This policy was originally created in 2003 and was updated regularly with searches of the MEDLINE database. The most recent literature search was performed through July 2012. The following is a summary of the key literature to date:
Surface electromyography (SEMG) has been used as a research tool to evaluate the performance of paraspinal muscles in patients with back pain and to further understand the etiology of low back pain. (1-5) However, validation of its use as a clinical diagnostic technique involves a sequential 3-step procedure as follows:
- Technical performance of a device is typically assessed by studies that compare test measurements with a gold standard and those that compare results taken with the same device on different occasions (test-retest).
- Diagnostic performance is evaluated by the ability of a test to accurately diagnose a clinical condition in comparison with the gold standard. The sensitivity of a test is the ability to detect a disease when the condition is present (true-positive), while specificity indicates the ability to detect patients who are suspected of disease but who do not have the condition (true-negative). Evaluation of diagnostic performance, therefore, requires independent assessment by the 2 methods in a population of patients who are suspected of disease but who do not all have the disease.
- Evidence related to improvement of clinical outcomes with use of this testing assesses the data linking use of a test to changes in health outcomes (clinical utility). While in some cases, tests can be evaluated adequately using technical and diagnostic performance, when a test identifies a new or different group of patients with a disease; randomized trials are needed to demonstrate impact of the test on the net health outcome.
The following discussion focuses on these three steps as they apply to SEMG.
Several studies using different SEMG devices have suggested that paraspinal SEMG, in general, is a reliable technique, based on coefficients of variation or test-retest studies. (2, 3) No studies were identified that compared the performance of SEMG to a gold standard reference test.
No articles that compare the results of SEMG (which tests groups of muscles) with needle electromyography (which tests individual muscles) for diagnosing any specific muscle pathology were identified in literature searches. However, the pathology of individual muscles (i.e., radiculopathy, neuropathy, etc.) may represent a different process than the pathology of muscle groups (i.e., muscle strain, spasm, etc.), and thus SEMG may be considered by its advocates as a unique test for which there is currently no gold standard. Nevertheless, even if one accepts this premise, there are inadequate data to evaluate the diagnostic performance of SEMG. For example, no articles were identified in the published peer-reviewed literature that established definitions of normal or abnormal SEMG. In some instances, asymmetrical electrical activity may have been used to define abnormality, results may be compared to a “normative data base.” However, there was no published literature defining what degree of asymmetry would constitute abnormality or how a normative database was established. (4)
In the absence of a gold standard diagnostic test, correlation with the clinical symptoms and physical exam is critical. De Luca has published a series of studies investigating a type of SEMG called the Back Analysis System (BAS), consisting of surface electrodes and other components to measure the electrical activity of muscles during isometric exercises designed to produce muscle fatigue. (5) Using physical exam and clinical history as a gold standard, the author found that BAS was able to accurately identify control and back pain patients 84% and 91% of the time, respectively, with the values increasing to 100% in some populations of patients. (Accuracy is the sum of true-positive and true-negative results.) However, these studies were not designed as a clinical diagnostic tool per se but were intended to investigate the etiology of back pain and to investigate muscular fatigue patterns in patients with and without back pain.
A 2010 study from Hong Kong used a different type of analysis of SEMG findings called dynamic topography. (6) Using SEMG, they evaluated 20 healthy men and 15 men with low-back pain and found different dynamic topography e.g., a more symmetric pattern in healthy controls. After physical therapy, the dynamic topography images of back pain patients were more similar to the healthy controls on some of the parameters that were assessed. However, there are no data that analyze how changes in the SEMG correlate to clinical response, whether a clinical response in the face of persisting SEMG abnormalities suggests ongoing pathology, or whether persistent symptoms in the face of a normal SEMG represent malingering.
Improvement of clinical outcomes
Several articles describe the use of SEMG as an aid in classifying low back pain. (7-9) Much of the research in this application has focused on the use of spectral analysis to assess muscle fatigability. However, it is unclear how this information may be used in the management of the patient. For example, while the innovators of the BAS system indicate that SEMG can suggest potential therapies by distinguishing deconditioning from muscle inhibition secondary to pain-related behavior, (7) no clinical studies describe the use of SEMG in suggesting therapy. In another application of SEMG, Arena and colleagues assessed the amplitude of SEMG recordings as a measure of paraspinal muscle tension in 66 patients and reported that the degree of muscle tension did not correlate with pain levels. These findings raised questions about the role of biofeedback, muscle relaxants, or other therapies designed to reduce muscle tension. (10)
While SEMG may be used to objectively document muscle spasm or other muscular abnormalities, it is unclear how such objective documentation would supplant or enhance clinical evaluation, or how this information would be used to alter the treatment plan. Part of the difficulty in clinical interpretation is understanding to what extent the SEMG abnormalities are primary or secondary. In addition, as noted in the Background section, no specific workup is recommended for acute low back pain without warning signs.
There are no data regarding the final health outcome. For example, SEMG has been proposed as a technique to differentiate muscle spasm from muscle contracture, with muscle spasm treated with relaxation therapy and contracture treated with stretching exercises. However, there are no data to validate that such treatment suggested by SEMG results in improved outcomes. (11,12)
A review of spinal muscle evaluation in low-back pain patients, published in 2007, indicates that the validity of SEMG remains controversial. (13) The authors note that although many studies show increased fatigability of the paraspinal muscles in patients with low back pain, it is not known whether these changes are causes or consequences of the low back pain. Also, “the considerable inter-individual variability and the absence of normative data complicate the description of normal or abnormal profiles, thereby limiting the diagnostic usefulness of SEMG.”
Practice Guidelines and Position Statements
In 2007, the American College of Physicians and the American Pain Society issued a joint clinical guideline on the diagnosis and treatment of low-back pain. The guideline did not specifically mention paraspinal surface electromyography. (14) It included the recommendations:
- “Clinicians should not routinely obtain imaging or other diagnostic tests in patients with nonspecific low back pain (strong recommendation, moderate-quality evidence).”
- “Clinicians should perform diagnostic imaging and testing for patients with low back pain when severe or progressive neurologic deficits are present or when serious underlying conditions are suspected on the basis of history and physical examination (strong recommendation, moderate-quality evidence).”
There are inadequate data on the technical and diagnostic performance of paraspinal SEMG compared to a gold standard reference test. Moreover, there is insufficient evidence regarding how findings from paraspinal SEMG impact patient management and/or how use of the test improves health outcomes. Thus, paraspinal surface electromyography for diagnosing and monitoring back pain is considered experimental, investigational, and unproven.
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