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ORIGINAL ARTICLE
Year : 2012  |  Volume : 39  |  Issue : 3  |  Page : 124-129

Carpal tunnel syndrome: Assessment of correlation between clinical, neurophysiological and ultrasound characteristics


1 Department of Neurology, J.N. Medical College, Nehru Nagar, Belgaum, Karnataka, India
2 Department of Radiology, J.N. Medical College, Nehru Nagar, Belgaum, Karnataka, India

Date of Web Publication11-Jan-2013

Correspondence Address:
B Hemeshwar Rao
Department of Neurology, J.N. Medical College, Nehru Nagar, Belgaum - 590 010, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0974-5009.105914

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  Abstract 

Objectives: To evaluate the relationship between symptoms, clinical severity, neurophysiological characteristics with median nerve cross-sectional area (CSA) at the level of carpal tunnel inlet at ultrasonography (USG) and its utility in diagnosis of carpal tunnel syndrome (CTS). Materials and Methods: Prospective study of 30 patients with symptoms of CTS, attending to the Neurology out patient department (OPD) at University Teaching Hospital. A multidimensional assessment of CTS was done using historic and objective scale (Hi-Ob scale) for clinical severity, Boston carpal tunnel questionnaire (BCTQ) for patient-oriented measures, neuro physiologic studies of median nerve at wrist and USG to measure median nerve CSA at carpal tunnel inlet. Results: Thirty patients included in the study (22 women and 8 men). Mean of CSA was 12.69 mm 2 (SD2.67). Association between BCTQ score value and inlet values was assessed by Karl Pearson correlation coefficient ( r = 0.376, P = 0.04). There was positive association with BCTQ scores and CSA of median nerve at carpal tunnel inlet. To compare clinical severity scale (Hi-Ob) and USG CSA, analysis of variance was performed (F value) and Scheffe's multiple comparison test was used to find group difference (grades 1 and 2 P < 0.001, grades1 and 2P P < 0.001, grade 2 differs with grade 2P P < 0.006). As the number of patients is less in minimal, mild and severe groups, the difference between neurophysiological groups and mean of CSA was not statistically significant. Conclusion: A positive correlation exists between USG findings and all the conventional measures of CTS severity.

Keywords: Boston carpal tunnel questionnaire, carpal tunnel syndrome, historic and objective scale, median nerve, neurophysiological studies, ultrasound


How to cite this article:
Rao B H, Kutub M, Patil SD. Carpal tunnel syndrome: Assessment of correlation between clinical, neurophysiological and ultrasound characteristics. J Sci Soc 2012;39:124-9

How to cite this URL:
Rao B H, Kutub M, Patil SD. Carpal tunnel syndrome: Assessment of correlation between clinical, neurophysiological and ultrasound characteristics. J Sci Soc [serial online] 2012 [cited 2019 Sep 15];39:124-9. Available from: http://www.jscisociety.com/text.asp?2012/39/3/124/105914


  Introduction Top


Carpal tunnel syndrome (CTS) is a most common entrapment neuropathy. It is the best defined and most carefully studied entrapment neuropathy. In most cases, the clinical examination consists of history, physical findings and provocative tests, which are specific and diagnosis is easily made. In moderate and severe stages of CTS, median nerve-innervated muscles are weak, atrophy of thenar eminence and common provocative tests are positive. However, in some patients, findings may be atypical, in such cases, it requires further investigations to diagnose CTS. [1]

Over the past 12 years, a multidimensional protocol including clinical, neurophysiologic, patient-oriented measures has been developed by the Italian CTS study group to comprehensively assess CTS impairment. [2] CTS is not a simple but a complex condition, as well as an ideal model for evaluation of focal nerve entrapment and impairment. [3]

The most reliable method to confirm clinical diagnosis of CTS is electro diagnostic testing. Ultrasound has been shown to be useful diagnostic tool for CTS, providing information about median nerve anatomy and surrounding structures. [4] Recent advances in ultrasonography (USG) technology allowed to obtain exquisite depiction of variety of superficial soft-tissue structures in the limbs and extremities including peripheral nerves. If both USG and neurophysiological studies are performed, they provide complementary but not interchangeable information, which greatly increases the diagnostic power and therapeutic workup of patients with mononeuropathies. The ability of USG to assess the morphology of median nerve and surrounding structures may help diagnose atypical cases of CTS and some misdiagnosis as CTS.

The purpose of this study was multidimensional assessment of CTS to confirm the relationship between USG findings and patient's perception of symptoms and hand functions (Boston carpal tunnel questionnaire [BCTQ]), to evaluate the relationship between USG findings and clinical severity of CTS as assessed by validated clinical scale (historic and objective scale [Hi-Ob scale]) and evaluate the relationship between USG and neurophysiologic findings.


  Materials and Methods Top


This is a prospective study conducted on patients with symptoms of CTS attending to Neurology outpatient department (OPD) at University Teaching Hospital from 1 st January 2011 to 31 st December 2011. Patients with history of wrist surgeries, carpal tunnel injuries/fractures, proximal median nerve neuropathy, cervical radiculoneuropathy and polyneuropathies were excluded from the study. We studied dominant wrist of 30 patients who were diagnosed as CTS. Diagnosis of CTS was based on the American Academy of Neurology Clinical Diagnostic Criteria (1993). [5] Ten normal persons were taken as controls for neurophysiological study.

A modified version of the BCTQ was used to obtained a patient-oriented measurement. [6] This questionnaire is most commonly used in the assessment of patients with CTS. [7] The BCTQ evaluates two domains of CTS, namely 'symptoms', assessed with an 11-item scale and 'functional status' assessed with an 8-item scale. The questionnaire was presented in multiple-choice format, and scores were assigned from 1 point (mildest) to 5 points (most severe). No response to a certain question was given 0 points. Each score is calculated as the mean of the responses of the individual items. Patients were divided into five groups according to their mean score: Extreme (4.1-5 points), severe (3.1-4 points), moderate (2.1-3 points), mild (1.1-2 points) and minimal (0.1-1 point).

Before examination, each patient was asked to complete a form with his/her personal data. Questions concerning patient's activities were included to evaluate whether hand stress was present. Both standard neurological and physical examination of the hand, consisting of the Phalen'smotor and sensory function, have been performed in all patients. For clinical examination, a Hi-Obscale of CTS was used. [2] This scale is based on two measures. This scale is claimed to be both physician- and patient-oriented data and better than just patient-oriented data. [7] The first Hi-Ob score is graded on the basis of clinical history and objective findings. It includes the following: Grade 1 - nocturnal paresthesia only; grade 2 - nocturnal and diurnal paresthesia; grade 3 - sensory deficit; grade 4 - hypotrophy or motor deficit of the thenar muscle innervated by median nerve; grade 5 - plegia of thenar muscle innervated by median nerve. The second valuates the presence or absence of pain as dichotomous score obtained by the patients answer YES/NO. The Hi-Ob score was indicated by the number 1-5 that was linked to the letter P (P = PAIN) in patients who has pain.

Neurophysiological study was done according to American Association of Electro diagnostic Medicine, American Academy of Neurology and American Academy of Physical Medicine and Rehabilitation. Practice parameter for electro diagnostic studies in CTS: Summary statement (neurology 2002;581589). [8],[9] Neurophysiological study included the measurement of motor conduction velocity (MCV), distal motor latency (DML) and compound muscle action potential amplitude (CMAP), sensory conduction velocity (SCV), and sensory nerve action potential amplitude (SNAP) of ulnar and median nerves (Nihon Khoden MEB9200). Values that differed by 2SDs from the mean of the control group were considered abnormal. [10] A validated CTS neurophysiological severity scale was used for statistical analysis: Negative-normal findings in all tests; minimal-abnormal segmental/comparative tests only; mild-abnormal digit-wrist segment SCV and normal DML; moderate-abnormal digit-wrist segment SCV and abnormal DML; severe-absence of SNAP in the digit-wrist segment and abnormal DML; severe-SNAP and CMAP absence.

Ultrasound imaging was performed using high-resolution USG (system HD11Philips; 12 MHz) by experienced radiologist [Figure 1]. Subjects were seated facing the examiner. The arms were extended, the wrists were rested on a hard flat surface, the forearms were supinated, and the fingers were semi-flexed. First, the volar was examined to exclude space occupying lesions or anatomical variants; second, the bony structures that limit the carpal tunnel proximally (pisiform, scaphoid) and distally (trapezium and hamate) were examined; third, transverse carpal ligament is identified as an arched hyper echoic strip; fourth, the median nerve was identified. The cross-sectional area (CSA) of the median nerve was measured at the following levels: [1] At the carpal tunnel inlet at the level of pisiform and scaphoid bones [2] and at the carpal tunnel outlet at the level of the hook of the hamate and trapezium bone. By means of direct tracing with electronic calipers around the margin of the nerve on sonogram, particular attention was paid to maintaining adequate probe orientation, to keep the US beam perpendicular to the nerve. [11] Cutoff value for diagnosis of CTS was considered 10 mm. [2],[12],[13] Depending on CSA of median nerve at inlet, it is classified as follows: Mild -10-13 mm 2 ;moderate - >13-15 mm 2; and severe - >15 mm 2 . [14]
Figure 1: Illustration of USCSA of right median nerve atcarpaltunne linlet (15.9 mm2) and at out let 14.6 (mm2)

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The university research ethics committee approved the study protocol; written informed consent was obtained in all patients.

Statistical analysis

Data obtained was tabulated and analyzed using SSPS software version 12. USG CSA was expressed as mean and standard deviation. To compare means of BCTQ scores and USG CSA of median nerve at inlet unpaired "t" test was done. ANOVA test was used for comparison between Hi-Ob score and USG CSA (P value of <0.05 was considered statistically significant).


  Results Top


A total of 30 patients, clinically diagnosed with CTS, who fulfilled the eligibility criteria and provided informed consent were included in the study. There were 22 female patients and eight male patients with age range 28-70 years (mean 43.6 ± 12.1). Mean duration between electrophysiological study and US examination was 2.86 days (range 0-5 days). Based on the patient-oriented data BCTQ score, 21 patients are classified as mild, nine as moderate and none as severe. According to Hi-Ob scale which is used to know the clinical severity, eight patients are in grade 1 and 22 patients in grade 2. In these 22 patients, three patients complained of pain classified as 2P.

All patients' underwent nerve conduction studies for both the hands, for analysis only symptomatic hand was taken, if symptoms were bilateral, dominant hands was take. Abnormal neurophysiological findings were found in all patients. Based on neurophysiological results, patients were categorized as follows: Five patients as minimal, two as mild, twenty as moderate, and three as severe. Among 30 patients on ultrasound examination, none had anatomic variants or space occupying lesions. According to CSA of median nerve at carpal tunnel inlet, eight patients were classified as mild, twelve patients as moderate, five patients as severe and five as nonsignificant.Mean of CSA was 12.69 mm 2 ± 2.67 (range 7.8 mm 2 -20 mm 2 ).

Association between BCTQ score value and USG inlet values were assessed by Karl Pearson correlation coefficient (r = 0.376, P = 0.04). There was positive association with BCTQ scores and ultrasound CSA of median nerve at carpal tunnel inlet [Table 1]. As the severity of hand function impairment and severity of symptoms increases, the CSA of the median nerve increases. The mean USCSA of median nerve at inlet of mild category was 12.08 and that of moderate was 14.12 mm 2 . The difference was marginally significant (t = 2.013, P = 0.054).
Table 1: Correlation between hand function (Boston carpal tunnel questionnaire) and ultrasound median nerve cross-sectional area


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To compare clinical severity scale (Hi-Ob) and USG CSA, analysis of variance was performed. Scheffe's multiple comparison tests was used to find group difference. The mean CSA of median nerve in grade 1of Hi-Ob scale differs from mean CSA of median nerve in grade 2 (P < 0.001) and 2P (P < 0.001). Similarly CSA of median nerve in grade 2 differs with grade 2P (P = 0.006). There was significant group difference in the CSA. There was a positive correlation between clinical impairment and median nerve CSA [Table 2].
Table 2: Comparison between clinical severity and median nerve


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As the number of patients is less in minimal, mild, and severe groups, the correlation between neurophysiological studies and USG CSA was not statistically significant (P > 0.05). But greater the severity of neurophysiological findings greater is the median nerve CSA [Table 3].
Table 3: Comparison between neurophysiological studies of median nerve and median nerve


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  Discussion Top


It is commonly accepted that clinical evaluation is gold standard for the diagnosis of CTS. The value of provocative physical tests such as Tinel's or phalens test for CTS is controversial, and results are often of doubtful significance. [15]

Neurophysiological investigation is a reliable method to test nerve function and provides additional information to support the diagnosis. In entrapment neuropathies, nerve conduction velocity is generally thought to be sensitive indicator of the severity of demyelination and ischemia at entrapment point. As conduction velocity measurements can identify subclinical lesions, it is of particular value in initial diagnosis. However, in segment nerve injuries where nerve component is compressed locally, electrophysiological findings may not necessarily reflect the disease state entirely.

In patients with CTS, anatomical evaluation of the carpal tunnel is important in diagnosis and management. Chronic focal compression of the median nerve can lead to alteration in its morphology and cause demyelination by mechanical stress, deforming the myelin lamellae. Ischemia can account for the intermittent paresthesia that can occur at night or with wrist flexion. [16] Imaging techniques were considered unimportant in the assessment of CTS until recently. [17] Buchberger et al., were the first to quantify changes in CTS using sonography. In addition, ultrasound evaluation not only helps in diagnosis of CTS but also as follow-up evaluation in certain cases. [18]

There are several studies that analyzed the correlation between ultrasound findings in CTS and neurophysiological findings in CTS. Sernik et al., concluded that CTS patients have increased carpal tunnel anteroposterior diameter, flexor retinaculum thickening, reduced median nerve mobility and decreased median nerve echogenicity. They concluded that median nerve diameter 10 mm 2 as a cutoff value for diagnosis of CTS. [19]

In our study, we measured median nerve CSA at the level of inlet, outlet, looked for increased echogenicity and space occupying lesions. For statistical analysis, we have taken only CSA at the level of inlet as it is more sensitive and specific. [20] None of our patients had increased echogenicity and space occupying lesions. In our study, we have taken 10 mm 2 as a cutoff value for CSA of median nerve. The mean CSA in our study is 12.69 mm 2 , which is in concordant with other similar study done by Pauda et al., in 2008. [21]

On assessing the correlation among modalities assessed, a highly significant positive correlation was observed between ultrasound with patient-oriented measures (both the symptom and functional severity scales) and clinical severity scale as assessed by Hi-Ob scale. In our study, 5 patients' median nerve CSA was less than 10 mm 2 , all of them were in mild group hand function scale as assessed by BCTQ and in Hi-Ob scale grade 1 with minimal clinical severity. Three patients who were in 2P of Hi-Ob scale showed >15 mm 2 CSA. Therefore, as the clinical severity with pain increases, the median nerve CSA also increased. There is a linear correlation between USG CSA, hand function and clinical severity as indicated by nerve swelling detected by calculation of CSA, which reflects the degree of nerve damage as expressed by clinical picture.

In agreement with the literature, we found a significant relationship between severity of nerve damage as assessed by neurophysiologic studies and USG findings. From pathophysiological point of view, the nerve swelling in compressive neuropathies leads to intraneural edema, which increases the median nerve CSA. The increase in water content responsible for nerve swelling seems to be directly correlated to the cascade of events that ultimately leads to axon loss.

In our study, there is a good correlation between CSA of median nerve and neurophysiological studies. However, they are not statistically significant because of very few cases in minimal, mild and severe groups. In this study, even minimal changes in neurophysiological studies were associated with mild to moderate increase in CSA.

Finally, in our study, neurophysiological studies were negative in none of the patients, but USG did not showed increased CSA in 6 patients. When CTS is mild, USG did not show more anomalies than neurophysiological studies. In conclusion that still clinical examination is gold standard for diagnosis of CTS. This study showed significant relation to the patient-oriented measures and clinical severity and USG assessment of median nerve CSA. Both neurophysiological studies and USG are complementary to each other rather than replacing one with other. Pit falls of our study are small number of patients, less number of patients falling into groups of minimal, mild and severe grades of neurophysiological studies, there was no statistically significant correlation between USG finding and neurophysiological assessment.

 
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    Figures

  [Figure 1]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]


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