Dorsal Ulnar Cutaneous Nerve Conduction Study Based on Nerve Ultrasound

doi:10.21203/rs.3.rs-4008931/v1

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Dorsal Ulnar Cutaneous Nerve Conduction Study Based on Nerve Ultrasound

https://doi.org/10.21203/rs.3.rs-4008931/v1

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published 03 Sep, 2024

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This study investigates the impact of the anatomical separation point of the dorsal ulnar cutaneous nerve (DUCN) on nerve conduction studies (NCS). Involving 26 subjects with DUCN NCS findings, it utilizes ultrasound to mark the DUCN's divergence from the ulnar nerve. NCS was performed at four points relative to the separation point. The findings indicate the maximal amplitudes occurred 2cm distal to the separation point, with significant amplitude reduction observed at 4cm. The study suggests optimal NCS results when stimulation occurs between the separation point and 2cm distal to it.

dorsal ulnar cutaneous nerve

Nerve ultrasound

Nerve conduction study

The dorsal ulnar cutaneous nerve (DUCN), a terminal branch of the ulnar nerve, plays a critical role in sensory functions of the ulnar aspect of the hand.^1,2 This branch supplies sensation to the dorso-ulnar aspect of the hand, dorsum of the little finger, and dorso-ulnar aspect of the ring finger.^3,4 Neuropathy of the DUCN may result in numbness, dysesthesia, and pain in the innervated area of the DUCN.⁵ The DUCN has a variable origin in the forearm and may arise from either the proximal, middle, or most commonly the distal third of the forearm.^1,6 Due to its superficial positioning, the DUCN is susceptible to neuropathy caused by lacerations and blunt trauma. Additionally, its anatomical variability can lead to iatrogenic injuries during surgical procedures in the ulnar area.^5–7

Although sensory nerve conduction studies help identifying DUCN lesions⁸, the technique for nerve conduction studies(NCS) of the DUCN lacks standardization, and they may not adequately account for the variability in the branching pattern of the DUCN⁹, presenting challenges in accurately diagnosing ulnar neuropathies.^10,11 Meanwhile, in previous research, ultrasonography has been reported as a valuable tool in assessing conditions related to nerves¹², as it enables precise localization through confirmation of the nerve's anatomical structure.¹³

This study aims to bridge this gap by investigating the impact of the anatomical separation point of the DUCN on NCS results, utilizing ultrasonography to enhance the precision of these evaluations. By identifying the optimal stimulation points for maximum amplitude in NCS, we seek to improve the diagnostic accuracy for conditions involving the DUCN. The research integrates ultrasonographic findings with NCS, providing a comprehensive analysis of the DUCN's behavior in various anatomical positions.

This study was approved by the Institutional Review Board of Yeouido St. Mary’s Hospital (SC24RISI0024) and was conducted in compliance with the principles of the Declaration of Helsinki and its contemporary amendments and Good Clinical Practice. Participants were recruited, and written informed consent was obtained. Total 26 subjects were studied who showed normal ulnar sensory, motor, and DUCN NCS findings without any history of neuropathy or injury involving distal upper extremities. Nerve ultrasound using a 7 to 12 MHz linear array transducer performed on each participant’s unilateral arm, and the dorsal cutaneous ulnar nerve was evaluated by experts with more than 2 years of experience in musculoskeletal ultrasound. The separation point of DUCN from ulnar nerve was marked on subject’s skin and distance from ulnar styloid process were measured.

Nerve conduction study

The studies were performed by a qualified electromyographer. To study the dorsal cutaneous ulnar nerve, the active electrode was placed on proximal web space between fourth and fifth metacarpal bones. Reference electrode placed on base of the fifth digit. The DUCN was stimulated with the intensity of 25 mA at 4 different points; 2cm proximal to separation point(P2), DUCN separation point(S), 2 cm distal to separation point(D2), 4 cm distal to separation point(D4) according to DUCN course identified with ultrasound. Peak latencies and amplitudes of each stimulation points were measured. Difference between these NCS data were statistically analyzed. (Fig. 1)

Statistical analysis

Demographic factors, distances between the separation points and anatomic landmarks, cross-sectional areas, and all nerve conduction study results are presented as mean ± SD. The Spearman correlation test was performed to investigate the correlation between the location of the separation point and demographic factors. Analyses were performed using SPSS software (12.0; SPSS Inc, Chicago, IL). P values less than 0.05 were considered statistically significant.

The demographics of all subjects are shown in Table 1. The age, height, weight, and body mass index of the 26 participants (9 men and 17 women) were 52 ± 16.54 years, 163.34 ± 8.51 cm, 60.94 ± 11.67 kg, and 22.72 ± 2.90 kg/m2, respectively.

Table 1

Dermographic characteristics of subjects
Total subjects	26
Sex M : F	9 : 17
Age (years)	52 ± 16.54
Side (right : left)	15 : 11
Height (cm)	163.34 ± 8.51
Weight ( Kg)	60.94 ± 11.67
BMI (Kg/m²)	22.72 ± 2.90
Distance from styloid process (cm)	3.92 ± 1.29
All values are presented as mean ± SD. The distance was measured between the separation point of dorsal ulnar cutaneous nerve and the ulnar styloid process.

In examining the dorsal ulnar cutaneous nerve (DUCN) via ultrasonography, (Fig. 2) we noted the average distance from the ulnar styloid process to the separation point of the DUCN to be 3.92 ± 1.29 cm (range 1.5 ~ 6.5 cm). The results of the sensory nerve conduction study are shown in Table 2. The mean SNAP amplitudes at these points varied, with the highest amplitude observed 2cm distal to the separation point.

Table 2

Mean SNAP amplitude of dorsal ulnar cutaneous nerve
Stimulation Site	P2	S	D2	D4
Amplitude (µV)	23.7 ± 12.1	28.9 ± 14.3	31.9 ± 15.5	29.4 ± 15.6
All values are presented as mean ± SD. The largest amplitude is presented in bold.
S : Separation point of dorsal ulnar cutaneous nerve, P2 : 2cm proximal to separation point, D2 : 2cm distal to separation point, D4 : 4cm distal to separation point

In Table 3, statistical analysis revealed significant differences in SNAP amplitudes at certain points, with a noteworthy difference observed when comparing the point 2 cm proximal to the separation point and 2 cm distal to it (p-value: 0.04), suggesting anatomical variations at these points influence SNAP outcomes.

Table 3

T-test results of each points
Stimulation site	P2	S	D2	D4
P2 (p-value)	-	0.16	0.04*	0.15
S(p-value)		-	0.48	0.93
D2 (p-value)			-	0.56
All values are presented as mean ± SD.
S : Separation point of dorsal ulnar cutaneous nerve, P2 : 2cm proximal to separation point, D2 : 2cm distal to separation point, D4 : 4cm distal to separation point
*: Statistaically significant difference (p-value < 0.05)

Our study shows that separation point may have a significant effect on sensory nerve conduction of the DUCN. The distance between the separation points and the ulnar styloid process has been reported to vary between 4.8 and 10.0cm^1,2,14, which is longer than the average of 3.92 ± 1.29 cm in the present study. This discrepancy may be attributed to the fact that the current study enrolled only Korean subjects and had a gender distribution skewed towards females. Additionally, as can be observed from the results of previous studies, it is apparent that there is considerable variation contingent upon the population group studied.

Based on the previous study^15,16, the conventional conduction study for the DUCN is performed by placing the active electrode between the fourth and fifth metacarpals and positioning the reference electrode at the base of the fifth digit, with stimulation applied 8cm proximal to the active electrode. However, conventional nerve conduction studies may not fully reflect the anatomical variations of the DUCN, and in previous study, they exhibited decreased latency compared to sono-guided conduction studies.¹⁰

DUCN can be well visualized from its point of branching from the ulnar nerve at the distal third of the forearm to the point where it pierces the antebrachial fascia to become subcutaneous in sonography.^1,13 We identified the separation point of the DUCN using ultrasonography and stimulated the DUCN at four different stimulation sites based on the separation point and the statistical analysis revealed a significant difference when comparing 2 cm proximal (P2) and 2 cm distal (D2) from the separation point (p-value: 0.04). However, there was no significant difference between P2 and D4. This result may be caused by the mixed effect of anatomic variations such as the depth of the nerve from skin, fascia penetration effect, physiologic temporal dispersion or stimulus artifact. In addition, when performing DUCN conduction, the ulnar nerve is often unintentionally stimulated and the posterior part of the SNAP wave of the DUCN is obscured by the CMAP of thenar muscles such as the abductor digiti minimi. Stimulating only DUCN with appropriate intensity helps obtain a clear SNAP waveform.

The results of our study showed that DUCN stimulation at D2 had significantly higher SNAP amplitudes than those at other stimulation points, suggesting that the separation point should be considered in DUCN conduction studies. Thus, stimulating around D2 will be helpful for acquiring a more reliable SNAP amplitude in the dorsal ulnar cutaneous nerve.

Our study had several limitations. First, this study enrolled only healthy subjects. The parameters in this study may not be directly applied in the patient with dorsal ulnar cutaneous neuropathy. The question of whether nerve ultrasound should be performed together during nerve conduction study is still controversial and requires consideration of various factors. It will cause additional costs and facilities. However, if it is performed by experts, it has the advantage of reducing painful electrical stimulation to the patient without increasing the test time.¹⁷ and also can increase the accuracy and reliability of the diagnosis in reports studying other nerves.¹⁸

Second, the small sample size and the sex ratio being biased toward women are other limitations of this study. Large-scale studies with similar sex ratios are required for reaching a generalized conclusion. Third, this study did not compare side-to-side discrepancies. According to previously research, the bilateral difference in an individual's DUCN SNAP can reach up to 21%.¹⁹ Therefore, further study is thus necessary in patients including on side-to-side discrepancies.

In conclusion, the result of this study suggests to stimulate between separation point and 2cm distal to separation point according to the DUCN course identified with nerve ultrasound, to obtain the maximal amplitude of DUCN.

Competing interests

The author(s) declare no competing interests.

ACKNOWLEDGMENTS

This research was supported by a grant from the Institute of Clinical Medicine Research in Yeouido St. Mary’s Hospital, Catholic University of Korea.

Data availability statement

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

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No competing interests reported.

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You are reading this latest preprint version

Dorsal Ulnar Cutaneous Nerve Conduction Study Based on Nerve Ultrasound

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Abstract

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Introduction

Method

Nerve conduction study

Statistical analysis

Results

Discussion

Declarations

References

Additional Declarations

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