Prevalence of denervation in paraspinal and foot intrinsic musculature

Redundant nerve roots on magnetic resonance imaging can predict ongoing denervation in patients with lumbar spinal stenosis

INTRODUCTION/AIMS

Redundant nerve roots (RNRs) are abnormally elongated and tortuous nerve roots that develop secondary to degenerative spinal stenosis. RNRs have been associated with poorer clinical outcomes after decompression surgery; however, studies on their clinical characteristics are limited. This study aimed to investigate the association between RNRs and denervation potentials, that is, abnormal spontaneous activity (ASA), on electromyography.

METHODS

We retrospectively reviewed data of patients who underwent an electrodiagnostic study of the lower extremities between January 2020 and March 2023. Of these, patients with lumbar central spinal stenosis, as seen on magnetic resonance imaging, were included. We analyzed clinical and imaging data, including presence of ASA, and compared them according to the presence of RNRs. Multivariable logistic regression analysis was employed to identify factors associated with development of ASA.

RESULTS

Among the 2003 patients screened, 193 were included in the study. RNRs were associated with advanced age (p < .001), longer symptom duration (p = .009), smaller cross-sectional area of the dural sac at the stenotic level (p < .001), and higher frequency of ASA (p < .001). Higher probability of ASA was correlated with greater RNR severity (p < .001). In the multivariable logistic regression analysis, ASA occurrence was associated with smaller cross-sectional area, multiple stenotic sites, and severe-grade RNRs.

DISCUSSION

The presence of RNRs, particularly severe-grade RNRs, was identified as a significant risk factor for the development of ASA on electromyography. This finding may aid physicians in estimating the prognosis of patients with central spinal stenosis.

A review of electromyography techniques of the cervical paraspinal muscles

Electrodiagnosis for cervical radiculopathy often involves exploration of the cervical paraspinal muscles. Accurate and reproducible results require a technique with specific anatomic localization, direction of insertion, extent of insertion, scoring system for insertion, and criteria for determining abnormality. We sought to understand if a published technique met these criteria. A Medline search found 39 articles with original research and 10 review articles involving the cervical paraspinals. A library search found 19 textbooks since 2000, but 9 were not available. Only two studies were specific to the question. Neither had reproducible techniques and they contradicted each other. Studies in which the paraspinals were used for comparison or inclusion did not provide any specific technique. The review articles and textbooks typically met none of our criteria and the few that discussed technique at all provided no reproducible methods. Despite 80 years of electrodiagnostic testing, there is no useful, reproducible technique for exploring the cervical paraspinal muscles. Yet such a paraspinal mapping technique has proven invaluable in the lumbar region. For cervical electromyography to be of value, the next step is to understand the anatomy and propose a reproducible technique. Subsequent research will determine whether the neck muscles are helpful in the diagnosis of cervical radiculopathy. The absence of a valid reproducible cervical paraspinal technique impedes clinical and scientific understanding of cervical radiculopathy.

Volume conduction: Extracellular waveform generation in theory and practice

The extracellular waveform manifestations of the intracellular action potential are the quintessential diagnostic foundation of electrodiagnostic medicine, and clinical neurophysiology in general. Volume conduction is the extracellular current flow and associated voltage distributions in an ionic conducting media, such as occurs in the human body. Both surface and intramuscular electrodes, in association with contemporary digital electromyographic systems, permit very sensitive detection and visualization of this extracellular spontaneous, voluntary, and evoked nerve/muscle electrical activity. Waveform configuration, with its associated discharge rate/rhythm, permits the identification of normal and abnormal waveforms, thereby assisting in the diagnosis of nerve and muscle pathology. This monograph utilizes a simple model to explain the various waveforms that may be encountered. There are a limited number of waveforms capable of being generated in excitable tissues which conform to well-known volume conductor concepts. Using these principles, such waveforms can be quickly identified in real time during clinical studies.

Electrodiagnostic Assessment of Radiculopathies

This article discusses the electrodiagnostic assessment of radiculopathy. Relevant anatomy initially is reviewed followed by discussion surrounding the approach to nerve conduction studies and needle electrode examination when it comes to radiculopathy evaluation. Pitfalls of the electrodiagnosis versus clinical diagnosis of radiculopathy and the definitions of acute versus chronic, and active versus inactive, are reviewed.

Evaluation of persons with suspected lumbosacral and cervical radiculopathy: Electrodiagnostic assessment and implications for treatment and outcomes (Part II)

The electrodiagnostic (EDX) examination with needle electromyography (EMG) is the most important means of testing for radiculopathy. This test has modest sensitivity but high specificity and complements imaging of the spine. In this second of a two-part review, the implications of electrodiagnostic findings for diagnosis and clinical management of persons with radiculopathy are reviewed. An EMG confirmed lumbosacral radiculopathy is associated with better clinical outcomes for persons undergoing aggressive conservative management. A positive EMG test portends a better clinical response to epidural corticosteroid injections. If a person undergoes spine surgery, a positive pre-operative EMG for radiculopathy is also associated with better outcomes.

Quantitative electromyography: Normative data in paraspinal muscles

BACKGROUND

Quantitative electromyography of paraspinal muscle is a valuable diagnostic tool, but normative data are lacking.

METHODS

Needle electromyography (EMG) was obtained in 65 healthy subjects (49% men, 51% women) aged 21 to 82 years at C7, Th10, and L5 segments bilaterally. The incidence of spontaneous activity; motor unit potential (MUP) amplitudes, durations, and the incidence of polyphasic potentials; and the recruitment pattern at maximal voluntary contraction (MVC) were evaluated.

RESULTS

The incidence of fibrillation potentials was similar to limb muscles. The mean MUP duration and amplitude, and the amplitude at MVC increased caudally, while the incidence of polyphasic potentials was similar at all levels. EMG parameters did not correlate with sex or age.

CONCLUSIONS

In contrast to limb muscles, EMG parameters did not change with age, while polyphasic potentials were more frequent in paraspinal muscle than in limb muscles. The EMG gradient suggests larger motor units at more caudal segments.

Electrodiagnostic Abnormalities Associated with Fibromyalgia

PURPOSE

Increasing evidence suggests that fibromyalgia most likely represents a neurological dysfunction. We previously hypothesized that at least some fibromyalgia cases may be caused by irritation of nerve root fibers and sensory neurons due to moderately increased cerebrospinal pressure. Because of the rostro-caudal hydrostatic pressure gradient, neurogenic abnormalities are expected to be most pronounced in sacral nerve roots. The purpose was to review electrodiagnostic tests of patients with fibromyalgia.

METHODS

A retrospective review of electrodiagnostic test results, including the lumbar and sacral nerve root myotomes of patients diagnosed with fibromyalgia according to the 1990 criteria of the American College of Rheumatology was done.

RESULTS

All 17 patients were female. Sural nerve responses could not be elicited in 12% and S1-Hoffmann reflex latencies were increased in 41%. In 12% of the patients, fibular motor nerve distal latency and conduction velocity were outside normal limits. Needle-EMG revealed neurogenic motor unit potentials in 0% of L2, 6% of L3, 29% of L4, 71% of L5, 47% of S1, 94% of S2, and 76% of S3-S4 myotomes. S3-S4 nerve-supplied anal reflexes were delayed in 94%.

CONCLUSION

This is the first time that electrodiagnostic data of both lumbar and sacral nerve root myotomes in fibromyalgia patients are presented. All patients showed neurogenic abnormalities that were more pronounced in the sacral than in the lumbar myotomes with a rather patchy distribution pattern. We propose that, in addition to skin punch biopsies to assess small fiber neuropathy, assessment of the anal reflex may be a useful part of the diagnostic pathway in patients with fibromyalgia.

Prevalence of denervation in the intrinsic foot muscles in patients with distal predominantly small fiber neuropathy

BACKGROUND

We aimed to evaluate the significance of electromyographic findings in the intrinsic foot muscles (IFMs) of patients with skin biopsy proven small fiber neuropathy (SFN).

METHODS

This was a single-center retrospective analysis of patients who underwent skin biopsy for intra-epidermal nerve fiber density (IENFD) measurement and electrodiagnostic (EDX) study for evaluation of polyneuropathy.

RESULTS

A total of 1416 patents with normal lower extremity EDX studies proximal to the foot were included. Active denervation was seen in 16.1% of IFMs in patients with skin biopsy proven SFN and 4.1% of patients without SFN (P < .0001). Reinnervation changes without active denervation were observed in 30.4% of SFN patients and 23.8% of patients without SFN (P = .01). IENFD was lower in SFN patients with active denervation in IFMs than without (P < .0001).

CONCLUSIONS

Evaluation of active denervation in the IFMs can reveal large fiber dysfunction in SFN patients with otherwise normal routine EDX findings.

Average proportional consecutive interval difference accurately differentiates spontaneous activity from motor unit potentials

INTRODUCTION

An objective method is required to detect spontaneous activity (SA) for prevalence studies in needle electromyography (EMG). Because of frequent similarities in the morphology of SA and motor unit potentials (MUP), identification of SA depends on assessment of firing regularity, which has not yet been quantitated through a modern interface.

METHODS

Prospective recordings obtained from patients referred for electrodiagnostic evaluation were analyzed by using decomposition-based quantitative EMG (DQEMG) customized to calculate descriptive statistics.

RESULTS

Forty-four MUP recordings (39 participants) and 80 SA recordings (62 participants) were analyzed. One hundred one of 124 recordings successfully interfaced with DQEMG. The remaining recordings were analyzed in Audacity. Average proportional consecutive interval differences differentiated SA from MUPs with 97.5% sensitivity (confidence interval [CI] 91.3%-99.7%) and 100.0% specificity (CI 92%-100%). There was substantial overlap, however, for SD and mean consecutive differences.

DISCUSSION

Average proportional consecutive interval difference accurately differentiates SA from MUPs and may be useful in future prevalence studies of SA.

Longtime Neurologic Outcome of Extracorporeal Membrane Oxygenation and Non Extracorporeal Membrane Oxygenation Acute Respiratory Distress Syndrome Survivors

Neurologic complications following acute respiratory distress syndrome (ARDS) are well described, however, information on the neurologic outcome regarding peripheral nervous system complications in critically ill ARDS patients, especially those who received extracorporeal membrane oxygenation (ECMO) are lacking. In this prospective observational study 28 ARDS patients who survived after ECMO or conventional nonECMO treatment were examined for neurological findings. Nine patients had findings related to cranial nerve innervation, which differed between ECMO and nonECMO patients (p = 0.031). ECMO patients had severely increased patella tendon reflex (PTR) reflex levels (p = 0.027 vs. p = 0.125) as well as gastrocnemius tendon reflex (GTR) (p = 0.041 right, p = 0.149 left) were affected on the right, but not on the left side presumably associated with ECMO cannulation. Paresis (14.3% of patients) was only found in the ECMO group (p = 0.067). Paresthesia was frequent (nonECMO 53.8%, ECMO 62.5%; p = 0.064), in nonECMO most frequently due to initial trauma and polyneuropathy, in the ECMO group mainly due to impairments of N. cutaneus femoris lateralis (4 vs. 0; p = 0.031). Besides well-known central neurologic complications, more subtle complications were detected by thorough clinical examination. These findings are sufficient to hamper activities of daily living and impair quality of life and psychological health and are presumably directly related to ECMO therapy.

Role of sonography in the diagnosis and treatment of a ganglion cyst compressing the lateral branch of deep peroneal nerve

Selective compression neuropathy of the lateral branch of the deep peroneal nerve is rare. A 55-year-old woman with ankle instability and mild weakness of extension of the toes was examined with sonography (US), which revealed the presence of a ganglion cyst compressing selectively the lateral branch of the deep peroneal nerve. US-guided aspiration of the cyst resulted in nerve decompression and progressive resolution of symptoms. This case demonstrates the importance of examining the deep peroneal nerve and its branches when performing US in the clinical setting of ankle instability. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound 45:108-111, 2017.

Idiopathic pes cavus in adults is not associated with neurophysiological impairment in the lower limbs

The nerve conduction characteristics of adults with idiopathic pes cavus/hammer toes have not been studied extensively. Among 2048 out-patients (59.5 ± 13.9 years) referring to a laboratory of Neurophysiology in Rome, we recruited 18 patients with idiopathic pes cavus (61.3 ± 12.5 years). Fifty-four age/sex-matched controls were also studied. No nerve conduction differences were observed between patients with and without cavus foot (p > 0.05). The absence of deep tendon reflexes and slight muscle weakness and hypotrophy in the lower limbs were more common in subjects with cavus foot deformity than in controls (p < 0.001). Adult patients with idiopathic pes cavus/hammer toes do not differ from healthy controls from a neurophysiological standpoint, but they could show minor signs of clinical impairment, such as lower limb weakness, hypotrophy and areflexia.

Anterior tarsal tunnel syndrome: a misunderstood and a misleading entrapment neuropathy

Anterior tarsal tunnel syndrome (ATTS) is a rare entrapment neuropathy of the deep peroneal nerve beneath the extensor retinaculum on the top of the ankle. ATTS is often asymptomatic or olygosymptomatic. There are few reports describing the ATTS. We describe the clinical and electrophysiological features of 85 patients with unilateral or bilateral ATTS prospectively collected between January 2000 and December 2010 in our laboratory of Clinical Neurophysiology. This entrapment neuropathy remains poorly diagnosed and it might be misleading when performing a diagnostic EMG-ENG examination for suspected polyneuropathy or lumbosacral radiculopathy.

Contribution of QSART to the diagnosis of small fiber neuropathy

INTRODUCTION

We evaluated incorporation of the quantitative sudomotor axon reflex test (QSART) into the diagnostic criteria for small fiber neuropathy (SFN) as an addition to quantitative sensory testing (QST) and intraepidermal nerve fiber density (IENFD) testing.

METHODS

One hundred one patients with clinically suspected SFN underwent QSART, QST, and skin biopsy. The diagnostic yield of existing SFN criteria in these patients was compared with criteria incorporating QSART. The new combined diagnostic criteria were evaluated.

RESULTS

SFN was diagnosed in 38 of the 101 patients (38%) using current criteria. Addition of QSART existing SFN criteria resulted in an increased diagnostic yield to 67 patients (66%). Applying new SFN criteria requiring abnormality in at least 2 assessments among QSART, QST, and IENFD resulted in a diagnosis of SFN in 57 patients (56%).

CONCLUSION

Assessment of both somatic and peripheral autonomic small nerve fibers enhances diagnostic criteria for SFN.

Electrodiagnostics and clinical correlates in acquired polyneuropathies

Peripheral neuropathies result from a variety of inherited and acquired pathologies. They display an assortment of clinical signs and symptoms and present with a broad range of severity. Electrodiagnosis can play a key role in the evaluation of a suspected peripheral neuropathy. A peripheral nerve disorder is first suspected on the basis of history and physical examination findings. Electrodiagnosis is then used to confirm the diagnosis and to characterize the peripheral neuropathy, providing information about its distribution, pathophysiologic process (demyelinating vs axonal), and chronicity.

Evaluating the patient with suspected radiculopathy

Persons with back, neck, and limb symptoms are commonly seen by health care providers. They constitute a major referral population to specialists in electrodiagnostic medicine. The evaluation of these patients involves consideration of both the common and less common disorders. The electrodiagnostic examination with needle electromyography is the most important means of testing for radiculopathy. This test has modest sensitivity but high specificity. It complements imaging of the spine. Electromyography in combination with nerve conduction testing is valuable in excluding entrapment neuropathies and polyneuropathy, conditions that frequently mimic radicular symptoms. A streamlined examination with 6 muscles, 1 of which is the paraspinal, has a high diagnostic yield, yet minimizes patient discomfort and examiner time. This article presents an overview of the electrodiagnostic evaluation for patients with suspected radiculopathy.

Electrodiagnosis of lumbar radiculopathy

The evaluation of patients with suspected lumbar radiculopathy is one of the most common reasons patients are referred for electrodiagnostic testing. The utility of this study depends on the expertise of the physician who plans, performs, and completes the study. This article reviews the strengths and weaknesses of electrodiagnosis to make this diagnosis, as well as the clinical reasoning of appropriate study planning. The current use of electrodiagnostic testing to determine prognosis and treatment outcomes is also discussed.

Pitfalls in using electrophysiological studies to diagnose neuromuscular disorders

Electrodiagnostic testing is used widely for the full characterization of neuromuscular disorders and for providing unique information on the processes underlying the pathology of peripheral nerves and muscles. However, such testing should be considered as an extension of anamnesis and physical examination, not as pathognomonic of a specific disease entity. There are many pitfalls that could lead to erroneous interpretation of electrophysiological study results when the studies are not performed properly or if they are performed in the presence of anatomical aberrations. The diagnostic reliability of electrodiagnostic studies can be improved and the associated pitfalls overcome if the physician is familiar with all of those possible pitfalls. In this article we discuss the most common and important pitfalls associated with electrodiagnostic medicine.

Spontaneous high-frequency action potential

Action potential, which is the foundation of physiology and electrophysiology, is most vital in physiological research. This work starts by detecting cardiac electrophysiology (tachyarrhythmias), combined with all spontaneous discharge phenomena in vivo such as wound currents and spontaneous neuropathic pain, elaborates from generation, induction, initiation, to all of the features of spontaneous high-frequency action potential-SSL action potential mechanism, i.e., connecting-end hyperpolarization initiates spontaneous depolarization and action potential in somatic membrane. This work resolves the conundrums of in vivo spontaneous discharge in tachyarrhythmias, wounds, denervation supersensitivity, neurogenic pain (hyperalgesia and allodynia), epileptic discharge and diabetic pain in pathophysiological and clinical researches that have puzzled people for a hundred years.

The utility of lumbar paraspinal mapping in the diagnosis of lumbar spinal stenosis

OBJECTIVE

The aim of this prospective, blinded and controlled study is to evaluate the utility of lumbar paraspinal mapping in the diagnosis of lumbar spinal stenosis.

DESIGN

The subjects were assessed and allocated into three groups according to clinical and radiologic features with a standardized assessment protocol. These three groups were clinical and radiologic lumbar spinal stenosis, radiologic lumbar spinal stenosis, and the control group. The measurements of magnetic resonance imaging studies were performed by a blinded radiologist. An electromyographer who was masked to patients' data performed all the nerve conduction tests, lower-limb needle electromyography, and lumbar paraspinal mapping. The relations of clinical, radiologic, and electrophysiologic findings were investigated.

RESULTS

Sixty-two patients were enrolled in the study. Two patients were eliminated because electrophysiologic studies showed polyneuropathy. There were 28, 16, and 16 patients in clinical and radiologic lumbar spinal stenosis, radiologic lumbar spinal stenosis, and control groups, respectively. In the clinical and radiologic lumbar spinal stenosis group, the findings of limb needle electromyography were inconsistent with 50% acute and 46.4% chronic radiculopathy. However, the paraspinal mapping showed that there were fibrillation potentials and positive sharp waves in at least two levels in 92.8% of the patients in clinical and radiologic lumbar spinal stenosis. The mean total paraspinal mapping score was 33.64 ± 21.17, which was significantly higher than the radiologic lumbar spinal stenosis and control groups. In the radiologic lumbar spinal stenosis group, the findings of paraspinal mapping were normal in 93.8% of the patients. Paraspinal mapping technique was found to be better correlated to the clinical findings than magnetic resonance imaging in asymptomatic patients. In the control group, 6 of 14 patients had high total paraspinal mapping scores (range, 0-9). Those patients with higher paraspinal mapping scores in the control group were mostly diagnosed with acute monoradiculopathy caused by disc herniation.

CONCLUSIONS

Paraspinal mapping technique is a sensitive method in the diagnosis of lumbar spinal stenosis and reflects physiology of nerve roots better than the limb electromyography.

A prospective, masked 18-month minimum follow-up on neurophysiologic changes in persons with spinal stenosis, low back pain, and no symptoms

OBJECTIVES

To describe neurophysiologic changes over time in persons with and without spinal complaints and to assess whether paraspinal denervation predicts change in stenosis on magnetic resonance imaging (MRI) and clinical course.

DESIGN

Prospective, controlled, masked trial.

SETTING

University spine program.

PARTICIPANTS

Persons aged 55 to 80 years, screened for polyneuropathy and determined on clinical examination to have spinal stenosis, mechanical low back pain, or no spinal symptoms.

INTERVENTIONS

A comprehensive codified history was obtained and subjects underwent physical examination, ambulation testing, masked electrodiagnostic testing including paraspinal mapping, and MRI, repeated at greater than 18 months. This study presents detailed technical information and additional analyses not reported previously.

MAIN OUTCOME MEASUREMENTS

Change in electrodiagnostic findings. Among persons with clinical stenosis, relationship of change in paraspinal mapping scores to MRI findings and clinical changes.

RESULTS

Of 149 initial subjects, 83 (79.3% of eligible subjects) repeated testing at 20 (+/-2 SDs) months. No significant change in limb muscle spontaneous activity or motor unit pathology was noted in any group. In 23 persons with initial diagnosis of stenosis, paraspinal mapping electromyography related to change in diagnosis over time (analysis of variance F = 3.77, P = .037), but not to most initial magnetic resonance imaging measurements or to change in spinal canal diameter.

CONCLUSIONS

Clinical spinal stenosis is neurophysiologically stable in most persons. Paraspinal electromyographic changes reflect large changes in clinical course, but neither neurophysiologic nor clinical changes relate to change in spinal geometry over 20 months.

Clinical importance of the lateral branch of the deep peroneal nerve

Persistent recalcitrant dorsolateral foot pain after ankle sprain cannot always be explained by known anatomic nerve pathways. To determine whether an impingement of a lateral branch of the deep peroneal nerve might be responsible for atypical pain, we conducted a cadaveric anatomic study to identify the anatomy and course of the nerve. Furthermore, using this information, we conducted a clinical study to determine if targeted treatment to a lateral branch of the deep peroneal nerve would resolve these symptoms. We dissected 22 cadaveric feet to identify a large lateral branch of the deep peroneal nerve. This nerve arborized into five main branches. We identified two areas of compression in the lateral branch of the deep peroneal nerve. We also performed a prospective clinical study including 11 consecutive patients with a 1-year minimum followup. Pain and clinical findings corresponded to the anatomic compression sites in all 11 patients. All patients responded to a local anesthetic injection or surgical release of the lateral branch of the deep peroneal nerve. We identified a previously unreported complex course of the lateral branch of the deep peroneal nerve that correlated with clinical impingement syndrome and responded to specifically targeted treatment.

Needle EMG has a lower false positive rate than MRI in asymptomatic older adults being evaluated for lumbar spinal stenosis

OBJECTIVE

False positive imaging tests--disk herniation or spinal stenosis--occur in a significant number of asymptomatic persons, increasing with age. A similar or greater prevalence probably occurs in people who present to physicians with mechanical back pain, potentially causing therapeutic misadventure. Electrodiagnostic testing may be normal in persons with asymptomatic pathology, but has not been directly tested.

METHODS

As part of a larger study of older persons with lumbar stenosis, 35 asymptomatic adults were evaluated by an extensive questionnaire, codified history and physical examination, masked electrodiagnostic testing, and masked lumbar magnetic resonance imaging, with repeated procedure at 18 months. Thirty-two subjects remained after removal of three with neuromuscular disease.

RESULTS

The radiologist characterized 18 (56%) asymptomatic subjects as having spinal stenosis. There was no relationship between electrodiagnostician diagnosis and radiologist diagnoses. Among the 13 whom the electrodiagnostician identified as abnormal, 2 had technical data within normal limits and the only abnormality in 5 was >2/10 polyphasic motor units (considered a 'soft' finding by many). One muscle in 1 subject had abnormal spontaneous activity, and 3 persons scored >4 on paraspinal mapping. Electrodiagnostic findings were normal in the 5 (16%) who had disk herniations. None of the 22 re-examined acquired symptoms over 18 months and follow-up electrodiagnosis was essentially normal (one muscle in 1 subject had 3/10 polyphasic motor units).

CONCLUSIONS

MRI changes, motor unit changes on EMG needle examination, and low paraspinal mapping scores are not uncommon in asymptomatic older adults with spinal stenosis or disk herniation and may lead to false positive tests. The stricter criterion of abnormal spontaneous activity on needle examination and paraspinal mapping scores greater than 6 offered in this paper lowers the risk of false positive EMG testing.

SIGNIFICANCE

EMG is less likely to be abnormal (false positive) in asymptomatic adults than MRI.

Cervical paraspinal electromyography: normal values in 100 control subjects

The normal electromyographic values and the significance of spontaneous activity, when examining the cervical paraspinal muscles, has been studied rarely, and there are very few studies concerning this issue. To obtain muscle unit potential (MUP) reference values for cervical paraspinal muscles, we examined 100 volunteers. Spontaneous activity and the analysis of 20 MUPs in every individual were checked by the automated MUP analysis program. In those individuals ages 20 to 40 years, no spontaneous activity was observed, and in the ones ages 40 to 60 years and 60 years or older, fibrillations and/or positive sharp waves were seen in 8% and 92%, respectively. MUP values were found to be close to those of upper limb muscles. Age has no significant effect on MUP values, except for mean amplitude that was increased in individuals ages 60 to 80 years.Our findings suggest that fibrillations and positive sharp waves do not have much electrodiagnostic value in the study of cervical paraspinal muscles of middle-aged and elderly subjects, when it is an isolated finding, and there is a need for an extended electromyographic examination, including other muscles, to exclude radiculopathy. Automated MUP analysis is easily performed, and our results may serve as reference values.

Axon loss is an important determinant of weakness in multifocal motor neuropathy

BACKGROUND

Multifocal motor neuropathy (MMN) is characterised by asymmetrical weakness and muscle atrophy, in the arms more than the legs, without sensory loss. Despite a beneficial response to treatment with intravenous immunoglobulins (IVIg), weakness is slowly progressive. Histopathological studies in MMN revealed features of demyelination and axon loss. It is unknown to what extent demyelination and axon loss contribute to weakness. Unlike demyelination, axon loss has not been studied systematically in MMN. Aims/

METHODS

To assess the independent determinants of weakness in MMN, 20 patients with MMN on IVIg treatment were investigated. Using a standardised examination in each patient, muscle strength was determined in 10 muscles. In the innervating nerve of each muscle, axon loss was assessed by concentric needle electromyography, and conduction block or demyelinative slowing by motor nerve conduction studies. Multivariate analysis was used to assess independent determinants of weakness.

RESULTS

Needle electromyography abnormalities compatible with axon loss were found in 61% of all muscles. Axon loss, and not conduction block or demyelinative slowing, was the most significant independent determinant of weakness in corresponding muscles. Furthermore, axon loss and conduction block were independently associated with each other.

CONCLUSION

Axon loss occurs frequently in MMN and pathogenic mechanisms leading to axonal degeneration may play an important role in the outcome of the neurological deficit in patients with MMN. Therapeutic strategies aimed at prevention and reduction of axon loss, such as early initiation of treatment or additional (neuroprotective) agents, should be considered in the treatment of patients with MMN.

Cervical paraspinal spontaneous activity in asymptomatic subjects

Paraspinal fibrillation potentials or positive sharp waves (PSWs) reportedly may be the only electrodiagnostic abnormality in patients with radiculopathies. However, spontaneous activity may be present in muscles of asymptomatic subjects. To determine whether abnormal spontaneous activity in the cervical paraspinal muscles is clinically relevant, we evaluated the prevalence of such activity in asymptomatic individuals and examined its relationship with age. Sixty-six asymptomatic subjects underwent a needle electromyographic examination of the paraspinal muscles bilaterally at the C5/6 and C6/7 levels. All of the recorded potentials were captured and their firing rates and waveforms were evaluated. The potentials were considered to be abnormal if reproducible trains of PSWs or fibrillation potentials were present. Eight of the 66 (12%) subjects showed PSWs, five bilaterally; none showed fibrillation potentials. A statistical analysis for the effect of age could not be performed due to the small sample size. Because electromyographic cervical paraspinal abnormalities can be found in asymptomatic subjects, caution should be exercised when attributing the etiology of neck pain to radiculopathy if the only electrodiagnostic findings are electromyographic cervical paraspinal abnormalities.

Electromyographic technique for lumbar multifidus examination: comparison of previous techniques used to localize the multifidus

OBJECTIVES

To verify and compare established techniques for needle localization in the multifidus muscle and to explore more practical techniques.

DESIGN

Human cadaver study.

SETTING

Anatomy laboratory in a university setting.

CADAVERS

Six fresh human cadavers.

INTERVENTION

A 22-gauge needle was inserted into the multifidus muscle fascicle of 6 cadavers using 2 different techniques described previously in the electrodiagnostic literature by Haig and Stein and colleagues. A mixture of colored latex and contrast dyes (0.1 mL) was injected bilaterally into each fascicle at levels L1 to L5. Two electromyographers performed injections into 60 targeted muscles, affording 120 total insertions. Separate investigators dissected the muscles to determine dye position.

MAIN OUTCOME MEASURES

Not applicable.

RESULTS

A total of 88 (73%) and 79 (66%) injections were successfully delivered to the targeted multifidus muscles using the Haig and the Stein techniques, respectively. With the Haig method, 22 injections (18%) were delivered to different superficial muscles. With the Stein method, 24 injections were delivered to a common tendon and 3 injections were delivered to the spinal canal.

CONCLUSIONS

This study highlights the nonoptimizing accuracy of previous techniques for multifidus needle electromyography. A modified Haig method involving less acute needle angulation relative to the skin surface and closer insertion from the midline may increase accuracy and safety.

Paraspinal electromyography: age-correlated normative values in asymptomatic subjects

STUDY DESIGN

Cross-sectional study.

OBJECTIVES

To determine if the amount of lumbar paraspinal denervation increases with age and present normative data on the amount of denervation present in asymptomatic subjects.

SUMMARY OF BACKGROUND DATA

To our knowledge, there are no data on the relationship of paraspinal denervation with age or normative data on the amount of denervation expected in asymptomatic older adults.

METHODS

We combined the data from our current study of asymptomatic adults, age 55-79 years, and a previous study of asymptomatic adults, age 18-58 years, who underwent lumbar paraspinal muscle needle electromyography using a validated needle electromyography (MiniPM) technique. We then compared the results of the age group 55-79 to that of the age group 18-54.

RESULTS

The older group scored significantly higher than the younger group by 1.7 (P = 0.008, 95% confidence interval 0.5-3.0). Linear regression showed that age was a significant predictor of the MiniPM score (beta = 0.04, and P = 0.04). For subjects 55 years and older, mean MiniPM score on one side was 2.3 (standard deviation 3.6). The upper range of the 95th percentile was 10.

CONCLUSIONS

The amount of lumbar paraspinal muscle denervation does increase with age. Understanding the range of findings in asymptomatic subjects will help us interpret lumbar paraspinal needle electromyography findings in patients with spinal disorders.

Paraspinal Electromyography That Compares Concentric with Monopolar Needles

OBJECTIVE

To establish interrater reliability for paraspinal muscle needle electromyography study with both monopolar and concentric needles in symptomatic and asymptomatic persons and to further establish normative data for paraspinal needle study.

DESIGN

At a university spine center, participants with and without radiating low back pain were evaluated with the mini-paraspinal mapping paraspinal needle technique by an unblinded and a blinded electromyographer.

RESULTS

In the symptomatic group, the intraclass correlation coefficient between concentric and monopolar needles was 0.793; between monopolar needles, it was 0.876; and between concentric needles, it was 0.966. In the asymptomatic group, the mean total score was 0.25.

CONCLUSIONS

The good interrater reliability with the same needle type helps support the validity of the needle electromyography study of the paraspinal muscles. The good correlation between the concentric and monopolar needles shows the data published using monopolar needle data also apply to studies using paraspinal needle electromyography with concentric needles. The low score with the asymptomatic group reaffirms that using a cutoff score of >2 as abnormal has a false-positive rate of <5%.

Needle EMG of abductor hallucis and peroneus tertius in normal subjects

Normal values for standard concentric-needle electromyography (EMG) of the abductor hallucis (AH) and peroneus tertius (PT) muscles have not been established to date, yet both are potentially useful muscles in the diagnosis of length-dependent peripheral nerve disorders. Forty-three normal asymptomatic subjects stratified by age underwent a standard set of nerve conduction studies and concentric-needle examination to exclude asymptomatic disease and develop normal values for the AH and the PT for various EMG parameters. Fibrillation potentials were observed in the AH in 21% of normal subjects (10% < 60 years old, 30% > 60 years old); 19% of subjects were unable to voluntarily activate the AH. All subjects could activate the PT regardless of age. No fibrillation potentials were observed in subjects < 60 years of age, whereas 9% of those older than 60 years had mild fibrillation potentials in the PT. The PT is a useful muscle in the evaluation of length-dependent peripheral neuropathy and other peripheral nerve disorders of the lower extremities, on the basis of ease of motor unit potential activation and analysis, and relative infrequency of fibrillation potentials in normal subjects.

Electrodiagnostic approach to patients with weakness

Electrodiagnosis has a key role in the evaluation of patients presenting with weakness. The electrodiagnostician should maintain a broad inclusive differential diagnosis and tailor the examination using a sound conceptual framework. A clear understanding of what is normal provides the proper foundation upon which to judge electrodiagnostic findings. Many peripheral neuromuscular conditions manifest themselves in characteristic ways on NEE and nerve conduction testing, making them identifiable to the skilled electrodiagnostic medicine consultant.

Electrodiagnostic challenges in the evaluation of lumbar spinal stenosis

Taken together, the most common electromyographic finding in lumbar spinal stenosis is bilateral multilevel radiculopathy. The sensitivity of electrodiagnostic testing for radiculopathy is difficult to quantify because there is no criterion standard. Differentiating peripheral neuropathy and lumbar spinal stenosis on electromyography and routine nerve-conduction studies can be clinically challenging, especially when the two entities may be present simultaneously in older patients.

Influence of age of horse on results of quantitative electromyographic needle examination of skeletal muscles in Dutch Warmblood horses

OBJECTIVE

To determine the influence of age on results of quantitative analysis of electromyographic (EMG) needle examination in the subclavian, triceps, and lateral vastus muscles of Dutch Warmblood horses.

ANIMALS

7 healthy young Dutch Warmblood horses (range, 13 to 18 months old), 7 healthy adult Dutch Warmblood horses (range, 4 to 10 years old), and 7 healthy elderly Dutch Warmblood horses (range, 18 to 21 years old).

PROCEDURE

An EMG needle examination was performed to evaluate insertional activity, spontaneous activity, and motor unit action potential (MUAP) variables. Although all horses were conscious, young horses were sedated prior to examination.

RESULTS

Mean insertional activity in young horses was significantly lower than in elderly horses. Pathologic spontaneous activity was rarely found in young and adult horses but was frequently evident in all muscles in all elderly horses. The MUAP duration and amplitude were significantly lower in all muscles of young horses, compared with values for adult and elderly horses. The MUAP duration and number of phases and turns were significantly lower in adult horses than in elderly horses. Group differences for percentages of polyphasic and complex MUAPs were also found. The 95% confidence intervals for MUAP duration, MUAP amplitude, and number of phases and turns for the subclavian, triceps, and lateral vastus muscles were significantly lower in young horses than in adult or elderly horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Age of the horse being examined should be considered when EMG examination is performed.

Paraspinal denervation and the spinal degenerative cascade

BACKGROUND CONTEXT

The aging of the spine has been reported to follow a degenerative cascade described by Kirkaldy-Willis. This cascade does not take into account the paraspinal muscles. Substantial recent knowledge of the anatomy, physiology and pathophysiology of the paraspinal muscles suggests that they should play a role in the degenerative cascade. Pain relates to paraspinal denervation in a number of disorders. Using new needle electromyographic technique, MiniPM, we may be able to quantify the extent of paraspinal muscle denervation.

PURPOSE

To explore the potential interactions between paraspinal muscle denervation and the degenerative cascade.

STUDY DESIGN

Literature review, reanalysis of a blinded electromyographic study and case reports.

PATIENT SAMPLE

A previously reported group of 35 asymptomatic paid volunteers, ages 18 to 58 years. Two elderly volunteers with moderate to severe spinal stenosis on magnetic resonance imaging (MRI), one significantly disabled, one asymptomatic.

OUTCOME MEASURES

Blinded electromyographic testing, including MiniPM, a codified, quantified needle electromyography technique for the paraspinal muscles. In the two case reports, magnetic resonance imaging and 15-minute timed ambulation.

METHODS

The 35 volunteers were tested by a blinded electromyographer using the MiniPM technique. The two older subjects underwent MRI, MiniPM and extensive electrodiagnostic evaluations, functional testing, complete history and physical examination.

RESULTS

The patient with symptomatic stenosis had a MiniPM score of 6 on each side, and the asymptomatic volunteer had a score of 0. In the asymptomatic subject group, reproducible evidence for denervation was found in 20 subjects (57%), sparsely distributed, but more caudal than cranial (p<.0001). Based on conservative estimates of nerve regeneration rates, the population averaged a detected axonotemesis denervating event approximately once every 120 days.

CONCLUSIONS

Paraspinal denervation may be proven to be a better marker than MRI findings for symptomatic spinal stenosis. Subtle paraspinal muscle denervation occurs frequently in asymptomatic persons. Whether a cause or an effect, paraspinal denervation might lead to hypermobility and thus progression along the degenerative cascade.

Electrodiagnostic approach to patients with suspected radiculopathy

This article reviews the electrodiagnostic testing for persons suspected of having radiculopathies and the expected sensitivities that different testing modalities provide. One cannot minimize the importance of the clinical evaluation and differential diagnosis formulation by the electrodiagnostician to guide testing. The needle EMG examination is the most useful electrodiagnostic test but is limited in sensitivity. Electromyographic screening examinations using six muscles are possible that optimize identification yet minimize patient discomfort. Electrodiagnostic findings must be interpreted relative to the patient's clinical presentation, and the consultant should tailor the electrodiagnostic study to the clinical situation.

Electrophysiology of radiculopathies

The anatomy, pathophysiology, and clinical evaluation of radiculopathies are discussed. Defining whether root injury is present and which roots are involved can be difficult but critical for patient management. In conjunction with clinical and radiological information, studies that establish physiological abnormalities of roots should be helpful and important. Clinical neurophysiological studies for radiculopathies are performed frequently but have yet to achieve a universally accepted role in the evaluation of these patients. Electrophysiological techniques for the evaluation of radiculopathies are reviewed. Needle electromyography is the best established of these procedures but has the disadvantage of requiring injury to motor fibers of both a certain degree and distribution. Nerve conduction studies may rarely be abnormal in radiculopathies but are needed to be certain other conditions that may produce similar symptoms and signs are not present. H reflexes and F waves probably have roles in the evaluation of radiculopathies but published reports about F waves in radiculopathies have been marred by inadequate methodology. There is evidence based on large series of patients that somatosensory evoked potentials can be helpful for evaluating patients with multilevel injury such as spinal stenosis, patients where electrophysiological studies may have their greatest clinical utility. Further work using either electrical stimulation with needles or magnetic stimulation of roots seems warranted. The demonstration of meaningful electrophysiological changes with activities that reproduce radicular symptoms may be a promising experimental approach. Available information does not necessarily answer critical questions about the role of electrophysiology in patients with radiculopathies. This cannot be done using analyses based on current ideas about evidence based medicine given the absence of a 'gold standard' for defining radiculopathies as well the absence of blinded studies. The available information provides strong arguments for further investigations evaluating different clinical neurophysiological techniques in the same patient, and for evaluating the value of these techniques by concentrating on their clinical import.