Lumbar radiculopathy, a prevalent neurological condition, is characterized by
compression or irritation of a spinal nerve root. This condition often manifests as
radiating leg pain, motor weakness, sensory disturbances, and diminished reflexes.
Accurate diagnosis is essential for appropriate management, and electrodiagnostic
studies—particularly needle electromyography (EMG)—are commonly employed to
evaluate suspected cases. While EMG is a useful tool in confirming lumbar
radiculopathy, a normal EMG result does not exclude the diagnosis. The test has
limitations in sensitivity, anatomical sampling, and timing, all of which contribute to
potential false-negative outcomes.
The sensitivity of needle EMG for detecting lumbar radiculopathy in the general
population varies widely, typically reported between 50% and 90%. In patients with pain
as the only symptom or sign, the sensitivity of EMG for the diagnosis of radiculopathy
ranges from 36% to 64% while for patients with pain and an abnormal clinical
examination finding, the sensitivity is 51% to 86% (Narayanaswami et al., 2016). This
variability is dependent on factors such as the examiner’s expertise, the chronicity of the
condition, and the selection of muscles tested (Dumitru, 2001; Katirji, 2007). EMG
primarily detects signs of denervation and reinnervation in muscles innervated by the
affected spinal root. However, such changes require a significant degree of axonal
damage to become detectable. These electrophysiological changes generally take two to
three weeks to manifest after the initial nerve injury (Daube & Rubin, 2009). Thus, if
EMG is conducted too early, the absence of abnormalities may not reflect the absence
of disease but rather the timing of the examination.
Another important consideration is the limited anatomical sampling inherent in the
EMG procedure. Only a finite number of muscles are typically examined, and these
muscles may not include those most affected by the radiculopathy. Deep paraspinal or
pelvic muscles, such as the quadratus lumborum or psoas, which are often impacted in
lumbar radiculopathy, can be difficult to access and may be omitted from routine
testing. Consequently, electrophysiological abnormalities may go undetected if the
examination does not adequately cover the relevant myotomes (Jablecki et al., 2002).
Additionally, some radiculopathies are not associated with axonal injury. For example,
purely demyelinating lesions or intermittent nerve root compressions may cause
significant clinical symptoms without producing EMG-detectable changes (Krarup,
2003). These cases highlight the limitation of EMG in detecting non-axonal pathology
and further emphasize the need for comprehensive clinical correlation. A normal EMG in
such scenarios should not lead to dismissal of a clinical diagnosis that is otherwise
supported by history, physical examination, or imaging.
While low back pain is very common, the prevalence (number of cases of a condition at
a specific time) and incidence (number of new cases in a specific time period) of lumbar
radiculopathy is low. The prevalence of lumbar radiculopathy in the entire population is
between 3% to 5% (Tamarkin & Isaacson 2022). As stated previously, the examiner’s
proficiency, selection of muscles examined, and patient population demographics
influence the rate of EMG exam results that are positive for lumbar nerve root
compromise. A recent internal analysis of providers who are all board certified in clinical
electrophysiologic physical therapy, who utilize the same protocol for examination
template, in the same geographic area, and during a specific time period yielded the
following results. In 479 cases of people who had an EMG exam of the lumbar spine and
lower extremities between October 2022 through September 2023 and October 2024
through November 2024 performed by 8 different specialists, only 69 had an impression
indicating lumbar nerve root compromise. This is an incidence rate of EMG exam
confirmed lumbar nerve root compromise of 14%.
Magnetic resonance imaging (MRI) plays a complementary role in the diagnostic
evaluation of lumbar radiculopathy. MRI can visualize structural abnormalities such as
disc herniation, spinal stenosis, or foraminal narrowing that may not be evident on
EMG. Importantly, there are instances where imaging confirms nerve root compression
consistent with patient symptoms, despite a normal EMG. This discordance underscores
the necessity of a multi-modal diagnostic approach. The American Association of
Neuromuscular & Electrodiagnostic Medicine (AANEM) emphasizes that EMG findings
should always be interpreted in the context of the overall clinical picture and should not
be used in isolation to confirm or exclude radiculopathy (AANEM, 2010).
In conclusion, while needle EMG remains a valuable diagnostic tool in the evaluation of
lumbar radiculopathy, it is not definitive. A normal EMG does not rule out the diagnosis,
particularly in early, mild, or anatomically complex cases. Understanding the limitations
of EMG—such as its variable sensitivity, dependence on timing, and constrained
anatomical sampling—is essential for clinicians. Accurate diagnosis requires a
comprehensive approach that integrates EMG findings with clinical assessment and
imaging studies to guide appropriate treatment and management.
John Lugo, PT, DPT, ECS
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[Updated 2022 Sep 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls
Publishing; 2025 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK563224/
