An important question any pain physician needs to address is a how to properly evaluate spine pain. Specifically, how does one objectively measure pain? Is the treatment plan helping the patient get better? How does one know if a patient is ‘symptom magnifying?’ Prescribing controlled medications in the absence of clearly documented need is fraught with risk. Medical licensing boards have taken action against physicians for alleged over prescription of controlled substances absent substantiating documentation. On the other hand, failure to adequately treat pain has also resulted in civil lawsuits with multi-million dollar judgments.
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Diagnosis of Low Back Pain
Diagnosis of Neck and Upper Extremity Pain
In the area of Workers’ Compensation and personal injury practice, deciding who really has cervical or low back pain — as well as assessing severity for those that do — is of critical importance. Low back litigation has been estimated to cost over $5 billion annually. Cervical spine injuries from motor vehicle accidents have reached epidemic proportions. Sapega¹ observed that in the nineteenth century physicians assessed muscular performance by conducting “crude manual muscle testing and observing posture, gait, and active range of motion.” At the present time disability determination is still based on these very supposedly “objective” techniques. It is therefore no wonder that there is little agreement among physicians, medical consultants, insurance clerks, and the general public about what constitutes a legitimate reason for work absence.
Background
At the present time the evaluation of spine pain is based to a great extent on subjective complaints. Starting a few years ago the Veterans Administration mandated that each patient being seen in it’s emergency rooms be asked about the severity of their pain using the Visual Analogue Scale (VAS). On discharge from the emergency room, the patient is asked if his pain needs have been met. The limitations of the VAS are well-known: it is a subjective evaluation. Chronic pain patients will often say that their pain is a ‘10.’
Range of motion measurements are often used in the evaluation of spine pain. The AMA guides to permanent impairment evaluates spine dysfunction using range of motion limitations. These tests are also subjective to a great extent. Although there are ways to check to see if the patient is giving a legitimate lumbar flexion, it is well know that this testing does have significant limitations. Standardized questionnaires are used in chronic pain evaluation, but these are also subjective and cannot be used to prove or disprove a patient’s pain complaints.
While lumbar spine x rays are routinely ordered it is well known that these studies are not generally useful in the evaluation of chronic lower back pain (LBP). Rockey et al.² reviewed the treatment and outcome of treatment in 440 patients with back pain. One hundred and six (24%) of those had spinal x-rays. It was determined that the spinal radiographs contributed minimally to the diagnosis, had little effect on the therapeutic decisions, and had no appreciable effect on the therapeutic outcome. Menges³ noted that radiologic abnormalities were not necessarily associated with subjective experience of pain. He concluded that roentgenograms were of little or no diagnostic value.
Other imaging studies such as MRI’s and CAT scans have high false positive rates. Jensen et al.⁴ found that the MRI’s of 64% of a population of 98 subjects under age 60 without low back pain revealed at least one positive finding.
SEMG and Objective Measurement
Surface electromyography is an inexpensive, noninvasive method of evaluating spine pain. SEMG evaluates abnormal electrophysiological activity of the motor unit. The basic principles of electromyography involve measurements of the action potentials generated during muscle contraction. SEMG and ECGs both measure muscular activity. The main difference is that in cardiac muscle measurements, the gap junctions account for the observation that the heart behaves as an electrical syncytium, whereas in skeletal muscle measurements gap junctions are absent and electrical syncytium is not present since skeletal muscle behaves as a single unit. Skeletal muscles undergo depolarization and repolarization when electrical impulses travel along individual muscle fibers and create recordable action potentials. Current SEMG units are designed to filter out the “noise” from underlying muscle groups while the signals generated by the deeper layers are too weak to produce recordable signal. Technically speaking, both EKG and SEMG are relatively easy to do. Surface electromyography is completely different from needle EMG testing which is considerably more difficult to perform.
Ambroz et al.⁵ showed that both static and dynamic SEMG can reliably differentiate low back pain patients from controls. Nederhand⁶ showed statistically significant different EMG levels between four neck pain disability subgroups. Ambroz et al.⁷ recently reviewed 44 clinical trials published in peer-reviewed journals which documented the utility of surface electromyography in the evaluation of spine. In these 44 studies a total of 1248 chronic spine pain patients were compared to 836 controls. It was concluded from these studies that SEMG is able to differentiate spine pain patients from subjects without pain. The consistency of positive findings observed in these studies, despite the wide variety of analytical techniques used, was felt to strengthen the overall conclusion. At the present time that group is preparing a meta-analysis of close to 50 trials in collaboration with the University of Michigan spine program. This review will be published within the next year. Preliminary results reveal that SEMG can evaluate spine pain with good sensitivity and specificity.
Static vs. Dynamic SEMG Modes
Surface EMG can be used in static or dynamic modes. Static (SEMG) measures the electrical activity of the motor unit of the spine during weight bearing. It can allow for the quantification of abnormal electrophysiological activity of the spine when injury is present. Dynamic SEMG evaluates the ability of the lumbar spine muscles to perform activities.
Static testing is done using two electrodes which are placed on the patient’s skin. An example of a static surface EMG graph is presented in Figure 1. This patient had complained of severe pain resulting from injuries sustained in a coal mine cave-in and he reported significant limitations in activities of daily living. This patient’s MRI scans revealed bulging discs in his neck and back. Neurologic examination was not focal.
Figure 2, on the other hand, are test results from a patient who was claiming incapacitating low back pain. It was believed that there was a significant element of symptom magnification. The surface electromyography test revealed the absence of significant abnormalities. This type of result has also proven useful in persuading patients to cut down or eliminate their use of scheduled medications.
Figure 3 presents SEMG test results for a patient who complained of severe neck pain without any lower back problems. He came in requesting refills of his hydrocodone. The surface electromyography results corroborated his pain complaints and provided grounds for writing his hydrocodone refill prescription.
In dynamic SEMG, electrodes are placed in the patients back and he or she is asked to bend forward and back a few times. The flexion-relaxation phenomenon is critical in analysis of the onset of muscle fatigue and associated muscle damage. The results of this testing in normal subjects is figure 5. For someone with low back pain a pattern such as figure 6 would be seen. Graberski-Matasovic et al.⁸ found that dynamic surface electromyographic range of motion measurements of the lumbar spine were correlated with different grades of pain severity.
According to the American Academy of Neurology, surface electromyography is considered an acceptable tool for kinesiologic analysis of movement disorders; for differentiating types of tremors, myoclonus, and dystonia; for evaluating gait and posture disturbances; and for evaluating psychophysical measures of reaction and movement time.
Outcome Measurements
Surface electromyography is also a useful method to document outcomes. Figure 4 presents an example of an individual who came in complaining of severe low back pain in August of 2002. He was diagnosed with myofascial pain disorder. After treatment, a repeat static surface electromyography done on December 11, 2002 revealed significant improvement. It should be noted that the SEMG measurements are independent of the initial pain mechanism as well as the treatment selected. The electromyography simply and objectively documents the improvement in symptomatology. If, after treatment, the patient were still complaining of problems and outcome SEMG measurements revealed abnormalities, one could conclude that additional and/or different treatments were needed.
Conclusion
Surface electromyography has been shown to be useful in the evaluation of spine pain in much the same way that EKGs have become indispensable for chest pain evaluation. SEMG testing is easy to do, inexpensive, has no morbidity, and provides important information for the pain practitioner.