A “Clear” Carpal Tunnel Syndrome Diagnosis on Ultrasound Examination Does Not Predict Improved Outcomes When Compared With a “Borderline” Diagnosis

Abstract

Background:

Nerve conduction studies (NCS) and ultrasound (US) remain imperfect compared with clinical diagnosis and/or diagnostic tools such as carpal tunnel syndrome-6 (CTS-6) for diagnosis of carpal tunne syndrome (CTS). One potential reason for the discrepancy between clinical diagnosis and testing is “borderline” case inclusion. This study aims to compare clinical outcomes after carpal tunnel release (CTR) between “borderline” and “clear” patients with CTS determined by NCS and US.

Methods:

This was a retrospective review of patients who underwent CTR. We collected NCS and US measurements of the median nerve cross-sectional area (MNCSA) at the carpal tunnel inlet, and the Boston Carpal Tunnel Questionnaire (BCTQ) scores comprised of the Symptom Severity Scale (SSS) and the Functional Status Scale (FSS). Ultrasound measurements defined patients as having “borderline” (MNCSA < 13 mm²) or “clear” (MNCSA ≥ 13 mm²) CTS.

Results:

The study included 94 unilateral patients with CTS. “Borderline” CTS was diagnosed in 58 patients (62%), and “clear” CTS was diagnosed in 36 patients (38%). No significant differences in BCTQ scores were found between groups. At greater than 6-month follow-up, the mean FSS was 1.44 and 1.45 for clear and borderline groups, respectively (P = .97) and the mean SSS was 1.47 and 1.51, respectively (P = .84). However, a significant difference between groups when comparing distal motor latency (DML) and distal sensory latency (DSL) existed. The mean DSL was 3.71 and 4.44 for the clear and borderline groups, respectively (P = .02). The mean DML was 4.59 and 5.36 (P = .048).

Conclusion:

Categorizing CTS diagnosis into “borderline” and “clear” based on preoperative US and NCS testing did not correlate with BCTQ changes after CTR. It remains unclear whether the BCTQ is a valid postoperative assessment tool, despite its frequent use in literature.

Keywords

carpal tunnel syndrome nerve diagnosis Boston Carpal Tunnel Questionnaire nerve conduction studies distal motor latency distal sensory latency carpal tunnel release procedure median nerve cross-sectional area ultrasound carpal tunnel diagnostic testing

Introduction

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy of the upper extremity, affecting up to 6% of the general population.¹ Several factors, including body mass index, sex, genetics, and occupation, may contribute to the development of CTS.² Regardless of the etiology, patients with CTS tend to experience numbness, pain, sensory loss, weakness, and/or tingling in the radial three and one-half fingers due to compression of the median nerve at the wrist.^2,3 Clinically, a combination of history and physical examination is commonly used to make the diagnosis of CTS. There has been interest in an objective confirmatory diagnostic test; however, nerve conduction studies (NCS) and ultrasound (US) remain imperfect when compared with clinical diagnosis and/or diagnostic tools such as carpal tunnel syndrome-6 (CTS-6).

The reason for the discrepancy between clinical diagnosis, NCS, and US is unclear. Fowler et al⁴ noted high rates of false positives for both NCS and US in the setting of patients with no clinical signs and symptoms of CTS. Others have found no difference in clinical outcomes with carpal tunnel release (CTR) between patients with NCS-confirmed CTS and those with CTS confirmed by clinical findings alone.⁵ One potential reason for the discrepancy between clinical diagnosis and diagnostic testing is the inclusion of “borderline” cases. The cutoff values for NCS and US have been debated and may differ between institutions.^6
-8 It is possible that one institution would diagnose a patient with CTS based on its specific cutoff value and a second institution would give a negative CTS diagnosis to the same patient. One would assume that a group of patients with a “clear” CTS diagnosis would have better clinical outcomes with CTR than a group of patients with a “borderline” CTS diagnosis; however, this has not been studied extensively.

The purpose of this study was to compare clinical outcomes after CTR between patients with “borderline” CTS and “clear” CTS as determined by NCS and US. The null hypothesis is that there is no difference in the Boston Carpal Tunnel Questionnaire (BCTQ) score between the groups at short-term follow-up.

Materials and Methods

After obtaining institutional review board approval, a retrospective medical record review was performed from August 2013 to August 2020. The senior author maintains a database of patients who present to an upper extremity practice with complaints of numbness and/or tingling in the upper extremity. Patients who underwent CTR were included in this study. Patients were excluded for the following reasons: (1) missing preoperative NCS data; (2) missing preoperative US data; and (3) lack of >6-month follow-up data. Demographic data, including age, sex, height, weight, and ethnicity, were recorded.

The BCTQ was the primary outcome score used in this study. The BCTQ comprises an 11-item Symptom Severity Scale (SSS) and 8-item Functional Status Scale (FSS) that was completed preoperatively and at 2 weeks, 6 weeks, 6 months, and 1 year after CTR. Nerve conduction studies were performed by an independent electrodiagnostic physician according to the standards of the American Association of Neuromuscular and Electrodiagnostic Medicine. Distal motor latency (DML) and distal sensory latency (DSL) were recorded from the NCS report. In cases where there was “no response” for DML and/or DSL, a value that was 2 SDs higher than the mean data was inserted in place of the “no response” to allow for statistical analysis. The US examination was performed by a fellowship-trained hand surgeon using standard techniques.⁹ The median nerve cross-sectional area (MNCSA) at the carpal tunnel inlet was recorded.

For the purposes of the study, the individuals were divided into 2 groups: MNCSA <13 mm² and MNCSA ≥13 mm². Patients with an MNCSA <13 mm² were classified as having a “borderline” CTS diagnosis, whereas patients with an MNCSA ≥13 mm² were classified as having a “clear” CTS diagnosis. This cutoff was based on 13 mm² being 1 SD above the mean diagnostic value at our institution.

Data Analysis

All 2-tailed independent t tests assuming equal variance were completed for the SSS, FSS, DML, and DSL data using Microsoft Excel 2016. Individual analyses were performed for each data collection time. A 2-tailed independent t test assuming unequal variance was conducted if a violation of the Levene test occurred. Specific cut points of 5.0 and 4.5 ms were used in the DML and DSL analyses, respectively. The data used in this study exhibited good normality. A value of P < .05 was used to define statistical significance in this study.

Results

Ninety-four unilateral patients with CTS with a total of 78 female and 16 male participants were evaluated in this study. The mean age of the cohort was 51 years. The right hand (n = 57, 61%) of participants was more commonly affected by CTS than the left hand (n = 37, 39%) of participants. “Borderline” CTS (n = 58, 62%) was diagnosed in many patients than “clear” CTS (n = 36, 38%). The mean BCTQ score was 2.81, and the mean CTS-6 score was 14.5. Demographic information is further represented in Table 1.

Table 1.

Demographic Parameters.

Category	Measurement
Patient volume (n)	94
Age (mean year)	51.2
Median CSA	12.3
BCTQ (mean)	2.81
CTS-6 (mean)	14.5
Borderline CTS diagnosis (n)	58
Clear CTS diagnosis (n)	36
Height, in (mean)	65.1
Weight, kg (mean)	43.9
Sex (n)
Male	16
Female	78
Affected hand (n)
Right	57
Left	37
Ethnicity (n)
White	56
Black	17
Asian	2

Note. CSA = cross-sectional area; BCTQ = Boston Carpal Tunnel Questionnaire; CTS = carpal tunnel syndrome.

In this study, we first analyzed patient-reported BCTQ scores, specifically the SSS and FSS, to determine whether any differences existed between the “borderline” and “clear” CTS groups. The results showed that no significant differences (P < .05) existed between the cohort BCTQ scores. Analyses were conducted at baseline and postoperatively at 2 weeks, 6 weeks, and >6 months. “Borderline” and “clear” CTS data compared with BCTQ scores are found in Table 2.

Table 2.

Clear Versus Borderline CTS BCTQ Outcomes.

BCTQ assessment	Time of assessment	CTS classification	Mean score	P value**
SSS	Baseline	Borderline	2.98	.35
	Baseline	Clear	3.13	.35
	2 wk	Borderline	1.69	.89
	2 wk	Clear	1.71	.89
	6 wk	Borderline	1.66	.86
	6 wk	Clear	1.62	.86
	>6 mo	Borderline	1.47	.84
	>6 mo	Clear	1.51	.84
FSS	Baseline	Borderline	2.60	.80
	Baseline	Clear	2.56	.80
	2 wk	Borderline	2.07	.31
	2 wk	Clear	2.36	.31
	6 wk	Borderline	1.62	.70
	6 wk	Clear	1.71	.70
	>6 mo	Borderline	1.44	.97
	>6 mo	Clear	1.45	.97

Note. CTS = carpal tunnel syndrome; BCTQ = Boston Carpal Tunnel Questionnaire; SSS = Symptom-Severity Scale; FSS = Functional Status Scale.

A significant value defined as P < .05.

We further analyzed NCS outcomes, specifically the DML and DSL, to determine whether any differences existed between the “borderline” and “clear” CTS cohorts. Analyses determined that patients diagnosed with “clear” CTS had significantly prolonged NCS times than those with a “borderline” diagnosis. For example, the mean DSL (cut point: 4.5 ms) in the “borderline” CTS group was 3.74 compared with 4.41 in the “clear” CTS group, P = .02. The mean DML (cut point: 5.0 ms) in the “borderline” CTS group was 4.59 compared with 5.40 in the “clear” CTS group, P = .048. “Clear” and “borderline” CTS data compared with NCS are found in Table 3.

Table 3.

Clear Versus Borderline CTS NCS Outcomes.

Time of assessment	Nerve conduction measurement type	CTS classification	Mean time, ms	P value
Baseline	DML	Borderline	4.59	.05**
	DML	Clear	5.36	.05**
	DSL	Borderline	3.74	.02**
	DSL	Clear	4.41	.02**

Note. CTS = carpal tunnel syndrome; NCS = nerve conduction studies; DML = distal motor latency; DSL = distal sensory latency.

A significant value of P < .05.

Discussion

This study found no difference in BCTQ scores between patients with a “clear” diagnosis of CTS and those with a “borderline” diagnosis of CTS based on US cross-sectional area of the median nerve at the carpal tunnel inlet. This would suggest that different institutions using slightly different cutoff values for the diagnosis of CTS is not the cause of false positives and false negatives.

It remains uncertain whether the BCTQ is a valid method to assess CTS outcomes. This study demonstrated that patients with a “clear” CTS diagnosis did not have significantly different BCTQ scores over those with “borderline” CTS. Like the results of this study, Trybus et al¹⁰ showed that no correlations exist between the subscales of the BCTQ and MNCSA. Kim et al¹¹ demonstrated a significant correlation exists between preoperative MNCSA and BCTQ score, but not postoperative. It was noted that the reason for this postprocedural outcome could be due to the recovery time needed for swelling and functional aspects of the median nerve after surgery.¹¹ This same logic could apply to the postoperative results of this study. However, it is unknown why a lack of significance was demonstrated before operation. Another potential reason for the lack of significance between MNCSA and BCTQ scores could be due to the method of reporting in the assessment. The subjective reporting of symptoms as interpreted by the patients does not set an objective standard across individuals and populations. This makes diagnosing the condition of CTS even more complicated as different patients may not interpret symptoms in the same manner while having the same diagnosis. It is possible for patients to report average BCTQ scores but fall into the “clear” diagnosis category making the analyses nonsignificant. The BCTQ also does not consider that a patient could have peripheral neuropathy from a different condition other than CTS. In such instances, a patient may score highly on the BCTQ but have an average MNCSA, which would also produce a nonsignificant result.

Contrary to the results of this study, it has been recommended that the BCTQ is a valid assessment in the evaluation of CTS severity.¹² In a study performed by Karabinov et al,¹² the sample population selected already had a confirmed diagnosis of CTS with positive patient symptom reports, and clinical and electrodiagnostic testing results before the evaluation of the BCTQ at preoperative and postoperative time frames. It is important to discern that the study mentioned proposed validity of the BCTQ only after CTS diagnoses were already confirmed. Therefore, it should be distinguished that the study cannot determine the BCTQ to be a valid diagnostic tool of CTS. However, it is reasonable to think that the BCTQ is a good assessment to use at preoperative and postoperative time frames as Karabinov et al¹² mentioned because these procedures generally allow patients to feel a relief of symptoms which should be reflected in their BCTQ scores. Contrary to this idea, Kim et al¹¹ suggest that postoperative reductions in median nerve swelling were not found to reflect postoperative reductions in clinical symptoms or functional disabilities.

Patients with a “clear” CTS diagnosis were found to have prolonged DML and DSL times when compared with “borderline” CTS individuals. Several studies have demonstrated a correlation between increasing US of the MNCSA and increasing DML and DSL on NCS. Nkrumah et al¹³ found that a US with a cutoff MNCSA >12 mm² predicts severe changes on electrodiagnostic studies with a sensitivity and specificity of 37.5% and 81.9%, respectively. It is possible that any MNCSA cutoff higher than 12 mm² would replicate similar results if an MNCSA >12 mm² is the minimum measurement to predict severe changes in NCS. The outcomes of this study show similar outcomes to Nkrumah et al,¹³ but at a cutoff of MNCSA ≥13 mm². Phongamwong et al¹⁴ further demonstrated that patients who had ≥14 mm² MNCSA have a very high probability of moderate to severe CTS. Therefore, based on these findings, there is potential that a minimum measurement of MNCSA >12 mm² should be used to predict severity changes in NCS for patients with CTS.

A limitation of this study is the choosing of a subjective cutoff value for US. Choosing an MNCSA of 13 mm² to classify patients as having a “clear” or “borderline” CTS diagnosis was specific to this study. Other studies could recommend different cutoff values that would be suitable for a clear diagnosis of CTS.^15,16 Regardless, most would agree that patients with an MNCSA of 13 mm² have CTS. Another limitation is the selection of the sample population. Participants for this study were chosen based on having a CTS diagnosis. This study lacked an asymptomatic population to reference as a control. Therefore, it is not known whether similar results would be present in individuals without a CTS diagnosis. A difference in results from this study in a population without CTS would further verify the results concerning the CTS population selected in this one.

In conclusion, dividing CTS diagnosis into “borderline” and “clear” diagnostic categories based on preoperative US and NCS testing did not correlate with changes in BCTQ after CTR. It remains unclear whether the BCTQ is a valid postoperative assessment tool, despite its frequent use in the literature.

Footnotes

Acknowledgements

We would like to thank Dr Godwin Dogbey for assistance in the production of this article.

Ethical Approval

This study was approved by our institutional review board.

Statement of Human and Animal Rights

All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008.

Statement of Informed Consent

Informed consent was obtained from all individuals included in this study. The purpose of this study was to explore the diagnostic criterion of carpal tunnel syndrome. This was a retrospective study, so participant information was not evaluated until after their participation was complete. Subject participation in this study consisted of individuals undergoing nerve conduction studies, filling out the Boston Carpal Tunnel Questionnaire, and undergoing ultrasound measurement of the median nerve in the diagnosed hand with carpal tunnel prior to surgery. Individuals also completed the Boston Carpal Tunnel Questionnaire and ultrasound of the median nerve in the hand diagnosed with carpal tunnel syndrome after carpal tunnel release as well. Risks, benefits, and alternative procedures were discussed with all patients before evaluation of their condition. Participation was voluntary and confidentiality of the patients will be maintained. All policies and procedures conducted in this study have been Institutional Review Board (IRB)-approved, and this study was conducted in accordance with IRB guidelines. Any questions or concerns about the study may be brought to the attention of the principal investigator of this study.

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: J.R.F.J. is an advisor for Integra LifeSciences. R.C.V. has no conflicts of interest.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Robert C. Vernick

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