Normative data for ulnar nerve conduction and the influence of gender and height on ulnar nerve conduction velocity in healthy Nigerians.

Background: Despite the usefulness of ulnar nerve conduction studies in identifying disorders of ulnar nerves, there is a lack of normative values for the ulnar nerve in Nigerian population. Objective: The objective of the study was to generate normative values for motor and sensory ulnar nerve conduction studies (NCSs) in Nigerian population and to determine the influence of gender and height on ulnar nerve conduction velocity (NCV). Materials and
Methods: A total of 200 healthy volunteers were selected after clinical evaluation to exclude common causes of ulnar neuropathy. We carried out NCS of ulnar nerves on all the healthy volunteers according to a standardized protocol. The NCS parameters included in the final analysis were amplitude, latency, NCV, and f-wave latency. Ethical approval was obtained for the study.
Results: The mean ulnar nerve sensory velocity was 55.22 ± 5.67 with 2.5 and 97.5 percentile of 46.9 and 70.1, respectively. The mean latency of the ulnar nerve (sensory) was 2.97 ± 0.62 with 2.5 and 97.5 percentile of 2.00 and 4.52, respectively. The mean amplitude of the ulnar nerve (sensory) was 35.56 ± 9.97 with 2.5 and 97.5 percentile of 15.9 and 57.7, respectively). The ulnar NCV was significantly (P = 0.0202) higher in male. Mild inverse correlation (r = 0.2) was found between ulnar NCV and height of the participants (P = 0.0089).
Conclusion: In the Nigerian population, normative values of motor and sensory ulnar nerve conduction parameters are similar to the existing values in the literature. The ulnar NCV appeared to be influenced by height and gender.

INTRODUCTION

The role of nerve conduction studies (NCSs) in the diagnosis of diseases of the peripheral nervous system (PNS) cannot be overemphasized. Central to the diagnosis of any PNS disease is the ability to distinguish between healthy individuals and those with the disease.[1] NCS is used to assess the function of the conduction of the motor and the sensory nerves. It is often used in the diagnosis of polyneuropathies, mononeuropathies, radiculopathies, compressive neuropathies, and other common diseases of the PNS.

Ulnar neuropathy is a commonly encountered peripheral neuropathy either in acute diseases such as after elbow trauma or in chronic diseases such as in diabetic neuropathy and chronic compression neuropathy.[2] In any case, meticulous clinical assessment and discerning evaluation of neurophysiologic assessment are veritable means of diagnosing and finding out the extent and distribution of peripheral nerve injury as well as in determining the prognosis of recovery of ulnar nerve disorder with management. Consequently, for diagnostic purposes, definitions of the upper and lower limits of the routinely recorded NCS parameters such as latency, amplitude, and velocity is imperative.

The relevance NCS in evaluation of peripheral nerve abnormality is becoming increasingly recognized in Nigeria. The neurophysiology laboratories available in Nigeria adopted the reference values generated outside the country to diagnose different ulnar nerve abnormalities. To identify the abnormality of ulnar nerve, there is a need for reference data from the local population. Literatures on nerve conduction parameter normative values for different nerves including ulnar nerves are enormous worldwide.[13456] It is often most desirable and encouraged in a clinical setting to have reference values that are derived from the same population or from a sample population that approximates, as closely as possible, the demographic characteristics of the patient being tested.[3] The few reports available on NCS normative values from Nigeria were focused on median[7] and sural nerves,[8] but there is no published account on ulnar nerves in the country.

Nerve conduction velocity (NCV) is affected by many fact1ors such as temperature, height, age, and gender, which in turn may vary in the different geographic region and ethnic groups. Quite ironically, NCV is very rarely correlated with these physiological variables.

This study was designed to obtain reference values for ulnar motor and sensory nerve conduction from healthy Nigerians and evaluate the relationship of the nerve conduction parameters with the demographic and anthropometric parameters.

MATERIALS AND METHODS

Study site

The data were collected over a 6-month period at the neurodiagnostic laboratory of the Aminu Kano Teaching Hospital (AKTH), Bayero University, Kano, Nigeria. The hospital is the reference hospital in the region, serving the residents of Kano and the neighboring northwestern states of Nigeria. The hospital has a neurophysiology center with electromyography (EMG) and electroencephalography machines.

Study design and participants

The study was a cross-sectional study with a total sample of 200 healthy volunteers, calculated using Cochran's sample size formula for continuous data.[9] The volunteers were selected using simple random sampling technique.

All individuals that volunteered to participate in the study were screened for inclusion criteria that comprised apparently healthy volunteers with normal neurological physical examination, absence of symptoms of neuropathy from any cause, and nonuse of alcohol.

We used a standardized questionnaire to exclude those with a history of systemic or neuromuscular diseases. Individuals that were excluded included those with a history of alcohol abuse or medications that might affect the results of NCS and those with a history of diabetes, hypothyroidism, and systemic diseases. None of the individuals was taking any medication at the time of conducting the EMG study. We performed a basic neurological examination to assess muscle power, stretch reflexes, and sensations. The clinical parameters obtained from the participants were age, gender, dominant hand, and temperature. Anthropometric parameters obtained from the participants included height, second digit (2D) and fourth digit (4D) length with 2D/4D ratio, weight, and body mass index (BMI). Anthropometric measurements of participants were carried out while they stood in light clothing without shoes, and digital caliper was used to measure the second digit length (2D) and fourth digit length (4D) using a standard protocol.

Nerve conduction study

NCS was carried out using a four-channel EMG machine (Nihoen Kohden Inc., Tokyo, Japan). The procedure was performed with the participants lying comfortably in the supine position. A standardized technique was used to obtain and record action potentials for motor and sensory functions.[10] The protocol adopted in the current was like that elsewhere, with minor alteration.[11]

The setting used in the study was as follows: for ulnar motor nerve conduction, the low cut filter was 3 Hz and the high cut was 10 KHz, the sweep was at 2–5 ms/division, and a stimulus duration of 50 μs–1000 μs and current 0–50 mA were used for effective nerve stimulation. Supramaximal stimulation (20%–30% more than the current required for maximal action potential) was used. For sensory ulnar nerve conduction, low cut was set at 10 Hz, high cut was set at 2 KHz; the amplification between 20,000 and 100,000 times; electrode impedance was kept below 5 kΩ, and the sweep speed for sensory nerve conduction was maintained at 1–2 ms/division.

We collected data for proximal and distal latency measured from the onset of the action potential, conduction velocity, amplitude, and minimum f-wave latency of compound muscle action potential (CMAP) and sensory nerve action potential measured from positive peak to the negative peak. All the studies were performed with surface recordings and stimulations.

Ulnar motor nerve study

We performed distal stimulation of the ulnar (orthodromic) nerve at the wrist 3–4 cm proximal to distal wrist crease just medial to the flexor carpi ulnaris tendon to activate the CMAP at the center of abductor digiti minimi recorded with an active electrode (G1) and reference recording electrode (G2) placed at the fifth metacarpophalangeal joint. The proximal stimulation point was at elbow 3–4 cm distal to the medial epicondyle, with the wrist and the elbow in 90° of flexion. The ground electrode was placed between the stimulator and the active electrode. Motor amplitude, distal latency, proximal latency, and motor conduction velocity (MCV) were the parameters measured.

Ulnar nerve F-wave

The F-waves were acquired using standard electrode locations for routine motor studies. It was done with the gain changed to 200 V per division, and the sweep speed increased to 5 ms per division. At least ten supramaximal stimuli were delivered. The minimum latency (F-min), maximum latency (F-max), and range of F-wave latencies (F-range) were acquired.

Ulnar sensory study

The ulnar sensory stimulation (antidromic) was at the wrist 14 cm from the active recording electrode. Active recording electrode of the ulnar sensory nerve was placed on proximal phalanx (G1) of digit 5 and reference electrode distal to G1. The ground electrode was placed between the stimulator and the active electrode.

Sensory peak to peak amplitude, distal latency, and MCV were the parameters measured.

Statistical analysis

Statistical analysis was performed using STATA version 12 (Stata Corp, Texas, USA). For both motor and sensory (median and ulnar) nerves, the following parameters were analyzed: the distal motor latency, CMAP amplitude, MCV, and minimum latency of the motor nerves. Descriptive statistics including means with standard deviation for continuous variables and proportions for categorical variables such as gender were computed. The normal reference range of nerve conduction values was set by the 2½ (lower limit) and 97½ (upper limit) percentiles, so that reference ranges contain the central 95% of the distribution. The differences in means of parametric variables such as latency, amplitude, and velocity by gender were assessed using student t-tests numerical variables. The strength of correlation of the nerve conduction parameters with height was calculated with Pearson correlation coefficients (r). The value of the correlation coefficient varies from −1 to +1 with a value near −1 indicates a strong negative correlation, and a value near +1 indicates a strong positive correlation. All statistical tests of hypotheses were two sided at 5% significance level.

Ethical approval

Informed consent was taken from each of the participants, and ethical approval was obtained from the ethics review committee of the AKTH, Kano.

RESULTS

Sociodemographic and clinical characteristics

A total of 200 participants were seen during the study period. Their age ranged between 11 and 91 years, with a mean age of 44.95 ± 20.7 years. Table 1 shows the distribution of their age by gender. They comprised 84 (42%) females with a mean age of 44.9 ± 16.9 and 116 (58%) males with a mean age of 44.8 ± 21 years. There was no significant difference in their age (P = 0.9593). About two-third (64%) of the participants were civil servants. The mean height, weight, and BMI of the participants were 167.6 ± 11 cm (M = 167 ± 11, F = 167.6 ± 10), 68.8 ± 17 kg (M = 64.3 ± 16, F = 75.1 ± 16), and 24.8 ± 6.7 (M = 23.3 ± 7, F = 26.9 ± 7). There was a statistically significant difference in weight (P < 0,001) and BMI (P = 0.0001) but not height (P = 0.7115) by gender of the participants.

Table 1

Age distribution of the healthy volunteers

Age group	Male	Female	Total
10–19	18	8	26
20–29	12	9	21
30–39	27	8	35
40–49	7	26	33
50–59	25	20	45
60–69	10	4	14
70–79	0	3	3
80–89	13	6	19
90–99	4	0	4
Total	116	84	200

Normative values for ulnar motor nerve conduction parameters

The mean ulnar nerve motor velocity in the healthy volunteers was 57.9 ± 3.2 with 2.5 and 97.5 percentile of 49.9 and 61.7, respectively. The mean latency of ulnar nerve was 2.7 ± 0.9 with 2.5 and 97.5 percentile of 1.5 and 4.6, respectively. The mean amplitude of ulnar nerve was 7.2 ± 1.4 with 2.5 and 97.5 percentile of 4.9 and 10.6, respectively. The minimum median f-wave latency of ulnar nerve (motor) was 26.5 ± 5.2 with 2.5 and 97.5 percentile of 17.5 and 36.5, respectively [Table 2].

Table 2

Velocity, latency, and amplitude of median nerve (Motor) in healthy volunteers

Ulnar nerve (motor)	Velocity	Distal latency	Proximal latency	Amplitude	F-wave maximum latency
Mean	57.9	2.7	6.6	7.2	26.5
Standard deviation	3.2	0.9	1.3	1.4	5.2
2.5 percentile	49.9	1.5	4.1	4.9	17.5
97.5 percentile	61.7	4.6	8.8	10.6	36.5

*Ulnar

Normative values for ulnar sensory nerve conduction parameters

The mean ulnar nerve sensory velocity was 55.22 ± 5.67 with 2.5 and 97.5 percentile of 46.9 and 70.1, respectively. The mean latency of ulnar nerve (sensory) was 2.97 ± 0.62 with 2.5 and 97.5 percentile of 2.00 and 4.52, respectively. The mean amplitude of median nerve (sensory) was 35.56 ± 9.97 with 2.5 and 97.5 percentile of 15.9 and 57.7, respectively [Table 3]. Table 4 shows a comparison between the reference values for ulnar nerve from the current study and elsewhere.

Table 3

Velocity, latency, and amplitude of ulnar nerve (sensory) in healthy volunteers

Median nerve (sensory)	Velocity (m/s)	Latency (ms)	Amplitude (μv)
Mean	55.22	2.94	35.76
Standard deviation	5.67	0.62	9.97
2.5 percentile	46.9	2.0	15.9
97.5 percentile	70.1	4.52	57.7

Table 4

Comparison of ulnar motor nerve conduction study parameters to studies elsewhere

Study	Sample size	Age group	Distal latency*	Amplitude*	Velocity
Motor
Kimura	65	13–74	2.59±0.39	5.7.0±2.0	58.7±5.1
Misra and Kalita	30	16–65	2.59±0.40	8.51±2.0	61.45±5.73
Hennessey WJ, Falco WJ	44	Young adult	2.6±0.3	12.6±3.6	63±4.8
Shehab et al.	50	16–56	2.4±0.3	11.07±2.8	56.5±3.5
Current study	200	11–86	2.7±0.9	7.2±1.4	57.9±3.2
Sensory
Kimura	65	13–74	2.54±0.29	35.0±14.7	54.8±5.3**
Misra and Kalita	30	16–65	2.83±0.4	5.54±2.4	54.2±6.1**
Shehab et al.	50	16–56	2.0±0.2	54.5±18.4 male, 63.9 ±16.8 female	52.3±5.3
Current study	200	11–86	2.94±0.6	35.76±14.7	55.2±5.7**

*Below elbow, **Base to peak

Relationship between ulnar nerve parameters, demographic, and anthropometric variables

The mean value of ulnar conduction velocity was significantly (P = 0.0202) higher in male volunteers (58.27 m/s) than their female counterparts (57.33 m/s). Figure 1 shows the distribution of ulnar nerve conduction parameters by the gender of the participants. Mild inverse correlation (r = 0.2) was found between ulnar NCV and height of the participants (P = 0.0089) [Table 5]. Figure 2 shows the best line of fit with 95% confidence interval of the relationship between ulnar MCV and height. No significant relationship was found between ulnar NCV, age, and D2/D4 ratio. Table 5 displays the correlation matrix among ulnar motor NCV, the demographic and anthropometric variables. No significant relationship was found between ulnar sensory NCV and height (r = 0.006, P = 0.9296) [Figure 3 and Table 5]. Similarly, no significant correlation was found between ulnar sensory conduction velocity, the demographic and anthropometric variables [Table 5].

Figure 1

The distribution of ulnar nerve conduction parameters by gender

Table 5

The correlation matrix between ulnar nerve conduction velocity, age, height, and average D2/D4 ratio

Variables	Ulnar nerve conduction velocity
	Coefficient of correlation (r)	P
Motor
Age	0.05	0.04078
Height	−0.2	0.0089**
Average D2/D4*	−0.1	0.1705
Sensory
Age	0.1	0.0658
Height	0.01	0.9296
Average D2/D4*	0.06	0.3962

*Ratio of second to fourth digit, **Statistically significant

Figure 2

The best line of fit with 95% confidence interval of the relationship between ulnar motor conduction velocity and height

Figure 3

The best line of fit with 95% confidence interval of the relationship between ulnar sensory conduction velocity and height

DISCUSSION

Reliable and locally generated normative data are fundamentally important for everyday interpretation of diagnostic evaluation and the practice of neurology. Our study examined the nerve conduction parameters of ulnar of young and old healthy individuals. We drew a comparison between the results of our study and existing studies published data in the literature. Our results for the motor parameters of the ulnar NCS agree generally with Kimura et al.,[10] Mistra and Kalita,[12] Shehab et al.,[13] and Hennessey and Falco et al.[4] Similarly, the data in the current study for the sensory parameters of the ulnar NCS conform largely, with little difference, with those of Kimura et al.,[10] Mistra and Kalita,[12] and Shehab et al.[13]

The little variation observed among the studies could be attributed to differences in demography, anthropometry, and race of the different population in the different studies underscoring the need for the necessity of reference values for every neurophysiology laboratory. In addition, differences in the methodology adopted in these various studies ranging from heterogeneous sample sizes, sample selection, and nerve conduction techniques to method of data analysis could also have contributed to the observed differences in the reference values.[3456]

The current study found significantly higher ulnar conduction velocity in male than their female counterparts. The effect of gender on nerve conduction parameters is shrouded in controversy. Varying data exists in the literature on influence of gender on nerve conduction latencies, amplitudes, and velocities with some reports in favor of greater parameter values in males than females[141516] while the others showed the reverse.[417]

Our study did not find a strong correlation between ulnar nerve conduction parameters and age. Evidence from the literature, however, showed that the influence of age is most remarkable at the extremes of age.[18] Because of incomplete myelination at birth, the nerve conduction velocities are about a half of what obtains in adulthood reaching approximately 75% by the end of 1st year of life and attains adult level by 3–5 years of age when full myelination has been achieved. This trend could not have been captured in the current study as the minimum age of the participants was 11 years. On the order hand, NCV decreases with age on account of decreasing number of nerve fiber, a continuously diminishing fiber diameter, and some molecular changes in the nerve membrane that occurs with age.[19]

We found an inverse relationship between height and conduction velocity. This observation is in agreement with reports from other studies in the literature.[20212223] The influence of height on nerve conduction parameters has long been ascribed to distal tapering of axons in taller individuals, shorter intermodal distance, and progressive reduction in axonal diameter in taller individuals.[12] The same reasons the lower limb nerves generally are slower than the nerves in the upper limbs.[12]

Strength and limitations of the study

The decision as to whether the value derived from the assessment of ulnar nerve, in a patient from a particular population, is normal or abnormal is hinged on what is considered normal for that particular population. The normative values in the current study were derived from one of the largest sample size on normative data derivation studies. Our study also explored the influence of demographical variables that could impact the outcome of a NCS in an electrophysiology laboratory such as age, gender, and height. To the best of our knowledge, this study is the first of its kind to emanate from Nigeria.

It is worthy of note that there are many sources of error that should be taken into consideration while interpreting NCS parameter from any nerve. Temperature affects NCS parameters. In the current study, temperature control beyond ambient and participant body temperature was not focused on; thus, these results might be more applicable to patients seen in routine neurophysiology laboratories in a poor-resource setting where there is a dearth of facilities for temperature control.

CONCLUSION

Normative values of ulnar nerve were established for the Nigerian population. Overall, sensory and motor nerve conduction parameters for the ulnar nerve compared favorably with the existing literature data. Ulnar conduction velocity appeared to be influenced by height and gender.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.