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Ultrasonographic median nerve cross-section areas measured by 8-point "inching test" for idiopathic carpal tunnel syndrome: a correlation of nerve conduction study severity and duration of clinical symptoms

Ultrasonographic median nerve cross-section areas measured by 8-point "inching test" for... Background: Incremental palmar stimulation of the median nerve sensory conduction at the wrist, the “inching test”, provides an assessment with reference to segments proximal and distal to the entrapment. This study used high-resolution ultrasonography (US) to measure the median nerve’s cross-section areas (CSAs) like the “inching test” and to correlate with the nerve conduction study (NCS) severity and duration of carpal tunnel syndrome (CTS). Methods: Two hundred and twelve (212) “CTS-hands” from 135 CTS patients and 50 asymptomatic hands (“A-hands”) from 25 control individuals were enrolled. The median nerve CSAs were measured at the 8-point marked as i4, i3, i2, i1, w, o1, o2, and 03 in inching test. The NCS severities were classified into six groups based on motor and sensory responses (i.e., negative, minimal, mild, moderate, severe, and extreme). Results of US studies were compared in terms of NCS severity and duration of clinical CTS symptoms. Results: There was significantly larger CSA of the NCS negative group of “CTS-hands” than of “A-hands”. The cut- 2 2 2 off values of the CSAs of the NCS negative CTS group were 12.5 mm , 11.5 mm and 10.1 mm at the inlet, wrist crease, and outlet, respectively. Of the 212 “CTS-hands”, 32 were NCS negative while 40 had minimal, 43 mild, 85 moderate, 10 severe, and two extreme NCS severities. The CSAs of “CTS-hands” positively correlated with different NCS severities and with the duration of CTS symptoms. By duration of clinical symptoms, 12 of the 212 “CTS- hands” were in the 1 month group; 82 in >1 month and ≤12 months group, and 118 in >12 months group. In “inching test”, segments i4-i3 and i3-i2 were the most common “positive-site”. The corresponding CSAs measured at i4 and i3, but not at i2, were significantly larger than those measured at points that were not “positive-site”. Conclusions: Using the 8-point measurement of the median nerve CSA from inlet to outlet similar to the “inching test” has positive correlations with NCS severity and duration of CTS clinical symptoms, and can provide more information on anatomic changes. Combined NCS and US studies using the 8-point measurement may have a higher positive rate than NCS alone for diagnosing CTS. * Correspondence: cwenneng@ms19.hinet.net Department of Neurology, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan Full list of author information is available at the end of the article © 2011 Chen et al. ; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Chen et al. BMC Medical Imaging 2011, 11:22 Page 2 of 9 http://www.biomedcentral.com/1471-2342/11/22 or stroke) that might result in numbness or paresthesia. Background Participants with a variant of carpal tunnel, such as Carpal tunnel syndrome (CTS) is a common entrapment accessory muscles, bifid median nerve, and persistent neuropathy of the median nerve [1]. Currently, nerve median artery were also excluded. None of the female conduction study (NCS) is used to confirm the diagnosis participants were pregnant at the time of the study. The and indicate the level of the lesion [2,3]. Among various hospital’s Ethics Committee approved the study (IRB NCS methods for evaluating CTS, incremental palmar 100-1390B). stimulation of the median nerve sensory conduction at Twophysicians(DrsCSF and TNW) previously the wrist, the so-called “inching test”, permits an assess- trained by musculoskeletal radiologists and with more ment with reference to nerve segments proximal and than three years of experience in patients with related distal to the entrapment [4]. Aside from NCS, peripheral disorders, especially those with clinical CTS, performed nerve ultrasonography (US) is a promising complemen- the US examinations. The clinical symptoms of each tary tool [3,5-9]. However, because of different US individual were recorded and the collected data were methods, the measured values of the median nerve in fully analyzed. CTS also vary [7-10]. This study introduced an 8-point measurement of the median nerve’s cross-sectional area Clinical definition of “CTS-hands” (CSA) from inlet to outlet similar to those performed in In this study, CTS was defined according to the criteria the “inching test”. The measured CSAs were also com- of the American Academy of Neurology practice para- pared to NCS severity and duration of CTS symptoms. meters as follows [11,12]: Methods 1. Paresthesia, pain, swelling, weakness, or clumsi- This prospective case-control study conducted over a per- ness of the hand provoked or worsened by sleep, iod of three years (2006-2008) enrolled 160 participants sustained hand or arm position, or repetitive action and 262 hands. Of the 160 participants, 135 with 212 of the hand or wrist that is mitigated by a change in hands had clinical symptoms of CTS (“CTS-hands”) while posture or by shaking of the hand; the other 25 participants of 50 hands were asymptomatic 2. Sensory deficits in the median nerve innervated (“A-hands”) and acted as controls. Of the 135 sympto- regions of the hand; matic participants, 105 were women and 30 were men, 3. Motor deficit or hypotrophy of the median nerve aged 22-83 years (mean, 52.2 ± 11.7 years). Their body innervated thenar muscles; and height ranged from 142 to 177 cm (mean, 158 ± 6.3 cm), 4. Positive provocative clinical tests (positive Phalen’s body weight 40 to 86 kg (mean, 60.7 ± 8.7 kg), and body mass index 17.5 to 35.3 (mean, 24.1 ± 3.4). The basic maneuver and/or Tinel’s sign) information of the controls is listed in Table 1. The term The term “CTS-hand” was defined as criterion 1 and “A-hands” was defined as a hand with normal NCS find- one or more of criteria 2-4 were fulfilled. For compara- ings and not fulfilling any clinical definition of CTS. tive analysis, the duration of CTS symptoms was classi- In order to avoid other interfering factors, none of the fied into three groups, i.e. ≤1month,>1and ≤12 160 participants had diabetes mellitus, gout, rheumatoid months, and > 12 months. arthritis, renal or liver disease, abnormal thyroid func- tion, abnormal serum cortisol level, or elevated serum Neuro-physiologic assessment anti-nuclear antibody. None of the participants had a The NCS was performed for all participants according history of previous wrist surgery or fracture, or a history to the recommended protocol of the American Associa- or clinical evidence of neurologic disorders (e.g. ulnar tion of Electrodiagnostic Medicine (AAEM) [2] using a neuropathy, radiculopathy, polyneuropathy, myelopathy, Table 1 Basic information of the control participants and the patients with NCS negative “CTS” hands “A-hands” (n = 50) NCS negative “CTS hands” (n = 32) p value Sex 14 hands in man/36 hands in woman 4 hands in man/28 hands in woman 0.100 Age (yr) 44.2 ± 9.8 (46, 25-68) 48.6 ± 11.9 (49, 27-73) 0.135 BH (cm) 163 ± 7.2 (163, 148-174) 159 ± 6.9 (157.5, 150-177) 0.004* BW (kg) 61.0 ± 8.1 (60, 46-76) 59.6 ± 10.8 (56, 46-86) 0.282 BMI 22.8 ± 3.0 (22.7, 17.5-28.3) 23.6 ± 4.4 (22.9, 17.5-35.3) 0.711 Abbreviations: A-hands, asymptomatic hands; CTS, carpal tunnel syndrome; NCS, nerve conduction study; BH, body heigh; BW, body weight; BMI, body mass index; Mean ± standard deviation (Median, minimum-maximus); *p < 0.01 by Mann-Whitney U test Chen et al. BMC Medical Imaging 2011, 11:22 Page 3 of 9 http://www.biomedcentral.com/1471-2342/11/22 Nicolet Viking Select system (Nicolet Biomedical Inc. digit/wrist sensory nerve conduction velocity and abnor- Madison, USA). All tests were done in the same room mal distal motor latency; severe, for absence of sensory under similar temperature conditions. Skin temperature response and abnormal distal motor latency; and extreme, was maintained at ≥32°C. As regards NCS, the onset for the absence of motor and sensory response. latency, amplitude, distance, and velocity of median, ulnar, and radial motor and sensory nerves were mea- Ultrasound assessment technique sured. The comparative tests included: 1) median-ulnar High-resolution US was performed using a scanner with sensory conduction between the wrist and ring finger, 2) a 12/5-MHz linear array transducer for the carpal tunnel median sensory nerve conduction comparison between study (Philips HDI 5000; Philips Medical Systems, the wrist and palm, 3) median-radial sensory conduction Bothell, WA, USA) on the same day as the NCS. During between the wrist and thumb, and 4) antidromic sensory the examination, the patient sat in a comfortable position test using 1-cm increments of the median nerve with facing the examiner, with the measured forearm resting the wrist crease as the zero reference point extending on the table, the palm supine, and fingers semi-extended proximally by 3 cm and distally by 4 cm. In total, eight in the neutral position [18]. The median nerve was first points (Figure 1) were marked in the subsequent inching imaged in a longitudinal scan, placing the US probe at test. the midline between the radius and ulna with the center The cut-off points used in the NCS were the following: of the probe at the distal wrist crease, to obtain an initial 1) median nerve distal sensory latency <3.4 ms [13], 2) general overview of the median nerve. This was then median nerve distal motor latency over the thenar <4.2 ms used to assist the examiner in obtaining optimal axial [13], 3) difference between the median and ulnar nerve (cross-sectional) images. The transducer was placed distal sensory latencies <0.4 ms [14], 4) trans-carpal med- directly on the patient’s skin with gel. ian motor conduction velocity <40.6 ms [15], and 5) anti- A transverse scan, keeping the probe directly perpendi- dromic sensory using 1-cm increments of the median cular to the long axis of the median nerve in order to nerve <0.4 ms [16]. Based on the NCS results, the CTS ensure that the area measured indeed reflected CSA, was hands were categorized into six severity groups [17]: nega- then performed to record the CSA (calculated by contin- tive, for normal findings on all tests; minimal, for abnor- ual tracing of the nerve circumference, excluding the mal segmental or comparative tests only; mild, for hyper-echoic epineurial rim) and elliptical diameters abnormal digit/wrist sensory nerve conduction velocity (transverse and antero-posterior). Measurements were and normal distal motor latency; moderate, for abnormal conducted from the tunnel inlet of the forearm (i4, i3, i2, Figure 1 The 8-point for recording in both “inching test” and ultrasonography. The i4, i3, i2, i1 represent levels at 4, 3, 2, and 1 cm distal to the wrist crease in the inlet of the carpal tunnel; w represents the level of the wrist crease and o1, o2, and o3 represent levels at 1, 2, and 3 cm proximal to the wrist crease in the outlet of the carpal tunnel. Chen et al. BMC Medical Imaging 2011, 11:22 Page 4 of 9 http://www.biomedcentral.com/1471-2342/11/22 i1) to the wrist crease (w) and to the tunnel outlet (o1, o2, Measured CSAs at the 8-point of CTS-hands with different o3) (Figure 1). NCS severities The measured CSAs were compared. The NCS negative Statistical analysis group and the mild to extreme NCS severity groups, Dataweregivenasmean±standard deviation. Subse- except the minimal severity group, showed significantly larger CSA (Table 3). Because of limited case numbers, quent ANOVA analysis followed by Scheffe’smultiple both severe and extreme groups were excluded from comparison procedures were used to calculate the mean subsequent group comparisons; i.e. only the negative, values of CSA among different symptom duration minimal, mild, and moderate groups were included for groups, NCS types, and inching sites. To evaluate differ- ences in CSA value at the 8-point tested between further analysis. Mean CSAs of these four groups asymptomatic and CTS hands in the NCS negative showed that the mean CSAs increased in accordance to group, the Mann-Whitney U test was used for compari- severity, from negative to moderate (Figures 2 and 3). son, as a consequence of limited data. Significance was set at p <0.05 inthe ANOVAand p <0.01inthe Frequent positive sites of the “inching test” and their Mann-Whitney U tests. The area under the ROC (Recei- correspondence to the sizes of measured CSAs ver Operating Characteristic) curves and the CSA cut- The “positive-site” was defined as conduction delay off-values were calculated for the negative NCS CTS (>0.4 ms) between the interval of the nearby marks in hands. The Statistical Package for Social Science (SPSS antidromic sensory test with 1 cm increments of the Inc., version 13.0 for Windows) was used for all statisti- median nerve at the 8-point marks (Figure 4). Results cal analyses. showed that the most common “positive-site” were i4-i3 and i3-i2 (Table 4). The comparative results showed Results that CSAs corresponding to the “positive site” at i4-i3 Based on the NCS severity classification, 32 of the 212 were significantly larger than the CSAs of intervals that “CTS-hands” were in the negative group, 40 in the mini- were not “positive-site” (Table 5). The CSAs measured mal group, 43 in the mild group, 85 in the moderate at i2 did not show significant difference between the group, 10 in the severe group, and two in the extreme positive and the non-positive sites. group. If classified according to the duration of clinical Comparison of CSAs of A-hands with those of CTS-hands symptoms, 12 of the 212 “CTS-hands” were in the ≤1 by CTS symptom duration monthgroup,82in >1month and ≤12 months group, The comparative results showed that CSAs of the “CTS- and 118 in >12 months group. hands” with symptom duration >1 month and ≤12 Comparison of CSAs at the 8-point of A-hands and NCS months, and >12 months were significantly larger than negative CTS-hands the CSAs of “A-hands”. The difference between the The comparative results revealed significantly larger CSAs of the “A-hands” and the “CTS-hands” with symp- CSA of the latter group of hands at six points (i4, i3, i2, tom duration > 1 month was not significant. The “CTS- i1, w,and o3). After comparison of the CSAs under the hands” with >12 months duration had significantly lar- ROC, the cut-off-values of the significant sites were 12.5 ger CSA than the “CTS-hands” with <1 month duration 2 2 2 mm , 11.5 mm , and 10.1 mm , respectively (Table 2). (Table 6). Table 2 Comparison of CSAs measured at the 8-point of the A-hands and NCS negative CTS-hands CSAs p value Cut-off values of CSA Sensitivity Specificity A-hands (n = 50) NCS negative CTS-hands(n = 32) i4 11.8 ± 2.4 (11, 8-19) 14.3 ± 4.6 (13, 7-28) 0.003* 12.5 0.688 0.720 i3 11.5 ± 2.3 (11, 8-19) 14.0 ± 4.3 (13, 8-28) 0.001* 12.5 0.688 0.760 i2 10.9 ± 1.9 (11, 8-16) 11.9 ± 2.1 (12, 8-17) 0.033* 11.5 0.563 0.660 I1 10.7 ± 1.7 (10.5, 8-15) 12.2 ± 2.7 (11.1, 7-20) 0.006* 11.1 0.500 0.680 w 10.7 ± 2.0 (10.5, 7-17) 12.2 ± 2.9 (12, 7-22) 0.002* 11.5 0.594 0.760 o1 10.1 ± 2.2 (10, 6-16) 11.0 ± 2.3 (10, 7-16) 0.082 10.5 0.469 0.600 o2 10.2 ± 2.1 (10, 7-17) 10.6 ± 2.0 (10.5, 6-15) 0.164 10.5 0.500 0.600 o3 9.4 ± 1.9 (9, 6-15) 10.6 ± 2.7 (11, 5-17) 0.031* 10.1 0.563 0.740 Abbreviations: CSAs, cross-section areas; A-hands, asymptomatic hands; CTS-hands, carpal tunnel syndrome hands; NCS, nerve conduction study Markers of the 8-point: i4, i3, i2, i1, w, o1, o2, and o3 Unit of CSA = mm *p < 0.05, by Mann-Whitney U test Chen et al. BMC Medical Imaging 2011, 11:22 Page 5 of 9 http://www.biomedcentral.com/1471-2342/11/22 Table 3 CSAs measured at the 8-point of the CTS-hands with different NCS severities (n = 212) Negative Minimal Mild Moderate Severe Extreme (n = 32) (n = 40) (n = 43) (n = 85) (n = 10) (n = 2) i4 14.3 ± 4.6 (7-28) 15.4 ± 4.7 (8-30) 17.3 ± 5.3 (8-34)* 19.8 ± 6.8 (8.9-41)* 17.3 ± 8.9 (8-40.8) 15.5 ± 3.5 (13-18) i3 14.0 ± 4.3 (8-28) 15.0 ± 4.6 (8-27) 16.0 ± 4.6 (8-26) 18.4 ± 5.9 (8.9-42)* 17.3 ± 8.9 (8-40.8) 15.5 ± 3.5 (16-22) i2 11.9 ± 2.1 (8-17) 12.0 ± 3.0 (7-21) 12.3 ± 2.4 (6-18) 13.8 ± 3.8 (7-29) 13.4 ± 4.7 (8-23.6) 17.0 ± 1.4 (16-18) i1 12.2 ± 2.7 (7-20) 12.6 ± 3.1 (7-20) 14.8 ± 4.9 (8-28) 15.4 ± 5.0 (7-34.4)* 16.7 ± 6.7(11.1-34.3)* 14.5 ± 7.8 (9-20) w 12.2 ± 2.9 (7-22) 12.9 ± 3.4 (7-22) 14.6 ± 3.4 (7-23) * 17.5 ± 5.8 (9-40.4)* 16.0 ± 5.7 (8.9-26) 26.5 ± 9.2 (20-33)* o1 11.0 ± 2.3 (7-16) 12.2 ± 2.8 (8-20.7) 12.9 ± 3.0 (8-20) * 14.3 ± 3.2(8.7-27.4)* 13.9 ± 4.5 (7-20.3) 22.5 ± 4.9 (19-26)* o2 10.6 ± 2.0 (6-15) 11.6 ± 2.6 (8-21) 12.0 ± 2.2 (8-17) * 12.8 ± 2.7 (7-21.3)* 13.9 ± 3.6 (9-19.9) 17.0 ± 0.0 (17-17)* o3 10.6 ± 2.7 (5-17) 10.9 ± 2.0 (7-15) 11.2 ± 1.9 (7-15) 11.5 ± 2.5 (6-19) 12.0 ± 2.2 (9-16) 19.0 ± 0.0 (19-19)* Abbreviations: CSAs, cross-section areas; CTS-hands, carpal tunnel syndrome hands; NCS, nerve conduction study Markers of the 8-point: i4, i3, i2, i1, w, o1, o2, and o3 Unit of CSA = mm *p < 0.01, by Mann-Whitney U test (comparing CSAs of the minimal to extreme groups with the negative group) term debates [1-6,10-20]. In the meantime, although NCS Discussion in CTS diagnosis is highly specific [2], 10-25% of cases are For CTS evaluation, several kinds of NCS measurement unrecognized by classic NCS depending on the disease methods are used for confirmation. As to which measure- severity and the type of NCS technique used [2,21-23]. ment method is optimum remains the subject of, long- Figure 2 Cross-section areas (CSAs) at the 8-point of the 212 carpal tunnel syndrome hands ("CTS-hands”) with different nerve conduction study (NCS) severities. (A) Comparison of CSAs of the NCS minimal to NCS extreme groups with the CSAs of the NCS negative group using analysis of variance (ANOVA), followed by Scheffe’s multiple comparison analysis. black triangle denoting the significant difference between the NCS minimal and NCS moderate groups; black square denoting the significant difference between the NCS negative and NCS moderate groups; black circle denoting the significant difference at w level between the NCS mild and NCS moderate groups, black diamond denoting the significant difference at o1 level between the NCS negative and NCS mild groups. Chen et al. BMC Medical Imaging 2011, 11:22 Page 6 of 9 http://www.biomedcentral.com/1471-2342/11/22 Figure 3 The mean CSAs of “CTS-hands” with different NCS severities. Figure 4 An example of “positive-site” between i4and i3 corresponding to the relatively smaller cross-section area (CSA) at i2.The peak latencies (arrowhead) at i4 and i3 are 1.9 ms and 2.9 ms, respectively, and the difference between them is 1.0 ms, i.e. >0.4 ms. The CSA measured at i2 (arrow) is smaller than those measured at nearby levels. Markers of the 8-point: i4, i3, i2, i1, w, o1, o2, and o3. Chen et al. BMC Medical Imaging 2011, 11:22 Page 7 of 9 http://www.biomedcentral.com/1471-2342/11/22 Table 4 Distributions of the positive sites in inching test of all tested hands Inching None i4-i3 i3-i2 i2-i1 i1-WW-o1 o1-o2 o2-o3 double Total N (%) 119 37 (25.9) 55 (38.5) 6 (4.2) 10 (7.0) 8 (5.6) 2 (1.4) 0 (0) 25 (17.4) 262 Markers of the 8-point: i4, i3, i2, i1, W, o1, o2, and o3 “double” means more than two sites existed Thus, “CTS-hands” with a negative NCS poses a diagnos- Except for the NCS minimal group, all of the other tic challenge when using electrophysiologic study alone for groups of “CTS-hands” (from mild to extreme) have sig- confirmation. nificant differences in CSA measurement when compared In this study, 15.3% (32/212) of “CTS-hands” are NCS to that of the NCS negative group (Table 3 and Figures 2 negative. This incidence rate is consistent with those of pre- and 3) and a positive correlation with the severities of vious reports [2,21-23]. With the 8-point CSA measure- NCS findings. Although some insignificant enlargements ment, there are significant differences on several levels detected in CSA measurement are shown by inter-group between the “A-hands” and NCS negative “CTS-hands”. comparison (Tables 2 and 3), the present study demon- Most of the significant enlargements are located at the inlet strates that slower NCS means a larger CSA by US study. (Table 2). It is known that in patients with a clinical diagno- As shown in Table 3 and Figures 2 and 3, CSAs mea- sis of CTS, the accuracy of US is similar to that of EMG but sured at the 8-point of the NCS minimal group are all lar- is probably preferable because it is painless, easily accessi- ger than those of the NCS negative group, but this ble, and favored by patients [24]. The findings of the pre- difference is not statistically significant. This insignificance sent study further strengthen the importance of the can be explained partly by the trivial difference in NCS complementary role of US in confirming the diagnosis of and measured CSAs in these two groups of “CTS-hands”. idiopathic CTS in the NCS negative group. This is also However, this study does not offer enough evidence to suf- noted in a study of US correlation of CTS in NCS negative ficiently explain the difference. Further large-scale study is “CTS-hands” reported by Rahmani et al. [19]. Therefore, needed for better delineation of the US findings between US can be recommended as a useful technique in diagnos- the NCS negative and NCS minimal groups. Nevertheless, ing CTS patients when NCS results are not confirmatory in with a measurement of CSA at the 8-point, US remains an patients suspected of having median neuropathy. The pre- important complementary tool for confirming clinical sent study also posits the following cut-off values of CSA CTS. for CTS confirmation: 12.5 mm at the tunnel inlet, 11.5 As shown in Table 4, the segments between i4and i3, 2 2 mm at the wrist crease, and 10.1 mm at the tunnel outlet. and i3and i2 are the most frequent “positive sites”,and their respective CSAs are larger than those measured at “non-positive sites” (Table 5). This suggests a positive cor- relation in NCS severities and measured areas of CSA in Table 5 Comparison of CSAs at the 8-points among the the CTS study, a correlation also noted in other studies two most frequent positive sites and the negative site in [10,20,25,26]. The present study (Tables 4 and 5) also the inching test revealsthatmostofthe “positive sites” detected in the none (n = 119) i4-i3 (n = 37) i3-i2 (n = 55) “inching test” involve the distal part (i2-14) of the inlet, i4 13.9 ± 4.8(7-40.8) 19.5 ± 6.9 (9-37)* 19.0 ± 6.9 (8-41)* and the CSA measured at i2 is the smallest. These show i3 13.6 ± 4.8 (8-40.8) 17.4 ± 5.0 (8-32) * 17.9 ± 6.3 (8-42)* that the area around i2 is the most possible site of nerve i2 12.0 ± 3.1 (8-29) 12.4 ± 3.1 (6-19) 13.2 ± 3.4 (8-25) entrapment in idiopathic CTS, which may provide addi- i1 12.4 ± 4.1 (7-34.4) 13.6 ± 4.5 (7-31) 14.6 ± 4.3 (7.4-25)* tional guidance for a more precise location for treatment. w 12.5 ± 4.0 (7-31) 14.5 ± 4.6 (7-27) 15.6 ± 4.9 (7-33)* As shown in Table 6, there is a positive correlation o1 11.3 ± 2.8 (6-20.7) 13.1 ± 2.9 (9-20) 13.6 ± 3.6 (8-26)* between the measured CSA with the symptom duration of o2 11.0 ± 2.4 (6-18.5) 12.2 ± 2.4 (8-18) 12.8 ± 2.7 (8-21.3)* clinical idiopathic CTS such that the longer the duration o3 10.5 ± 2.6 (5-19) 10.5 ± 2.3 (6-16) 11.8 ± 2.4 (8-19)* of symptoms correlated to larger measured CSA. This Note: CSA, cross-section area; none, no conductive delay >0.4 ms in median finding has not been previously reported. Nonetheless, US inching test in centimeter across the carpal tunnel; i4-i3, conductive delay provides reproducible median nerve measurements [27]. >0.4 ms in inching test between 4 cm and 3 cm distal to the wrist crease; i3- i2, conductive delay >0.4 ms in inching test between 3 cm and 2 cm distal to As such, it can be used to assess changes in median nerve the wrist crease characteristics during follow-up studies of idiopathic CTS. Markers of the 8-point: i4, i3, i2, i1, w, o1, o2, and o3 This study has several limitations. First, although 212 i4-i3and i3-i2: the difference of latency measured between locations of i4and i3, and i3and i2 in the inching test “CTS-hands” were included for examination, further Unit of CSA = mm large-scale study is warranted for a more even distribu- *p < 0.05 in comparing the two most frequent positive sites and the negative tion of the case number in the different sub-groups of one in inching test using analysis of variance (ANOVA) followed by Scheffe’s multiple comparison procedure “CTS-hands”. Second, the limitations of accuracy in Chen et al. BMC Medical Imaging 2011, 11:22 Page 8 of 9 http://www.biomedcentral.com/1471-2342/11/22 Table 6 Comparison of CSAs at the 8-point of the ‘A-hands’ with the “CTS-hands” of different symptom durations A-hands CTS-hands (n = 50) 1 month(n = 12) > 1 month and 12 months (n = 82) >12 months (n = 118) i4 11.8 ± 2.4 (8-19) 14.1 ± 4.7 (8-24) 16.6 ± 5.1 (7-34)* 18.5 ± 6.9 (8-41)* ,# i3 11.5 ± 2.3 (8-19) 12.7 ± 2.9 (8-17) 16.0 ± 5.0 (8-28) * 17.3 ± 6.0 (8-42)* i2 10.9 ± 1.9 (8-16) 11.2 ± 2.6 (7-17) 12.8 ± 2.8 (7-20) * 13.1 ± 3.7 (6-29)* i1 10.7 ± 1.7 (8-15) 12.8 ± 2.0 (10-16) 13.6 ± 4.1 (7-24) * 15.0 ± 5.1 (7-34.4)* w 10.7 ± 2.0 (7-17) 11.7 ± 3.3 (7-18) 14.8 ± 5.2 (7-40.4) * 16.0 ± 5.2 (7-33)* o1 10.1 ± 2.2 ( 6-16) 11.2 ± 2.9 (7-16) 12.8 ± 3.2 (7-23) * 13.7 ± 3.4 (8-27.4)* o2 10.2 ± 2.1 (7-17) 10.8 ± 2.0 (8-15) 11.6 ± 2.3 (6-19) * 12.7 ± 2.8 (7-21.3)* o3 9.4 ± 1.9 (6-15) 10.5 ± 2.6 (7-17) 11.1 ± 2.2 (5-16) * 11.4 ± 2.6 (6-19)* Abbreviations: A-hand, asymptomatic hands; CTS-hands, carpal tunnel syndrome hand; CSAs, cross section areas Markers of the 8-point: i4, i3, i2, i1, w, o1, o2, and o3. Unit of CSA = mm *p < 0.05 (a comparison of CSAs of the ‘A-hands’ with the CSAs of the ‘CTS-hands’ of different symptom durations using analysis of variance (ANOVA) followed by Scheffe’s multiple comparison procedure) p < 0.05 (a comparison of CSAs of the CTS-hands with <1 month duration with the CSAs of the ‘CTS-hands’ with >12 months duration using analysis of variance (ANOVA) followed by Scheffe’s multiple comparison procedure) contributed to the conception and design, and clinical data analysis; and inching techniques need to be taken into consideration. WNC contributed to the conception and design, data analysis, and critical This limitation is also noted in other studies [28,29]. revision and final approval of the manuscript. Third, there is difficulty in accurately obtaining a chron- Competing interests ology of the length of symptom duration. Fourth, there The authors declare that they have no competing interests. is a lack of using neuroimaging studies such as com- puted tomography and/or magnetic resonance imaging Received: 30 June 2011 Accepted: 21 December 2011 Published: 21 December 2011 to test the accuracy of CSA measurement at varying levels and to delineate the local change of carpal tunnel. References Fifth, besides CSA measurement, there are other useful, 1. Phalen GS: The carpal-tunnel syndrome. Clinical evaluation of 598 hands. additional measurements of the median nerve with US Clin Ortho Relat Res 1972, 83:29-40. 2. Jablecki CK, Andary MT, Floeter RG, Miller CA, Quartly CA, Vennix MJ, such as the measurement of width and circumference of Wilson JR, American Association of Electro-diagnostic Medicine; American the wrist [30]. In this study we did not perform these Academy of Neurology; American Academy of Physical Medicine and additional measurements for CSA correlation. Lastly, Rehabilitation: Practice parameter; Electro-diagnostic studies in carpal tunnel syndrome. Report of the American Association of Electro- there is a discrepancy of median nerve length between diagnostic Medicine, American Academy of Neurology, and the the conventional surface measurement and US measure- American Academy of Physical Medicine and Rehabilitation. Neurology ment [31]. 2002, 58:1589-1592. 3. Hobson-Webb LD, Massey JM, Juel VC, Sanders DB: The ultrasonographic wrist-to-forearm median nerve area ratio in carpal tunnel syndrome. Conclusions ClinNeurophysiol 2008, 119:1353-1357. More than 15% of “CTS-hands” have negative NCS. The 4. Kimura J: The carpal tunnel syndrome: localization of conduction abnormalities within the distal segment of median nerve. Brain 1979, 8-point measurement of the median nerve CSA from 102:619-635. inlet to outlet similar to the “inching test” provides 5. Wong SM, Griffith JF, Hui ACF, Lo SK, Fu M, Wong KS: Carpal tunnel more information on anatomic changes. This US finding srndrome: diagnostic usefulness of ultrasonography. Radiology 2004, 232:93-99. has positive correlation with NCS severity and the dura- 6. Ziswiler HR, Reichenbach S, Vogelin E, Bachmann LM, Villiger PM, Juni P: tion of CTS clinical symptom. A combination of NCS Diagnostic value of sonography in patients with suspected carpal tunnel and US studies, especially the 8-point measurement, syndrome: a prospective study. Arthritis Rheum 2005, 52:304-311. 7. Beekman R, Visser LH: Sonography in the diagnosis of carpal tunnel mayhavea higher positive rate than NCS alone for syndrome: a critical review of the literature. Muscle Nerve 2003, 27:26-33. diagnosing CTS 8. Koyuncuoglu HR, Kutluhan S, Oyar O, Guler K, Ozden A: The value of ultrasonographic measurement in carpal tunnel syndrome in patients with negative electro-diagnostic tests. Eur J Radiol 2005, 56:365-369. Author details 9. Mondelli M, Filippou G, Gallo A, Frediani B: Diagnostic utility of Department of Neurology, Kaohsiung Chang Gung Memorial Hospital and ultrasonography versus nerve conduction studies in mild carpal tunnel Chang Gung University College of Medicine, Kaohsiung, Taiwan. syndrome. Arthritis Rheum 2008, 59:357-366. Department of Biological Science, National Sun Yat-Sen University, 10. Padua L, Pazzaglia C, Caliandro P, Granata G, Foschini M, Briani C, Kaohsiung, Taiwan. Martinoli C: Carpal tunnel syndrome: ultrasound, neurophysiology, clinical and patient-oriented assessment. Clin Neurophysiol 2008, Authors’ contributions 119:2064-2069. All authors have read and approved the submitted manuscript. 11. Practice parameter for carpal tunnel syndrome (summary statement): SFC contributed to the conception and design, data acquisition and analysis, Report of the Quality Standards Subcommittee of the American and drafting and revision of the manuscript; CHL, CRH, YCC, NWT, and CCC Academy of Neurology. Neurology 1993, 43:2406-2409. Chen et al. BMC Medical Imaging 2011, 11:22 Page 9 of 9 http://www.biomedcentral.com/1471-2342/11/22 12. You H, Simmons Z, Freivalds A, Kothari MJ, Naidu SH: Relationships between clinical symptom severity scales and nerve conduction measures in CTS. Muscle Nerve 1999, 22:497-501. 13. Jackson DA, Clifford JC: Electro-diagnosis of mild carpal tunnel syndrome. Arch Phys Med Rehabil 1989, 70:199-204. 14. Uncini A, Lange DJ, Solomon M, Soliven B, Meer J, Lovelace RE: Ring finger testing in CTS: a comparative study of diagnostic utility. Muscle Nerve 1989, 12:735-741. 15. Walters RJL, Murray NMF: Trans-carpal motor conduction velocity in carpal tunnel syndrome. Muscle Nerve 2001, 24:966-968. 16. Nathan PA, Meadows KD, Doyle LS: Sensory segmental latency values of the median nerve for a population of normal individuals. Arch Phys Med Rehabil 1988, 69:499-501. 17. Padua L, LoMonaco M, Gregori B, Valente EM, Padua R, Tonali P: Neuro- physiologic classification and sensitivity in 500 CTS hands. Acta Neurol Scand 1997, 96:211-217. 18. Kuo MH, Leong CP, Cheng YF, Chang HW: Static wrist position associated with least median nerve compression: sonographic evaluation. Am J Phys Med Rehabil 2001, 80:256-260. 19. Rahmani M, Ghasemi Esfe AR, Bozorg SM, Mazloumi M, Khalilzadeh O, Kahnouji H: The ultrasonographic correlates of carpal tunnel syndrome in patients with normal electro-diagnostic tests. Radiol Med 2011, 116:489-496. 20. Lee CH, Kim TK, Yoon ES, Dhong ES: Correlation of high-resolution ultrasonographic findings with the clinical symptoms and electro- diagnostic data in carpal tunnel syndrome. Ann Plast Sur 2005, 54:20-23. 21. Seror P: Sensitivity of the various tests for diagnosis of carpal tunnel syndrome. J Hand Surg Br 1994, 19:725-728. 22. Preston DC: Compressive and entrapment neuropathies of the upper extremity. In Neuromuscular Disorders in Clinical Practice. Edited by: Katirji B et al. Boston: Butterworth-Heinemann; 2002:744-773. 23. Witt JC, Hentz JG, Stevens JC: Carpal tunnel syndrome with normal nerve conduction studies. Muscle Nerve 2004, 29:515-522. 24. Karadag YS, Karadag O, Cicekli E, Ozturk S, Kiraz S, Ozbakir S, Filippucci E, Grassi W: Severity of carpal tunnel syndrome assessed with high frequency ultrasonography. Rheumatol Int 2010, 30:761-765. 25. Mohammadi A, Afshar A, Etemadi A, Masoudi S, Baghizadeh A: Diagnostic value of cross-sectional area of median nerve in grading severity of carpal tunnel syndrome. Arch Iran Med 2010, 13:516-521. 26. Visser LH, Smidt MH, Lee ML: High-resolution sonography versus EMG in the diagnosis of carpal tunnel syndrome. J Neurol Neurosurg Psychiatry 2008, 79:63-67. 27. Impink BG, Gagnon D, Collinger JL, Boninger ML: Repeatability of ultrasonographic median nerve measures. Muscle Nerve 2010, 41:767-773. 28. Kimura J: Principles and pitfalls of nerve conduction studies. Ann Neurol 1984, 16:415-429. 29. Geiringer SR: Inching Techniques are of limited usage. Muscle Nerve 1998, 21:1557-1561. 30. Claes F, Meulstee J, Claessen-Oude Luttikhuis TT, Huygen PL, Verhagen WI: Usefulness of additional measurements of the median nerve with ultrasonography. Neurol Sci 2010, 31:721-725. 31. Rha DW, Im SH, Kim SK, Chang WH, Kim KJ, Lee SC: Median nerve conduction study through the carpal tunnel using segmental nerve length measured by ultrasonographic and conventional tape method. Arch Phys Med Rehabil 2011, 92:1-6. 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Ultrasonographic median nerve cross-section areas measured by 8-point "inching test" for idiopathic carpal tunnel syndrome: a correlation of nerve conduction study severity and duration of clinical symptoms

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Copyright © 2011 by Chen et al.; licensee BioMed Central Ltd.
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Medicine & Public Health; Imaging / Radiology
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Abstract

Background: Incremental palmar stimulation of the median nerve sensory conduction at the wrist, the “inching test”, provides an assessment with reference to segments proximal and distal to the entrapment. This study used high-resolution ultrasonography (US) to measure the median nerve’s cross-section areas (CSAs) like the “inching test” and to correlate with the nerve conduction study (NCS) severity and duration of carpal tunnel syndrome (CTS). Methods: Two hundred and twelve (212) “CTS-hands” from 135 CTS patients and 50 asymptomatic hands (“A-hands”) from 25 control individuals were enrolled. The median nerve CSAs were measured at the 8-point marked as i4, i3, i2, i1, w, o1, o2, and 03 in inching test. The NCS severities were classified into six groups based on motor and sensory responses (i.e., negative, minimal, mild, moderate, severe, and extreme). Results of US studies were compared in terms of NCS severity and duration of clinical CTS symptoms. Results: There was significantly larger CSA of the NCS negative group of “CTS-hands” than of “A-hands”. The cut- 2 2 2 off values of the CSAs of the NCS negative CTS group were 12.5 mm , 11.5 mm and 10.1 mm at the inlet, wrist crease, and outlet, respectively. Of the 212 “CTS-hands”, 32 were NCS negative while 40 had minimal, 43 mild, 85 moderate, 10 severe, and two extreme NCS severities. The CSAs of “CTS-hands” positively correlated with different NCS severities and with the duration of CTS symptoms. By duration of clinical symptoms, 12 of the 212 “CTS- hands” were in the 1 month group; 82 in >1 month and ≤12 months group, and 118 in >12 months group. In “inching test”, segments i4-i3 and i3-i2 were the most common “positive-site”. The corresponding CSAs measured at i4 and i3, but not at i2, were significantly larger than those measured at points that were not “positive-site”. Conclusions: Using the 8-point measurement of the median nerve CSA from inlet to outlet similar to the “inching test” has positive correlations with NCS severity and duration of CTS clinical symptoms, and can provide more information on anatomic changes. Combined NCS and US studies using the 8-point measurement may have a higher positive rate than NCS alone for diagnosing CTS. * Correspondence: cwenneng@ms19.hinet.net Department of Neurology, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan Full list of author information is available at the end of the article © 2011 Chen et al. ; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Chen et al. BMC Medical Imaging 2011, 11:22 Page 2 of 9 http://www.biomedcentral.com/1471-2342/11/22 or stroke) that might result in numbness or paresthesia. Background Participants with a variant of carpal tunnel, such as Carpal tunnel syndrome (CTS) is a common entrapment accessory muscles, bifid median nerve, and persistent neuropathy of the median nerve [1]. Currently, nerve median artery were also excluded. None of the female conduction study (NCS) is used to confirm the diagnosis participants were pregnant at the time of the study. The and indicate the level of the lesion [2,3]. Among various hospital’s Ethics Committee approved the study (IRB NCS methods for evaluating CTS, incremental palmar 100-1390B). stimulation of the median nerve sensory conduction at Twophysicians(DrsCSF and TNW) previously the wrist, the so-called “inching test”, permits an assess- trained by musculoskeletal radiologists and with more ment with reference to nerve segments proximal and than three years of experience in patients with related distal to the entrapment [4]. Aside from NCS, peripheral disorders, especially those with clinical CTS, performed nerve ultrasonography (US) is a promising complemen- the US examinations. The clinical symptoms of each tary tool [3,5-9]. However, because of different US individual were recorded and the collected data were methods, the measured values of the median nerve in fully analyzed. CTS also vary [7-10]. This study introduced an 8-point measurement of the median nerve’s cross-sectional area Clinical definition of “CTS-hands” (CSA) from inlet to outlet similar to those performed in In this study, CTS was defined according to the criteria the “inching test”. The measured CSAs were also com- of the American Academy of Neurology practice para- pared to NCS severity and duration of CTS symptoms. meters as follows [11,12]: Methods 1. Paresthesia, pain, swelling, weakness, or clumsi- This prospective case-control study conducted over a per- ness of the hand provoked or worsened by sleep, iod of three years (2006-2008) enrolled 160 participants sustained hand or arm position, or repetitive action and 262 hands. Of the 160 participants, 135 with 212 of the hand or wrist that is mitigated by a change in hands had clinical symptoms of CTS (“CTS-hands”) while posture or by shaking of the hand; the other 25 participants of 50 hands were asymptomatic 2. Sensory deficits in the median nerve innervated (“A-hands”) and acted as controls. Of the 135 sympto- regions of the hand; matic participants, 105 were women and 30 were men, 3. Motor deficit or hypotrophy of the median nerve aged 22-83 years (mean, 52.2 ± 11.7 years). Their body innervated thenar muscles; and height ranged from 142 to 177 cm (mean, 158 ± 6.3 cm), 4. Positive provocative clinical tests (positive Phalen’s body weight 40 to 86 kg (mean, 60.7 ± 8.7 kg), and body mass index 17.5 to 35.3 (mean, 24.1 ± 3.4). The basic maneuver and/or Tinel’s sign) information of the controls is listed in Table 1. The term The term “CTS-hand” was defined as criterion 1 and “A-hands” was defined as a hand with normal NCS find- one or more of criteria 2-4 were fulfilled. For compara- ings and not fulfilling any clinical definition of CTS. tive analysis, the duration of CTS symptoms was classi- In order to avoid other interfering factors, none of the fied into three groups, i.e. ≤1month,>1and ≤12 160 participants had diabetes mellitus, gout, rheumatoid months, and > 12 months. arthritis, renal or liver disease, abnormal thyroid func- tion, abnormal serum cortisol level, or elevated serum Neuro-physiologic assessment anti-nuclear antibody. None of the participants had a The NCS was performed for all participants according history of previous wrist surgery or fracture, or a history to the recommended protocol of the American Associa- or clinical evidence of neurologic disorders (e.g. ulnar tion of Electrodiagnostic Medicine (AAEM) [2] using a neuropathy, radiculopathy, polyneuropathy, myelopathy, Table 1 Basic information of the control participants and the patients with NCS negative “CTS” hands “A-hands” (n = 50) NCS negative “CTS hands” (n = 32) p value Sex 14 hands in man/36 hands in woman 4 hands in man/28 hands in woman 0.100 Age (yr) 44.2 ± 9.8 (46, 25-68) 48.6 ± 11.9 (49, 27-73) 0.135 BH (cm) 163 ± 7.2 (163, 148-174) 159 ± 6.9 (157.5, 150-177) 0.004* BW (kg) 61.0 ± 8.1 (60, 46-76) 59.6 ± 10.8 (56, 46-86) 0.282 BMI 22.8 ± 3.0 (22.7, 17.5-28.3) 23.6 ± 4.4 (22.9, 17.5-35.3) 0.711 Abbreviations: A-hands, asymptomatic hands; CTS, carpal tunnel syndrome; NCS, nerve conduction study; BH, body heigh; BW, body weight; BMI, body mass index; Mean ± standard deviation (Median, minimum-maximus); *p < 0.01 by Mann-Whitney U test Chen et al. BMC Medical Imaging 2011, 11:22 Page 3 of 9 http://www.biomedcentral.com/1471-2342/11/22 Nicolet Viking Select system (Nicolet Biomedical Inc. digit/wrist sensory nerve conduction velocity and abnor- Madison, USA). All tests were done in the same room mal distal motor latency; severe, for absence of sensory under similar temperature conditions. Skin temperature response and abnormal distal motor latency; and extreme, was maintained at ≥32°C. As regards NCS, the onset for the absence of motor and sensory response. latency, amplitude, distance, and velocity of median, ulnar, and radial motor and sensory nerves were mea- Ultrasound assessment technique sured. The comparative tests included: 1) median-ulnar High-resolution US was performed using a scanner with sensory conduction between the wrist and ring finger, 2) a 12/5-MHz linear array transducer for the carpal tunnel median sensory nerve conduction comparison between study (Philips HDI 5000; Philips Medical Systems, the wrist and palm, 3) median-radial sensory conduction Bothell, WA, USA) on the same day as the NCS. During between the wrist and thumb, and 4) antidromic sensory the examination, the patient sat in a comfortable position test using 1-cm increments of the median nerve with facing the examiner, with the measured forearm resting the wrist crease as the zero reference point extending on the table, the palm supine, and fingers semi-extended proximally by 3 cm and distally by 4 cm. In total, eight in the neutral position [18]. The median nerve was first points (Figure 1) were marked in the subsequent inching imaged in a longitudinal scan, placing the US probe at test. the midline between the radius and ulna with the center The cut-off points used in the NCS were the following: of the probe at the distal wrist crease, to obtain an initial 1) median nerve distal sensory latency <3.4 ms [13], 2) general overview of the median nerve. This was then median nerve distal motor latency over the thenar <4.2 ms used to assist the examiner in obtaining optimal axial [13], 3) difference between the median and ulnar nerve (cross-sectional) images. The transducer was placed distal sensory latencies <0.4 ms [14], 4) trans-carpal med- directly on the patient’s skin with gel. ian motor conduction velocity <40.6 ms [15], and 5) anti- A transverse scan, keeping the probe directly perpendi- dromic sensory using 1-cm increments of the median cular to the long axis of the median nerve in order to nerve <0.4 ms [16]. Based on the NCS results, the CTS ensure that the area measured indeed reflected CSA, was hands were categorized into six severity groups [17]: nega- then performed to record the CSA (calculated by contin- tive, for normal findings on all tests; minimal, for abnor- ual tracing of the nerve circumference, excluding the mal segmental or comparative tests only; mild, for hyper-echoic epineurial rim) and elliptical diameters abnormal digit/wrist sensory nerve conduction velocity (transverse and antero-posterior). Measurements were and normal distal motor latency; moderate, for abnormal conducted from the tunnel inlet of the forearm (i4, i3, i2, Figure 1 The 8-point for recording in both “inching test” and ultrasonography. The i4, i3, i2, i1 represent levels at 4, 3, 2, and 1 cm distal to the wrist crease in the inlet of the carpal tunnel; w represents the level of the wrist crease and o1, o2, and o3 represent levels at 1, 2, and 3 cm proximal to the wrist crease in the outlet of the carpal tunnel. Chen et al. BMC Medical Imaging 2011, 11:22 Page 4 of 9 http://www.biomedcentral.com/1471-2342/11/22 i1) to the wrist crease (w) and to the tunnel outlet (o1, o2, Measured CSAs at the 8-point of CTS-hands with different o3) (Figure 1). NCS severities The measured CSAs were compared. The NCS negative Statistical analysis group and the mild to extreme NCS severity groups, Dataweregivenasmean±standard deviation. Subse- except the minimal severity group, showed significantly larger CSA (Table 3). Because of limited case numbers, quent ANOVA analysis followed by Scheffe’smultiple both severe and extreme groups were excluded from comparison procedures were used to calculate the mean subsequent group comparisons; i.e. only the negative, values of CSA among different symptom duration minimal, mild, and moderate groups were included for groups, NCS types, and inching sites. To evaluate differ- ences in CSA value at the 8-point tested between further analysis. Mean CSAs of these four groups asymptomatic and CTS hands in the NCS negative showed that the mean CSAs increased in accordance to group, the Mann-Whitney U test was used for compari- severity, from negative to moderate (Figures 2 and 3). son, as a consequence of limited data. Significance was set at p <0.05 inthe ANOVAand p <0.01inthe Frequent positive sites of the “inching test” and their Mann-Whitney U tests. The area under the ROC (Recei- correspondence to the sizes of measured CSAs ver Operating Characteristic) curves and the CSA cut- The “positive-site” was defined as conduction delay off-values were calculated for the negative NCS CTS (>0.4 ms) between the interval of the nearby marks in hands. The Statistical Package for Social Science (SPSS antidromic sensory test with 1 cm increments of the Inc., version 13.0 for Windows) was used for all statisti- median nerve at the 8-point marks (Figure 4). Results cal analyses. showed that the most common “positive-site” were i4-i3 and i3-i2 (Table 4). The comparative results showed Results that CSAs corresponding to the “positive site” at i4-i3 Based on the NCS severity classification, 32 of the 212 were significantly larger than the CSAs of intervals that “CTS-hands” were in the negative group, 40 in the mini- were not “positive-site” (Table 5). The CSAs measured mal group, 43 in the mild group, 85 in the moderate at i2 did not show significant difference between the group, 10 in the severe group, and two in the extreme positive and the non-positive sites. group. If classified according to the duration of clinical Comparison of CSAs of A-hands with those of CTS-hands symptoms, 12 of the 212 “CTS-hands” were in the ≤1 by CTS symptom duration monthgroup,82in >1month and ≤12 months group, The comparative results showed that CSAs of the “CTS- and 118 in >12 months group. hands” with symptom duration >1 month and ≤12 Comparison of CSAs at the 8-point of A-hands and NCS months, and >12 months were significantly larger than negative CTS-hands the CSAs of “A-hands”. The difference between the The comparative results revealed significantly larger CSAs of the “A-hands” and the “CTS-hands” with symp- CSA of the latter group of hands at six points (i4, i3, i2, tom duration > 1 month was not significant. The “CTS- i1, w,and o3). After comparison of the CSAs under the hands” with >12 months duration had significantly lar- ROC, the cut-off-values of the significant sites were 12.5 ger CSA than the “CTS-hands” with <1 month duration 2 2 2 mm , 11.5 mm , and 10.1 mm , respectively (Table 2). (Table 6). Table 2 Comparison of CSAs measured at the 8-point of the A-hands and NCS negative CTS-hands CSAs p value Cut-off values of CSA Sensitivity Specificity A-hands (n = 50) NCS negative CTS-hands(n = 32) i4 11.8 ± 2.4 (11, 8-19) 14.3 ± 4.6 (13, 7-28) 0.003* 12.5 0.688 0.720 i3 11.5 ± 2.3 (11, 8-19) 14.0 ± 4.3 (13, 8-28) 0.001* 12.5 0.688 0.760 i2 10.9 ± 1.9 (11, 8-16) 11.9 ± 2.1 (12, 8-17) 0.033* 11.5 0.563 0.660 I1 10.7 ± 1.7 (10.5, 8-15) 12.2 ± 2.7 (11.1, 7-20) 0.006* 11.1 0.500 0.680 w 10.7 ± 2.0 (10.5, 7-17) 12.2 ± 2.9 (12, 7-22) 0.002* 11.5 0.594 0.760 o1 10.1 ± 2.2 (10, 6-16) 11.0 ± 2.3 (10, 7-16) 0.082 10.5 0.469 0.600 o2 10.2 ± 2.1 (10, 7-17) 10.6 ± 2.0 (10.5, 6-15) 0.164 10.5 0.500 0.600 o3 9.4 ± 1.9 (9, 6-15) 10.6 ± 2.7 (11, 5-17) 0.031* 10.1 0.563 0.740 Abbreviations: CSAs, cross-section areas; A-hands, asymptomatic hands; CTS-hands, carpal tunnel syndrome hands; NCS, nerve conduction study Markers of the 8-point: i4, i3, i2, i1, w, o1, o2, and o3 Unit of CSA = mm *p < 0.05, by Mann-Whitney U test Chen et al. BMC Medical Imaging 2011, 11:22 Page 5 of 9 http://www.biomedcentral.com/1471-2342/11/22 Table 3 CSAs measured at the 8-point of the CTS-hands with different NCS severities (n = 212) Negative Minimal Mild Moderate Severe Extreme (n = 32) (n = 40) (n = 43) (n = 85) (n = 10) (n = 2) i4 14.3 ± 4.6 (7-28) 15.4 ± 4.7 (8-30) 17.3 ± 5.3 (8-34)* 19.8 ± 6.8 (8.9-41)* 17.3 ± 8.9 (8-40.8) 15.5 ± 3.5 (13-18) i3 14.0 ± 4.3 (8-28) 15.0 ± 4.6 (8-27) 16.0 ± 4.6 (8-26) 18.4 ± 5.9 (8.9-42)* 17.3 ± 8.9 (8-40.8) 15.5 ± 3.5 (16-22) i2 11.9 ± 2.1 (8-17) 12.0 ± 3.0 (7-21) 12.3 ± 2.4 (6-18) 13.8 ± 3.8 (7-29) 13.4 ± 4.7 (8-23.6) 17.0 ± 1.4 (16-18) i1 12.2 ± 2.7 (7-20) 12.6 ± 3.1 (7-20) 14.8 ± 4.9 (8-28) 15.4 ± 5.0 (7-34.4)* 16.7 ± 6.7(11.1-34.3)* 14.5 ± 7.8 (9-20) w 12.2 ± 2.9 (7-22) 12.9 ± 3.4 (7-22) 14.6 ± 3.4 (7-23) * 17.5 ± 5.8 (9-40.4)* 16.0 ± 5.7 (8.9-26) 26.5 ± 9.2 (20-33)* o1 11.0 ± 2.3 (7-16) 12.2 ± 2.8 (8-20.7) 12.9 ± 3.0 (8-20) * 14.3 ± 3.2(8.7-27.4)* 13.9 ± 4.5 (7-20.3) 22.5 ± 4.9 (19-26)* o2 10.6 ± 2.0 (6-15) 11.6 ± 2.6 (8-21) 12.0 ± 2.2 (8-17) * 12.8 ± 2.7 (7-21.3)* 13.9 ± 3.6 (9-19.9) 17.0 ± 0.0 (17-17)* o3 10.6 ± 2.7 (5-17) 10.9 ± 2.0 (7-15) 11.2 ± 1.9 (7-15) 11.5 ± 2.5 (6-19) 12.0 ± 2.2 (9-16) 19.0 ± 0.0 (19-19)* Abbreviations: CSAs, cross-section areas; CTS-hands, carpal tunnel syndrome hands; NCS, nerve conduction study Markers of the 8-point: i4, i3, i2, i1, w, o1, o2, and o3 Unit of CSA = mm *p < 0.01, by Mann-Whitney U test (comparing CSAs of the minimal to extreme groups with the negative group) term debates [1-6,10-20]. In the meantime, although NCS Discussion in CTS diagnosis is highly specific [2], 10-25% of cases are For CTS evaluation, several kinds of NCS measurement unrecognized by classic NCS depending on the disease methods are used for confirmation. As to which measure- severity and the type of NCS technique used [2,21-23]. ment method is optimum remains the subject of, long- Figure 2 Cross-section areas (CSAs) at the 8-point of the 212 carpal tunnel syndrome hands ("CTS-hands”) with different nerve conduction study (NCS) severities. (A) Comparison of CSAs of the NCS minimal to NCS extreme groups with the CSAs of the NCS negative group using analysis of variance (ANOVA), followed by Scheffe’s multiple comparison analysis. black triangle denoting the significant difference between the NCS minimal and NCS moderate groups; black square denoting the significant difference between the NCS negative and NCS moderate groups; black circle denoting the significant difference at w level between the NCS mild and NCS moderate groups, black diamond denoting the significant difference at o1 level between the NCS negative and NCS mild groups. Chen et al. BMC Medical Imaging 2011, 11:22 Page 6 of 9 http://www.biomedcentral.com/1471-2342/11/22 Figure 3 The mean CSAs of “CTS-hands” with different NCS severities. Figure 4 An example of “positive-site” between i4and i3 corresponding to the relatively smaller cross-section area (CSA) at i2.The peak latencies (arrowhead) at i4 and i3 are 1.9 ms and 2.9 ms, respectively, and the difference between them is 1.0 ms, i.e. >0.4 ms. The CSA measured at i2 (arrow) is smaller than those measured at nearby levels. Markers of the 8-point: i4, i3, i2, i1, w, o1, o2, and o3. Chen et al. BMC Medical Imaging 2011, 11:22 Page 7 of 9 http://www.biomedcentral.com/1471-2342/11/22 Table 4 Distributions of the positive sites in inching test of all tested hands Inching None i4-i3 i3-i2 i2-i1 i1-WW-o1 o1-o2 o2-o3 double Total N (%) 119 37 (25.9) 55 (38.5) 6 (4.2) 10 (7.0) 8 (5.6) 2 (1.4) 0 (0) 25 (17.4) 262 Markers of the 8-point: i4, i3, i2, i1, W, o1, o2, and o3 “double” means more than two sites existed Thus, “CTS-hands” with a negative NCS poses a diagnos- Except for the NCS minimal group, all of the other tic challenge when using electrophysiologic study alone for groups of “CTS-hands” (from mild to extreme) have sig- confirmation. nificant differences in CSA measurement when compared In this study, 15.3% (32/212) of “CTS-hands” are NCS to that of the NCS negative group (Table 3 and Figures 2 negative. This incidence rate is consistent with those of pre- and 3) and a positive correlation with the severities of vious reports [2,21-23]. With the 8-point CSA measure- NCS findings. Although some insignificant enlargements ment, there are significant differences on several levels detected in CSA measurement are shown by inter-group between the “A-hands” and NCS negative “CTS-hands”. comparison (Tables 2 and 3), the present study demon- Most of the significant enlargements are located at the inlet strates that slower NCS means a larger CSA by US study. (Table 2). It is known that in patients with a clinical diagno- As shown in Table 3 and Figures 2 and 3, CSAs mea- sis of CTS, the accuracy of US is similar to that of EMG but sured at the 8-point of the NCS minimal group are all lar- is probably preferable because it is painless, easily accessi- ger than those of the NCS negative group, but this ble, and favored by patients [24]. The findings of the pre- difference is not statistically significant. This insignificance sent study further strengthen the importance of the can be explained partly by the trivial difference in NCS complementary role of US in confirming the diagnosis of and measured CSAs in these two groups of “CTS-hands”. idiopathic CTS in the NCS negative group. This is also However, this study does not offer enough evidence to suf- noted in a study of US correlation of CTS in NCS negative ficiently explain the difference. Further large-scale study is “CTS-hands” reported by Rahmani et al. [19]. Therefore, needed for better delineation of the US findings between US can be recommended as a useful technique in diagnos- the NCS negative and NCS minimal groups. Nevertheless, ing CTS patients when NCS results are not confirmatory in with a measurement of CSA at the 8-point, US remains an patients suspected of having median neuropathy. The pre- important complementary tool for confirming clinical sent study also posits the following cut-off values of CSA CTS. for CTS confirmation: 12.5 mm at the tunnel inlet, 11.5 As shown in Table 4, the segments between i4and i3, 2 2 mm at the wrist crease, and 10.1 mm at the tunnel outlet. and i3and i2 are the most frequent “positive sites”,and their respective CSAs are larger than those measured at “non-positive sites” (Table 5). This suggests a positive cor- relation in NCS severities and measured areas of CSA in Table 5 Comparison of CSAs at the 8-points among the the CTS study, a correlation also noted in other studies two most frequent positive sites and the negative site in [10,20,25,26]. The present study (Tables 4 and 5) also the inching test revealsthatmostofthe “positive sites” detected in the none (n = 119) i4-i3 (n = 37) i3-i2 (n = 55) “inching test” involve the distal part (i2-14) of the inlet, i4 13.9 ± 4.8(7-40.8) 19.5 ± 6.9 (9-37)* 19.0 ± 6.9 (8-41)* and the CSA measured at i2 is the smallest. These show i3 13.6 ± 4.8 (8-40.8) 17.4 ± 5.0 (8-32) * 17.9 ± 6.3 (8-42)* that the area around i2 is the most possible site of nerve i2 12.0 ± 3.1 (8-29) 12.4 ± 3.1 (6-19) 13.2 ± 3.4 (8-25) entrapment in idiopathic CTS, which may provide addi- i1 12.4 ± 4.1 (7-34.4) 13.6 ± 4.5 (7-31) 14.6 ± 4.3 (7.4-25)* tional guidance for a more precise location for treatment. w 12.5 ± 4.0 (7-31) 14.5 ± 4.6 (7-27) 15.6 ± 4.9 (7-33)* As shown in Table 6, there is a positive correlation o1 11.3 ± 2.8 (6-20.7) 13.1 ± 2.9 (9-20) 13.6 ± 3.6 (8-26)* between the measured CSA with the symptom duration of o2 11.0 ± 2.4 (6-18.5) 12.2 ± 2.4 (8-18) 12.8 ± 2.7 (8-21.3)* clinical idiopathic CTS such that the longer the duration o3 10.5 ± 2.6 (5-19) 10.5 ± 2.3 (6-16) 11.8 ± 2.4 (8-19)* of symptoms correlated to larger measured CSA. This Note: CSA, cross-section area; none, no conductive delay >0.4 ms in median finding has not been previously reported. Nonetheless, US inching test in centimeter across the carpal tunnel; i4-i3, conductive delay provides reproducible median nerve measurements [27]. >0.4 ms in inching test between 4 cm and 3 cm distal to the wrist crease; i3- i2, conductive delay >0.4 ms in inching test between 3 cm and 2 cm distal to As such, it can be used to assess changes in median nerve the wrist crease characteristics during follow-up studies of idiopathic CTS. Markers of the 8-point: i4, i3, i2, i1, w, o1, o2, and o3 This study has several limitations. First, although 212 i4-i3and i3-i2: the difference of latency measured between locations of i4and i3, and i3and i2 in the inching test “CTS-hands” were included for examination, further Unit of CSA = mm large-scale study is warranted for a more even distribu- *p < 0.05 in comparing the two most frequent positive sites and the negative tion of the case number in the different sub-groups of one in inching test using analysis of variance (ANOVA) followed by Scheffe’s multiple comparison procedure “CTS-hands”. Second, the limitations of accuracy in Chen et al. BMC Medical Imaging 2011, 11:22 Page 8 of 9 http://www.biomedcentral.com/1471-2342/11/22 Table 6 Comparison of CSAs at the 8-point of the ‘A-hands’ with the “CTS-hands” of different symptom durations A-hands CTS-hands (n = 50) 1 month(n = 12) > 1 month and 12 months (n = 82) >12 months (n = 118) i4 11.8 ± 2.4 (8-19) 14.1 ± 4.7 (8-24) 16.6 ± 5.1 (7-34)* 18.5 ± 6.9 (8-41)* ,# i3 11.5 ± 2.3 (8-19) 12.7 ± 2.9 (8-17) 16.0 ± 5.0 (8-28) * 17.3 ± 6.0 (8-42)* i2 10.9 ± 1.9 (8-16) 11.2 ± 2.6 (7-17) 12.8 ± 2.8 (7-20) * 13.1 ± 3.7 (6-29)* i1 10.7 ± 1.7 (8-15) 12.8 ± 2.0 (10-16) 13.6 ± 4.1 (7-24) * 15.0 ± 5.1 (7-34.4)* w 10.7 ± 2.0 (7-17) 11.7 ± 3.3 (7-18) 14.8 ± 5.2 (7-40.4) * 16.0 ± 5.2 (7-33)* o1 10.1 ± 2.2 ( 6-16) 11.2 ± 2.9 (7-16) 12.8 ± 3.2 (7-23) * 13.7 ± 3.4 (8-27.4)* o2 10.2 ± 2.1 (7-17) 10.8 ± 2.0 (8-15) 11.6 ± 2.3 (6-19) * 12.7 ± 2.8 (7-21.3)* o3 9.4 ± 1.9 (6-15) 10.5 ± 2.6 (7-17) 11.1 ± 2.2 (5-16) * 11.4 ± 2.6 (6-19)* Abbreviations: A-hand, asymptomatic hands; CTS-hands, carpal tunnel syndrome hand; CSAs, cross section areas Markers of the 8-point: i4, i3, i2, i1, w, o1, o2, and o3. Unit of CSA = mm *p < 0.05 (a comparison of CSAs of the ‘A-hands’ with the CSAs of the ‘CTS-hands’ of different symptom durations using analysis of variance (ANOVA) followed by Scheffe’s multiple comparison procedure) p < 0.05 (a comparison of CSAs of the CTS-hands with <1 month duration with the CSAs of the ‘CTS-hands’ with >12 months duration using analysis of variance (ANOVA) followed by Scheffe’s multiple comparison procedure) contributed to the conception and design, and clinical data analysis; and inching techniques need to be taken into consideration. WNC contributed to the conception and design, data analysis, and critical This limitation is also noted in other studies [28,29]. revision and final approval of the manuscript. Third, there is difficulty in accurately obtaining a chron- Competing interests ology of the length of symptom duration. Fourth, there The authors declare that they have no competing interests. is a lack of using neuroimaging studies such as com- puted tomography and/or magnetic resonance imaging Received: 30 June 2011 Accepted: 21 December 2011 Published: 21 December 2011 to test the accuracy of CSA measurement at varying levels and to delineate the local change of carpal tunnel. References Fifth, besides CSA measurement, there are other useful, 1. Phalen GS: The carpal-tunnel syndrome. Clinical evaluation of 598 hands. additional measurements of the median nerve with US Clin Ortho Relat Res 1972, 83:29-40. 2. Jablecki CK, Andary MT, Floeter RG, Miller CA, Quartly CA, Vennix MJ, such as the measurement of width and circumference of Wilson JR, American Association of Electro-diagnostic Medicine; American the wrist [30]. In this study we did not perform these Academy of Neurology; American Academy of Physical Medicine and additional measurements for CSA correlation. 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