What is the role of electromyography (EMG) and nerve conduction studies (NCS) in the workup of mechanical low back pain?

Updated: Mar 06, 2018
  • Author: Everett C Hills, MD, MS; Chief Editor: Stephen Kishner, MD, MHA  more...
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Answer

Electrodiagnostic studies such as electromyography (EMG) and nerve conduction studies (NCS) can be very helpful in the evaluation of neurologic symptoms and/or neurologic deficits seen during the physical examination.

In the context of patients with low back pain (LBP) and neurologic symptoms/signs in the lower limb(s), EMG/NCS can objectively assess whether those symptoms/signs are due to lumbosacral radiculopathy versus peripheral polyneuropathy, myopathy, or peripheral nerve entrapment, among other conditions.

Further, EMG/NCS can often help identify which specific nerve root is involved in a given radiculopathy, which can be extremely helpful for correlation with any abnormal lumbosacral imaging study results (especially when the MRI shows multilevel abnormalities, while the nerve root compromise may be occurring in only 1 specific level). Identifying the specific nerve root involved can help ensure that any spinal injections or eventual surgery are performed at the appropriate level or site within the lumbar spine.

EMG/NCS is considered to have a relatively high degree of sensitivity for detecting radiculopathy, particularly with use of the needle EMG portion of the testing, when performed by an appropriately skilled physician. Further, because a patient is unable to voluntarily influence the appearance of abnormal EMG/NCS findings, the testing can be helpful in providing objective evidence of nerve pathology (or lack of evidence for such nerve pathology) in cases in which symptom magnification or malingering is suspected.

Many of the abnormal EMG/NCS findings take a couple of weeks to appear after an acute injury; hence, many electromyographers wait 2-4 weeks before performing the testing.


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