I had a recent conversation with a physician asking why EMG/NCV should be ordered on most patients presenting to a chronic pain practice. This provider complained that the studies were often equivocal or conclusions vague without much definitive information to help with treatment decisions. I had to agree after a brief review of sample reports. It is appalling to find conclusions not supported by the data provided, or worse yet, the correct diagnosis ignored when the data clearly supported a specific diagnosis. An additional problem when waveforms were available for review, was to find multiple ‘technical’ errors, the most common being the failure to recognize abnormal motor and sensory amplitudes indicative of axonal neuropathy, or incorrect nerve latencies where the latency marker was over an abnormal baseline easily recognized as 60-cycle interference, or missing a reduced motor amplitude indicative of axonal damage due to focal entrapment neuropathy. For example, CTS was recognized but never quantified so that the referring physician would be unable to determine evidence based treatment based on the actual severity of nerve entrapment. Or one of my pet peeves, waveforms described as “positive sharp waves” (indicative of nerve root injury) that are actually motor end plate potentials, a normal finding. Because of my former experience interpreting over 16,000 nerve conductions in a little over four years for a mobile nerve testing company utilizing technicians, I became convinced that absolute integrity of results requires the physician to either be physically present in the room while the nerve testing is being performed, or better yet, the physician should do the entire test himself or herself. In this regard I have never used technicians except for a brief stint covering for an ill physician—I filled in and accepted my role of supervising technicians for the nerve test after which I would look at the results then perform the needle EMG exam on that patient. My bias is clearly supported by observing literally hundreds of technical ‘errors’ committed by technicians and supervising physicians well as my experience performing nearly 200 EMG’s per month in which I daily observe the importance of the supreme advantage the physician has when able to observe every nerve response and wrestle with the correct amount of current, electrode placement, stimulation site, and patient clinical response. The process is both art and science– what and where to test based on the observed response. I also find I have a clear idea of what I will find on EMG based on what I have already observed during the nerve conduction studies. With that in mind I have put together a statistical analysis below of recent results in a chronic pain management setting where the majority of patients are referred with radicular symptoms.
Nerve conduction studies (NCS) are considered the gold standard in the diagnosis of peripheral nerve disease. With steady improvement and standardization of methods, they have become a reliable test of neuropathy. NCS are now widely used for precise localization of a lesion as well as accurate characterization of peripheral nerve function. Evoked potentials either from the muscle or from the nerve itself can be recorded following electrical stimulation. Although the methods for stimulating nerves are relatively simple, various technical factors influence the measurements and can lead to a wrong or misleading conclusion. Recognition of the inherent limitations of the method can minimize such errors. NCS reports should include bilateral conduction velocities, distal latencies, proximal latencies, and amplitudes and characteristics of evoked motor and sensory potentials.
Electromyography (EMG) can provide accurate assessment of muscle function and precisely localize levels of nerve or nerve root injury when subsequent axonal damage results in impaired neuronal flow to individual muscles. EMG is most useful in the diagnosis of radiculopathy where the level and severity and duration of nerve root injury can be diagnosed and aid in treatment plans as well as prognosis for recovery. EMG correlates physiological status of the nerve root with the anatomical findings on imaging studies. EMG is also helpful in determining the severity of focal entrapment neuropathy by measuring the relative amount of axonal damage to muscles supplied by the affected nerve. Again, technical factors may enter into the accurate assessment of muscle function. Reports of EMG function should include commentary on insertional and spontaneous activity as well as analysis of configuration, duration, amplitude, firing rate, and recruitment of motor units.
An important question to ask in the pain management setting is for what specific acute and chronic pain entities are NCS and EMG most useful for either diagnostic or treatment considerations? I conducted a statistical analysis of 645 consecutive patient referrals to me over a six-month period. Since some patients were referred for both upper and lower extremity studies, the total number of studies was 686 of which 165 were normal (24%) and 521 were abnormal (76%).
Among the more startling statistics were the numbers of patients in a pain management setting with multifactorial disease resulting in more than one abnormal finding on either NCS or EMG or both. A total of 366 studies (53%) were positive for cervical radiculopathy (5%), lumbar radiculopathy (25%), or carpal tunnel syndrome (23%). Of the 32 patients with cervical radiculopathy, 25 (78%) had a co-morbid abnormal finding. Of the 175 patients with lumbar radiculopathy, 113 (65%) had a co-morbid abnormal finding. Of the 159 patients with carpal tunnel syndrome, 50 (31%) had a co-morbid abnormal finding.
The most common co-morbid finding was peripheral neuropathy. This was a common finding in patients with lumbar radiculopathy. Common neuropathies (45% of studies) include polyneuropathy, sensory axonal neuropathy, and diabetic neuropathy. Sensory axonal neuropathy was frequently associated with an aging population and an increased incidence of thyroid disease, adult onset diabetes, and peripheral vascular disease. Recognizing co-morbid neuropathy in patients with radiculopathy may influence patient satisfaction with lumbar procedures as much as it affects differential diagnosis. Patients unhappy with persistence of numbness after epidural or medial branch block may become more realistic in expectations after realizing their symptoms are related to more than one site of pathology.
Of the 159 patients with CTS, more than half were unaware of their diagnosis prior to testing. NCS and EMG were important to not only establish or confirm a suspected diagnosis of nerve entrapment, but to quantify severity. Evidence based studies support surgical decompression when there is evidence for axonal damage to motor and/or sensory fibers. Mild to moderate CTS has been shown to respond just as favorably at three and twelve months to carpal tunnel injection as to surgery. A significant number of patients unaware they had CTS were found to have severe enough axonal damage to precipitate a referral for a hand surgery consultation.
Less frequent diagnoses among this population of only 645 patients included: tarsal tunnel syndrome (15), ulnar neuropathy (20), EDB atrophy (7), peroneal or tibial neuropathy (7), brachial plexus lesions (3),Polymyositis (1), axillary nerve palsy (1), long thoracic nerve palsy (1), suprascapular nerve palsy (1), cauda equina syndrome (1), radial nerve palsy 3), and myotonic dystrophy (1).
EDB atrophy presents a unique problem in pain management in the presence of radicular pain and/or weakness. The differential diagnosis includes L5 radiculopathy, peroneal palsy, motor axonal neuropathy, local trauma and congenital absence or atrophy. NCS and EMG are critical to correct diagnosis in differentiating nerve root from peripheral nerve pathology. A significant number of patients with normal electrical findings had a positive past medical history for trauma including ankle fracture, blunt trauma, or recurrent ankle sprain. In other words, the suspected neurological cause of atrophy was incorrect as the observed EDB atrophy in these cases was secondary to an orthopedic musculoskeletal injury.
EMG and NCS were useful in identifying neurological conditions requiring neurology consultation in addition to pain management including unusual findings of myopathy, myotonic dystrophy, pseudobulbar palsy, and cauda equina syndrome. None of these diagnoses could have been arrived at based on physical exam alone.
In addition to my position as electromyographer for a pain group I served for over four years as medical director of a medicare certified independent testing facility. In that role I interpreted over 16,000 nerve conduction studies in addition to training their technicians and physicians. This provided me the opportunity to complete several large statistical reviews of results for medical groups concerned about medical necessity as well as clinical guidelines for referral. A primary care group of over 100 physicians referred over 1800 patients for studies over a period of 18 months. The referring diagnosis was incorrect in approximately 1/3 of cases. Abnormal findings were present in 64% of patients. The most common abnormal findings were CTS and peripheral neuropathy. Radiculopathy was suspected in only 11% of referrals. These numbers were very similar to another study of 454 consecutive referrals from a primary care internal medicine clinic in Tucson Arizona. A third study of 466 consecutive referrals from podiatry clinics in Southern California treating a high percentage of diabetics revealed 92% of diabetic patients had abnormal findings. As a qualified medical examiner for the State of California I performed over 800 EMG’s in an orthopedic surgery clinic on patients referred for second opinion evaluations for the California Division of Workers Compensation. 67% of these patients had abnormal findings. Comparing these studies with our results supports the appropriate usage and value of EMG and NCS in a pain setting. Our percentage of patients with abnormal findings was higher.
These comparative numbers indicate pain clinics and orthopedic clinics appear to see 2-3 times as many patients with radiculopathy and about the same percentage of patients with CTS compared to primary care. In this pain setting 2/3 of patients with lumbar radiculopathy and 1/3 of patients with CTS had additional abnormal findings other than the primary suspected diagnosis. In primary care 55% of patients with findings consistent with the referring diagnosis also had evidence for a second abnormal diagnosis. Of particular note were the diabetic patients. Of these, 12-15% had co-morbid focal entrapment neuropathies that were not suspected or identified at the time of referral. Many of these patients had severe enough entrapment neuropathies to require surgical intervention. The most common sites of entrapment in the diabetic were median nerve at the wrist, ulnar nerve at the wrist and elbow, peroneal nerve at the fibular head, and tarsal tunnel syndrome.
It should be noted that the more severe the diabetic neuropathy the greater the risk for concurrent autonomic neuropathy. The obese diabetic with moderate to severe PN is at significant risk for sudden death due to cardiovascular arrhythmia, not to mention ischemic gangrene, loss of limb, impotence, renal failure, and gastroparesis. Pain clinics, like podiatry, are often the front line of defense for the symptomatic diabetic seeking care for an immediate need while ignoring silent risk factors of a more serious underlying manifestation of chronic neuropathy.
Carpal tunnel syndrome is a common finding among pain patient populations. In this review of 645 patients 23% had CTS and of those with CTS, 31% had additional abnormal test findings. For patients with CTS, several studies have shown the clinical exam and patient history to be inconsistent and very unreliable at predicting presence or severity of CTS. While a Tinel’s sign is promoted as definitive, many physicians do not perform this test (or Phalen’s) correctly, and relative sensitivity and specificity in large studies never exceeds the thirty percent range compared to NCV at over 90% accuracy. In other words, NCV is the gold standard for confirming presence and severity of median nerve entrapment at the wrist. Physical exam to determine weakness is very unreliable as well due mostly to pain inhibition limiting patient voluntary effort. EMG and NCV are the only means of reliably assessing severity of axonal loss due to median neuropathy and is an important issue in this age of evidence-based medicine. Evidence based studies show that conservative care (including injection) is equally or more effective than surgical intervention at three months and one year in mild to moderate CTS. When there is evidence for axonal damage threatening permanent impairment of motor and/or sensory function, these studies support surgical decompression. Our studies show that with any patient with upper extremity pain and paresthesias, CTS should be considered as part of the differential diagnosis. CTS is “The Great Masquerader” for a reason–patients often present with multiple complaints involving extremity, shoulder, neck and upper back that are ultimately identified as median entrapment at the wrist.
Referral guidelines for electrodiagnostic studies have been established by the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM). The goals of EMG and NCS are to make a diagnosis, define severity, location, and chronicity of a lesion, and provide information useful for treatment or intervention. Radicular pain and paresthesias are probably the most common presenting complaint. EMG and NCS are helpful in identifying cervical and lumbar root lesions, peripheral neuropathy, and focal entrapment neuropathy such as CTS, ulnar entrapment neuropathy at the elbow, peroneal palsy and tarsal tunnel syndrome. From the list of confirmed diagnosis, it is evident the electromyographer also needs to have experience in identifying and quantifying entrapment neuropathies of the shoulder girdle. The electrodiagnostic exam may also be useful to rule out a neurological cause of symptoms in the anxious patient with myofascial pain, fibromyalgia, or degenerative joint disease. There may also be a need to rule out concurrent lower motor neuron disease in a patient with a suspected upper motor neuron lesion such as MS or other central nervous system disorder.
According to Medicare and the AANEM as well as the respective organizations of neurology and physiatry, the following are among symptoms and signs that should be recorded in the progress note to justify referral for EMG: numbness, tingling, pins and needles, burning paresthesias, weakness, wrist drop, foot drop, neck or back pain, wrist pain, foot pain, muscle atrophy, reflex loss, and cramping. Clinical issues that further support the need for EMG are unequivocal neurological findings, unclear neuromuscular examination, to clarify the differential diagnosis, define the degree of impairment, or to reassess a patient unresponsive to treatment or experiencing a progression of symptoms after treatment. EMG and NCS may be indicated to rule out a non-structural disorder in the absence of a structural lesion.
Unfortunately, there will always be issues of disagreement regarding medical necessity, particularly with repeat testing. Medicare requires an interval of at least six months before repeat testing. Criteria for repeat testing include: confirm initial test or second opinion, repeat a test with equivocal results, monitor marked clinical changes in a condition, follow conditions expected to respond to surgical or medical treatments, and to evaluate a new set of symptoms.
It is hopefully evident from the above discussion that EMG/NCS is recommended to determine physiologic, not anatomic, evidence for impairment. These guidelines suggest EMG should be routinely obtained in concert with, if not before, anatomic studies such as MRI in the evaluation of pain, paresthesia, sensory deficit, weakness, atrophy, or reflex loss. Studies on sensitivity and specificity also indicate NCS is far superior to clinical exam in identifying presence and severity of neuropathy or focal entrapment neuropathy. Based on the high frequency of abnormal findings in diabetic patients, it appears prudent to screen all diabetics for neuropathy and undiagnosed entrapment neuropathy as part of a comprehensive pain clinic workup. The infrequent but important finding of shoulder girdle entrapment neuropathies and distal focal entrapment neuropathies including CTS and UNE in patients presenting with symptoms of cervical radiculopathy indicate EMG/NCS should be considered in the workup of these patients as the percentage of patients with actual proven cervical radiculopathy remains relatively small. Screening for lumbar radiculopathy frequently reveals an unsuspected neuropathy leading to referral for workup of undiagnosed diabetes, thyroid disease, or peripheral vascular disease in aging populations with pain and multi-organ system dysfunction. Of importance to the pain physician is a clear delineation of symptoms both for consideration of diagnostic and therapeutic options as well as helping patients to understand that the procedure that eliminated their back pain did not relieve distal numbness because they have two different disease processes.
Finally, what should you look for in the electrodiagnostic report?
NCS findings should include:
• Motor latency, conduction velocity, and amplitude. • Sensory latency and amplitude. • Fwave and Hwave latencies. • Right to left comparisons. • Nerve to nerve comparisons. • Are findings motor or sensory or both.
• Are findings demyelinating (conduction slowing) or axonal (reduced amplitudes) or a combination of both.
EMG findings should include:
• Insertional and spontaneous activity. • Abnormal “denervation” (positive sharp waves, fibrillations). • Motor unit analysis: configuration, duration, amplitude. • Motor unit firing rates and recruitment patterns. • Chronicity and severity as well as nerve root level of findings.
What to expect from an NCS report:
• Clinically and physiologically relevant interpretation and diagnosis • Outline of the localization, severity, and acuity of the abnormal findings • Notation of other diagnosis detected and/or excluded • Explanation of any technical problems • Need for re-evaluation in the future • Urgent need for medical/surgical intervention
In summary, EMG/NCS are more than just adjunct diagnostic procedures in the management of acute and chronic pain. Electrodiagnostic studies are more accurate in the diagnosis of neuropathy and entrapment neuropathy than physical exam. EMG is more accurate than physical exam and imaging in confirming objective axonal damage to nerve roots, identifying level of nerve root pathology, and assessing severity and chronicity of a specific lesion. Electrodiagnosis is helpful in differentiating objective neurological injury from musculoskeletal pain syndromes in patients where the legitimate need for opioid medications is in question. Appropriate referral for EMG/NCS appears to correlate with the percentage of patients with abnormal findings. In this pain management setting, the percentage of patients with abnormal findings is unusually high, between 70-80% of tests on a given day, indicating a high level of pathology seen on a daily basis, and a very appropriate referral of patients with suspected nerve root or peripheral nerve disease. It is the observation of this author that clinics where more than 60% of referred patients for EMG/NCS have positive findings are meeting exceptional criteria for appropriate referral. If the percentage of patients with abnormal findings falls well below 50%, then criteria for referral may not be selective enough. If the percentage of referrals with abnormal findings is above 80% you may be too selective and you may be missing pathology by referring too few.
AS A FOOTNOTE TO THIS ARTICLE, I AM NOW (LATE 2023) PERFORMING EMG'S IN A NEUROLOGY CLINIC LOCATED IN A RETIREMENT AREA OF WEST PHOENIX--THE AMOUNT OF PATHOLOGY ENCOUNTERED ISAMAZING! PERCENTAGE OF PATIENTS WITH ABNORMAL TEST FINDINGS HAS INCREASED REMARKEDLY. IT IS NOT
UNCOMMON TO HAVE DAYS WHERE ONLY 1-2/15 TESTS ARE NORMAL.