Abstract
Background
Nerve conduction studies are a common clinical investigation for evaluating peripheral nerve abnormalities. Various sets of normal values exist; ideally, each laboratory should establish its own set of normal values.
Purpose
Develop normative data of nerve conduction study (NCS) studies for upper and lower limbs.
Methods
Nerve conduction studies were conducted on the upper and lower extremities of meticulously screened, healthy participants of both genders, among the Himachal and Punjab population, using Natus Synergy on Nicolet TM EDX EMG/NCV/EP system. They were all within the age range of 20–60 years. Velocities were calculated by onset latencies, and amplitudes were measured from baseline to the negative peak. Descriptive statistics were computed. Mann–Whitney U tests were used to look for the effect of gender. Linear regression was used to evaluate the effect of age and height.
Results
The study population include 50 males and 50 females. The age and body mass index (BMI) of subjects were similar across gender. Proximal motor latency (Right (R) & Left (L) Median and Ulnar, R tibial, R Peroneal), Distal motor latency (L median, peroneal), sensory onset and peak latencies (R&L ulnar nerves) were significantly longer in males as compared to females. Motor NCV (L Median, R Ulnar, R&L Tibial and Peroneal), compound muscle action potential (CMAP) Amplitude (R&L Median, Tibial, Peroneal and R ulnar), Sensory NCV (R Median, L Ulnar), sensory nerve action potential (SNAP) amplitude (R&L median and ulnar) were significantly decreasing with age.
Conclusion
This study established normative conduction parameters of commonly tested nerves of the upper and lower limbs. investigated the effects of age, gender and height for our clinical neurophysiology laboratory.
Introduction
A diagnostic method for determining peripheral nervous system dysfunctions is nerve conduction studies. This kind of research records a nerve’s reaction to an applied electrical stimulus in order to assess both motor and sensory nerve functions. A peripheral nerve is stimulated, and the electrical activity that results from a muscle it controls is recorded in order to evaluate motor nerves. Studies of sensory nerves, on the other hand, entail stimulating a mixed nerve and recording the signal from a corresponding cutaneous or mixed nerve.
Clinically, these studies have long been used to pinpoint the site of peripheral nerve disease—whether in a single nerve or along its pathway—and to distinguish these conditions from muscular or neuromuscular junction diseases. A standard nerve conduction study (NCS) involves assessing the compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) of accessible nerves in the upper and lower extremities, such as the median, ulnar, radial, common peroneal, tibial, and sural nerves. For CMAP, the most frequently measured metrics are latency, amplitude, duration, and conduction velocity. Likewise, these same parameters are routinely measured for SNAP.
Multiple factors, such as temperature, age, height, BMI, and others, can influence the results of nerve conduction studies and must be considered during testing.1–5 However, these factors can vary across different geographic regions. These parameters are also known to vary with demographic profile, anthropometric measurements of the population studied and laboratory conditions of the test.6–8 In literature, various sets of normal values exist.
Normative Data Task Force (NDTF) by the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) had evaluated the data for NCS from 1990 to 2012 and provided a set of normal values among the American population. The authors have provided statistical and methodological standards for establishing normative data in nerve conduction studies, providing a framework that can be consistently applied in subsequent research. 9 This study’s main goal was to establish a set of normal electrophysiological values for common upper and lower limb nerves from a sample of carefully chosen healthy adults. Creating such population-specific normative data is considered ideal for any clinical neurophysiology lab, as it allows for a more precise diagnosis of abnormalities in patients. As part of this research, the influence of variables such as gender, age, and height on nerve conduction parameters was also analysed.
Methods
For this study, 100 healthy adult volunteers (50 male, 50 female) were enrolled on our electrophysiology lab. The men had a mean age of 40 ± 14 years, and the females were at 37.6 ± 12 years. We made sure to get written informed consent from every single volunteer, and the whole research protocol was approved by the Institutional Ethics Committee. A full screening, which included a clinical history and neurological exam, was done on everyone to rule out any systemic or neuromuscular conditions. Subjects with a history of neuropathy, alcohol or drug abuse, diabetes mellitus, limb injury, or any neuromuscular transmission disorders or myopathy were excluded from the study. Procedures were performed at a controlled room temperature of 20°C–27°C, and before recording anything, we checked the equipment setup and got the subjects familiarised with the whole environment, instructing them to relax completely.
Electrophysiological Methods
All tests were conducted using a Natus Elite Synergy machine, a system equipped with a digital signal processor, stimulators, recording electrodes, and other essential components. The procedure involved using surface electrodes for the active, reference, and ground leads. The machine’s settings were adjusted based on the type of test; motor NCS was performed with a 2 Hz–5 kHz filter, 5 ms/division sweep speed, and 5mV/division sensitivity, while sensory NCS used a 20 Hz–3 kHz filter, 2 ms/division sweep speed, and 20 µV/division sensitivity.
Motor NCS Parameters
Motor nerve conduction studies of the median, ulnar, tibial, and peroneal nerves were performed according to standardised techniques. 10 A belly-tendon montage was applied, positioning the cathode and anode 3 cm apart. The stimulus intensity was gradually increased from zero but never surpassed 100 mA. To record two distinct CMAPs, supramaximal stimulation (a strength 20% greater than maximal) was delivered at both distal and proximal sites. Latency and amplitude were measured for each stimulation point. The conduction velocity was calculated by the software after the distance between the two stimulation sites was measured in millimetres and entered into the software.
Sensory NCS Variables
Surface electrodes were used to perform antidromic studies for the sensory nerve evaluation. The electrodes were positioned, and the median, ulnar, and sural nerves were stimulated in accordance with established procedures. 10 In addition to evaluating onset and peak latencies, the analysis also measured baseline-to-peak (NP) and peak-to-peak (PP) amplitudes. The software then used the measured distance (in millimetres) between the active electrode and the stimulating cathode, as well as the onset delay, to determine the conduction velocity.
Statistical Methods
Demographic characteristics like age, height, weight and BMI of the population were summarised for both genders in terms of mean and standard deviation (SD). For each of the parameters measured during motor or sensory nerve conduction studies, the normality of data for both genders was tested using the Shapiro-Wilk test. Descriptive statistics for CMAP (proximal and distal latencies and amplitudes), motor NCV, SNAP (onset and peak latencies and NP and PP amplitudes) and sensory NCV of all recorded nerves were computed and reported as mean ± SD for normally distributed data or median (25th percentile, 75th percentile) for the skewed data. To evaluate the effect of gender, normally distributed variables were analysed with unpaired t-tests and skewed data were assessed with the Mann–Whitney U test. Univariate regression analysis for each parameter was also performed to look for the effect of age and height as independent variables. p Value less than .05 were considered significant; however, a Bonferroni correction for multiple comparisons was not done. All the data analysis was performed using standard Python libraries like pandas, NumPy and SciPy. Stats. The plots were plotted using the matplotlib library.
Results
Effect of Gender on Physical and Anthropometric Variables
Among the physical and anthropometric parameters, height and weight were significantly greater among males as compared to females. However, gender wise differences in age and body mass index (BMI) were not found to be statistically significant. The results are mentioned in Table 1.
Anthropometric Profile of the Study Population.
BMI = Body mass index.
*p < .05.
Effect of Gender on MNCS Parameters
Latencies on proximal stimulation of all recorded nerves and on distal stimulation of L Median, R ulnar and R and L peroneal nerves were significantly longer in males as compared to females. No significant difference between males and females was reported for conduction velocity. The amplitudes on distal stimulation of the R Ulnar and R Tibial nerve were significantly higher among males as compared to females. All the values are listed in Table 2.
Gender-based Comparison of Motor Nerve Conduction Study (MNCS) on Stimulation of the Median, Ulnar, Peroneal, and Tibial Nerves of Both Limbs.
†Variable analysed using an independent samples t-test.
‡Variable analysed using a Mann–Whitney U test.
*p < .05. mV: millivolt, ms: millisecond, m/s: meters/second.
Effect of Age and Height on MNCS Parameters
Proximal (except for L ulnar and L Peroneal nerves) and distal (except for R Tibial, L Tibial, L Ulnar and L Peroneal nerves) latencies were significantly increasing with age. Proximal (except for L ulnar nerve) and distal (except for R Tibial, L Tibial, L Ulnar and L Peroneal nerves) amplitudes were significantly decreasing with age. Conduction velocities were significantly decreasing with age for all the recorded nerves.
Proximal (for all the nerves) and distal (for R and L Peroneal nerves) latency were significantly increasing with height. Distal amplitude was significantly decreasing with height for the R and L Tibial nerves. There was no significant relation reported between height and conduction velocity.
The results of regression analysis are listed in Table 3.
Effect of Age and Height on Motor Nerve Conduction Study (MNCS) Parameters.
r = regression coefficient.
*p < .05.
Effect of Gender on SNCS Parameters
Onset and peak latencies among males were significantly longer in R and L ulnar nerves as compared to females. NP and PP amplitudes were significantly higher among females in the R and L ulnar nerves as compared to males. There was no significant difference between males and females for any other parameter in any other recorded nerves. All the values are listed in Table 4.
Gender-based Comparison of Sensory Nerve Conduction Study (SNCS) Parameters on Stimulation of the Median, Ulnar, and Sural Nerves of Both Limbs.
†Variable analysed using an independent samples t-test.
‡Variable analysed using a Mann–Whitney U test.
*p < .05. µV : microvolts, ms: milliseconds, m/s: meters/second.
Effect of Age and Height on SNCS Parameters
Onset and peak latencies were significantly increasing, and conduction velocities were significantly decreasing with age for bilateral median and ulnar nerves. For the R sural nerves, only the conduction velocity shows a significant decrement with age. NP and PP amplitudes were significantly decreasing with age for all the recorded nerves except the bilateral sural nerve.
The effect of height was not consistent across different parameters for all the recorded nerves. The results of the regression analysis are shown in Table 5.
Effect of Age and Height on Sensory Nerve Conduction Study (SNCS) Parameters.
r = regression coefficient.
*p < .05.
Discussion
Establishing NCS norms for the local population is essential because reference values differ among geographical regions and population groups. 9 Demographic features, body-size measurements, laboratory environments, and the specific testing techniques in use all contribute to this variability.9, 11 Depending on data drawn from populations with different ethnic backgrounds or climates, can therefore produce misleading interpretations of local NCS findings. The American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM), through its Normative Data Taskforce (NDTF), stresses that reference values must be built on rigorous methods and adequately large samples. 9 Although the NDTF compiled reference ranges from studies that met its criteria, it also called for additional work by other laboratories and regions to confirm the broader applicability of those ranges. 9 Many earlier studies, especially some from Western countries, 12 no longer meet modern statistical and methodological standards.12, 13 Creating population-specific norms, as we have done in this study, therefore offers a more precise foundation for diagnosing peripheral-nerve disorders.
Our analysis of how demographic and anthropometric factors shape NCS results is consistent with numerous previous reports.11, 12 Age, for example, independently affects older adults, producing longer latencies and lower conduction velocities and amplitudes. 12 Height likewise plays a major role: taller individuals generally show prolonged latencies and slower velocities, possibly because of distal axonal tapering. 11 However, in our study, we have obtained prolonged latencies but not slower velocities with an increase in height.
We also found that sex significantly affects several parameters, including proximal and distal motor latency, sensory onset and peak latency, and SNAP amplitude. The higher sensory amplitudes we observed in females mirror earlier findings.13, 14 Proposed explanations for these sex differences include anatomical and physiological variation, 12 differences in height 12 or limb length, 14 and varying subcutaneous-tissue thickness, which alters recording distance, particularly in sensory tests. 12 While some publications suggest that sex has little effect on velocity or latency, 13 our results, similar to those of Taksande et al., 15 demonstrate a clear influence on distal motor latencies.
When our motor reference values are compared with earlier studies, the ulnar and median nerve parameters closely match previous reports. Such agreement for motor metrics has also been documented when other populations are set against the existing literature.11–17 In contrast, our sensory amplitudes are slightly lower than those reported by Shehab. 8 Variations in amplitude-measurement technique (e.g., baseline-to-peak vs. baseline-to-negative-peak) may partly account for these discrepancies. 14 Population-focused work, such as Anton et al.’s study of an older rural cohort, 12 has likewise shown generally longer latencies, emphasising how demographic specifics shape normative ranges. Finally, using standardised procedures and controlled temperatures, as in our protocol and as recommended by many authors,9, 11–17 is vital for generating reliable, comparable data, yet even with such controls, methodological, instrumental, and population differences can still create inter-study variation.
Conclusion
The primary outcome of this study is a set of normative conduction parameters for common upper and lower limb nerves, which will be valuable for evaluating patients with peripheral nerve abnormalities in our local geographic area. The analysis revealed that gender had an impact on the sensory amplitudes and distal motor latencies of the median and ulnar nerves; the observed gender differences in CMAP latencies may be attributable to height differences. Furthermore, the study confirmed an age-related decline in both sensory and motor nerve conduction velocities and in the amplitudes of CMAP and SNAP.
Footnotes
Abbreviations
AANEM: American Association of Neuromuscular and Electrodiagnostic Medicine
BMI: Body mass index
CMAP: Compound muscle action potential
L: Left
NCS: Nerve conduction study
NCV: Nerve conduction velocity
NDTF: Normative data task force
NP: Baseline-to-peak
PP: Peak-to-peak
R: Right
SNAP: Sensory nerve action potential
Acknowledgement
We gratefully acknowledge Ms Mangal Jyoti, our technician, for her invaluable assistance in recording the NCS of all participants.
Authors’ Contribution
Rupali Parlewar: Concept, design of methodology, statistical analysis, preparation of manuscript.
Prashant Kumar Saini: Data analysis, manuscript preparation.
Madhu Bala: Data collection, literature search, manuscript preparation.
Punam Verma: Concept, design of methodology.
Hitesh Jani: Literature search, manuscript preparation.
Priti Bhanderi: Concept, definition of intellectual content, data collection.
Bhoopendra Patel: Literature search, data collection, manuscript review.
Navdeep Ahuja: Data analysis, manuscript preparation.
Harshali Rankhambe: Design of methodology, manuscript preparation.
Ashish Sharma: Concept, data collection
Data Availability Statement
Data will be provided to the seekers by contacting the corresponding author.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Part of a larger ICMR-funded project titled ‘A cross-sectional study of neurophysiological and biochemical parameters in hypothyroid patients of hilly regions of Himachal Pradesh’ with ID:2021-13627.
Patient Consent
Informed consent was obtained from each of the patient before their participation in the study.
Statement of Ethics
Approval from the Institutional Ethics Committee of All India Institute of Medical Sciences, Bilaspur, Himachal Pradesh, was obtained before conducting the study.
