Carpal Tunnel: Nerve Assessment Using Ultrasound Technology

Carpal Tunnel: Nerve Assessment Using Ultrasound Technology

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Background

Carpal Tunnel Syndrome (CTS) is a reasonably prevalent nerve condition that affects many people worldwide. It happens when the median nerve, which transverses from the forearm into the palm of the hand, becomes compressed or squeezed at the wrist. This compression causes numbness, pain, and tingling in the hand and fingers, making everyday tasks difficult. To diagnose CTS, doctors typically rely on a combination of symptoms reported by the patient, physical examination findings, and nerve conduction studies (NCS), which measure how well the nerves in the hand are functioning
[1].

While NCS help diagnose CTS, they may not always detect the condition, particularly in cases where symptoms are present but nerve function appears normal. Research suggests that up to 15% of patients with clinical symptoms of CTS may have typical NCS results [2].

Experts recommend using ultrasound (US) imaging in conjunction with NCS to improve diagnostic accuracy. US allows doctors to visualize the structures inside the wrist, including the median nerve and can provide additional information to support the diagnosis of CTS [3].

One of the challenges in using the US for diagnosing CTS is determining the most accurate parameter to measure. Recent studies have focused on examining the median nerve’s cross-sectional area (CSA) at the wrist, as this parameter has shown promise in distinguishing between patients with CTS and those without [4].

However, researchers still need to agree on the specific cutoff values that indicate abnormal CSA, making it challenging to establish standardized diagnostic criteria [5].

Additionally, variations in scanning protocols and differences in US devices used in previous studies have made it difficult to compare results and apply findings to clinical practice [6].

Recently, a new ultrasound-based technique called Shear Wave Elastography (SWE) has gained attention for its potential role in diagnosing CTS. SWE measures the stiffness of tissues by analyzing the speed of shear waves passing through them. Preliminary research suggests that SWE can detect changes in median nerve stiffness associated with CTS, offering a complementary approach to traditional diagnostic methods [7].

However, further investigation is needed to determine the optimal use of SWE in diagnosing and monitoring CTS and to establish its place in clinical practice [8].

 

The Study Method

The study recruited 47 patients who volunteered for ultrasound (US) examination following an electrodiagnostic survey, which included nerve conduction studies (NCS) and needle electromyography (EMG). These patients were referred to the Department of Clinical Neurophysiology due to various symptoms in their upper extremities, excluding those with findings suggestive of cervical radiculopathy or polyneuropathy. The study was ethically approved, and all participants provided written informed consent. Patients were asked about symptoms such as numbness, nocturnal pain, and tingling in the median nerve (MN) distribution. These symptoms are typical early signs of Carpal Tunnel Syndrome (CTS). The severity of CTS was assessed based on NCS results, classifying wrists into four groups: normal, mild, moderate, and severe to extreme CTS.

The US examinations were conducted by a trained clinical neurophysiologist using a Samsung RS85 Prestige device with a linear transducer LA2-14A.

The protocol followed recommendations for nerve Shear Wave Elastography (SWE), which involved studying nerves in a longitudinal orientation and reporting SWE results as shear wave velocity (SWV) in meters per second (m/s). During the examination, patients sat with their examined hand placed on a table, palm facing upwards, fingers in relaxed semi-flexion, and elbow at approximately 90 degrees to avoid traction of the MN. Care was taken to ensure no extra pressure was applied during the SWE examination. 

The median nerve’s cross-sectional area (CSA) was measured at the wrist crease and distal forearm in transverse orientation using conventional B-mode imaging. SWE was also performed at three sites: wrist crease, forearm at the distal forearm CSA measurement site, and carpal tunnel. Measurements were taken using a 2D color stiffness map applied to a B-mode image, and three regions of interest points were selected for each site to ensure reliable measurements. The mean of these points was recorded for each measurement site, and the wrist-to-forearm ratio for both CSA and SWE measurements was calculated to assess nerve stiffness. The study protocol included detailed imaging procedures to ensure standardized and reliable participant measurements.

 

Analysis

 
The statistical analysis of the research data was conducted using IBM SPSS Statistics 26 software. Correlations between variables were tested using Spearman’s rho, a nonparametric measure of association. To assess differences between groups, statistical tests such as ANOVA (Analysis of Variance), Mann-Whitney U test, or Kruskal-Wallis test were employed, depending on the nature of the data and the number of groups being compared. In cases where multiple comparisons were made, Bonferroni correction was used to control for the raised risk of Type I error. This rigorous statistical approach ensured the accuracy and reliability of the findings by accounting for potential confounding factors and minimizing the likelihood of spurious results.

 

Results

1. Patient Demographics:

• The study involved 86 wrists from 47 patients, including 17 male and 30 female patients.

2. Association between NCS Results and Ultrasound Measurements:

• The cross-sectional area at the wrist (wCSA) and shear wave elasticity (wSWE) were significantly smaller in the NCS negative group compared to the NCS positive group (p < .001 for both).
• Both wCSA and wSWE showed positive correlations with the severity of Carpal Tunnel Syndrome (CTS) (r = .619, p < .001; r = .582, p < .001, respectively).
• The CSA-WFR (Wrist to Forearm ratio) and SWE-WFR also correlated positively with CTS severity groups (r = .377, p < .001; r = .409, p < .001, respectively).

3. No Significant Correlations with Shear Wave Elastography at Other Sites:

• The shear wave elastography (SWE) measurements at the carpal tunnel (tSWE) and forearm (fSWE) did not show significant correlations with CTS severity groups.
• No significant differences were found in tSWE between the NCS negative and positive groups.

4. Diagnostic Performance of Ultrasound Parameters:

• The receiver operating characteristic (ROC) curve investigation showed good diagnostic performance for both wCSA and wSWE in differentiating between the NCS negative and positive groups.
• The area under the curve (AUC) was 0.895 for wCSA and 0.868 for wSWE, with optimal cutoff values identified as 10.5 mm² for wCSA and 4.12 m/s for wSWE.

 

5. Symptomatology and Ultrasound Measurements:

• Both wCSA and wSWE were significantly higher among symptomatic patients than asymptomatic patients (p = .002 and p = .009, respectively).
• There was no significant correlation between the duration of symptoms and wCSA or wSWE.

6. Additional Findings:

• In the NCS negative group, wCSA correlated positively with patient BMI but not age, height, or weight.
• No correlations were found between wSWE, fSWE, or tSWE and patient BMI, age, height, or weight.

These results highlight the diagnostic potential of wCSA and wSWE in distinguishing between CTS positive and negative cases, providing valuable insights into the severity and symptomatology of CTS. Additionally, the study expounds on the importance of considering multiple parameters in diagnosing and assessing CTS severity.

 

 

DISCUSSION

The discussion delves into the implications of the study’s findings regarding the use of Shear Wave Elastography (SWE) in diagnosing Carpal Tunnel Syndrome (CTS) [1]. SWE could offer additional diagnostic insights beyond traditional methods. The positive correlation between wSWE and CTS severity indicates that wSWE may be as effective as the commonly used parameter, wCSA, in diagnosing CTS [1].

Despite wCSA demonstrating slightly higher specificity, wSWE exhibits greater sensitivity, particularly when compared to nerve conduction studies (NCS), which serve as a gold standard [1].

Furthermore, the study highlights the importance of choosing the optimal site for SWE measurement. Conducting SWE at the carpal tunnel inlet proved more reliable than within the tunnel itself, as measurements within the tunnel did not correlate with CTS severity. This disparity could be attributed to variations in intra-tunnel pressure and the restrictive anatomy of the carpal tunnel, impacting SWE accuracy [1].

Comparisons with previous research reveal consistency in findings, albeit with minor differences in absolute values, possibly due to variations in ultrasound devices and protocols [1]. The discussion also addresses the influence of patient characteristics on SWE results. While factors like age, height, and weight did not significantly affect wSWE, a mild positive association was observed between wCSA and BMI, warranting further investigation [1].

 

Moreover, the integration of patient-reported symptoms alongside objective measures is emphasized. Given the potential for NCS to miss some symptomatic cases, incorporating subjective symptoms in diagnostic assessments could enhance accuracy. However, the discussion acknowledges the limitations of NCS sensitivity, particularly in detecting very mild cases of CTS, necessitating a comprehensive approach to diagnosis [1].

Overall, the discussion underscores the promising role of SWE in augmenting CTS diagnosis, advocating for further research to validate these findings in more extensive and diverse patient cohorts. Such investigations should integrate objective measures and subjective symptoms to ensure comprehensive diagnostic accuracy in clinical practice [1].

 
 

LIMITATIONS

1. Small Sample Size:

• The study’s small sample size poses a significant limitation, although the results align with previous literature.

2. Lack of Blinding in Measurements:

• Both Cross-Sectional Area (CSA) and Shear Wave Elastography (SWE) measurements were conducted by the same physician without blinding to ultrasound (US) results during SWE, potentially introducing bias. However, the objectivity of parameters and pre-agreed measurement sites mitigates this concern.

3. Limited Measurement Area for CSA:

• CSA was solely measured from the inlet of the carpal tunnel, potentially overlooking nerve enlargement distal to the tunnel. Scanning the entire tunnel area could have strengthened the association between CSA enlargement and CTS severity. However, the study’s primary aim was to compare SWE with wCSA and NCS, not to assess wCSA’s diagnostic accuracy.

4. Questionable Relevance of Palmar Area Measurement:

• The study’s measurement of SWE at the palmar area raises questions about its relevance, as this area comprises various tissue types with differing elasticity properties overlying the median nerve (MN).

5. Challenges of Using SWE in Anisotropic Tissues:

• Caution is warranted when applying SWE in anisotropic tissues like nerves. The SWE application, including the reliable measurement index algorithm, is primarily designed for isotropic tissues, potentially limiting its adequacy in anisotropic tissues. However, the study utilized the reliable measurement index to guide the placement of region of interest points.

These limitations highlight areas for further refinement and investigation in future studies, particularly regarding sample size, measurement protocols, and the applicability of SWE in various tissue types and anatomical locations.

 

 

CONCLUSION

In conclusion, this study emphasizes the significance of measuring median nerve shear wave velocity (MNSWV) at the carpal tunnel inlet, demonstrating its correlation with the neurophysiological graveness of carpal tunnel syndrome (CTS) similar to median nerve cross-sectional area (MN CSA) at the wrist.

Additionally, a wrist-to-forearm ratio (WFR) based on SWV measurements proves valuable in CTS assessment, indicating SWV’s independence from MN size. Shear wave elastography (SWE) offers a complementary perspective alongside conventional ultrasound B-mode imaging and nerve conduction studies (NCS), enriching the evaluation of MN status in CTS diagnosis. Further research is needed to identify scenarios where SWE enhances diagnostic accuracy, particularly for patients with obesity.

Establishing a universally recognized nerve SWE scanning protocol and addressing differences in SWE applications among ultrasound device manufacturers is crucial for maximizing clinical utility. Continuous innovation and standardization in this area are essential for advancing the field of CTS diagnosis.

 

References

 

1. Padua L, Coraci D, Erra C, et al. Carpal tunnel syndrome: clinical features, diagnosis, and management. Lancet Neurol. 2016;15:1273–1284.(https://doi.org/10.1016/S1474-4422(16)30231-9)
2. Pelosi L, Arányi Z, Beekman R, et al. Expert consensus on the combined investigation of carpal tunnel syndrome with electrodiagnostic tests and neuromuscular ultrasound. Clin Neurophysiol. 2022;135:107–116. (https://doi.org/10.1016/j.clinph.2021.09.326)
3. Grimm A, Axer H, Heiling B, Winter N. Nerve ultrasound normal values–a readjustment of the ultrasound pattern sum score UPSS. Clin Neurophysiol. 2018;129:1403–1409. (https://doi.org/10.1016/j.clinph.2018.03.019)
4. Martikkala L, Himanen SL, Virtanen K, Mäkelä K. The neurophysiological severity of carpal tunnel syndrome cannot be predicted by median nerve cross-sectional area and wrist-to-forearm ratio. J Clin Neurophysiol. 2021;38:312–316. (https://doi.org/10.1097/WNP.0000000000000815)
5. Werner RA, Andary M. Electrodiagnostic evaluation of carpal tunnel syndrome. Muscle Nerve. 2011;44:597–607. (https://doi.org/10.1002/mus.22152)
6. Cipriano KJ, Wickstrom J, Glicksman M, et al. A scoping review of musculoskeletal soft tissue and nerve shear wave elastography studies methods. Clin Neurophysiol. 2022;140:181–195. (https://doi.org/10.1016/j.clinph.2021.11.036)
7. Carpenter EL, Lau HA, Kolodny EH, Adler RS. Skeletal muscle in healthy subjects versus those with GNE-related myopathy: evaluation with shear-wave US–a pilot study. Radiology. 2015;277:546–554. (https://doi.org/10.1148/radiol.2015141664)
8. Hobson-Webb LD, Cartwright MS. Advancing neuromuscular ultrasound through research: finding a common sound. Muscle Nerve. 2017;56:375–378. (https://doi.org/10.1002/mus.25615)
9. Martikkala L, Himanen SL, Virtanen K, Mäkelä K. Shear Wave Elastography in Carpal Tunnel Syndrome. J Ultrasound Med. 2024;9999:1–11. (https://doi.org/10.1002/jum.16450).

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