Utility of EDX Testing in Evaluating Patients with Lumbosacral Radiculopathy

AANEM PRACTICE TOPIC

S. CHARLES CHO, MD,¹ MARK A. FERRANTE, MD,² KERRY H. LEVIN, MD,³
ROBERT L. HARMON, MD, MS,⁴ and YUEN T. SO, MD, PhD¹
 

1.	Stanford University School of Medicine, Stanford, California, USA
2.	Ohio State University School of Medicine, Columbus, Ohio, USA
3.	Cleveland Clinic, Cleveland, Ohio, USA
4.	Pain Management and Rehabilitation Specialists, PC and Medical College of Georgia, Augusta, Georgia, USA

ABSTRACT: This is an evidence-based review of electrodiagnostic (EDX) testing of patients with suspected lumbosacral radiculopathy to determine its utility in diagnosis and prognosis. Literature searches were performed to identify articles applying EDX techniques to patients with suspected lumbosacral radiculopathy. From the 355 articles initially discovered, 119 articles describing nerve conduction studies, electromyography (EMG), or evoked potentials in adequate detail were reviewed further. Fifty-three studies met inclusion criteria and were graded using predetermined criteria for classification of evidence for diagnostic studies. Two class II, 7 class III, and 34 class IV studies described the diagnostic use of EDX. One class II and three class III articles described H-reflexes with acceptable statistical significance for use in the diagnosis and confirmation of suspected S1 lumbosacral radiculopathy. Two class II and two class III studies demonstrated a range of sensitivities for use of muscle paraspinal mapping. Two class II studies demonstrated the utility of peripheral myotomal limb electromyography in radiculopathies.
Muscle Nerve 42: 276–282, 2010

The diagnosis of lumbosacral radiculopathy is based on clinical history and examination, imaging studies, and electrodiagnostic (EDX) testing. Converging lines of evidence localize the lesion, establish the diagnostic certainty, and assist with prognostication. In those cases with negative imaging findings or atypical clinical presentations, EDX is especially useful; whereas, in those with abnormal imaging findings, it serves a complementary diagnostic role. A correct diagnosis of lumbosacral radiculopathy is important for implementation of timely and appropriate treatments.

Abbreviations: AANEM, American Association of Neurology and Electrodiagnostic Medicine; EDX, electrodiagnostic; EMG, electromyographic; MEP, motor evoked potential; MeSH, medical subject heading; NPV, negative predictive value; PM, paraspinal mapping; PPV, positive predictive value; SEP, somatosensory evoked potential

Key words: electrophysiology; herniated disk; lumbosacral radiculopathy; lumbosacral radiculitis; low back pain; root compression; sciatica This report is provided as an educational service of the AANEM. It is based on an assessment of the current scientific and clinical literature. It is not intended to include all possible methods of care for a particular clinical problem, or all legitimate criteria for choosing to use a specific procedure. Neither is it intended to exclude any reasonable alternative methodologies. This statement is not intended to address all possible uses of, or issues regarding, the evaluation of lumbosacral radiculopathy, and in no way reflects upon the usefulness of electrodiagnostic studies in those areas not addressed. The AANEM recognizes that specific patient care decisions are the prerogative of the patient and his/her physician and are based on all of the circumstances involved. These guidelines are not a substitute for the experience and judgment of a physician. This review was not written with the intent that it be used as a basis for reimbursement decisions. This report was developed by committees of the AANEM. It did not undergo additional peer review by Muscle & Nerve.


Copyright 2010 Wiley Periodicals, Inc.
Published online 15 July 2010 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mus.21759

The primary difficulty in this systematic review was the lack of an established reference standard for the diagnosis of lumbosacral radiculopathy. This lack of a standard makes comparison of reported sensitivity and specificity impossible. Structural abnormalities by imaging modalities had high rates of false positives,^1–4 and occasional false negatives.^5,6 Surgical visualization also did not consistently translate into clinical symptoms or physiological changes.⁵ In addition, the clinical presentation itself may be inconclusive. For example, injuries affecting the sacroiliac and zygapophysial joints, ligaments, muscles, and the peripheral disk annulus may cause referred pain suggestive of radiculopathy.^7–9

The Lumbosacral Radiculopathy Task Force was charged by the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) to perform a systematic review of the available literature to evaluate the utility of EDX studies in the diagnosis of lumbosacral radiculopathies. Task force members were selected on the basis of their EDX and methodological expertise. This practice parameter describes the results and recommendations of this systematic review.

METHODS
A search of the United States National Library of Medicine’s MEDLINE database was performed in October 2003 for articles in English pertaining to humans, using the medical subject headings (MeSHs) of lumbosacral radiculopathy, radiculitis, low back pain, sciatica, herniated disk, root compression (limited to the lumbosacral region), electrophysiology, neurophysiology, nerve conduction studies, electromyography, and spinal nerve root compression. A second search was conducted in October 2005, a third in January 2006, and a fourth in August 2006, using the expanded search criteria based on the original search, additional MeSH terms from the final articles, bibliographies, relevant textbooks, and relevant articles presented by the AANEM members and committees. All the abstracts were reviewed by at least two authors, and articles that described EDX in the diagnosis or prognosis of lumbosacral radiculopathy were obtained and evaluated in further detail.

Inclusion Criteria. The author panel limited the scope of the review to standard electrophysiological methods, including electromyography (EMG), paraspinal mapping (PM), nerve conductions (including H-reflex and F-waves, and motor evoked potentials with nerve root stimulation), and somatosensory evoked potentials (SEPs).^10,11 Articles that applied thermography, magnetic stimulation, and composite mathematical calculations in the diagnosis of radiculopathy were excluded. Case reports and uncontrolled case series were also excluded. The author panel limited the review to published studies that met at least four of the following eight criteria of high-quality studies:
 

1.	Prospective cohort survey or case–control study.
2.	Masking of EDX results when applying the reference standard.
3.	Criteria for patient selection clearly defined.
4.	Valid reference standard for the diagnosis of lumbosacral radiculopathy, including clinical, imaging, or surgical confirmation.
5.	The EDX procedure described in enough detail or referenced to a prior publication to allow duplication of the technique.
6.	The reference values and criteria for interpreting the results adhered to the accepted standards of EDX practice.
7.	For papers applying nerve conduction and SEP techniques, criteria for abnormal results were defined adequately in statistical terms using data from a reference population.
8.	For papers applying nerve conduction and SEP techniques, limb temperature is reported.

​
Three hundred fifty-five articles met the broad search criteria. One hundred nineteen of these articles applied EDX testing in the diagnosis of lumbosacral radiculopathy, and 53 of these 119 articles fulfill at least four of the criteria. For these 53 studies, the panel abstracted citation information, elements relevant to broad application (inclusion criteria, source, and spectrum of patients), and quality of evidence (study design, comparison/control group, objectiveness of the outcome variables, and presence or absence of masking). The quality of evidence provided by each article was rated by at least two members of the author panel, using a previously published classification scheme for diagnostic studies adopted by the AANEM and the American Academy of Neurology.¹²

In the literature review, the authors did not find any consensus for a reference case definition of lumbosacral radiculopathy. Case definitions considered potentially acceptable included an appropriate combination of clinical findings, imaging studies demonstrating a structural lesion and surgical confirmation of root pathology, and a consensus diagnosis based on unanimous independent clinical opinions of a team consisting of a physiatrist, a radiologist, and a neurosurgeon.¹³

 

RESULTS

Nine articles providing Class II or Class III evidence were identified.^13–21 Three articles studied the use of F-wave latencies^13,14,17 and evoked potentials,^14,16,21 and four articles addressed H-reflexes^13,14,17,20 and EMG.^13,15,18,19 Four studies applied the EDX test in a blinded evaluation.^13,15,18 The outcome assessments in the remaining articles were not blinded, but were classified as Class III as the EDX measures were objective (i.e., F-wave, H-reflex, and SEP studies, or EMG interpretation limited to the presence or absence of fibrillations potentials and positive sharp waves). Class IV studies are not considered further in this review.

Study Characteristics. The study design and cohort assembly method varied. Two studies were prospective, masked, and controlled^13,15; five studies were prospective and case-controlled^13,14,18,20; and three studies were retrospective and case-controlled.^16,17,21 All of these studies, except two,^13,18 have a narrow spectrum of patients who had lumbosacral radiculopathy, both clinically and by various other tests. Conversely, the two studies that employed a broad spectrum of patients included asymptomatic patients and those with low back pain who did not have spinal stenosis. The number of patients with lumbosacral radiculopathy in each study ranged from 16 to 206. Mean ages ranged from 18 to 80 years, although one study did not state the inclusive ages.²⁰

In two Class II prospective, controlled studies, the EDX physician was blinded to the clinical diagnosis.^13,15 In one study, subjects were designated normal control, low back pain without spinal stenosis, or spinal stenosis.¹³ The reference standard was an independent consensus agreement of the physiatrist, neuroradiologist, and neurosurgeon for the presence of spinal stenosis. However, the definition of spinal stenosis was not provided, and no attempt was made to correlate the EMG findings to the level or the side of radiologic or clinical abnormality. Another Class II study utilized data from Knutsson’s 1961 article to evaluate the lumbosacral EMG screen.¹⁵ The clinical data were presented in adequate detail to permit this reformulation. The data compared EMG, myelogram, and clinical symptoms to the intraoperative findings of a narrow spectrum of 206 patients who had sciatica. One hundred eighty-five patients had intraoperative confirmation of root compromise. The study group included subjects with sciatica and intraoperative abnormalities, whereas the control group consisted of patients with sciatica and no abnormal intraoperative findings. The EMG assessments were blinded, performed prospectively, and compared with an objective ‘‘gold standard.’’

The spectrum of clinical presentations varied. Two studies mandated dermatomal sensory deficits and an L5 or S1 pattern of weakness (dorsiflexion or plantarflexion),^14,20 whereas another allowed clinical symptoms to include or exclude sensory paresthesias in a dermatomal distribution.¹⁶ Clinical presentations included back pain, pain radiation, reflex abnormalities, strength deficits, and ambulation ability in both the radiculopathy cohort and the group with low back pain that did not have a radiculopathy.¹³ Other symptoms were sciatica over a certain amount of time, and 60% of patients had a reduced Achilles tendon reflex, 17% had a reduced patellar reflex, 61% had weakness of great toe extension, 30% had reduced sensation, 40% had muscular atrophy, and 95% had positive straight leg raises.¹⁵ Most of the studies used radicular pain as an initial screen^{13,14,16,18,20,21}; however, one article did not explicitly state the clinical features of presentation.¹⁷ Four articles included diminished ankle jerks and positive straight leg raises as part of the clinical criteria.^14–16,20 Three studies did not detail the clinical examination.^17,18

Two studies explicitly excluded patients with previous surgery.^16,18 Another two studies implied exclusion because surgery was part of the reference standard, but the authors did not explicitly state the surgery exclusion.^14,17 Although the spectrum of disease and the associated presentations varied, the common feature among the prospective patient assembly was radiating lower back pain. Four groups included surgical observations as part of the ‘‘gold standard.’’^14,15,17,19 Others used some form of EDX,^14,16,19,20 and most implemented various imaging studies.^13,16,18,21 A recent study implemented a unanimous consensus among the physiatrist, neuroradiologist, and neurosurgeon as the case definition of spinal stenosis.¹³

EMG/Paraspinal Mapping.   Several studies investigated the use of limb myotomal EMG and PM, using abnormal spontaneous activities as the definition of abnormalities (Table 1). A Class III study compared PM with imaging (either computed tomography or magnetic resonance imaging) in 43 patients and extremity EMG in 110 patients.¹⁹ The patient groups were classified by the degree of certainty of lumbosacral radiculopathy. Imaging was classified as normal and abnormal with abnormalities classified as possible, probable, single level, or multilevel. Extremity EMG was given in mean and standard deviation scores of abnormal spontaneous activity, motor unit potential changes, and composite EMG rather than raw data. Comparing only the certain (and excluding the possible and probable) single-level abnormality imaging findings to PM, the sensitivity was 63%, specificity 92%, positive predictive value (PPV) 87%, and negative predictive value (NPV) 75%; the values were 71%, 92%, 83%, and 85%, respectively, for the multilevel imaging abnormalities. Compared with imaging, the false-positive rate was 8% (1 of 13) and the false-negative rate was 33% (6 of 18). The false negative rate decreased to 5% with the addition of lower extremity EMG. All 7 patients with an isolated S1 radiculopathy had normal PM studies.

In another Class III study, PM was compared with imaging, extremity EMG, physical examination, and combined EMG/imaging as separate reference standards.¹⁸ Of note, the authors calculated different values than what were recorded, and they presented those calculations. Using imaging as the reference standard the sensitivity of PM was 66% and the specificity was 92%; using extremity EMG as the reference standard, these values were 50% and 85%, respectively; using physical examination as the gold standard, they were 54% and 69%, respectively; and using combined EMG/imaging as the gold standard, they were 58% and 90%, respectively.

A Class II study documented PM of four or more muscles. Abnormalities defined as membrane instability on one side demonstrated sensitivity of 30.4% and specificity of 100%, meeting statistical significance compared with control subjects (P ¼ 0.004).¹³ Additional EMG examination in an overlapping myotomal distribution in limb muscles (tensor fascia lata, vastus medialis, tibialis anterior, extensor hallucis longus, medial gastrocnemius) had sensitivity of 47.8% and specificity of 87.5% (P ¼ 0.008), when only fibrillation potentials were accepted as abnormal. When a combination of any needle EMG abnormalities was used (fibrillation potential, typical motor unit potential amplitude, number of polyphasic motor unit potential, motor unit potential recruitment), the sensitivity increased to 79.2%, and specificity fell to 50% (P ¼ 0.035).

In another Class II study,¹⁵ a four- and five-muscle extremity EMG screen that included PM had sensitivity in the range of 89–92%. Four- and five muscle screens without PM were not as sensitive (77–90%). Specificity could not be calculated because the data did not include false-positive or true-negative values.