In the practice of pain medicine, nerve conduction studies and electromyography provide useful information through the diagnosis of peripheral neurologic injury. By precisely identifying and localizing spinal root and peripheral nerve injury, these studies provide an important role in confirming the anatomical site active in pain generation. This knowledge increases the success of focal procedural and other interventions. It should be noted that these tools should be used to optimize patient care or help guide surgical and interventional practice.
Electromyography (EMG) and nerve conduction studies (NCS) are electrodiagnostic tests performed to evaluate the function of the peripheral nervous system. These tests are usually but not invariably performed together and interpreted in conjunction. Often the single term “EMG” is used to mean an examination comprising both NCS and EMG studies, though this is technically an imprecise usage. Both examinations evaluate and measure aspects of the electrophysiological properties inherent in peripheral nerve and muscle tissue. Through assessment of these neurophysiological parameters, these studies provide accurate diagnostic information to the clinician regarding the integrity and function of the spinal nerve roots, nerve plexi, peripheral nerves, neuromuscular junction, and muscle.
EMG/NCS are performed in patients for the following reasons:
To evaluate if a symptom is due to injury within the peripheral nervous system (PNS)
To localize the site of nerve injury within the PNS (ie, to spinal root, nerve plexus, peripheral nerve, neuromuscular junction, and/or muscle)
To assess the nature of the injury, including severity, chronicity, and at times pathophysiology
Symptoms consistent with possible peripheral nerve injury, either in isolation or combination, include the following:
NCS and EMG are relatively safe tests, with few potential associated complications or side effects. Some patients find the study uncomfortable; however, when performed correctly, both NCS and needle EMG examination are well tolerated by most patients.
There are no absolute contraindications to NCS/EMG; however, the following relative contraindications are considered:
Needle electromyography is performed with caution in patients on anticoagulation and/or on antiplatelet therapy.
The examination is generally modified to exclude muscles at noncompressible sites to eliminate the risk of hematoma.
Although not absolutely contraindicated, examination of the paraspinal musculature is generally avoided in patients on anticoagulation due to potential adverse effects of possible hematoma formation adjacent to spinal structures.
Needle electromyography is not performed in muscles where overlying skin infection or other tissue pathology is seen or suspected.
Needle electromyography is avoided in affected limbs of patients with lymphedema.
Nerve conduction studies requiring proximal stimulation at Erb point or the neck are not performed in patients with permanent pacemakers, internal defibrillators, ...