The Role of Confirmatory Testing in Carpal Tunnel Syndrome: Electrodiagnostic Study, Ultrasound and CTS-6

Introduction

Carpal tunnel syndrome (CTS) is the most prevalent compression neuropathy affecting the upper extremity, characterised by median nerve entrapment at the wrist.¹ Typical symptoms include painful paraesthesia, static numbness and thenar weakness, which can negatively impact quality of life and function.² Treatment options for CTS include nocturnal splinting, corticosteroid injection and carpal tunnel release (CTR) surgery.^3,4 Accurately and efficiently diagnosing CTS is important for decision-making regarding treatment while utilising resources effectively and optimising the patient experience. A thorough history and physical examination are crucial components of the clinical diagnosis of CTS. However, symptom variations and overlap with other conditions can make the diagnosis challenging in some cases.⁵ In these situations, confirmatory tests can serve as adjuncts to the diagnosis for the treating surgeon. These tests can be performed preoperatively for diagnostic purposes, and in some cases, postoperatively to evaluate outcomes and assess treatment effects if necessary.⁶ There is no universally accepted reference standard for the diagnosis of CTS.⁷ For instance, Teunis et al. found a notable discordance of 22% in the estimated prevalence of mild-to-moderate CTS between confirmatory tests and symptom-based clinical assessments.⁸ This finding emphasises the uncertainty that currently exists in the diagnosis of unclear cases of CTS and underscores the importance of improving diagnostic tools and strategies.

Common tools for diagnostic and confirmatory testing for CTS include electrodiagnostic studies (EDS), ultrasound and validated diagnostic aids such as the CTS-6 score. EDS comprises nerve conduction studies (NCS) with or without electromyography (EMG) and provides objective measurements of nerve conduction velocities, amplitudes, latencies and the presence of end-organ muscle denervation. Limitations of EDS include patient discomfort, high cost and potential delays to care.^9,10 There has been increasing evidence for the role of ultrasound for the diagnosis of CTS in recent years as an alternative to EDS.¹¹ Finally, the CTS-6 scoring system combines symptoms and signs related to CTS into a validated and accessible diagnostic aid.

EDS and ultrasonography are both useful in evaluating peripheral nerve function, using unique parameters. NCS measures conduction latency, amplitude and velocity. Latency refers to the time it takes for an electrical impulse to move between two points, amplitude is the magnitude of the electrical response and conduction velocity refers to the speed at which the impulse travels. In the clinical scenario of CTS, these values help assess the health and function of the median nerve and identify any delays or reductions in conduction that may suggest CTS. EMG identifies various factors including fibrillations, positive sharp waves and other spontaneous muscle activity, which are signs of muscle denervation. Neuromuscular ultrasound measurement is performed by placing a transducer on the skin above the carpal tunnel to visualise the median nerve and adjacent structures (Fig. 1). One of the key measurements in ultrasonography is the cross-sectional area (CSA) of the median nerve at the inlet of the carpal tunnel. An increased CSA suggests nerve oedema proximal to the carpal tunnel, which is typical in CTS (Fig. 2).

The goal of this review is to provide an overview of the current evidence on the role of EDS, ultrasound and the CTS-6 score in confirming the diagnosis and shaping treatment strategies for CTS. This review aims to guide clinicians in selecting the most appropriate tests, ultimately improving patient care and outcomes.

Electrodiagnostic Studies

EDS involves NCS and EMG, which are two techniques to objectively assess peripheral nerve function. They provide quantifiable metrics such as conduction latency, amplitude, velocity and evidence of end-organ muscle denervation. However, despite its advantages in offering precise measurements, EDS presents drawbacks including patient discomfort, high costs and potential delays in surgical treatment.^9,10 In recent years, the use of EDS for confirming CTS diagnoses and guiding treatment decisions has been subject to scrutiny and debate. In a cross-sectional study that included a large cohort of hand and upper-extremity surgeons, Crijns et al. highlighted variations in EDS utilisation and found that surgeons rely on EDS less frequently for older patients with classic signs of CTS.¹²

EDS can be an important prognostic tool for predicting outcomes of CTS after decompression. One study by Jarvik et al. revealed a significant correlation between abnormal EDS results, specifically median motor latency and positive postoperative outcomes in CTS patients.¹³ Additionally, a study by Mackenzie et al. demonstrated that abnormal preoperative EDS findings could predict the extent of symptom relief after CTS surgery, supporting the predictive utility of EDS.¹⁴ They observed that patients with CTS symptoms with normal preoperative EDS results experienced improvements in self-reported outcomes following CTR, but their postoperative Quick Disabilities of Arm, Shoulder and Hand (QuickDASH) scores showed less improvement compared to those with abnormal preoperative EDS results. Moreover, Zhang et al. reported on the potential utility of a baseline EDS for postoperative comparison following CTR.⁶ Out of 1,383 cases of CTR, they found that postoperative EDS was obtained in 9.3% of cases at a median of 2 years following surgery, with most cases assessing median nerve function.

Recent studies have shown conflicting results on the role of EDS in quantifying the severity of CTS. Dagtas et al. and Zhang et al. have shown that while EDS may help confirm the diagnosis of CTS, the degree of abnormalities does not consistently align with preoperative symptom severity or improvements after surgery.^9,10 Conversely, Yang et al. showed a mild correlation between CTS-6 score and physical examination manoeuvres and higher severity grading on EDS.¹⁵ When comparing pre- and post-test probabilities of diagnosing CTS, Graham et al. discovered that EDS did not significantly alter the likelihood of diagnosing CTS for most patients,¹⁶ casting uncertainty on its routine application in clinical practice. Furthermore, Daliri et al. studied 116 patients with CTS over 2 years and linked EDS parameters to QuickDASH score and pain levels on a scale of 0–10.¹⁷ They found no correlation between any EDS parameter and QuickDASH or pain scores. Giladi et al. highlighted the need to weigh the potential for false negatives against false positives in diagnostic testing due to variations in CTS prevalence between the general population and hand clinics.¹⁸

Concerns have also been raised about the cost-effectiveness and patient discomfort associated with EDS given the availability of diagnostic methods like ultrasound. For instance, Greenfield et al. reported that a significant portion of testing costs stemmed from EDS.¹⁹ In addition, EDS is more invasive than other diagnostic adjuncts. These procedures often involve uncomfortable sensations from electrical stimulation during the NCS or needle insertion during the EMG, which can lead to patient dissatisfaction and anxiety.²⁰

Considering these concerns, guidelines set by the American Academy of Orthopedic Surgeons (AAOS) reduced emphasis on EDS in 2016.²¹ Nonetheless, despite these evolving recommendations, there has been a rise in the use of EDS in clinical settings. Billig et al. highlighted a downside to widespread EDS use, noting that patients who underwent both pre-referral and post-referral EDS experienced nearly twice the wait time for CTS surgery.²² The use of EDS could lead to delays in treatment, which might hinder prompt intervention in symptomatic patients. While EDS continues to play a role in confirming CTS diagnoses and guiding treatment choices, further research is needed to determine how best to utilise this tool effectively within the evolving landscape of clinical guidelines.

Ultrasound

Although EDS has traditionally been used to confirm nerve dysfunction in patients with CTS, there has been growing evidence for the role of ultrasonography. Ultrasonography allows for real-time visualisation of the median nerve and its surrounding structures. In diagnosing CTS, a CSA value equal to or greater than 10 mm² is considered the threshold. This approach presents advantages over EDS due to its cost-effectiveness and widespread availability.¹¹ Nonetheless, it is essential to acknowledge both the constraints of ultrasound and the specific scenarios where this method is most appropriate for diagnosing CTS. Several studies have emphasised the diagnostic accuracy of ultrasound compared to EDS, particularly in specific patient groups. For instance, in a study of 519 manual labourers using the Katz diagram as the reference standard for CTS diagnosis, Cartwright et al. demonstrated that neuromuscular ultrasound is akin to EDS in screening for CTS. This underscores its potential as a less invasive and painless diagnostic tool when compared to EDS.²³ Similarly, El-Najjar et al. underscored the sensitivity and specificity of ultrasound in diagnosing CTS, recommending its use as an alternative or supplement to EDS in settings lacking EDS equipment.²⁴

Other studies have further supported the accuracy of ultrasound in CTS diagnosis. In a prospective study with 85 patients, Fowler et al. compared ultrasound and electrodiagnostic testing findings using a validated clinical tool, the CTS-6.²⁵ They found that ultrasound had a sensitivity of 89% and specificity of 90%, while EDS had a sensitivity of 89% and specificity of 80%. Ultrasound could confirm CTS diagnosis with better specificity and equal sensitivity compared to EDS, particularly in patients with a positive CTS-6, defined as ≥12. Another study by Fowler et al. compared EDS, ultrasound and CTS-6 using latent class analysis, a robust statistical tool useful in scenarios where there is no existing diagnostic test that makes the correct diagnosis with absolute certainty.²⁶ They found that ultrasound had a higher sensitivity at 91.4% compared to EDS at 90.9%. Additionally, ultrasound exhibited higher specificity at 94% compared to EDS at 83% and CTS-6 at 91%.

Advancements in ultrasound technology have led to the development of high-frequency ultrasound devices that provide improved resolution and detailed imaging of peripheral nerves. In a study comparing 40 patients with CTS with age- and sex-matched controls, El-Shintenawy et al. demonstrated the effectiveness of high-resolution ultrasound in diagnosing CTS and identifying anatomical variants such as bifid median nerve.²⁷ They also found significant correlations between ultrasonographic parameters, such as the CSA at the level of the pisiform and flattening ratio at the hamate, to be associated with electrophysiological grading severity. Despite anatomic differences between men and women and the concern that cutoff values for nerve compression could differ based on patient sex, Hacker et al. found that cutoff values were very similar in males and females, allowing a single standard cutoff value to be used.²⁸ Carrozzi et al. performed a prospective study of patient satisfaction and found that patients favoured ultrasound examination over EDS as a diagnostic tool.²⁹

Despite the growing popularity of ultrasound, it is important to recognise its limitations and contextualise its role in CTS diagnosis. Pimentel et al. reported on 115 patients likely to have CTS based on a CTS-6 score ≥12 and found that despite ultrasound and EDS having similar sensitivity and specificity, EDS demonstrated better concordance with surgical reference standards, defined as paraesthesia remission post-surgery.³⁰ Moreover, in a prospective study involving 31 patients with CTS and 25 asymptomatic controls, Singla et al. pointed out that while ultrasound can be an addition to EDS for screening purposes, EDS remains more sensitive and specific, especially in mild cases of CTS.³¹ Unlike EDS, which can detect various concomitant neuropathies like cubital tunnel syndrome (CuTS) and cervical radiculopathy, ultrasound focusses on measurements of the CSA of the median nerve at the wrist, thus limiting its diagnostic capabilities for confounding neuropathies.³²

Recent trends show a growing interest in incorporating ultrasound into CTS diagnostic algorithms, particularly when EDS results are inconclusive or due to patient preference. Future research should focus on clarifying the role of ultrasound in diagnosing CTS and developing evidence-based recommendations for its practical application.

CTS-6 Score

The CTS-6 evaluation tool is a validated aid for diagnosing CTS, offering a consistent approach to assessing clinical signs and symptoms associated with the condition. It has six components: loss of two-point discrimination, numbness, thenar atrophy and/or weakening, Tinel sign and Phalen test (Table 1).¹⁶ Some of the benefits of the CTS-6 are its simplicity, efficacy and accessibility, making it suitable for various treatment settings. In contrast to EDS, which can be time-consuming, expensive and uncomfortable, the CTS-6 offers a non-invasive low-cost way to identify individuals with a high probability of having CTS. A study conducted by Yang et al. found a mildly positive correlation between the CTS-6 score and EDS severity grading.¹⁵ Moreover, research by Fowler et al. demonstrated that the CTS-6 has higher sensitivity and specificity compared to EDS.²⁵ Another study by Grandizio et al. examined how consistently medical students, occupational hand therapists and hand surgeons trained in upper extremity fellowship programmes interpret the results of the CTS-6 assessment.³³ They determined that the CTS-6 can be effectively utilised by health care providers without specialised training in hand surgery to diagnose CTS. These findings show that CTS-6 is not only accurate, but also accessible.

There are some limitations to consider with the CTS-6. Some components of the CTS-6 rely on patients’ self-reports, and the test–retest reliability of the CTS-6 questionnaire is not known.³⁴ Moreover, the CTS-6 is not designed to predict outcomes after surgery. Aversano et al. studied the capability of the CTS-6 in determining outcomes after CTR.³⁵ They discovered that preoperative CTS-6 scores did not correlate with changes in Boston Carpal Tunnel Questionnaire (BCTQ) scores or post-operative patient satisfaction. Therefore, clinicians should understand the role of CTS-6 as a diagnostic aid rather than a predictor of treatment effect.

Despite its drawbacks, the CTS-6 is commonly used for screening and diagnosing CTS. This tool may be increasingly integrated into the diagnostic work up of CTS. Although the straightforwardness and effectiveness of this tool make it appealing for diagnosing CTS, health care providers must be aware of its constraints and apply their expertise when interpreting CTS-6 scores. Further studies should focus on defining the test–retest reliability of the CTS-6, confirming its prognostic capabilities and further defining its role in aiding CTS treatment.

Conclusion

The diagnosis of CTS centres on clinical assessment with the option of confirmatory testing. EDS, ultrasound and the CTS-6 score each offer unique advantages and limitations as adjuncts to the diagnosis of CTS. EDS may be particularly helpful in cases where there is concern for concomitant conditions such as CuTS, cervical radiculopathy or in patients with diabetes mellitus.³⁶ EDS is also generally recommended prior to revision CTR cases. The United States offers distinct advantages, including reduced discomfort, cost and delay, making it a favourable option in certain situations. In cases where there is a high clinical suspicion of CTS, the CTS-6 score alone may suffice for diagnosis.

By considering the strengths and drawbacks of each of these tests, clinicians can customise their approach based on the unique needs of each patient. This approach not only improves accuracy, but also helps in the timely management of CTS. With continued research, efforts to improve the CTS diagnostic algorithm may improve access, reduce costs and lead to improved outcomes for patients.

Declarations

Conflict of Interest:

The authors do NOT have any potential conflicts of interest with respect to this manuscript.

Funding:

The authors received NO financial support for the preparation, research, authorship and/or publication of this manuscript.

Ethical Approval:

This study was approved by the Mass General Brigham institutional review board. The IRB protocol number is 2010P002462, and the latest approval date of this protocol is 01/19/2022.

Informed Consent:

There is NO information (names, initials, hospital identification numbers or photographs) in the submitted manuscript that can be used to identify patients.

Acknowledgements:

None.