Dynamic F waves in neurogenic claudication

Evaluation of dynamic F wave parameters before and after physical activity in normal population

Objectives

F wave is one of the nerve conduction studies, mainly used to study the proximal pathway of peripheral nerves. One of its applications is dynamic assessment, i.e., before and after physical activity, when symptoms develop in some patients. Best to our knowledge, few studies evaluate normal dynamic F wave values in healthy individuals. This study aims to determine and compare normal values of several parameters of Compound Muscle Action Potential (CMAP) and F waves of tibial nerves dynamically before and after physical activity in the lower extremities of 34 normal subjects. These parameters were recorded before and after 15 min of continuous walking at intervals of 1, 5, and 10 min after the end of physical activity.

Results

Normal values of CMAP onset latency and amplitude, minimum, maximum, and mean latency of 10 F waves, F chronodispersion, and F persistence were dynamically collected before and during 10 min after physical activity in three phases. Some of the parameters showed significant changes (P < 0.05). Although physical activity showed statistically significant effects on some CMAP and F wave parameters (especially F chronodispersion) in normal subjects, none of them exceeded the normal clinical values introduced in the literature.

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

Persons with back, neck, and limb symptoms constitute a major referral population to specialists in electrodiagnostic (EDX) medicine. The evaluation of these patients involves consideration of both the common and less common disorders. The EDX examination with needle electromyography (EMG) is the most important means of testing for radiculopathy. This test has modest sensitivity but high specificity and well complements imaging of the spine. Needle EMG in combination with nerve conduction testing is valuable in excluding entrapment neuropathies and polyneuropathy-conditions that frequently mimic radicular symptoms. In this first of a two-part review, the optimal EDX evaluation of persons with suspected radiculopathy is presented. In part two, the implications of EDX findings for diagnosis and clinical management of persons with radiculopathy are reviewed.

Unilateral repetitive tibial nerve stimulation improves neurogenic claudication and bilateral F-wave conduction in central lumbar spinal stenosis

BACKGROUND

Repetitive electrical nerve stimulation of the lower limb may improve neurogenic claudication in patients with lumbar spinal stenosis (LSS) as originally described by Tamaki et al. We tested if this neuromodulation technique affects the F-wave conduction on both sides to explore the underlying physiologic mechanisms.

METHODS

We studied a total of 26 LSS patients, assigning 16 to a study group receiving repetitive tibial nerve stimulation at the ankle (RTNS) on one leg, and 10 to a group without RTNS. RTNS conditioning consisted of a 0.3-ms duration square-wave pulse with an intensity 20% above the motor threshold, delivered at a rate of 5 Hz for 5 min. All patients underwent the walking test and the F-wave and M-wave studies for the tibial nerve on both sides twice; once as the baseline, and once after either the 5-min RTNS or 5-min rest.

RESULTS

Compared to the baselines, a 5-min RTNS increased claudication distance (176 ± 96 m vs 329 ± 133 m; p = 0.0004) and slightly but significantly shortened F-wave minimal onset latency (i.e., increased F-wave conduction velocity) not only on the side receiving RTNS (50.7 ± 4.0 ms vs 49.2 ± 4.2 ms; p = 0.00081) but also on the contralateral side (50.1 ± 4.6 ms vs 47.9 ± 4.2 ms; p = 0.011). A 5-min rest in the group not receiving RTNS neither had a significant change on claudication distance nor on any F-wave measurements. The M response remained unchanged in both groups.

CONCLUSIONS

The present study verified a beneficial effect of unilaterally applied RTNS of a mild intensity on neurogenic claudication and bilateral F-wave conduction. Our F-wave data suggest that this type of neuromodulation could be best explained by an RTNS-induced widespread sympathetic tone reduction with vasodilation, which partially counters a walking-induced further decline in nerve blood flow in LSS patients who already have ischemic cauda equina.

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.

Motor conduction time along the cauda equina in patients with lumbar spinal stenosis

STUDY DESIGN

Magnetic lumbar stimulation was used to detect spinal nerve degeneration in patients with lumbar spinal stenosis (LSS).

OBJECTIVE

To evaluate delays in the motor conduction time in the cauda equina of patients with LSS.

SUMMARY OF BACKGROUND DATA

Previous studies suggested a bilateral slowing of motor conduction in the cauda equina in LSS. Among several methods, only magnetic stimulation is sufficiently sensitive for detecting potential degeneration in LSS. A recent study demonstrated the direct calculation of the cauda equina motor conduction time using magnetic stimulation at proximal and distal sites of the cauda equina. We used this technique to determine potential degeneration in patients with LSS.

METHODS

Twenty adult subjects and 15 patients with LSS were investigated. Lumbosacral roots were stimulated at intervertebral levels L1-L2 and L5-S1 by magnetic coil stimulation. The muscle responses to stimulation were recorded from the gastrocnemius-soleus, and anterior tibialis muscles on both sides with bipolar surface electrodes. The response latency from stimulations at the L5 spine level were subtracted from those at the L1 level on the same side. This value represented the conduction time from the proximal to distal ends of the cauda equina.

RESULTS

The mean conduction time along the cauda equina was significantly prolonged in patients with LSS compared with controls. The mean cauda equina motor conduction time was 1.97 +/- 0.67 milliseconds in controls and 3.57 +/- 2.22 milliseconds in patients with LSS (P = 0.00).

CONCLUSION

Determining the motor conduction time along the cauda equina using L1 and L5 magnetic stimulation provides an effective alternative method for evaluating the lumbar motor roots in patients with LSS.

Alterations of F wave parameters after exercise in symptomatic lumbar spinal stenosis

OBJECTIVES

The purpose of the study is to investigate changes in F wave parameters after exercise in subjects with symptomatic lumbar spinal stenosis.

DESIGN

A total of 19 older patients with lumbar spinal stenosis and neurogenic claudication participated in this cohort study. No one withdrew for adverse effects. All subjects underwent physical therapy, with half performing additional interval-walking exercises. Groups were treated for eight sessions, returning for follow-up at weeks 4 and 8. Changes in F wave indices--minimal latency, chronodispersion, and persistence--were calculated. The treatment group demonstrated worsening of F wave persistence at 8-wk follow-up (P < 0.01).

CONCLUSIONS

F wave indices worsened after an interval-walking exercise program. Subjects in the treatment group demonstrated worsening of F wave persistence at 8-wk follow-up.

Lumbar spinal stenosis: Assessment of cauda equina involvement by electrophysiological recordings

The objective of this study was to investigate the relationship between electrophysiological recordings and clinical as well as radiological findings in patients suggestive to suffer from a lumbar spinal stenosis (LSS). We hypothesise that the electrophysiological recordings, especially SSEP, indicate a lumbar nerve involvement that is complementary to the neurological examination and can provide confirmatory information in less obvious clinical cases. In a prospective cohort study, 54 patients scheduled for surgery due to LSS were enrolled in an unmasked, uncontrolled trial. All patients were assessed by neurological examination, electrophysiological recordings, and magnetic resonance imaging (MRI) of the lumbar spine. The electrophysiological recordings focused on spinal lumbar nerve involvement.

RESULTS

About 88% suffered from a multisegmental LSS and 91% of patients respectively complained of chronic lower back pain and/or leg pain for more than 3 months, combined with a restriction in walking distance. The neurological examination revealed only a few patients with sensory and/or motor deficits while 87% of patients showed pathological electrophysiological recordings (abnormal tibial SSEP in 78% of patients, abnormal H-reflex in 52% of patients).

CONCLUSIONS

Whereas the clinical examination, even in severe LSS, showed no specific sensory-motor deficit, the electrophysiological recordings indicated that the majority of patients had a neurogenic disorder within the lumbar spine. By the pattern of bilateral pathological tibial SSEP and pathological reflexes associated with normal peripheral nerve conduction, LSS can be separated from a demyelinating polyneuropathy and mono-radiculopathy. The applied electrophysiological recordings, especially SSEP, can confirm a neurogenic claudication due to cauda equina involvement and help to differentiate neurogenic from vascular claudication or musculo-skeletal disorders of the lower limbs. Therefore, electro-physiological recordings provide additional information to the neurological examination when the clinical relevance of a radiologically-suspected LSS needs to be confirmed.

Dynamic F wave study in patients suffering from peripheral arterial occlusive disease

OBJECTIVE

To prospectively detect significant transient F wave abnormalities obtained after exercise in patients with peripheral arterial disease (PAD) and to assess the potential diagnostic sensitivity of dynamic F wave study in such a context.

PATIENTS AND METHODS

A series of 40 electrical stimuli were delivered to the peroneal and the posterior tibial nerves of 25 patients with PAD in order to obtain F waves at rest and post-exercise. The following variables were estimated and the obtained pre- and post-exercise data were compared: F persistence, F wave latency, amplitude, duration and F chronodispersion. For each nerve studied, the minimum, average and maximum values were calculated. Conventional electrophysiological data were also collected pre- and post-exercise and the data obtained were also compared. Twenty-five healthy age-, gender- and height-matched individuals served as controls.

RESULTS

No evidence of conventional nerve conduction abnormalities was recorded either pre- or post-exercise in the group of patients. As regards the peroneal nerve, the significantly reduced F wave persistence (P = 0.007) and maximum F wave amplitude post- as opposed to pre-exercise (P = 0.05)- were the main findings to emerge. The average (P = 0.017) and the minimum duration (P = 0.005) of tibial F waves were also significantly increased post- compared with pre-exercise. Insignificant differences were observed between pre- and post-exercise neurophysiological and F wave values in the group of controls.

CONCLUSION

Given the observed absence of conventional neurophysiological abnormalities, the detection of dynamic F wave changes supports the view of an increased diagnostic sensitivity of this method in patients with mild PAD.

Factors influencing F-wave latency detection of lumbosacral root lesions using a detection theory based model

OBJECTIVE

To evaluate the F-wave dilution hypothesis; which implies that absolute F-wave latencies obscure the much smaller delay associated with slow intra-lesion conduction, such is caused by nerve root compression in lumbosacral radiculopathy. A corollary objective is to determine how F-wave measurement and pathological factors influence diagnostic accuracy.

METHODS

An analytical model is developed based on signal detection theory and a number of simplifying assumptions. Diagnostic accuracy, quantified by the area under the receiver operating characteristic (ROC) curve, is determined for various model realizations derived from the clinical and experimental neurophysiology literature. A preliminary experimental validation of model predictions is also performed.

RESULTS

Absolute F-wave latency does not influence the accuracy of focal lesion detection. F-wave latency variance and lesion pathology are the determinant factors. F-wave latencies and distal latencies are estimated to have qualitatively similar detection characteristics, although distal latencies have quantitatively better diagnostic efficacy for comparable focal pathology. Preliminary experimental results support the modeled dependence of diagnostic accuracy on latency variance and lesion severity.

CONCLUSIONS

Absolute F-wave latency does not dilute slow conduction within focal lesions, such as in lumbosacral radiculopathy. The dominant measurement factor is F-wave latency variance.

SIGNIFICANCE

To maximize the diagnostic utility of F-wave latencies, focus must be placed on reducing latency variance, such as through correction for demographic covariates. This model calls into question the F-wave dilution hypothesis.

F wave studies of neurogenic intermittent claudication in lumbar spinal stenosis

OBJECTIVE

Lumbar spinal stenosis (LSS) may result in neurogenic claudication (NC), which is thought to be a result of transient ischemia during exercise. In this study we evaluated the changes in F wave studies before and immediately after walking stress in patients with NC.

DESIGN

Twenty-six patients with LSS who had signs and symptoms of NC and 20 healthy volunteers were included in this study. Routine motor and sensory nerve conduction studies and tibial F wave studies were performed in both groups. Immediately after walking stress test, tibial F wave studies were repeated. Exercise treadmill protocol was used for ambulation. Time to first symptoms and total ambulation time were recorded.

RESULTS

After completion of the baseline electrophysiological examination, a walking stress test was performed using a treadmill, and 16 patients (61.5%) experienced neurogenic claudication during the trial. The mean time to first symptoms was 2.0 +/- 3.5 mins (minimum = 0, maximum = 14). In the control group 18 subjects (90%) completed the trial without any symptoms, and 2 (10%) subjects had to stop at an average of 10 mins because of generalized fatigue. Within 5 mins after the walking stress test, tibial F wave studies were repeated in both groups. There were significant increases in F latency values bilaterally in the patient group (P = 0.001 for both sides) but not in control subjects (P = 0.435 for right side and P = 0.122 for left side).

CONCLUSION

Our data suggest that F wave studies after walking stress test provide more information for the diagnosis of NC.

The sensitivity and specificity of electrodiagnostic testing for the clinical syndrome of lumbar spinal stenosis

STUDY DESIGN

Prospective, masked, double controlled diagnostic trial.

OBJECTIVES

To determine the sensitivity and specificity of electrodiagnostic consultation (EDX) for the clinical syndrome of lumbar spinal stenosis.

SUMMARY OF BACKGROUND DATA

EDX has been used for more than 50 years to diagnose spinal disorders but has not met the new standards of evidence-based medicine.

METHODS

A total of 150 subjects (asymptomatic volunteers and patients with MRIs suggesting back pain or spinal stenosis; 55-80 years of age) underwent physiatrist history and physical examination, MRI, and review of this data by a neurosurgeon, with each clinician masked to any outside information, leading to a unanimous consensus on diagnosis in 55. After masked EDX testing, 7 subjects with undiagnosed neuromuscular disease were discovered. EDX findings were related to "clinical gold standard" diagnoses in 48 persons.

RESULTS

Paraspinal mapping EMG score of >4 had 100% specificity and 30% sensitivity for stenosis compared with either the back pain or asymptomatic groups (each, P < 0.04). A composite limb and paraspinal fibrillation score had a sensitivity of 47.8% and specificity of 87.5% (P = 0.008), and H-wave sensitivity was 36.4, specificity 91.3 (P = 0.026) for stenosis versus all controls.

CONCLUSIONS

This first masked study in the 60-year history of needle electromyography also introduces anatomically validated needle placement, quantified and reproducible examination of the paraspinal muscles, and dual control populations to EDX research in spinal disorders. EDX has statistically significant, clinically meaningful specificity for spinal stenosis and detects neuromuscular diseases that may masquerade as stenosis.

Rehabilitation of orthopedic and rheumatologic disorders. 5. Lumbar spinal stenosis

This self-directed learning module highlights the pathoanatomy and pathogenesis of lumbar spinal stenosis. The areas covered include assessment and therapeutic options in the rehabilitation of patients with degenerative lumbar spinal stenosis. It is part of the study guide on rehabilitation of orthopedic and rheumatologic disorders in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation.

OVERALL ARTICLE OBJECTIVES

(a) To summarize the evaluation and management of lumbar spinal stenosis and (b) to review the pathoanatomy and pathogenesis of lumbar degenerative spinal stenosis.

Dynamic electrophysiological examination in patients with lumbar spinal stenosis: is it useful in clinical practice?

Neurogenic claudication (NC) is typical of lumbar spinal stenosis (LSS). One suspected pathophysiological mechanism underlying NC is intermittent hypoxia of cauda equina fibres resulting from venous pooling, which may lead to ischaemic nerve conduction failure and to transient clinical and electrophysiological changes after exercise. The aim of this study was to evaluate the appearance of significant transient electrophysiological abnormalities after walking exercise in patients with LSS and to establish the contribution of dynamic electrophysiological examination in the differential diagnostics of patients with LSS. The study participants were 36 consecutive patients with LSS demonstrated by computed tomography (CT). The control groups included, respectively, 28 patients with diabetes mellitus and clinically manifested polyneuropathy, and 32 healthy volunteers. The LSS patients were divided into four subgroups based on the clinical severity of the disease (with respect to the presence or absence of NC in the history and pareses on neurological examination). Soleus H-reflex, tibial F-wave and motor evoked potentials (MEPs) to abductor hallucis muscle were examined in all groups, before and after quantified walking on a treadmill. The electrophysiological parameters measured after an exercise treadmill test (ETT) in LSS patients and in both control groups were compared with the same parameters obtained before ETT. The study shows that the electrophysiological parameters reveal minimal but statistically significant changes after walk loading in patients with LSS (a prolongation of the minimal latency of the tibial F-wave and of the latency of the soleus H-reflex). The changes in these parameters were demonstrated not only in patients with NC but also in patients without NC. More pronounced changes were found in LSS patients exhibiting chronic lower extremity pareses.

CONCLUSIONS

From among a large battery of electrophysiological tests, only the minimal latency of the tibial F-wave and the latency of the soleus H-reflex exhibit changes after walk loading in patients with LSS. These are minimal but statistically significant. Dynamic electrophysiological examination can illustrate the pathophysiology of NC in LSS, but from a practical point of view its contribution to the differential diagnostics of LSS or diabetic polyneuropathy is limited by an absence of established cut-off values.

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.

Reversible prolongation of motor conduction time after transcranial magnetic brain stimulation after neurogenic claudication in spinal stenosis

STUDY DESIGN

A consecutive and controlled cohort study.

OBJECTIVES

To assess the value of motor conduction time (MCT) between cortex and symptomatic leg muscles after transcranial magnetic brain stimulation as an indicator of reversible root ischemia in patients with neurogenic claudication in spinal stenosis.

SUMMARY OF BACKGROUND DATA

Neurogenic claudication in spinal stenosis is thought to result from transient ischemia of active nerve root fibers. Subgroups of these patients have slowing of sensory or motor nerve root conduction during spinal claudication.

MATERIAL AND METHODS

Forty-two patients with spinal claudication and radiologically confirmed signs of spinal stenosis were consecutively recruited. Motor conduction time was measured before and repetitively after challenge of walking on a treadmill (four stimuli per minute) until disappearance of the symptoms. Data of 30 patients (65 +/- 10 years) with a defined onset of motor-evoked potentials were compared with those of 12 control subjects (62 +/- 12 years).

RESULTS

One minute after treadmill challenge, MCT increased in all 13 patients with signs of an exercise-dependent neurologic deficit by at least 1 msec (mean increase, 1.6 +/- 0.6 msec; < 0.001). Test-retest comparisons in six of these patients revealed good reproducibility of the MCT increase (coefficient of repeatability, 1.24 msec). In contrast, MCTs were unchanged or decreased in all 17 patients without exercise-dependent neurologic deficit ( < 0.01) and in the control subjects ( < 0.05).

CONCLUSIONS

Measurements of MCT before and after treadmill challenge can demonstrate reversible root ischemia in patients with spinal claudication and exercise-dependent deficit of thickly myelinated nerve root fibers.

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.

Recruitment curve of the soleus H reflex in patients with neurogenic claudication

The diagnosis of neurogenic claudication (NC) remains uncertain when no definite signs of radicular lesions are found in electrophysiological testing. However, the functional deficit could be demonstrated during the brief time in which the patients complain of pain and weakness in the muscles of the lower limbs after walking. We have used electrophysiological testing of the H reflex and the F wave to document the transient functional derangement expected to occur at the radicular level in patients with NC after walking. We examined the recruitment curve of the soleus H reflex, and the chronodispersion of the posterior tibial nerve F wave, at rest and after a walking exercise that triggered their symptoms in 10 patients with NC, with no positive electrophysiological findings of radicular lesion. The same studies were performed in 5 age-matched healthy volunteers, used as control subjects, who were asked to walk for 30 min. At rest before walking, no abnormalities were found in any of the patients. After walking, the H wave showed a transient increase in its threshold with respect to that of the M wave in 7 patients (70%). Such abnormality lasted for a mean period of 7 min. In 2 of these patients there was also an increase in the F-wave chronodispersion. Our data suggest that nerve conduction is transiently blocked in large myelinated fibers at a radicular level in patients with NC after walking. Partial interruption of the H-reflex circuit could be one of the pathophysiological mechanisms underlying NC.

Facts, fallacies, and fancies of nerve conduction studies: twenty-first annual Edward H. Lambert Lecture

Optimal application of the nerve conduction study depends on an understanding of the principles and a recognition of the pitfalls of the technique. The conventional methods deal primarily with distal nerve segments in an extremity. Other techniques allow one to assess nerve segments in less accessible anatomical regions, to improve the accuracy in precisely localizing a focal lesion, and to increase sensitivity in detecting subclinical abnormalities. Despite certain limitations, these methods can provide diagnostically pertinent information if they are used judiciously in appropriate clinical contexts. I wish to review the fundamental concepts of nerve stimulation techniques and their proper applications in the clinical domain. The discussion primarily relates to the importance of reproducibility of various measures and pitfalls in the evaluation of conduction block.