Repeatability of nerve conduction measurements using automation

Far-field potential of the compound muscle action potential as a reliable marker in amyotrophic lateral sclerosis

INTRODUCTION/AIMS

Reliable neurophysiological markers in amyotrophic lateral sclerosis (ALS) are of great interest. The compound muscle action potential (CMAP) amplitude has been a conventional marker, although it is greatly influenced by the electrode position. We propose the far-field potential of the CMAP (FFP-CMAP) as a new neurophysiological marker in ALS.

METHODS

Patients with ALS and age-matched healthy controls were enrolled. We used a proximal reference (pref) in addition to the conventional distal reference (dref). Routine CMAP was recorded from the belly-dref lead and FFP-CMAP from the dref-pref lead for the ulnar and tibial nerves. Multiple point stimulation motor unit number estimation (MUNE) was also examined in the ulnar nerve. Inter-rater reproducibility was evaluated by two examiners, and some patients were followed up every 3 mo for 1 y.

RESULTS

We tested 17 patients with ALS and 10 controls. The amplitudes of routine CMAP and FFP-CMAP in the ulnar and tibial nerves, and hypothenar MUNE value in the ulnar nerve were significantly decreased in ALS compared to controls. Ulnar FFP-CMAP achieved the highest inter-rater intraclass correlation coefficient (ICC) value (0.942) when compared with routine CMAP (0.880) and MUNE (0.839). The tibial FFP-CMAP had a higher ICC value (0.986) than the routine CMAP (0.697). In this way, the FFP-CMAP showed high inter-rater reproducibility because its shape was not much influenced by the electrode position. During 1-y follow-up, decline of CMAP, FFP, and MUNE showed significant correlations with the Amyotrophic Lateral Sclerosis Functional Rating Scale - Revised (ALSFRS-R).

DISCUSSION

The FFP-CMAP shows promise as a reliable marker for ALS.

Interrater Repeatability of Motor Nerve Conduction Velocity of the Ulnar Nerve

OBJECTIVE

The purpose of this study was to obtain data on interrater repeatability of the motor nerve conduction velocity (NCV) of the ulnar nerve of different segments, ulnar distal motor latency (DML), and compound muscle action potential (CMAP) amplitudes.

DESIGN

Twenty-four healthy volunteers were examined in consecutive order. Ulnar motor NCV of different segments, ulnar DML, and CMAP amplitudes were determined. Based on a randomization list of various combinations and sequences, 1 of 3 examiners performed the first measurement. A second examiner repeated the evaluation within half an hour.

RESULTS

There were no significant differences between the first and second measurements for all parameters. For the ulnar motor NCV of the different segments, the intraclass correlation coefficient (ICC) ranged from 0.38 to 0.51, and the coefficient of repeatability (CR) ranged from 8.0 to 11.6 m/s. For the ulnar DML, the ICC was 0.44, and the CR was 0.49 millisecond. For the CMAP amplitudes at the different stimulation sites, the ICC ranged from 0.53 to 0.76, and the CR ranged from 1.5 to 2.3 mV.

CONCLUSIONS

A moderate amount of interrater variability of the ulnar motor NCV must be taken into account. Compared with the CMAP amplitudes, the interrater repeatability of the ulnar motor NCV is poorer.

New vistas in the diagnosis of diabetic polyneuropathy

New modalities are now available to improve the diagnosis of diabetic polyneuropathy (DPN). The present review discusses the progress achieved in this area. First, the minimal diagnostic criteria have been better clarified. Moreover, there are now new bedside tests available, such as the indicator test Neuropad, NeuroQuick, Ipswich Touch Test (IpTT), Vibratip, NC-stat(®)/DPNCheck™ for automated nerve conduction study (NCS), tactile circumferential discriminator, steel ball-bearing, and SUDOSCAN(®), while more sophisticated modalities include skin biopsy and corneal confocal microscopy (CCM). Some tests can be used as screening tools, including primary care setting (Neuropad, IpTT, Vibratip, automated NCS), while others are more suitable for research, including evaluation of DPN in prospective studies (CCM, skin biopsy). Importantly, there is some evidence of earlier DPN diagnosis with the aid of some tests (Neuropad, skin biopsy, CCM). Further advantages provided by different tests are educational value and self-examination. Thus far, the potential of these tests has not been fully utilised. In particular, they have not been validated against standardised clinical examination scores in terms of predicting foot ulcers and amputations. Hence, it now remains to investigate the potential benefits from the widespread use of these tests for earlier and easier diagnosis of DPN in the everyday clinic.

Peripheral nerve function and lower extremity muscle power in older men

OBJECTIVE

To assess whether sensorimotor peripheral nerve function is associated with muscle power in community-dwelling older men.

DESIGN

Longitudinal cohort study with 2.3±0.3 years of follow-up.

SETTING

One clinical site.

PARTICIPANTS

Participants (n=372; mean age ± SD, 77.2±5.1y; 99.5% white; body mass index, 27.9±3.7kg/m(2); power, 1.88±0.6W/kg) at 1 site of the Osteoporotic Fractures in Men Study (N=5994).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

A nerve function ancillary study was performed 4.6±0.4 years after baseline. Muscle power was measured using a power rig. Peroneal motor nerve conduction amplitude, distal motor latency, and mean f-wave latency were measured. Sensory nerve function was assessed using 10-g and 1.4-g monofilaments and sural sensory nerve conduction amplitude and distal latency. Peripheral neuropathy symptoms at the leg and feet were assessed by self-report.

RESULTS

After adjustments for age, height, and total body lean and fat mass, 1 SD lower motor (β=-.07, P<.05) and sensory amplitude (β=-.09, P<.05) and 1.4-g (β=-.11, P<.05) and 10-g monofilament insensitivity (β=-.17, P<.05) were associated with lower muscle power/kg. Compared with the effect of age on muscle power (β per year, -.05; P<.001), this was equivalent to aging 1.4 years for motor amplitude, 1.8 years for sensory amplitude, 2.2 years for 1.4-g monofilament detection, and 3.4 years for 10-g detection. Baseline 1.4-g monofilament detection predicted a greater decline in muscle power/kg. Short-term change in nerve function was not associated with concurrent short-term change in muscle power/kg.

CONCLUSIONS

Worse sensory and motor nerve function were associated with lower muscle power/kg and are likely important for impaired muscle function in older men. Monofilament sensitivity was associated with a greater decline in muscle power/kg, and screening may identify an early risk for muscle function decline in late life, which has implications for disability.

Electrophysiological evaluation of chronic inflammatory demyelinating polyneuropathy and charcot-marie-tooth type 1: dispersion and correlation analysis

[Purpose] The purpose of this study was to analyze and compare electrophysiological characteristics observed in nerve conduction studies (NCS) of chronic inflammatory demyelinating polyneuropathy (CIDP) and Charcot-Marie-Tooth disease type 1 (CMT 1). [Subjects] A differential diagnosis of acquired and congenital demyelinating neuropathies was based on a study of 35 patients with NCS-confirmed CIDP and 30 patients with CMT 1 genetically proven by peripheral myelin protein-22 (PMP-22) gene analysis, pulsed-field gel electrophoresis (PFGE), and Southern blot analysis. [Methods] We analyzed values collected in motor nerve conduction studies. We conducted dispersion analysis of the amplitudes of the compound muscle action potential (CMAP) of various nerve types and correlation coefficient analysis of the motor nerve conduction velocity (MNCV). [Results] We found that CIDP and CMT 1 were clearly attributable to severe polyneuropathy. In dispersion analysis, CIDP showed greater differences in proximal-to-distal amplitude ratios. Moreover, CMT 1 showed relatively high correlations compared to CIDP based on correlation coefficient analysis of MNCV. [Conclusion] The results of this study suggest that CIDP showed greater asymmetry than CMT 1 in MNCV and CMAP amplitudes.

Reproducibility of sensory nerve conduction studies of the sural nerve using ultrasound-guided needle positioning

INTRODUCTION

In this study we sought to evaluate the reproducibility of sensory nerve conduction studies (NCS) using ultrasound-guided needle positioning (USNP).

METHODS

Orthodromic NCS of the sural nerve using needle electrodes with USNP as well as surface electrodes were conducted twice in 20 healthy volunteers.

RESULTS

The mean sensory nerve action potential (SNAP) amplitude in the initial examination was 39.5 μV using needle electrodes with USNP, and 12.5 μV using surface electrodes (P < 0.0001). The mean SNAP amplitude in the follow-up examination was 39.2 μV using needle electrodes with USNP, and 12.4 μV using surface electrodes (P < 0.0001). The mean intraindividual change in SNAP amplitude (test-retest) was 21.2% using needle electrodes with USNP, and 24.8% using surface electrodes (P = 0.6).

CONCLUSIONS

Sensory NCS of the sural nerve using needle electrodes with USNP have reliable test-retest reproducibility and yield greater SNAP amplitudes than sensory NCS using surface electrodes.

New diagnostic tests for diabetic distal symmetric polyneuropathy

Neuropathy needs to be diagnosed early to prevent complications, such as neuropathic pain or the diabetic foot. It is obvious that diagnosis of neuropathy needs to be improved. New peripheral nerve function tests that appear to facilitate diagnosis are now emerging. This review outlines the new tests that have been proposed for the diagnosis of diabetic distal symmetric polyneuropathy, the commonest form of neuropathy in diabetes. New tests are classified into those mainly assessing large-fiber function (tactile circumferential discriminator, steel ball-bearing, and automated nerve conduction study) and those mainly assessing small-fiber function (NeuroQuick and Neuropad). Emerging tests are promising but must be evaluated in prospective studies. Moreover, their cost-effectiveness needs more careful appraisal. The clinician should, therefore, still rely on established modalities to diagnose neuropathy, but wider use of the new tests is expected in the near future.

Nerve conduction studies: clinical challenges and engineering solutions

Nerve conduction studies (NCSs) have played an important role in the evaluation of neuromuscular disease for the past 50 years. When patients present with complaints of pain, numbness, tingling, or weakness, NCS is often one of the earliest tests obtained by physicians, because it enables the quantitative assessment of peripheral nerve and muscle function and, therefore, aid the physician in identifying the physiological source of the patient's symptoms. NCSs involve the delivery of electric stimuli to peripheral nerves at accessible locations on the human body and the recording of electrophysiological responses. This article reviews how NCS is traditionally performed. This paper also examines technical challenges associated with each step of performing an NCS and describes how engineering solutions could be realized to meet these challenges. The engineering goals were several: improvement in NCS workflow, use of prefabricated electrode arrays to standardize NCS technique and reduce the errors associated with electrode placement, and improvement of the overall accuracy and reliability of NCS.

Reproducibility of the CMAP scan

INTRODUCTION

The CMAP scan is a surface EMG method based on the successive activation of motor units. It provides information about reinnervation processes, the number of functional motor units and nerve excitability. The CMAP scan has potential value as a follow-up tool in monitoring disease progression, recovery or aging of the peripheral nerves. In this study, we assessed its interobserver and different-day reproducibility.

METHODS

Two investigators recorded CMAP scans in ten healthy subjects, each on two different days. Intraclass correlation coefficients (ICCs) and coefficients of variation (CoVs) were calculated for the parameters extracted from the CMAP scan.

RESULTS

All CMAP scan parameters had a good different day (ICCs >0.8 and CoVs <15%) and interobserver reproducibility (ICCs >0.7 and CoVs ≤ 15%). Different-day reproducibility was better than interobserver reproducibility.

CONCLUSION

CMAP scan test-retest variability is small, suggesting that as a follow-up tool it may be sensitive to fairly small (patho)physiological changes in the studied variables.

Repeatability of nerve conduction measurements derived entirely by computer methods

BACKGROUND

Nerve conduction studies are an objective, quantitative, and reproducible measure of peripheral nerve function and are widely used in the diagnosis of neuropathies. The purpose of this study is to determine the reliability of nerve conduction parameters derived entirely from computer based data acquisition and waveform cursor assignments and to quantify the relative contributions of test variability sources.

METHODS

Thirty volunteers, some with symptoms suggestive of neuropathies; of these, 29 completed the study. The median, ulnar, deep peroneal, posterior tibial, and sural nerves were evaluated bilaterally at two test sessions 3-7 days apart. Within each session, nerves were tested twice within 10 minutes. The analyzed nerve conduction parameters include motor latencies, motor conduction velocity (CV), compound muscle action potential (CMAP) amplitude, F-wave latencies (minimum, mean and maximum), sensory peak latency (DSL), sensory CV, and sensory nerve action potential (SNAP) amplitude. The primary outcome measure is variance component analysis and the corresponding coefficient of variation (CoV). The between-session-test variance is the sum of within-session variance and between-session variance, quantifying the total variation between test sessions. Additional statistical measures include the intraclass correlation coefficient (ICC) and relative interval variation (RIV).

RESULTS

Motor and sensory latencies, CV and F-wave latency parameters have low between-session-test CoVs, ranging from 4.2% to 9.8%. Amplitude parameters have a higher between-session-test CoVs in the range of 15.6--19.8%. Between-test CoVs are about 30--80% lower than between-session CoVs with the exception of F-wave latency parameters. Between-test ICC values are 0.96 or above for all parameters. Between-session ICC ranges from 0.98 for F-wave latency to 0.77 for sural sensory CV. All latency-related between-session ICCs have a value 0.83 or above. The RIVs are the tightest for F-wave latency parameters and widest for CMAP amplitude parameters. Repeatability in a sub-group of subjects with more severe symptom grades follows the same trend as the overall study population without substantial quantitative differences.

CONCLUSION

The study demonstrates the high repeatability of nerve conduction parameters acquired by modern electrodiagnostic instruments using computer based waveform cursor assignment. The reliability is comparable to benchmark studies in which the nerve conduction measurements were performed manually in controlled multi-center clinical trials. Furthermore, the ranking of reliability, whereby F-wave latencies have the best reproducibility and amplitudes the worst, is also consistent with the benchmark studies.

Multi-site testing with a point-of-care nerve conduction device can be used in an algorithm to diagnose diabetic sensorimotor polyneuropathy

OBJECTIVE

We aimed to establish whether multi-nerve testing with a point-of-care nerve conduction device could be used to diagnose diabetic sensorimotor polyneuropathy.

RESEARCH DESIGN AND METHODS

A total of 72 consecutive patients with diabetes underwent a full neurological examination and a concurrent evaluation for nine standard electrophysiological parameters using conventional nerve conduction studies (the reference standard) and a point-of-care device.

RESULTS

Spearman coefficients for correlation of point-of-care and conventional parameters ranged between 0.76 and 0.91 (P < 0.001 in all comparisons). Agreement by the method of Bland and Altman was acceptable despite small systematic biases. Fifty subjects (69%) had neuropathy according to conventional criteria. The sensitivity and specificity for the point-of-care device to identify such neuropathy was 88 and 82%, respectively.

CONCLUSIONS

A novel point-of-care device has reasonable diagnostic accuracy and thus may represent a sufficiently accurate alternative for detecting the diffuse electrophysiological criteria necessary to make the diagnosis of diabetic sensorimotor polyneuropathy.

The role of neurodiagnostic studies in nerve injuries and other orthopedic disorders

Neurodiagnostic techniques, such as nerve conduction studies, needle electromyography studies, intraoperative nerve monitoring, and evoked potentials provide useful information for practicing orthopedic surgeons to help localize central from peripheral nervous system lesions. For peripheral nerve lesions, it helps localize the level of the nerve dysfunction (for example, root versus plexus versus peripheral nerve). These techniques are well established and routinely used. Newer techniques have emerged that aim to simplify the technical process of performing these studies and help reduce the discomfort associated with these studies. Many of these newer techniques, however, are in their infancy, and their role in routine use for neurodiagnostic purposes is not clear. This review examines the various types of nerve injuries commonly encountered in orthopedic surgery practice and the role of electrodiagnostic (neurodiagnostic) techniques in diagnosing these conditions.