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

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.

Implementation and evaluation of a statistical framework for nerve conduction study reference range calculation

Nerve conduction studies (NCS) play a central role in the clinical evaluation of neuropathies. Their clinical utilization depends on reference ranges that define the expected parameter values in disease-free individuals. In this paper, a statistical framework is proposed and described in detail for deriving NCS parameter reference ranges. The bootstrap technique is used to identify demographic and physiologic covariates that influence the NCS measurements. Multi-variate linear regression is used to improve the accuracy and effectiveness of NCS interpretation by reducing parameter variance. Non-linear mappings are used to transform parameters into a Gaussian distribution in order to minimize the influence of outliers. Modeling of heteroscedasticity observed in this and other studies leads to more sensible normal limits for several parameters. The proposed reference range method is automated using the MATLAB programming language. Data from a large sample of healthy subjects are used to establish reference ranges for 24 commonly measured NCS parameters. All but three parameters follow Gaussian distributions in their respective transformed domains. Excluding the distal motor latency difference between median and ulnar nerves, the reduction of the parameter variance as a result of regression in the transform domain is greater than 50% for all F-wave latency parameters and at least 10% for all other NCS parameters. Subject age is found to influence normal limits of all but one parameter and height has a statistically significant impact on all but three parameters. These reference range specifications provide clinicians with an alternative to developing their own reference ranges as long as their NCS techniques are consistent with those described in this paper. The proposed method should also be applicable to reference range development for other NCS techniques and physiological measurements.

Submaximal stimulation and f-wave parameters

PURPOSE

This study evaluates the effect of submaximal stimulation and varying stimulus rates on F-wave parameters.

METHODS

F-waves were recorded from the abductor pollicis brevis muscle from 3 normal subjects stimulating at 25%, 50%, and 75% intensity in comparison with supramaximal stimulation based on peak-to-peak compound muscle action potential amplitude. The effect of varying stimulus intensity (0.5, 1.0, and 2.0 Hz) at 30% stimulus intensity was also evaluated. Data were evaluated based on "true" values obtained after 100 stimuli. F-wave parameters studied included latencies (minimal and mean), amplitudes, persistences, durations, chronodispersions, and mean F amplitudes/maximum compound muscle action potential amplitudes.

RESULTS

For varying stimulus intensities and rates, the following results were obtained: (1) no meaningful change in F latencies or durations; (2) mean latency values were more reproducible than minimum; (3) amplitudes, persistence, and mean F amplitudes/maximum M-wave amplitude ratios increase linearly with increase in stimulus intensities; (4) chronodispersion increases with increase in stimulus intensity; (5) 20 stimuli appear adequate for true values at supramaximal stimulation but more are needed at submaximal levels; (6) varying stimulus frequency at submaximal stimulation did not meaningfully affect the results.

CONCLUSIONS

F-parameters require more stimuli at submaximal stimulation and, except for latencies and durations, would require different normal values than at supramaximal stimulation.

Routine electrodiagnosis and a multiparameter technique in lumbosacral radiculopathies

OBJECTIVE

This study compares Routine nerve conductions studies (NCS)/needle electromyography (nEMG) with a multiparameter recording method (NC-stat; NeuroMetrix Inc., Waltham, MA, USA) in patients with lumbosacral radiculopathies (LSR).

METHODS

Charts from 34 consecutive patients with a clinical history and/or examination consistent with an LSR were retrospectively reviewed. All underwent both Routine NCS/nEMG studies and NC-stat EDX. NC-stat testing included peroneal and posterior tibial nerve distal motor latencies and amplitudes and F-wave analysis. Twenty-eight patients had magnetic resonance imaging of the lumbosacral spine, and two had post-myelogram computerized tomography scan.

RESULTS

In the 24 patients with abnormal routine NCS/nEMG, NC-stat EDX was abnormal in 22. Raw agreement values between specific abnormal Routine and NC-stat EDX parameters ranged from 065 to 0.76. NC-stat amplitude and F-wave data provide reasonable electrodiagnostic 'rule in, rule out' information for LSR. Routine and NC-stat EDX had comparable positive and negative likelihood ratios with radiographic findings based on blinded neuroradiological evaluation. This included good 'stand alone' values for NC-stat F-wave and compound muscle action potential (CMAP) amplitude abnormalities in patients with spinal stenosis.

CONCLUSIONS

This report supports the value of multiparameter clinical neurophysiological evaluations in patients with LSR including CMAPs and F-waves.

Utilization of nerve conduction studies for the diagnosis of polyneuropathy in patients with diabetes: a retrospective analysis of a large patient series

BACKGROUND

Diabetic polyneuropathy (DPN) is a disabling complication of diabetes mellitus. A population-based analysis of physician utilization of nerve conduction studies (NCS) for the assessment of DPN was conducted.

METHODS

All electrodiagnostic encounters over a 30-month period using a computer-based neurodiagnostic instrument linked to a data registry were analyzed retrospectively. The DPN case definition was abnormal sural and peroneal nerve conduction.

RESULTS

The study cohort consisted of a total of 63,779 electrodiagnostic encounters performed by 3468 physician practices. Primary care and internal medicine physicians represented 80.1% of the practices and accounted for 65.7% of the encounters. Endocrinologists represented 4.6% of the practices and 20.1% of the encounters. The demographics of patients were 52.7% female; 63.4+/-11.8 (mean+/-standard deviation) years (age); 168.1+/-10.9 cm (height); 92.2+/-22.6 kg (weight); and 32.6+/-7.2 kg/m(2) (body mass index). The most common peroneal abnormality was F-wave latency (33.6%). The sural nerve response latency and amplitude parameters had similar abnormality rates (58.3 and 62.7%). DPN was identified in 52.6% of the encounters; in another 19.3% no neuropathy was found.

CONCLUSIONS

For over 70% of the patients, the specific diagnostic question of the presence of DPN was addressed by NCS with evidence-based criteria. The demographic features were strongly associated with risk of diabetes and DPN, suggesting that NCS were applied to appropriate demographic subgroups. The rate of DPN was also comparable to levels seen by academic electromyography laboratories. In 32.6% of the encounters the NCS suggested a posttest diagnosis other than DPN. This rate was similar to the results of referral to traditional electromyography laboratories. This study demonstrated that NCS using computer-based electrodiagnostic equipment was a suitable tool for the diagnosis of DPN. Furthermore, this technology permits examination of DPN in large populations.

F-wave decomposition for time of arrival profile estimation

F-waves are distally recorded muscle responses that result from "backfiring" of motor neurons following stimulation of peripheral nerves. Each F-wave response is a superposition of several motor unit responses (F-wavelets). Initial deflection of the earliest F-wavelet defines the traditional F-wave latency (FWL) and earlier F-wavelet may mask F-wavelets traveling along slower (and possibly diseased) fibers. Unmasking the time of arrival (TOA) of late F-wavelets could improve the diagnostic value of the F-waves. An algorithm for F-wavelet decomposition is presented, followed by results of experimental data analysis.