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EMG and SEP 
Panel findings and recommendations: 
 -   Needle EMG and H-reflex tests of the lower limb may be useful in assessing questionable nerve root dysfunction in patients with leg symptoms lasting longer than 4 weeks (regardless of whether patients also have back pain).  (Strength of Evidence = C.) 
 -   If the diagnosis of radiculopathy is obvious and specific on clinical examination, electrophysiologic testing is not recommended.  (Strength of Evidence = D.) 
 -   Surface EMG and F-wave tests are not recommended for assessing patients with low back symptoms.  (Strength of Evidence = C.) 
 -   SEPs may be useful in assessing suspected spinal stenosis and spinal cord myelopathy.  (Strength of Evidence = C.)  
  Electrophysiologic tests are sometimes used in patients with sciatica to evaluate physiologic functioning of the spinal cord, nerve roots, and peripheral nerves.  Overall diagnostic objectives of these tests are to assess suspected myelopathy (dysfunction of the spinal cord), radiculopathy (dysfunction of a spinal nerve root), neuropathy (dysfunction of a peripheral nerve distal to the nerve root), and myopathy (muscle abnormalities).  The tests and their specific diagnostic objectives for low back problems are as follows: 
 -   Needle electromyography (EMG), used to assess acute and chronic nerve root dysfunction, myelopathy, and myopathy. 
 -   H-reflex, a test measuring sensory conduction through nerve roots, used mostly to assess S-1 radiculopathies. 
 -   F-wave response, a test measuring motor conduction through nerve roots, used to assess proximal neuropathies. 
 -   Surface EMG, used to assess acute and chronic recruitment patterns during static or dynamic tasks using surface electrodes instead of needle insertion. 
 -   SEPs, used to assess sensory neurons in peripheral and spinal cord pathways. 
 -   Nerve conduction studies, used to assess acute and chronic peripheral entrapment neuropathies that may mimic radiculopathies. 
Electrophysiologic Tests 
Literature Reviewed     Evidence on Efficacy    Potential Harms and Costs      Summary of Findings     Author's Example 
Electrophysiologic Tests 
  Literature Reviewed.  Of 52 articles screened for this topic, 8 met review criteria for adequate evidence about efficacy.21, 254, 255, 256, 257, 258, 259, 260  Also reviewed was one study that evaluated findings in asymptomatic subjects who had no history of low back problems.261  Other studies contained information used by the panel.49, 50, 147 
  Four studies evaluated needle EMG. 21, 254, 257, 260  Three studies evaluated H-reflex or F-wave tests.21, 254, 256  Two studies evaluated surface EMG.258, 261  One study evaluated SEPs.259  No studies were found evaluating nerve conduction for assessing low back problems.  All articles meeting review criteria involved groups of patients either with chronic problems or with unreported symptom duration. 
  Evidence on Efficacy.    Reference tests used to determine diagnostic accuracy (true positive and true negative rates) of needle EMG included surgical findings. 21,254,260  They also included clinical followup (pain rating and work status), with posttest at 1 year.257  The amount and quality of data that could be used to calculate diagnostic accuracy of these tests varied significantly between studies.  Many studies had major methodological flaws such as biased test interpretations, faulty cohort assembly, and poor clinical descriptions.  Determining the accuracy of EMG is difficult as well because anatomic defects seen at surgery, which are used in many of these studies as the reference standard for EMG, may or may not be the cause of symptoms.  This makes true positive and true negative rate determinations of questionable value. 
  For needle EMG, four articles evaluated the test's accuracy in diagnosing nerve root problems.  Aiello, Serra, Migliore, et al. 21 evaluated 25 patients who had clinical evidence of L3 and/or L4 nerve root impairment.  Needle EMG was abnormal in all 24 patients who had positive findings at surgery, but predicted the exact levels of nerve root pathology in only 9 percent of these 24 patients.  One patient had a false- positive EMG with no disc herniation found at surgery. 
  Aiello, Serra, Tugnoli, et al. 254 evaluated the accuracy of EMG for detecting and localizing nerve root compromise in patients who had surgical findings of a single lumbar disc prolapse at the L3-L4 level (100-percent true positive rate, 88-percent true negative rate), with disc herniation at L4-L5 (96-percent true positive rate, 38-percent true negative rate) and with disc herniation L5-S1 (71-percent true positive rate, 79-percent true negative rate). 
  Khatri, Baruah, and McQuillen257 evaluated outcomes at 1 year in patients with radicular leg pain who had needle EMGs and computerized tomography (CT) scans and then went on to have disc surgery or nonsurgical treatment (including conservative care and/or epidural steroids).  There were 35 patients who had abnormal EMGs and CT scan findings of a herniated lumbar disc.  Of the 16 patients treated with surgery, 81 percent were better at 1 year, while of the 19 who had nonsurgical treatments only 47 percent reported improvement at one year.  There were 24 patients whose EMGs and CT scans were both normal; none of these patients had surgery, and at 1-year followup 67 percent were improved. 
  Young, Getty, Jackson, et al.260 evaluated 100 patients with clinical evidence of L5 or S1 radiculopathy and found that needle EMG correctly predicted the level of nerve root pathology in 84 percent of the 95 patients with positive surgical findings.  The wrong level was predicted in seven patients, and in nine patients only one abnormal root was detected when two were involved.  EMGs were negative in all five patients who had no root pathology noted at surgery. 
  In cases of radiculopathy or neuropathy, EMG results may be unreliable in limb muscles until a patient has had significant leg symptoms for over 3 weeks.  Also, abnormal EMGs tend to normalize over time.  There is some evidence that greater accuracy can be obtained in diagnosing lumbar nerve root compromise when information from needle EMG is combined in a systematic fashion with information from imaging tests and clinical findings, rather than relying on the results of each test alone.49, 50  
  For H-reflex and F-wave tests, three articles reported on accuracy in diagnosing nerve root problems.  Aiello, Serra, Migliore, et al. 21 evaluated 25 patients with clinical evidence of L3 and/or L4 nerve root impairment.  H-reflex tests were abnormal on the affected side in 96 percent of the 24 patients with L3 and/or L4 nerve root compromise confirmed at surgery, but the test was also positive in the 1 patient with no nerve root pathology noted at surgery (96-percent true positive rate, 0-percent true negative rate). 
  Aiello, Serra, Tugnoli, et al. 254 evaluated H-reflex tests and EMGs for 50 patients in whom a single disc prolapse was found at surgery. H-reflex tests were positive in 71 percent of 7 patients with L3-L4 disc herniations, 58 percent of 26 patients with L4-L5 disc herniations, and 100 percent of 17 patients with L5-S1 disc herniations.  In addition, by combining information from H-reflex tests and needle EMG, 30 percent of single disc prolapses could be determined accurately. 
  Braddom and Johnson256 evaluated H-reflex tests in 25 patients with clinically suspected S1 radiculopathy.  A normal range was established in 100 asymptomatic subjects.  All 25 patients had H-reflex-test latencies greater than 2 standard deviations above the mean for the control group. Only three patients were reported as having surgery, and long-term followup results were not given. 
  For surface EMG, two articles evaluated efficacy in assessing patients with low back symptoms.  Arena, Sherman, Bruno, et al.255 evaluated surface EMG of lumbar paraspinal muscles as a function of pain state. Surface EMG results were not significantly able to differentiate back pain patients with high pain states from those in low pain states.  Sihvonen, Partanen, Hanninen, et al. 258 evaluated both needle and surface EMG of lumbar paraspinal muscles in 87 patients with back pain (not radiculopathy) longer than 6 months, but who had not had surgery, and in 25 controls with no history of back problems.  When compared to the asymptomatic controls, the patients with back pain had significantly increased surface EMG activity while standing and immediately after lumbar flexion. 
  For SEPs, the only article reviewed259 evaluated accuracy in 18 patients with clinical findings of suspected spinal stenosis who went on to have surgery.  At operation, all patients were found to have spinal stenosis.  In all but 1 of the 18, SEPs had been positive (94-percent rate). 
  Potential Harms and Costs.  Inserting small needle electrodes into muscle tissue is invasive, causes some patients discomfort, and may cause bruising.  Patients who have severe pain, low pain thresholds, excessive anxiety, or conflicting emotional symptoms may not be able to participate fully in the examination.147  EMG and other electrophysiologic tests are moderately expensive. 
  Summary of Findings.  The evidence suggests that in patients with low back problems who have a confusing clinical picture of severe leg symptoms of more than 3 to 4 weeks' duration, EMG and H-reflex tests appear to be useful (1) to document presence or absence of radiculopathy or neuropathy as the cause of symptoms in the lower extremities, (2) to provide more information on specific nerve roots that may be compromised, and (3) to help differentiate between acute and chronic nerve root dysfunction. Optimal time for needle-EMG testing is after the patient has had lower limb symptoms at least 3 to 4 weeks.  Test results are not reliable before this time. 
  SEPs appear to be useful in diagnosing spinal stenosis and spinal cord myelopathy.  However, F-wave tests and surface EMGs are not considered effective methods of assessing low back problems. 
  Accuracy of electro-physiologic testing is highly dependent on the skill with which the examination is performed.  Clinicians are urged to assess the qualifications of the diagnostician before referring a patient with suspected neurologic compromise. 
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