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Page 12 of 20 Kobylarz et al. Plast Aesthet Res 2023;10:2 https://dx.doi.org/10.20517/2347-9264.2022.38

reinnervation and the instability of neuromuscular transmission in nascent nerve fiber branches. As these
new fiber connections mature, transmission becomes faster and more stable, resulting in large, reinnervated
motor units that also follow a proximal to distal pattern. If this evolution matches well with the reported
duration of symptoms, this allows for more diagnostic certainty. The anatomic distribution of these changes
is also correlated with clinical exam findings to establish the likely localization. However, an advantage of
needle EMG is that even slight axonal loss or motor unit changes will be detected, making it much more
sensitive than a clinical exam for subtle weakness. Furthermore, since clinical testing of specific movements
can involve multiple muscles, needle EMG is more specific as it isolates a single muscle. Therefore, needle
EMG detects more subtle neurogenic changes and offers the advantage of providing information regarding
a lesion’s acuity.

Errors in electrodiagnosis of radiculopathies
EMG results that do not correlate well with clinical features or inconsistencies in electromyographic data
underscore the need to understand potential sources for error in electrodiagnostic studies. Errors can result
in underdiagnosis (type 2 error or false negative), overdiagnosis (type 1 error or false positive), or
misdiagnosis [Table 2]. One of the more important limitations is the nerve lesion’s age. Studies performed
during the hyperacute or acute period after injury (0-3 weeks) are likely to be normal. Reduced recruitment
of MUAPs can be seen if there is sufficient root demyelination to cause conduction block, but this is not
sensitive; conduction block requires significant demyelination, and the dual innervation of muscles by more
than one nerve root further dilutes the impact. Rarely, very brief trains of positive sharp waves can be seen
in the acute period reflecting motor axon loss. Increased abnormal spontaneous activity, fibrillation
potentials, and positive sharp waves appear in the acute to the subacute period (> 3 weeks post-injury), and
this is the phase in which studies can be most helpful. If fibrillation potentials and positive sharp waves are
seen without associated changes in motor unit action potential morphology, the lesion represents active
injury and is termed acute, active radiculopathy. The presence of changes in motor unit architecture with
increased duration, phases, and amplitude establishes the radiculopathy as chronic; if fibrillation potentials
and positive sharp waves are present, it becomes a chronic, active radiculopathy.

Another source of underdiagnosis occurs if only sensory fibers are involved in the root injury. The nerve
root’s ventral (motor) branch is adjacent to the protruding intervertebral disk and, therefore, at greater risk
than the dorsal (sensory) branch in the setting of a disk herniation. However, if a root injury affects only the
sensory branch, sparing motor axons, needle EMG will be normal even in the setting of radicular pain and
sensation change. This is similar to the situation if the root injury is purely demyelinating due to nerve root
compression. If there is insufficient conduction block to cause reduced recruitment, the electrodiagnostic
studies will also be normal. If there is only intermittent nerve root compression, as can be seen with spinal
stenosis where the symptoms are purely positional, fixed EMG changes may not occur .
[8]

Most errors in electrodiagnostic testing for radiculopathy affect the sensitivity rather than the specificity of
testing [Table 2]. However, specificity can be affected if the diagnosis relies solely on MUAP morphology
changes (49%-50% specificity) rather than fibrillation potentials and positive sharp waves (71%-89%
specificity). Similarly, if too few or inappropriate muscles are sampled during the needle EMG, a false
negative study may result. Therefore, the diagnosis should be based on a minimum of two muscles within
the same myotome with different peripheral nerve innervation. Needle EMG of paraspinal muscles
revealing active denervation potentials confirms the lesion is at or proximal to the nerve root level [24,25] . A
caveat to the interpretation of paraspinal muscle abnormalities is overlapping innervation, making it
[8]
difficult to localize a root lesion based on paraspinal denervation alone . Localization in the extremity can
also be limited by sampling error, myotomal overlap or variability in the innervation of muscles. A range