Low back pain and lumbar radiculopathy are common conditions affecting the general
population. Low back pain has a prevalence of 10%-30%, and lumbar radiculopathy, with a
prevalence of 3%-5% [1]. Differentiating between low back pain and lumbar radiculopathy can
be tricky as low back pain is often used to describe a variety of conditions from acute low back
discomfort, referred pain, radicular pain, discogenic pain, mechanical low back pain, and
radiculopathies [1,2]. Sorting through these various ailments can be tricky as multiple muscles
and structures can contribute to both low back pain and lower extremity pan (piriformis
syndrome, psoas syndrome, greater trochanteric pain syndrome and others) with a patient’s
subjective report resembling lumbar radiculopathy [1]. Diagnostically, lumbosacral radicular
pain is characterized by a radiating pain in one or more lumbar or sacral dermatomes. It may or
may not be accompanied by other radicular irritation symptoms and/or symptoms of decreased
function [3]. Due to the complexities and broad nature of the low back pain diagnosis, accurate
methods for identifying a true lumbar radiculopathy are an integral part of the diagnosis and
treatment process. Magnetic Resonance Imaging (MRI) and Electrodiagnostic assessment (EDX)
are two key tests that can aid in the assessment of nerve damage to allow for a definitive
lumbar radiculopathy diagnosis.
Patients are often referred to physical therapy and may undergo a course of corticosteroids to treat the initial
inflammatory response to allow for the patient to participate in exercise that will facilitate return to function. However, if these conservative methods do not work the patient may be a candidate for surgery.
In order to assess where the lesion is located, and the severity of injury, physicians will often order MRI and electrodiagnostic testing before deciding to refer for surgical intervention. However, is one test better than the other or should they be used together when building a differential diagnosis?
Mutaza et al. (2023) assessed 96 patients with complaints consistent with
lumbar radiculopathy. They found that while MRI has been shown to be very sensitive (75%
sensitivity) to disc herniations and anatomic abnormalities, it is not as specific (25% specificity)
and not all findings are considered pathologic and may not be the cause of the patient’s current
symptoms [4]. MRIs are primarily ordered to assess any physical compression of a nerve. It
does not allow for an assessment of the function of a given nerve that has been compressed, or
whether that compression is significant enough to cause the symptoms the patient is having.
Similarly, EDX is also very sensitive (75% sensitivity) to abnormalities of active and chronic nerve
injuries but is not very specific (25% specificity). The main difference between the two tests is
that MRI has been shown to have a higher false negative (says its ok when its not) and EDX has
a higher false positive (says there is damage when there is not) [4].
Yousif et al. (2020) examined 30 patients to assess any correlation between subjective
symptoms with MRI and EDX findings. They found 23 of the 30 patients examined were found
to have nerve root compression on MRI with 20 patients (66%) having an abnormal physical
exam and 3 (10% having no symptoms). Similarly, 22 of the 30 patients examined with NCS
were found positive findings (prolonged H-Reflex, prolonged F-waves, as well as changed in
amplitudes and/or conduction velocities in the tibial and fibular nerves) 17 (56%) of those
tested with EDX had an abnormal physical exam and 5 (17%) had a normal physical exam.
These findings agree with several previous and current studies [3-8]. The current
consensus is that there is no statistically significant association between MRI and EDX findings
with patient complaints individually, but they are both tools that should be used as supporting
evidence when building a differential diagnosis. EDX appears to give a higher false positive for
lumbar radiculopathy when compared to MRI [3,5] and can in part be explained by the different
nature of each test. MRI assesses structural abnormalities that can affect the nerve while EDX
examines the physiological function of the nerve, with EMG being more sensitive to past
injuries that may not be symptomatic at this time which can explain the common finding that
EDX is more sensitive and less specific when compared to MRI. In conclusion, both EDX and MRI
should be used together to assess the presence of a lesion (MRI) and the severity of physiologic
compromise (EDX) that may explain the patients’ current physical limitations/complaints.
Daniel Trapp, PT DPT
EMG Solutions Resident
BIBLIOGRAPHY
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