Volume 88, Issue 1, Pages 19-24 (January 2007)

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ABSTRACT

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The Relationship Between Electrodiagnostic Findings and Patient Symptoms and Function in Carpal Tunnel Syndrome

Abstract

Chan L, Turner JA, Comstock BA, Levenson LM, Hollingworth W, Heagerty PJ, Kliot M, Jarvik JG. The relationship between electrodiagnostic findings and patient symptoms and function in carpal tunnel syndrome.

Objective

To examine whether, in patients with carpal tunnel syndrome (CTS), electrodiagnostic study findings were associated with patient symptom severity and functional limitations after controlling for potentially confounding variables including depression, somatization, and pain-related catastrophizing.

Design

Cross-sectional design including data from 2 ongoing CTS studies.

Setting

Patients enrolled from hospitals and clinics in Washington State between October 2002 and February 2006.

Participants

Adults with CTS (N=215) (based on symptoms and abnormal electrodiagnostic findings) were analyzed. Exclusion criteria were any mass, tumor, severe trauma, or deformity in the hand or wrist, radiculopathy, polyneuropathy, pregnancy, lactation, or severe CTS.

Interventions

Not applicable.

Main Outcome Measures

The Carpal Tunnel Syndrome Assessment Questionnaire (CTSAQ) functional status scale assessed the ability to perform 9 common hand-related tasks. The CTSAQ symptom severity scale included 11 items that assess pain, numbness, and weakness. Patients also rated their average hand and wrist pain in the last month.

Results

With and without controlling for patient characteristics, including age, sex, body mass index, symptom duration, depression, somatization, and pain-related catastrophizing, there were no statistically significant relationships between the electrodiagnostic findings and patient functional status and symptom severity.

Conclusions

Electrodiagnostic findings and patient CTS-related symptoms and function appear to be independent measures. Clinicians and researchers interested in CTS outcomes need to assess both.

Key Words: Carpal tunnel syndrome, Electrodiagnosis, Rehabilitation, Treatment outcome

Article Outline

• Abstract

• Methods

• Participants and Setting

• Measures

• Statistical Analysis

• Results

• Discussion

• Study Limitations

• Conclusions

• References

• Copyright

CARPAL TUNNEL SYNDROME (CTS) is the most common entrapment neuropathy. The prevalence of CTS has been difficult to identify because few population-based studies have been performed. However, a recent study in Sweden estimated a prevalence of 2.1%.1 Other estimates have suggested a lifetime risk of 10% with an unadjusted incidence in adults of 1 per 1000 person-years.2 Because the direct medical costs of treating CTS exceed $1 billion per year (≈$5000 per affected limb),3 the manner in which CTS is diagnosed has profound economic implications.

Unfortunately, there is no recognized criterion standard for the diagnosis of CTS. Many clinicians and researchers suggest that a combination of clinical signs, symptoms, and electrodiagnostic study findings should be utilized.4 However, in practice, although some surgeons order electrodiagnostic studies to confirm the diagnosis of CTS prior to surgical release, many others do not.5

Prior studies have yielded mixed results when examining the association between electrodiagnostic findings and patient-reported symptoms. Some studies have shown no association,6, 7 others have shown strong associations,8, 9 and still others have found associations between electrodiagnostic findings and measures of physical functioning, but not CTS symptoms.10 However, to our knowledge, none of these studies have attempted to control for variables that could influence patient electrodiagnostic findings, such as age, sex, obesity, and duration of symptoms.11

In addition, the impact of patient psychologic characteristics has not been thoroughly examined in CTS. Depression, somatization (tendency to experience and communicate medically unexplained somatic symptoms in response to psychologic distress), and tendency to catastrophize (ruminate about pain, appraise pain as highly threatening, and perceive oneself as helpless to control pain) are important variables that have been demonstrated consistently to be associated with pain intensity and functional limitations in a variety of chronic pain patient populations.12, 13, 14, 15, 16, 17, 18 It is possible that the presence of psychologic dysfunction in these areas might override the role of physiologic factors (reflected in electrodiagnostic findings) when assessing CTS symptoms and function.

The objective of this study was to examine whether electrodiagnostic findings were associated with patient CTS symptom severity and functional limitations after controlling for a variety of potentially confounding variables (age, sex, comorbidities, body mass index [BMI], duration of symptoms). We focused on patients with nonsevere CTS because this is a population for whom there is significant controversy regarding treatment and for whom we had available data.19, 20 Our primary hypothesis was that the relationship between electrodiagnostic findings and CTS symptoms and function would be stronger among patients with less psychologic dysfunction, and less strong among patients with greater psychologic dysfunction.

Methods

Participants and Setting

We used data from 2 related National Institutes of Health (National Institute of Arthritis and Musculoskeletal and Skin Diseases) funded CTS studies. The first was a randomized controlled trial (RCT) of surgery (carpal tunnel release vs conservative care) for patients with CTS.21 This RCT was nested within a cohort study examining the natural history of CTS, which enrolled those patients who were not interested in the RCT.

To qualify for either study the patient needed to have a physiatrist or a neurologist make the diagnosis of CTS through nerve conduction studies. Subsequently, this diagnosis needed to be confirmed through a clinical evaluation of a hand surgeon.

Patients were candidates for the study if their electrodiagnostic studies revealed any one of the following: (1) median compound motor action potential (CMAP) distal latency (8cm) greater than or equal to 4.4ms, (2) a 10cm (thumb to wrist) median to radial sensory nerve action potential peak latency difference of more than 0.5ms, (3) an 8cm transcarpal median to ulnar mixed nerve action potential peak latency difference of more than 0.3ms, and (4) a 14cm (digit 4 to wrist) median to ulnar sensory nerve action potential peak latency difference of more than 0.4ms. These parameters were selected because they represent abnormal findings for studies performed at the University of Washington Academic Medical Center (UWAMC), where the vast majority of the studies were performed.

In addition to having abnormal electromyographic results and a confirmatory evaluation with a hand surgeon, other inclusion criteria for this study included age greater than 17 years, no previous surgery on the study hand or wrist, no carpal tunnel release on the contralateral hand in the previous 6 months, symptoms in at least 2 digits in a median motor nerve pattern, able and willing to answer research questionnaires in English, and classification using hand symptom diagrams as at least “possible CTS.”22, 23

We excluded patients if they had any mass, tumor, or deformity in the hand or wrist, any history of severe trauma to the wrist (such as a fracture), polyneuropathy, cervical radiculopathy, or if they were pregnant or lactating. Patients with other pain syndromes (fibromyalgia, arthritis), were tracked and these factors were controlled for in our multivariate analysis.

We excluded patients with evidence of severe CTS. These patients were excluded because the investigators viewed surgery as an appropriate treatment for these people and could not justify possibly randomizing them to conservative care. For the purposes of this study, severe CTS was defined as the presence of thenar atrophy or a median CMAP amplitude of 3.8mV or less (although patients with this reduced amplitude without needle electromyographic evidence of acute denervation in median nerve innervated hand muscles were still eligible).

Patients were enrolled between October 2002 and February 2006 from several sites in the state of Washington: UWAMC (affiliated practice sites include University of Washington Medical Center, UW Physicians Network, Harborview Medical Center, Puget Sound VA Health Care System), Virginia Mason Medical Center (Seattle), Seattle Hand Surgery (affiliated with Swedish Hospital in Seattle), Proliance Surgeons (affiliated with Overlake and Evergreen Hospitals), and Management Services Organization of Washington in Tacoma.

We recruited patients from primary care clinics as well as from specialty referral clinics (neurologic surgery, neurology, orthopedic surgery, physical medicine and rehabilitation). Research coordinators obtained permission to contact potential subjects. Electrodiagnostic findings were obtained, and a confirmatory clinic visit with a hand surgeon was performed. If the patient subsequently agreed to be enrolled in either the RCT or the cohort study, the baseline questionnaires were administered.

Because this was a multicenter study, a number of different providers performed the electrodiagnostic studies. However the vast majority of these studies (84%) were performed at 3 institutions (UWAMC, Virginia Mason, Swedish) and all 3 sites use standardized protocols.

Despite this standardization, the content of the studies varied slightly from patient to patient. Seventy-seven percent of the patients had at least 2 nerve conduction studies performed involving the median nerve. Overall, we analyzed data on 215 patients, 145 patients enrolled in the cohort study and 70 patients enrolled in the RCT. In all of the patients, median CMAPs at 8cm (n=215) were obtained; most had median-ulnar transcarpal studies (n=143) as well, so we focused this report on the participants who had these studies. In those cases where the median-ulnar transcarpal responses were absent, we analyzed other available data.

For patients with CTS on both sides, we used electrodiagnostic data from only 1 hand in our analysis. We designated this “study hand” based on the following priorities: most severe according to patient report and most severe based on electrodiagnostic reports.

Measures

We collected patient self-report measures in person at the time of enrollment. These instruments included the Carpal Tunnel Syndrome Assessment Questionnaire (CTSAQ), a self-report measure of CTS-related functional limitations and symptom severity.22 The functional status scale assesses ability to perform 9 common hand related tasks. The symptom severity scale includes 11 items that assess pain, numbness, and weakness at night and during the day. Each question is answered on a 1 to 5 scale, with higher scores indicating greater severity. The CTSAQ has established responsiveness, validity, and reliability.24 The patients were asked to rate their average hand or wrist pain in the last month on a numeric rating scale from 0 (no pain) to 10 (extreme pain).25, 26, 27 Subjects answered the CTSAQ questions for each hand, but for purposes of data analyses, only responses for the study hand were considered.

Study participants also completed the 12-item somatization and 13-item depression scales of the Symptom Check List−90 (SCL-90).28, 29 Participants responded to each question using a 5-point scale ranging from “not at all” to “extremely.” Higher scores indicate greater somatization and depressive symptom severity. Participants also completed the 13-item Pain Catastrophizing Scale.30 This scale has been demonstrated to be reliable and valid,30, 31, 32 and associated with pain-related disability.

In addition to these measures, we obtained information on patient age, sex, current smoking, duration of symptoms (0−6mo, 6−12mo, >12mo), BMI, and medical comorbidity. Comorbidity was assessed through the presence or absence of patient self-report of one of the following conditions that have shown to be risk factors for CTS33: fibromyalgia, diabetes, inflammatory arthritis, and rheumatoid arthritis. Patients were dichotomized into 2 groups, those with, and those without, any one of the comorbid conditions listed above. We used the 3-item version of the Alcohol Use Disorders Identification Test (AUDIT-C) to screen for alcohol consumption problems.34 The questions assess frequency and quantity of alcohol consumed in the previous year. The measure has been shown to be a valid screening test for heavy drinking and/or active alcohol abuse or dependence.34, 35 As recommended by Bush et al,34 we considered scores of 3 or more as indicative of a possible alcohol use problem.

Statistical Analysis

We used descriptive statistics to summarize the sociodemographic, electrodiagnostic, and psychologic measure data. We then conducted several sets of linear regression analyses to examine the relationship between the electrodiagnostic measures and the patient self-report measures. In the first set, we explored the bivariate relationships between each electrodiagnostic measure and each CTSAQ scale as well as average pain intensity. In the next set, we controlled for baseline patient characteristics (age, sex, smoking, BMI, AUDIT-C, duration of symptoms, presence, or absence of a comorbidity) by adding them to the models as a group. Next, the 3 psychologic measures, depression, somatization, and catastrophizing, were entered as a group. Finally, we included terms representing the interaction between each psychologic measure and each electrodiagnostic test in predicting CTSAQ scores. This was done to test our hypothesis that psychosocial characteristics would modify the relationship between electrodiagnostic findings and CTS symptom severity and functioning.

In these regressions, we examined the following electrodiagnostic measures: median CMAP (8cm) onset latency and amplitude and transpalmar (8cm) median-ulnar peak latency difference. In addition, we performed regression in the following sensory tests: median-radial peak latency difference to the thumb (10cm), median-ulnar peak latency difference to digit 4 (14cm). Finally, because of the possibility that changes in the way in which the electrodiagnostic results were categorized might reveal different associations, we also analyzed a summary variable that represented the grouping of patients into 1 of 3 mutually exclusive categories: (1) sensory abnormality, (2) motor abnormality, and (3) sensory and motor abnormality. Because all our results were similar for these groups, we present only the results from the studies containing median CMAP distal latency and transpalmar median-ulnar peak latency difference.

Results

Table 1 shows descriptive information about the study sample. Of note, the mean age ± standard deviation (SD) of the study patients was 48.9±10.0 years, and 59.1% of the patients were women. The median duration of symptoms was 28 months, although the sample showed a wide range of symptom duration (interquartile range [IQR], 8−82y). Most patients were overweight: median BMI was 29.7kg/m2 (IQR, 25.7−33.1kg/m2). The CTSAQ scores obtained from our patient cohort were similar to those of other groups of patients with CTS.22, 36, 37 The mean somatization and depression scores were about 1 to 1.5 SDs above the norm in a nonpatient sample.38 The mean Pain Catastrophizing Scale score (12.49) was considerably lower than that (27.96) reported in a study of patients evaluated at a multidisciplinary pain clinic for neck or back pain related to work or motor vehicle collisions.26

Table 1.

Patient Demographics and Characteristics (N=215)


	Characteristics	Values
	Age (y)	48.9±10.5
	Female (%)	59.1
	Smoker (%)	21.5
	Body mass index (kg/m2), median (IQR)	29.7(25.8−35.4)
	Alcohol consumption (AUDIT-C score ≥3), %	40.0
	Duration of symptoms (mo), median (IQR)	27.9(8.2−82.4)
	Diabetes, n (%)	17(7.9)
	Fibromyalgia, n (%)	13(6.0)
	Rheumatoid arthritis, n (%)	8(3.7)
	Inflammatory arthritis, n (%)	8(3.7)
	CTSAQ
	Symptom	2.8±0.8
	Function	2.3±0.9
	Average pain in last month	4.7±2.4
	SCL-90
	Somatization	0.9±0.6
	Depression	0.7±0.8
	Catastrophizing	12.7±12.2

NOTE. Values are mean ± standard deviation (SD) or as otherwise indicated.

Abbreviation: IQR, interquartile range.

Table 2 displays the electrodiagnostic data. The mean median CMAP distal latency was 4.89±1.16ms. The mean median-ulnar transpalmar difference was .83±.58ms.

Table 2.

Electrodiagnostic Test Results


	Test	Results
	Median CMAP (8cm) (N=215)
	Median motor latency (ms)	4.80±1.16
	Median motor amplitude (mV)	8.61±3.06
	Median mid-palm (8cm) (n=143)
	Peak latency (ms)	2.83±1.18
	Amplitude (μV)	36.65±24.95
	Ulnar mid-palm (8cm) (n=143)
	Peak latency (ms)	1.93±0.33
	Amplitude (μV)	23.54±14.03
	Median-ulnar latency difference (ms)	0.83±0.58

NOTE. Values are mean ± SD.

Table 3 displays the regression coefficients and P values reflecting the associations between the median motor latency and the median-ulnar transpalmar difference versus the 3 outcome measures (CTSAQ symptom, CTSAQ function, average pain in the past month). Results are shown for bivariate, multivariate (controlling for patient characteristics without the psychologic measures), and multivariate including the patient characteristics, psychosocial measures, and interaction terms. There were no statistically significant relationships between any electrodiagnostic finding and any patient self-report measure in any of these models.

Table 3.

Linear Regression Models


Regression Model	Bivariate		Multivariate		Multivariate and Psychosocial Measures
Regression Model	Coeff	P	Coeff	P	Coeff	P
CTSAQ function
Median motor distal latency	.03	.58	.03	.60	.03	.54
Transpalmar median-ulnar difference	−.01	.89	.04	.83	.12	.46
CTSAQ symptom
Median motor distal latency	−.03	.57	−.01	.95	.01	.80
Transpalmar median-ulnar difference	−.07	.24	−.01	.96	.08	.63
Average pain in the last month
Median motor distal latency	.12	.42	.17	.36	.18	.29
Transpalmar median-ulnar difference	−.09	.63	−.31	.54	−.13	.79

NOTE. The multivariate models include variables for sex, age, BMI, duration of symptoms, comorbid illnesses, and tobacco and alcohol use. The multivariate and psychosocial measures models add the variables for somatization, catastrophization, and depression, as well as interaction terms.

Abbreviation: Coeff, coefficient.

Table 4, Table 5 show the results of 2 multivariate analyses in detail. Table 4 summarizes the results of the regression predicting CTSAQ function scale scores from median motor distal latency, patient characteristics, and psychosocial measures. Median motor latency was not associated significantly with CTSAQ function scores. The only significant variables in the model were somatization and catastrophizing, suggesting that these measures correlate with CTSAQ function. Most important, none of the interaction terms entered to test our primary hypothesis were statistically significant. Therefore, the relationship between electrodiagnostic findings and symptoms and functioning does not appear to be strong, nor is it any stronger among patients with less psychologic dysfunction. The model predicting the CTSAQ symptom severity scale scores using transpalmar sensory differences was very similar and is shown in table 5.

Table 4.

Regression Model for CTSAQ Function Versus Median Motor Distal Latency


Predictor	Coefficient (SE)	P
Intercept	1.57(0.45)	Referent
Median motor distal latency	0.03(0.06)	.54
Female	−0.11(0.12)	.36
Age
<40	Referent	Referent
40−50	−0.15(0.17)	.38
50−60	−0.04(0.17)	.81
>60	0.05(0.22)	.80
BMI	0.00(0.01)	.66
Duration of symptoms (mo)
<6	Referent	Referent
6−12	−0.14(0.21)	.52
>12	−0.20(0.17)	.24
Comorbidity	0.18(0.18)	.31
Smoker	0.08(0.16)	.60
Alcohol user	−0.08(0.13)	.51
Somatization	0.47(0.13)	<.01
Catastrophization	0.03(0.01)	<.01
Depression	−0.11(0.12)	.36

Abbreviation: SE, standard error.

Table 5.

Regression of CTSAQ Function Versus Transpalmar Median-Ulnar Difference


Predictor	Coefficient (SE)	P
Intercept	1.41(0.46)	Referent
Palm sensory difference	0.12(0.15)	.46
Female	−0.06(0.17)	.75
Age
<40	Referent	Referent
40−60	0.04(0.20)	.86
50−60	0.06(0.21)	.78
>60	−0.06(0.28)	.82
BMI	0.01(0.01)	.44
Duration (mo)
<6	Referent	Referent
6−12	−0.08(0.24)	.75
>12	−0.17(0.20)	.40
Comorbidity	0.15(0.21)	.46
Smoker	0.25(0.22)	.26
Alcohol user	0.09(0.17)	.58
Somatization	0.45(0.15)	<.01
Catastrophization	0.02(0.01)	.02
Depression	−0.03(0.15)	.86

Discussion

In this study of patients with CTS, we found no statistically significant relationship between electrodiagnostic findings and self-reported CTS-related functional limitations and symptom severity, even after controlling for potentially important covariates such as age, sex, and comorbid illnesses. Furthermore, our results also suggest that patient psychologic factors such as depression, catastrophizing, and somatization are not “masking” a significant relationship between electrodiagnostic and CTS symptoms and functional limitations.

Our results are consistent with several studies,6, 7 but contradict the findings of others.8, 9, 10, 39 It is possible that these seemingly contradictory findings may be the result of differences in the patient populations, electrodiagnostic protocols, the outcomes instruments utilized, and statistical methodology. Indeed, in those studies where significant associations between electrodiagnostic and patient symptoms and function were found, only simple correlations were performed. In our study, we utilized common electrodiagnostic measures, a well validated CTS-specific outcomes instrument, and a multivariate analysis that controlled for important confounding variables.

The reason for the absence of an association between electrodiagnostic findings and patient symptoms and function is unclear. However, in the case of CTS, it is known that abnormal electrodiagnostic findings represent significant demyelination or axon loss in large myelinated nerve fibers.39 In CTS, patient symptoms could be more closely related to the function of small diameter myelinated and unmyelinated nerve fibers that are not assessed in a normal electrodiagnostic study.9

Giannini et al40 have suggested that duration of symptoms is an important issue to consider when examining electrodiagnostic findings and patient CTS outcomes. In this scenario, patient symptoms are worse early in the course of the disease, when the electrodiagnostic changes may be minimal. Later, as the electrodiagnostic findings worsen, the patient’s symptoms “burn out” or perhaps the patients habituate to the discomfort. However, we found no difference in CTS symptoms or functional limitations in patients with more recent (<6mo) versus longer term (>1y) symptom onset.

Study Limitations

There are several limitations to our findings. First, we did not include all patients with CTS. For ethical reasons, patients with severe CTS (based on electrodiagnostic criteria) were excluded because they were likely to benefit from surgery. In addition, because our recruitment occurred in physician offices, our patient population may have lacked those with very mild disease because the patient’s symptoms had to be severe enough to seek medical care. Therefore, our results are only applicable to a subset of those with CTS. Had we been able to include the full range of CTS patients, our findings might have been different. On the other hand, our baseline CTSAQ results suggest that our patients had symptoms similar to those in other CTS studies. In addition, many of those in our study had minimal abnormalities in their electrodiagnostic findings: 43% of the patients had a median motor distal latency of less that 4.4ms, and 27 patients had a median-ulnar transpalmar difference of 0.5ms or less.

Conclusions

Despite these limitations, our findings have important clinical and research implications. First, electrodiagnostic findings and patient CTS-related symptoms and function appear to be independent measures. Clinicians and researchers interested in CTS outcomes need to assess both. In addition, although the absence of a relationship between electrodiagnostic findings and patient symptoms may raise the question of the utility of electrodiagnostic findings in the work-up and treatment of CTS in some people’s minds, it is important to note that we have only examined patient symptoms and function at baseline and not after treatment. Our study does not address the question of whether electrodiagnostic results can predict a patient’s symptoms over time, or, more important, the patient’s response to treatment.21 In addition, electrodiagnostic findings has other utility in the work-up of CTS, because it is often useful in ruling out other conditions that can mimic CTS, such as peripheral polyneuropathy, cervical radiculopathy, or other focal neuropathies.41 Thus, despite the fact that electrodiagnostic findings and CTS patient symptoms and function do not to appear to be related in our patient population, electrodiagnostic findings still should play a central role in the assessment and treatment of this common focal neuropathy.

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a Department of Rehabilitation Medicine, University of Washington, Seattle, WA

b Department of Medicine, University of Washington, Seattle, WA

c Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, WA

d Department of Biostatistics, University of Washington, Seattle, WA

e Department of Neurosurgery, University of Washington, Seattle, WA

f Department of Health Services, University of Washington, Seattle, WA

g Department of Radiology, University of Washington, Seattle, WA.

Correspondence to Leighton Chan, MD, MPH, Dept of Rehabilitation Medicine, University of Washington, Box 356490, Seattle, WA 98195-6490.

Supported by the Multidisciplinary Clinical Research Center and the National Institute of Arthritis and Musculoskeletal and Skin Diseases (grant no. P60 AR48093).

No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. The views expressed here are those of the authors and not necessarily those of the University of Washington.

Reprints are not available from the author.

PII: S0003-9993(06)01421-3

doi:10.1016/j.apmr.2006.10.013

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