical intervention.

Errors in the electrodiagnosis of mononeuropathies
Several potential pitfalls exist in the routine electrodiagnostic evaluation of errors in the electrodiagnosis of
mononeuropathies (UNE). In particular, the position of the upper extremity when performing the studies
can have a significant effect on measurements used to calculate conduction velocities . The elbow should
[34]
be kept in a moderate flexion position to provide the greatest correlation between the surface skin
measurement and true nerve length . The distance between below and above elbow nerve conduction
[35]
testing sites should be 10 cm, as shorter segments may amplify errors and longer segments may dilute
[17]
abnormal findings . The below-elbow stimulation site should be 3 cm distal to the ulnar groove to include
the cubital tunnel across the elbow; however, it should not be too distal to possibly include a Martin-Gruber
[8]
anastomosis (MGA) in the forearm . MGA must be excluded in the setting of conduction block across the
forearm segment since there are rare reports of a proximal MGA mimicking UNE . Finally, subluxation of
[36]
the ulnar nerve with elbow flexion is a potential cause of a false negative study due to erroneous
overestimation of nerve length across the elbow.

Intraoperative monitoring of mononeuropathy
IONM can be quite beneficial to patients undergoing a variety of types of peripheral nerve surgeries,
including exploration and repair of entrapments, nerve transposition, resection of tumors and cysts,
neurolysis and nerve grafts post trauma. For all of these procedures, utilization of free-running and
triggered EMG, as well as NCS, can be helpful for locating and identifying peripheral nerves, thereby
protecting them from the risks posed by surgical manipulation, and also assessing their neurophysiologic
function intraoperatively. The latter can support pre-operative NCS where particularly proximal sites are
inaccessible. Whenever it is difficult to differentiate neural from non-neural tissue, free-running and
triggered EMG can be beneficial. Stimulation through normal tissue, scar and tumor can also help guide the
surgeon during dissection. An expanding mass can often result in significant alterations of the normal
anatomical relationships, such as the displacement of nerve fibers over the tumor capsule that needs to be
identified by the surgeon. In addition, blunt trauma and compression do not usually result in transection of
the peripheral nerve. The extent of recovery, i.e., regeneration through remyelination and regrowth of
axons, is related to the degree and type of injury (neuropraxic vs. axonal) to the internal nerve bundle,
[18]
which is not necessarily evident from gross visual inspection . Such a determination is essential when
deciding whether a nerve graft repair or decompression is indicated. The existence and location of
functioning nerve can be determined by means of nerve conduction when it is obscured by scarring, being
in the closest proximity to where the amplitude of the NAP response is the largest. Peripheral nerves and
their branches can also be identified by means of CMAPs generated in specific muscles with stimulation.
For example, stimulation of the median and ulnar nerves can elicit motor responses over the thenar