ORIGINAL RESEARCH
The Usefulness of Terminal Latency Index of Median Nerve and F-Wave Difference Between Median and Ulnar Nerves in Assessing the Severity of Carpal Tunnel Syndrome Kang Min Park, Kyong Jin Shin, Jinse Park, Sam Yeol Ha, and Sung Eun Kim
Summary: The calculated electrophysiological parameters, such as terminal latency index (TLI), residual latency, modified F ratio, and F-wave inversion, have been investigated as a diagnostic tool for detection of early stage of carpal tunnel syndrome (CTS) in the literature. However, the correlation of these calculated electrophysiological parameters with the clinical severity of CTS has not been reported. The aim of this study was to determine the correlation of the calculated electrophysiological parameters and clinical severity in patients with CTS. A retrospective study was performed with 212 hands of 106 CTS patients. The CTS hands were classified as asymptomatic, mild, moderate, and severe according to the clinical severity. The distal motor latency and distal motor conduction velocity of median nerve, minimal F-wave latency of median and ulnar nerves, and sensory nerve conduction velocity in the finger–wrist and palm–wrist segment of median nerve (SNCV f-w and SNCV p-w) were obtained in a conventional nerve conduction study. The TLI, residual latency, and modified F ratio of the median nerve and the difference of minimal F-wave latencies between the median and ulnar nerves (F-diff M-U) were calculated. The distal motor latency, residual latency, and F-diff M-U were significantly increased according to the clinical severity of CTS. The motor conduction velocity, SNCV p-w, SNCV f-w, TLI, and modified F ratio were significantly decreased according to the clinical severity of CTS. In analyses of variance and Kruskal–Wallis test, we used the Scheffe test as a post-hoc comparison analysis. The TLI, F-diff M-U, and SNCV f-w showed a significant difference among all groups of each CTS severity. The sensitivity, specificity, and cutoff value of TLI, F-diff M-U, and SNCV f-w between asymptomatic and mild, mild and moderate, and moderate and severe CTS groups were calculated by using receiver operating characteristic curve analysis. The cut-off values of TLI, F-diff M-U, and SNCV f-w between the asymptomatic and mild CTS groups were, respectively, 0.33 millisecond, 0.3 millisecond, and 40 cm/second. The cut-off values of TLI, F-diff M-U, and SNCV f-w between mild and moderate were, respectively, 0.27 millisecond, 2.3 milliseconds, and 34.8 cm/second. The cut-off values of TLI, F-diff M-U, and SNCV f-w between moderate and severe CTS groups were, respectively, 0.20 millisecond, 4.2 milliseconds, and 26.4 cm/second. We found that calculated electrophysiological parameters of conventional nerve conduction study could be a good indicator to determine the severity of CTS. Key Words: Carpal tunnel syndrome, Nerve conduction, Clinical severity, Median nerve, Ulnar nerve. (J Clin Neurophysiol 2014;31: 162–168)
From the Department of Neurology, Haeundae Paik Hospital, Inje University, Busan, South Korea. This work was supported by the 2012 Inje University research grant. Address correspondence and reprint requests to Kyong Jin Shin, MD, Department of Neurology, Haeundae Paik Hospital, Inje University, 875 Haeundaero, Haeundae gu, Busan 612-030, South Korea; e-mail: [email protected]. Copyright 2014 by the American Clinical Neurophysiology Society
ISSN: 0736-0258/14/3102-0162
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arpal tunnel syndrome (CTS) is the most common entrapment neuropathy. Its main symptoms are paresthesia and numbness in the distribution of median nerve. Motor weakness and atrophy of the thenar muscles may occur in advanced stage (Padua et al., 1997; Schrijver et al., 2005; Stevens, 1997; You et al., 1999). Early detection and treatment is very important to prevent hand weakness and atrophy and to improve quality of life in patients with CTS (Duncan et al., 1987; Katz et al., 1998; Spitzer, 1996; Wilson and Sumner, 1995). Conventional nerve conduction study (NCS) is the essential tool to diagnose CTS. Decreased conduction velocity in the palm– wrist or finger–wrist segment of median sensory NCS and delayed distal motor latency (DML) in median motor NCS are the hallmark of CTS (American Academy of Neurology, 1993a, 1993b; Jablecki et al., 1993). However, some patients show normal findings in conventional NCS although their symptoms and signs are very typical ones of CTS. Several calculated parameters, such as terminal latency index (TLI), residual latency (RL), modified F-wave latency ratio, and F-wave inversion, have been investigated to detect early stage of CTS (Aygul et al., 2009; Cevik et al., 2012; Simovic and Weinberg, 1997; Uzar et al., 2011). However, the correlation of the calculated parameters and the clinical severity in CTS was not well known. The aim of this study was to determine the correlation of the calculated electrophysiological parameters and clinical severity in patients with CTS. The calculated electrophysiological parameters include TLI, RL and modified F-wave latency ratio of median nerve, and difference of minimal F-wave minimal latencies between median and ulnar nerves. We also investigated the correlation of conventional NCS parameters according to clinical severity of CTS.
METHODS Patients We retrospectively investigated 164 CTS patients visiting a neurology outpatient clinic in the Haeundae Paik Hospital of Inje University, from March 2010 to March 2012. Twenty-seven patients aged $ 70 years and 31 patients with comorbidity with diabetes mellitus, rheumatoid arthritis, cervical radiculopathy, other upper extremity mononeuropathies, and neuropathic pain of other causes were excluded. A total of 106 patients and 212 hands were enrolled. Carpal tunnel syndrome was diagnosed if patients met criterion 1 and one or more of criteria 2 to 4 of the following American Academy of Neurology practice parameters (American Academy of Neurology, 1993a; American Academy of Neurology, 1993b; You et al., 1999): (1) paresthesia, pain, swelling, weakness, or clumsiness of the hand provoked or worsened by sleep, sustained hand or arm position, or repetitive action of the hand or wrist
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mitigated by a change in posture or by shaking of the hand; (2) sensory deficits in the median nerve innervated regions of the hand; (3) motor deficit or hypotrophy of the median nerve innervated thenar muscles; and (4) positive provocative clinical tests (positive Phalen maneuver and/or Tinel sign). We divided the enrolled CTS hands into four groups according to the clinical severity by applying a historical-objective scale (Hi-Ob scale) (Giannini et al., 2002). We simplified the 6 stages of the original Hi-Ob scale (stage 0: no symptoms suggestive of CTS, stage 1: only nocturnal paresthesia, stage 2: diurnal paresthesia, stage 3: sensory deficit, stage 4: hypotrophy and/or motor deficit of median innervated thenar muscles, and stage 5: complete atrophy or plegia of median innervated thenar muscles) into 4. Stage 0 of the Hi-Ob scale was defined as the group with asymptomatic hands, stages 1 and 2 as group with mild CTS hands, stage 3 as group with moderate CTS hands, and stages 4 and 5 as group with severe CTS hands.
Nerve Conduction Study Electrophysiological studies were performed according to the American Association of Electrodiagnostic Medicine guideline with a “Medelec Synergy” electromyographic device (Oxford Instruments Medical, Inc., Tubney Woods, Abingdon, United Kingdom) at a skin temperature above 328C (American Academy of Neurology, 1993a, 1993b; Jablecki et al., 2002; Stevens, 1997). We recorded the motor NCS of the median and ulnar nerves using the standard belly–tendon method in the setting of the filter bandpass at 3 Hz to 10 kHz, a sweep speed of 5 milliseconds/division, and amplifier gain at 1 to 5 mV/division. The recording muscles of the median and ulnar nerves were the abductor pollicis brevis and abductor digiti minimi, respectively. Supramaximal stimulation was applied to the wrist convolution at a distance of 6 cm from the each recorded muscles and elbow crease. F-wave was recorded in the median and ulnar nerves with supramaximal stimulation at the level of wrist convolution. The active and reference electrodes were placed at the same points used in motor NCS. The filter bandpass was 30 Hz to 10 kHz, the sweep speed was 10 milliseconds/division, and the sensitivity was 0.2 mV/division. At least 20 consecutive distal F wave were elicited, and the minimum Fwave latency was measured. We also recorded the sensory NCS orthodromically in the finger–wrist, palm–wrist, and wrist–elbow segments. The filter bandpass of sensory NCS was 20 Hz to 2 kHz, the sweep speed was 2 milliseconds/division, and the sensitivity was 10 to 20 mV/division.
Eletrophysiological Parameters The DML and distal motor conduction velocity (MCV) were obtained in median motor NCS. The TLI (Attarian et al., 2001; Cocito et al., 2001; Lissens and Bruyninckx, 1988; Simovic and Weinberg, 1997) and RL (Cocito et al., 2001; Kraft and Halvorson, 1983) were calculated as TLI ¼ distal conduction distance/(distal MCV · DML), and RL ¼ DML 2 (distal conduction distance/distal MCV). The difference of the minimal F-wave latencies between the median and ulnar nerves (F-diff M-U) (Cevik et al., 2012) and modified F ratio (MFR) (Attarian et al., 2001; Cocito et al., 2001) were calculated as F-diff M-U ¼ minimal F-wave latency of median nerve 2 minimal F-wave latency of ulnar nerve, and MFR ¼ (F 1 DML 2 2 · PML 2 1)/2 · DML, F means the minimal F-wave latency of median nerve. Copyright 2014 by the American Clinical Neurophysiology Society
Usefulness of Terminal Latency Index
The sensory nerve conduction velocity in the palm–wrist (SNCV p-w) and finger–wrist (SNCV f-w) segments of the median nerve were obtained in median sensory NCS. We also divided the CTS hands into 5 groups according to the neurophysiological classification proposed by Padua et al. (Padua et al., 1997): (1) extreme CTS, absence of thenar motor response; (2) severe CTS, absence of median SNAPs in the digit–wrist segment and abnormal DML; (3) moderate CTS, slowing of median digit–wrist segment and abnormal DML; (4) mild CTS, slowing of median digit wrist segment and normal DML; and (5) negative, normal findings in all tests. The normal values of digit–wrist SNCV and DML in our electrophysiological laboratory were above 40 cm/ second and below 3.60 milliseconds, respectively.
Statistical Analyses The ratio of neurophysiological classes in the groups with each CTS severity was evaluated by x2 test. The comparison of the electrophysiological parameters among groups with each CTS severity was assessed by analyses of variance and Kruskal–Wallis test. We also performed Scheffe test as a post-hoc comparison analysis. The sex ratio according to group with each CTS severity was assessed by x2 test. We performed receiver operating characteristic curve analysis to determine the cut-off value among groups with each CTS severity. The sensitivity and specificity were also obtained by receiver operating characteristic curve analysis. The regression analysis and Spearman correlation were performed to evaluate the change of electrophysiological parameters according to the clinical severity of CTS. Multivariate regression analysis was performed to clarify the correlation of electrophysiological parameters according to age, sex, and clinical severity. The significance level was taken to be P , 0.05.
RESULTS
The mean age was 52.9 6 10.3 years (range, 25 to 70 years). Eighty-five patients were female and 21 were male. Sixty-six patients had bilateral CTS, 24 had right-side CTS, and 16 had leftside CTS. Forty hands were asymptomatic, 103 were mild, 43 were moderate, and 26 were severe. The ratios of neurophysiological classes according to the group with each CTS severity are summarized in Fig. 1. Thirty-one hands were “negative,” six “mild CTS,” and three “moderate CTS” among 40 asymptomatic hands. Thirty-five hands were “negative,” 35 “mild CTS,” and 33 “moderate CTS” among 103 hands with mild CTS. Two hands were “negative,” 40 “mild CTS,” and 1 “severe CTS” among 43 hands with moderate CTS. Twelve hands were “moderate CTS,” 9 “severe CTS,” and 5 “extreme CTS” among 26 hands with severe CTS. The clinical CTS severity was significantly correlated with the neurophysiological CTS severity. The distribution of age, sex, and electrophysiological parameters according to the group with each CTS severity is illustrated in Table 1. There was no SNAP formation in 15 hands and no CMAP formation in 5 hands among the total of 212 hands. The 15 hands without formation of SNAP were excluded in the analysis of SNCV f-w and SNCV p-w. The five hands without formation of CMAP were excluded in the analysis of DML, MCV, TLI, RL, and MFR. Therefore, a total of 197 hands were included in the analysis of SNCV p-w and SNCV f-w, and a total of 207 hands were also included in the analysis of DML, MCV, TLI, RL, and F-diff M-U. Age and sex were not significantly different according to the CTS severity group (Table 1). The MCV, SNCV f-w, TLI, and MFR 163
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In analyses of variance and Kruskal–Wallis test, we used the Scheffe test as a post-hoc comparison analysis (Table 1). Distal motor latency, RL, and SNCV p-w showed a significant difference between asymptomatic and mild CTS and mild and moderate CTS but not between moderate and severe CTS. Motor conduction velocity showed a significant difference between mild and moderate CTS and moderate and severe CTS but not between asymptomatic and mild CTS. The MFR showed a significant difference between only the mild and moderate CTS. The TLI, F-diff M-U, and SNCV f-w showed a significant difference among all groups of CTS severity. We also calculated the sensitivity, specificity, and cut-off value of TLI, F-diff M-U, and SNCV f-w, which showed a significant difference among all groups of each CTS severity, using receiver operating characteristic curve analysis (Table 3). The cut-off values of TLI, F-diff M-U, and SNCV f-w between asymptomatic and mild CTS group were, respectively, 0.33 millisecond, 0.3 millisecond, and 40 cm/second. The cut-off values of TLI, F-diff M-U, and SNCV f-w between mild and moderate CTS group were, respectively, 0.27 millisecond, 2.3 milliseconds, and 34.8 cm/second. The cut-off values of TLI, F-diff M-U, and SNCV f-w between moderate and severe CTS group were, respectively, 0.20 millisecond, 4.2 milliseconds, and 26.4 cm/second.
FIG. 1. Ratios of neurophysiological classes according to the group with each CTS severity, x2 test, P , 0.01. CTS, carpal tunnel syndrome; NCS, nerve conduction study. according to the CTS severity were assessed using analyses of variance and regression analysis because they showed normal distribution. The DML, SNCV p-w, F-diff M-U, and RL according to the CTS severity were assessed by using Kruskal–Wallis test and Spearman correlation because they did not show normal distribution. The DML, RL, and F-diff M-U were significantly increased according to the clinical severity of CTS (Kruskal–Wallis test and Spearman correlation, P , 0.05, Figs. 2 and 3). The MCV, SNCV p-w, SNCV f-w, TLI, and MFR significantly decreased according to the clinical severity of CTS (analyses of variance, Kruskal–Wallis test, regression analysis, and Spearman correlation, all P , 0.05, Fig. 2). In the multivariate regression analysis, the MCV, SCV f-w, TLI, and MFR showed significant correlations with the clinical severity of CTS irrespective of age and sex (Table 2).
TABLE 1.
DISCUSSION Carpal tunnel syndrome is the most common entrapment neuropathy, with a 10% lifetime risk in the general population (American Academy of Neurology, 1993a, 1993b; Aygul et al., 2009; Duncan et al., 1987; Jablecki et al., 1993; Katz et al., 1998; Padua et al., 1997; Spitzer, 1996; Wilson and Sumner, 1995; You et al., 1999). Carpal tunnel syndrome results from compression of the median nerve during passage through the carpal tunnel under the transverse carpal ligament. The Boston questionnaire (BQ) including symptoms severity score and functional severity score is the most commonly used tool to assess the clinical feature of CTS (Greenslade et al., 2004; Heybeli et al., 2002; Levine et al., 1993; Mondelli et al., 2000; Sezgin et al., 2006).
Age, Sex, and Electrophysiological Parameters With Different Severity Groups of Carpal Tunnel Syndrome
Age, year Sex (M/F), n DML‡, millisecond MCV§, cm/second SNCV f-w¶, cm/second SNCV‡ p-w, cm/second F-diff M-U¶, millisecond TLI¶ RL‡, millisecond MFR#
Asymptomatic
Mild CTS
Moderate CTS
Severe CTS
P
51.0 (25–70) 8:32 3.05 (2.40–3.90) 57.2 6 2.8 43.8 6 4.4 36.5 (27.6–50.3) 0.15 (21.30 to 3.05) 0.35 6 0.04 2.95 (2.30–3.79) 2.06 6 0.29
53.0 (25–70) 22:81 3.45 (2.36–5.95) 56.8 6 3.0 39.2 6 6.4 31.7 (17.6–45.3) 0.9 (21.60 to 6.25) 0.31 6 0.05 3.34 (2.25–5.83) 1.92 6 0.35
54.0 (32–69) 4:39 4.85 (2.80–6.35) 54.7 6 3.6 30.1 6 5.7 24.1 (17–41) 3.50 (20.3 to 10.55) 0.23 6 0.04 4.74 (2.71–6.25) 1.47 6 0.31
51 (39–67) 8:18 6.63 (4.80–8.35) 49.3 6 5.6 24.4 6 5.0 19.4 (12.7–29) 7.55 (3.80–16.25) 0.19 6 0.06 6.51 (3.34–13.31) 1.26 6 0.49
0.36* 0.16† ,0.01* ,0.01k ,0.01k ,0.01* ,0.01* ,0.01k ,0.01* ,0.01k
CTS, carpal tunnel syndrome; DML, distal motor latency of median nerve; F-diff MU, difference of minimal F-wave latency between median and ulnar nerves; MCV, distal motor conduction velocity of median nerve; MFR, modified F-wave latency ratio; RL, residual latency of median nerve; SNCV f-w, sensory nerve conduction velocity at finger–wrist segment of median nerve; SNCV p-w, sensory nerve conduction velocity at palm–wrist segment of median nerve; TLI, terminal latency index of median nerve. *Kruskal–Wallis test. †Chi-square test. ‡P , 0.05 in comparison between asymptomatic and mild and mild and moderate CTS. §P , 0.05 in comparison between mild and moderate and moderate and severe CTS. kAVOVAs, post-hoc comparison analysis (Scheffe test). ¶P , 0.05 in comparison between asymptomatic and mild, mild and moderate, and moderate and severe CTS. #P , 0.05 in comparison between mild and moderate CTS.
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Usefulness of Terminal Latency Index
FIG. 2. Correlation of DML, SNCV p-w, F-diff M-U, and RL according to the groups of hand with asymptomatic, mild, moderate, or severe CTS. CTS, carpal tunnel syndrome; DML, distal motor latency of median nerve; SNCV p-w, sensory nerve conduction velocity in palm–wrist segment of median nerve; F-diff M-U, difference of minimal F-wave latencies between median and ulnar nerves; RL, residual latency of median nerve (Spearman correlation; DML, coefficient of correlation: 0.73, P , 0.01; SNCV p-w, coefficient of correlation: 20.67, P , 0.01; F-diff M-U, coefficient of correlation: 0.72, P , 0.01; RL, coefficient of correlation: 0.73, P , 0.01). The disability of arm, shoulder, and hand sore (Greenslade et al., 2004; Hudak et al., 1996) and Michigan hand outcomes questionnaire (Chung et al., 1998; Kotsis and Chung, 2005) are other tools to evaluate the functional status of upper extremity. However, these self-administered questionnaires have some disadvantages. They do not sufficiently reflect the objective neurologic signs because they mainly reflect the subjective symptoms and functional hand capacities of CTS patients. Moreover, the current physical, psycholgical, and emotional states of CTS patients may affect their results. These questionnaires mainly evaluate the bimanual function of CTS patients. Therefore, they are limited in separately evaluating the function of each side hand. These selfadministered questionnaires provide clinical diagnostic certainty of CTS, such as classic, probable, possible, and unlikely instead of defining the clinical severity of CTS. Copyright 2014 by the American Clinical Neurophysiology Society
We applied the Hi-Ob scale to the classification of CTS hands according to the clinical severity (Giannini et al., 2002). The Hi-Ob parameter was positively related to the neurophysiological classification and BQ in the validation test of Hi-Ob scale (Giannini et al., 2002). Caliandro et al. (2010) proposed the historical-objectivedistribution (Hi-Ob-Db) scale, which added the Hi-Ob scale to distribution of paresthesia. The Hi-Ob-Db was significantly correlated to the sensory nerve conduction velocity, DML, neurophysiological classification, and BQ scores. Presently, we divided the CTS patients into four severity groups according to the objective neurologic sign. We simplified the six stages of the original Hi-Ob scale into four (asymptomatic, mild, moderate, and severe CTS) because the boundaries between stages 1 and 2 and stages 4 and 5 were obscure in some cases. Asymptomatic is the normal hand of the unilateral CTS 165
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FIG. 3. Correlation of MCV, SNCV f-w, TLI, and MFR according to the groups of hand with asymptomatic, mild, moderate, or severe CTS. CTS, carpal tunnel syndrome; MCV, distal motor nerve conduction velocity of median nerve; SNCV f-w, sensory nerve conduction velocity in finger–wrist segment of median nerve; TLI, terminal latency index of median nerve; MFR, modified F ratio of median nerve (regression analysis; MCV, R2 ¼ 0.25, P , 0.01; SNCV f-w, R2 ¼ 0.47, P , 0.01; TLI, R2 ¼ 0.52, P , 0.01; MFR, R2 ¼ 0.35, P , 0.01).
patients. Mild CTS is indicated when the patient complains of the typical symptoms of CTS and shows Tinel sign or positive Phalene maneuver (inclusion of the aforementioned American Academy of Neurology practice parameters criteria 1 and 4), but the sensory and motor function tests of the affected hand are normal (exclusion of criteria 2 and 3). Moderate CTS is indicated when the patient complains of the typical symptoms of CTS and the sensory deficit in the median nerve territory of the affected hand is observed (inclusion of criteria 1, 2, and 4), but the motor function is normal (exclusion of criterion 3). Severe CTS is indicated when the patient complains of the typical symptoms of CTS, the sensory deficit and motor weakness, and atrophy in the median nerve territory of the affected hand are observed (inclusion of criteria 1, 2, 3, and 4). The classification is based on the clinical observations and scientific investigations that 166
nerve entrapment of CTS affects earlier sensory nerve than motor nerve (American Academy of Neurology, 1993a, 1993b; Aygul et al., 2009; Heybeli et al., 2002; Jablecki et al., 1993; Katz et al., 1998; Levine et al., 1993; Padua et al., 1997; Spitzer, 1996; You et al., 1999). The NCS findings show the following progression in pacing with the clinical progression of CTS: (1) abnormalities of segmental sensory NCT such as disto-proximal ratio (R); (2) SNCV slowing in digit–wrist segments; (3) increased DML; (4) disappearance of digit–wrist SNAPs; and (5) disappearance of motor response (Padua et al., 1997). In this study, the electrophysiological classification and each parameter showed a significant correlation with the clinical severity. This is consistent with the previous studies using the Hi-Ob and Hi-Ob-Db scales (Caliandro et al., 2010; Giannini et al., 2002). Especially, the TLI, F-diff M-U, and SNCV f-w Copyright 2014 by the American Clinical Neurophysiology Society
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TABLE 2. Analysis)
Usefulness of Terminal Latency Index
Correlation of MCV, SNCV f-w, TLI, and MFR According to Age, Sex, and CTS Severity (Multivariate Regression Unstandardized Coefficients
MCV
SNCV f-w
TLI
MFR
CTS severity Age Sex CTS severity Age Sex CTS severity Age Sex CTS severity Age Sex
Unstandardized Coefficients
Beta
Standard Error
Beta
t
P
22.226 20.840 1.668 26.698 20.141 21.359 20.055 20.001 0.012 20.289 20.005 20.050
0.273 0.023 0.592 0.508 0.039 1.039 0.004 0.000 0.008 0.028 0.002 0.061
20.474 20.213 0.162 20.668 20.184 20.066 20.705 20.117 1.463 20.578 20.128 20.046
28.156 23.668 2.819 213.172 23.625 21.307 214.641 22.432 1.463 210.306 22.287 20.829
,0.01 ,0.01 ,0.01 ,0.01 ,0.01 0.19 ,0.01 0.02 0.15 ,0.01 0.02 0.41
MCV, motor nerve conduction velocity of median nerve; MFR, modified F ratio of median nerve; SNCV f-w, sensory nerve conduction velocity of median nerve; TLI, terminal latency index of median nerve.
showed a significant difference among all groups of CTS severity. The TLI of median nerve and the F-diff M-U are well-known calculated electrophysiological parameters used to diagnose the early stage of CTS, although its sensitivity and specificity is variable according to investigations (Aygul et al., 2009; Cevik et al., 2012; Simovic and Weinberg, 1997; Uzar et al., 2011). We found that TLI and F-diff M-U can be used to assess the stages of CTS severity. We also calculated the sensitivity, specificity, and cutoff value of these parameters among groups with asymptomatic, mild, moderate, and severe CTS. The cut-off value between asymptomatic and mild CTS group may indicate a point of diagnosis of early stage of CTS. The cut-off value between mild and moderate CTS group may indicate a point of surgical treatment in CTS patients. The cut-off value between moderate and severe CTS group may indicate a point of poor outcome of treatment in CTS patients. The limitations of this study are its retrospective nature with small study sample size. As well, sometimes the boundary among the groups of each CTS severity was not clear-cut. We did not perform the NCS in normal controls. The NCS findings of asymptomatic hand of unilateral CTS patients and hands of normal control may differ.
TABLE 3. Results of Receiver Operating Characteristic Curve Analysis of SNCV, TLI, and F-diff M-U Between Asymptomatic and Mild, Mild and Moderate, and Moderate and Severe CTS Cut-off Value Sensitivity/ Asymptomatic Specificity and Mild SNCV f-w, cm/second, % TLI, ratio, % F-diff M-U, %
Mild and Moderate
Moderate and Severe
40.0, 60.2/85.0
34.8, 90.5/79.6
26.4, 75.0/73.8
0.33, 68.0/67.5 0.3, 68.0/57.5
0.27, 74.4/77.2 2.3, 81.4/85.4
0.20, 52.2/83.7 4.2, 96.2/76.7
F-diff M-U, difference of minimal F-wave latencies between median and ulnar nerves; SNCV f-w, sensory nerve conduction velocity in finger–wrist segment of median nerve; TLI, terminal latency index of median nerve.
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with carpal tunnel syndrome. AAEM Quality Assurance Committee. Muscle Nerve 1993;16:1392–1414. Jablecki CK, Andary MT, Floeter MK, et al. Practice parameter: electrodiagnostic studies in carpal tunnel syndrome. Report of the American Association of Electrodiagnostic Medicine, American Academy of Neurology, and the American Academy of Physical Medicine and Rehabilitation. Neurology 2002;58:1589–1592. Katz JN, Keller RB, Simmons BP, et al. Maine Carpal Tunnel Study: outcomes of operative and nonoperative therapy for carpal tunnel syndrome in a community-based cohort. J Hand Surg Am 1998;23:697–710. Kotsis SV, Chung KC. Responsiveness of the Michigan Hand Outcomes Questionnaire and the Disabilities of the Arm, Shoulder and Hand questionnaire in carpal tunnel surgery. J Hand Surg Am 2005;30:81–86. Kraft GH, Halvorson GA. Median nerve residual latency: normal value and use in diagnosis of carpal tunnel syndrome. Arch Phys Med Rehabil 1983;64: 221–226. Levine DW, Simmons BP, Koris MJ, et al. A self-administered questionnaire for the assessment of severity of symptoms and functional status in carpal tunnel syndrome. J Bone Joint Surg Am. 1993;75:1585–1592. Lissens MA, Bruyninckx FL. [Terminal latency index (TLI) of the median nerve and ulnar nerve: normal values and relation to carpal tunnel syndrome]. Acta Belg Med Phys 1988;11:91–94. Mondelli M, Reale F, Sicurelli F, et al. Relationship between the self-administered Boston questionnaire and electrophysiological findings in follow-up of surgically-treated carpal tunnel syndrome. J Hand Surg Br 2000;25:128–134.
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Padua L, LoMonaco M, Gregori B, et al. Neurophysiological classification and sensitivity in 500 carpal tunnel syndrome hands. Acta Neurol Scand 1997;96:211–217. Schrijver HM, Gerritsen AA, Strijers RL, et al. Correlating nerve conduction studies and clinical outcome measures on carpal tunnel syndrome: lessons from a randomized controlled trial. J Clin Neurophysiol 2005;22:216–221. Sezgin M, Incel NA, Serhan S, et al. Assessment of symptom severity and functional status in patients with carpal tunnel syndrome: reliability and functionality of the Turkish version of the Boston Questionnaire. Disabil Rehabil 2006;28:1281–1285. Simovic D, Weinberg DH. Terminal latency index in the carpal tunnel syndrome. Muscle Nerve 1997;20:1178–1180. Spitzer AR. Treatment of choice for carpal tunnel syndrome. Muscle Nerve 1996;19:531; author reply 2. Stevens JC. AAEM minimonograph #26: the electrodiagnosis of carpal tunnel syndrome. American Association of Electrodiagnostic Medicine. Muscle Nerve 1997;20:1477–1486. Uzar E, Tamam Y, Acar A, et al. Sensitivity and specificity of terminal latency index and residual latency in the diagnosis of carpal tunnel syndrome. Eur Rev Med Pharmacol Sci 2011;15:1078–1084. Wilson JR, Sumner AJ. Immediate surgery is the treatment of choice for carpal tunnel syndrome. Muscle Nerve 1995;18:660–662; discussion 3. You H, Simmons Z, Freivalds A, et al. Relationships between clinical symptom severity scales and nerve conduction measures in carpal tunnel syndrome. Muscle Nerve 1999;22:497–501.
Copyright 2014 by the American Clinical Neurophysiology Society
The Usefulness of Terminal Latency Index of Median Nerve and F-Wave Difference Between Median and Ulnar Nerves in Assessing the Severity of Carpal Tunnel Syndrome Kang Min Park, Kyong Jin Shin, Jinse Park, Sam Yeol Ha, and Sung Eun Kim
Summary: The calculated electrophysiological parameters, such as terminal latency index (TLI), residual latency, modified F ratio, and F-wave inversion, have been investigated as a diagnostic tool for detection of early stage of carpal tunnel syndrome (CTS) in the literature. However, the correlation of these calculated electrophysiological parameters with the clinical severity of CTS has not been reported. The aim of this study was to determine the correlation of the calculated electrophysiological parameters and clinical severity in patients with CTS. A retrospective study was performed with 212 hands of 106 CTS patients. The CTS hands were classified as asymptomatic, mild, moderate, and severe according to the clinical severity. The distal motor latency and distal motor conduction velocity of median nerve, minimal F-wave latency of median and ulnar nerves, and sensory nerve conduction velocity in the finger–wrist and palm–wrist segment of median nerve (SNCV f-w and SNCV p-w) were obtained in a conventional nerve conduction study. The TLI, residual latency, and modified F ratio of the median nerve and the difference of minimal F-wave latencies between the median and ulnar nerves (F-diff M-U) were calculated. The distal motor latency, residual latency, and F-diff M-U were significantly increased according to the clinical severity of CTS. The motor conduction velocity, SNCV p-w, SNCV f-w, TLI, and modified F ratio were significantly decreased according to the clinical severity of CTS. In analyses of variance and Kruskal–Wallis test, we used the Scheffe test as a post-hoc comparison analysis. The TLI, F-diff M-U, and SNCV f-w showed a significant difference among all groups of each CTS severity. The sensitivity, specificity, and cutoff value of TLI, F-diff M-U, and SNCV f-w between asymptomatic and mild, mild and moderate, and moderate and severe CTS groups were calculated by using receiver operating characteristic curve analysis. The cut-off values of TLI, F-diff M-U, and SNCV f-w between the asymptomatic and mild CTS groups were, respectively, 0.33 millisecond, 0.3 millisecond, and 40 cm/second. The cut-off values of TLI, F-diff M-U, and SNCV f-w between mild and moderate were, respectively, 0.27 millisecond, 2.3 milliseconds, and 34.8 cm/second. The cut-off values of TLI, F-diff M-U, and SNCV f-w between moderate and severe CTS groups were, respectively, 0.20 millisecond, 4.2 milliseconds, and 26.4 cm/second. We found that calculated electrophysiological parameters of conventional nerve conduction study could be a good indicator to determine the severity of CTS. Key Words: Carpal tunnel syndrome, Nerve conduction, Clinical severity, Median nerve, Ulnar nerve. (J Clin Neurophysiol 2014;31: 162–168)
From the Department of Neurology, Haeundae Paik Hospital, Inje University, Busan, South Korea. This work was supported by the 2012 Inje University research grant. Address correspondence and reprint requests to Kyong Jin Shin, MD, Department of Neurology, Haeundae Paik Hospital, Inje University, 875 Haeundaero, Haeundae gu, Busan 612-030, South Korea; e-mail: [email protected]. Copyright 2014 by the American Clinical Neurophysiology Society
ISSN: 0736-0258/14/3102-0162
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C
arpal tunnel syndrome (CTS) is the most common entrapment neuropathy. Its main symptoms are paresthesia and numbness in the distribution of median nerve. Motor weakness and atrophy of the thenar muscles may occur in advanced stage (Padua et al., 1997; Schrijver et al., 2005; Stevens, 1997; You et al., 1999). Early detection and treatment is very important to prevent hand weakness and atrophy and to improve quality of life in patients with CTS (Duncan et al., 1987; Katz et al., 1998; Spitzer, 1996; Wilson and Sumner, 1995). Conventional nerve conduction study (NCS) is the essential tool to diagnose CTS. Decreased conduction velocity in the palm– wrist or finger–wrist segment of median sensory NCS and delayed distal motor latency (DML) in median motor NCS are the hallmark of CTS (American Academy of Neurology, 1993a, 1993b; Jablecki et al., 1993). However, some patients show normal findings in conventional NCS although their symptoms and signs are very typical ones of CTS. Several calculated parameters, such as terminal latency index (TLI), residual latency (RL), modified F-wave latency ratio, and F-wave inversion, have been investigated to detect early stage of CTS (Aygul et al., 2009; Cevik et al., 2012; Simovic and Weinberg, 1997; Uzar et al., 2011). However, the correlation of the calculated parameters and the clinical severity in CTS was not well known. The aim of this study was to determine the correlation of the calculated electrophysiological parameters and clinical severity in patients with CTS. The calculated electrophysiological parameters include TLI, RL and modified F-wave latency ratio of median nerve, and difference of minimal F-wave minimal latencies between median and ulnar nerves. We also investigated the correlation of conventional NCS parameters according to clinical severity of CTS.
METHODS Patients We retrospectively investigated 164 CTS patients visiting a neurology outpatient clinic in the Haeundae Paik Hospital of Inje University, from March 2010 to March 2012. Twenty-seven patients aged $ 70 years and 31 patients with comorbidity with diabetes mellitus, rheumatoid arthritis, cervical radiculopathy, other upper extremity mononeuropathies, and neuropathic pain of other causes were excluded. A total of 106 patients and 212 hands were enrolled. Carpal tunnel syndrome was diagnosed if patients met criterion 1 and one or more of criteria 2 to 4 of the following American Academy of Neurology practice parameters (American Academy of Neurology, 1993a; American Academy of Neurology, 1993b; You et al., 1999): (1) paresthesia, pain, swelling, weakness, or clumsiness of the hand provoked or worsened by sleep, sustained hand or arm position, or repetitive action of the hand or wrist
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mitigated by a change in posture or by shaking of the hand; (2) sensory deficits in the median nerve innervated regions of the hand; (3) motor deficit or hypotrophy of the median nerve innervated thenar muscles; and (4) positive provocative clinical tests (positive Phalen maneuver and/or Tinel sign). We divided the enrolled CTS hands into four groups according to the clinical severity by applying a historical-objective scale (Hi-Ob scale) (Giannini et al., 2002). We simplified the 6 stages of the original Hi-Ob scale (stage 0: no symptoms suggestive of CTS, stage 1: only nocturnal paresthesia, stage 2: diurnal paresthesia, stage 3: sensory deficit, stage 4: hypotrophy and/or motor deficit of median innervated thenar muscles, and stage 5: complete atrophy or plegia of median innervated thenar muscles) into 4. Stage 0 of the Hi-Ob scale was defined as the group with asymptomatic hands, stages 1 and 2 as group with mild CTS hands, stage 3 as group with moderate CTS hands, and stages 4 and 5 as group with severe CTS hands.
Nerve Conduction Study Electrophysiological studies were performed according to the American Association of Electrodiagnostic Medicine guideline with a “Medelec Synergy” electromyographic device (Oxford Instruments Medical, Inc., Tubney Woods, Abingdon, United Kingdom) at a skin temperature above 328C (American Academy of Neurology, 1993a, 1993b; Jablecki et al., 2002; Stevens, 1997). We recorded the motor NCS of the median and ulnar nerves using the standard belly–tendon method in the setting of the filter bandpass at 3 Hz to 10 kHz, a sweep speed of 5 milliseconds/division, and amplifier gain at 1 to 5 mV/division. The recording muscles of the median and ulnar nerves were the abductor pollicis brevis and abductor digiti minimi, respectively. Supramaximal stimulation was applied to the wrist convolution at a distance of 6 cm from the each recorded muscles and elbow crease. F-wave was recorded in the median and ulnar nerves with supramaximal stimulation at the level of wrist convolution. The active and reference electrodes were placed at the same points used in motor NCS. The filter bandpass was 30 Hz to 10 kHz, the sweep speed was 10 milliseconds/division, and the sensitivity was 0.2 mV/division. At least 20 consecutive distal F wave were elicited, and the minimum Fwave latency was measured. We also recorded the sensory NCS orthodromically in the finger–wrist, palm–wrist, and wrist–elbow segments. The filter bandpass of sensory NCS was 20 Hz to 2 kHz, the sweep speed was 2 milliseconds/division, and the sensitivity was 10 to 20 mV/division.
Eletrophysiological Parameters The DML and distal motor conduction velocity (MCV) were obtained in median motor NCS. The TLI (Attarian et al., 2001; Cocito et al., 2001; Lissens and Bruyninckx, 1988; Simovic and Weinberg, 1997) and RL (Cocito et al., 2001; Kraft and Halvorson, 1983) were calculated as TLI ¼ distal conduction distance/(distal MCV · DML), and RL ¼ DML 2 (distal conduction distance/distal MCV). The difference of the minimal F-wave latencies between the median and ulnar nerves (F-diff M-U) (Cevik et al., 2012) and modified F ratio (MFR) (Attarian et al., 2001; Cocito et al., 2001) were calculated as F-diff M-U ¼ minimal F-wave latency of median nerve 2 minimal F-wave latency of ulnar nerve, and MFR ¼ (F 1 DML 2 2 · PML 2 1)/2 · DML, F means the minimal F-wave latency of median nerve. Copyright 2014 by the American Clinical Neurophysiology Society
Usefulness of Terminal Latency Index
The sensory nerve conduction velocity in the palm–wrist (SNCV p-w) and finger–wrist (SNCV f-w) segments of the median nerve were obtained in median sensory NCS. We also divided the CTS hands into 5 groups according to the neurophysiological classification proposed by Padua et al. (Padua et al., 1997): (1) extreme CTS, absence of thenar motor response; (2) severe CTS, absence of median SNAPs in the digit–wrist segment and abnormal DML; (3) moderate CTS, slowing of median digit–wrist segment and abnormal DML; (4) mild CTS, slowing of median digit wrist segment and normal DML; and (5) negative, normal findings in all tests. The normal values of digit–wrist SNCV and DML in our electrophysiological laboratory were above 40 cm/ second and below 3.60 milliseconds, respectively.
Statistical Analyses The ratio of neurophysiological classes in the groups with each CTS severity was evaluated by x2 test. The comparison of the electrophysiological parameters among groups with each CTS severity was assessed by analyses of variance and Kruskal–Wallis test. We also performed Scheffe test as a post-hoc comparison analysis. The sex ratio according to group with each CTS severity was assessed by x2 test. We performed receiver operating characteristic curve analysis to determine the cut-off value among groups with each CTS severity. The sensitivity and specificity were also obtained by receiver operating characteristic curve analysis. The regression analysis and Spearman correlation were performed to evaluate the change of electrophysiological parameters according to the clinical severity of CTS. Multivariate regression analysis was performed to clarify the correlation of electrophysiological parameters according to age, sex, and clinical severity. The significance level was taken to be P , 0.05.
RESULTS
The mean age was 52.9 6 10.3 years (range, 25 to 70 years). Eighty-five patients were female and 21 were male. Sixty-six patients had bilateral CTS, 24 had right-side CTS, and 16 had leftside CTS. Forty hands were asymptomatic, 103 were mild, 43 were moderate, and 26 were severe. The ratios of neurophysiological classes according to the group with each CTS severity are summarized in Fig. 1. Thirty-one hands were “negative,” six “mild CTS,” and three “moderate CTS” among 40 asymptomatic hands. Thirty-five hands were “negative,” 35 “mild CTS,” and 33 “moderate CTS” among 103 hands with mild CTS. Two hands were “negative,” 40 “mild CTS,” and 1 “severe CTS” among 43 hands with moderate CTS. Twelve hands were “moderate CTS,” 9 “severe CTS,” and 5 “extreme CTS” among 26 hands with severe CTS. The clinical CTS severity was significantly correlated with the neurophysiological CTS severity. The distribution of age, sex, and electrophysiological parameters according to the group with each CTS severity is illustrated in Table 1. There was no SNAP formation in 15 hands and no CMAP formation in 5 hands among the total of 212 hands. The 15 hands without formation of SNAP were excluded in the analysis of SNCV f-w and SNCV p-w. The five hands without formation of CMAP were excluded in the analysis of DML, MCV, TLI, RL, and MFR. Therefore, a total of 197 hands were included in the analysis of SNCV p-w and SNCV f-w, and a total of 207 hands were also included in the analysis of DML, MCV, TLI, RL, and F-diff M-U. Age and sex were not significantly different according to the CTS severity group (Table 1). The MCV, SNCV f-w, TLI, and MFR 163
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In analyses of variance and Kruskal–Wallis test, we used the Scheffe test as a post-hoc comparison analysis (Table 1). Distal motor latency, RL, and SNCV p-w showed a significant difference between asymptomatic and mild CTS and mild and moderate CTS but not between moderate and severe CTS. Motor conduction velocity showed a significant difference between mild and moderate CTS and moderate and severe CTS but not between asymptomatic and mild CTS. The MFR showed a significant difference between only the mild and moderate CTS. The TLI, F-diff M-U, and SNCV f-w showed a significant difference among all groups of CTS severity. We also calculated the sensitivity, specificity, and cut-off value of TLI, F-diff M-U, and SNCV f-w, which showed a significant difference among all groups of each CTS severity, using receiver operating characteristic curve analysis (Table 3). The cut-off values of TLI, F-diff M-U, and SNCV f-w between asymptomatic and mild CTS group were, respectively, 0.33 millisecond, 0.3 millisecond, and 40 cm/second. The cut-off values of TLI, F-diff M-U, and SNCV f-w between mild and moderate CTS group were, respectively, 0.27 millisecond, 2.3 milliseconds, and 34.8 cm/second. The cut-off values of TLI, F-diff M-U, and SNCV f-w between moderate and severe CTS group were, respectively, 0.20 millisecond, 4.2 milliseconds, and 26.4 cm/second.
FIG. 1. Ratios of neurophysiological classes according to the group with each CTS severity, x2 test, P , 0.01. CTS, carpal tunnel syndrome; NCS, nerve conduction study. according to the CTS severity were assessed using analyses of variance and regression analysis because they showed normal distribution. The DML, SNCV p-w, F-diff M-U, and RL according to the CTS severity were assessed by using Kruskal–Wallis test and Spearman correlation because they did not show normal distribution. The DML, RL, and F-diff M-U were significantly increased according to the clinical severity of CTS (Kruskal–Wallis test and Spearman correlation, P , 0.05, Figs. 2 and 3). The MCV, SNCV p-w, SNCV f-w, TLI, and MFR significantly decreased according to the clinical severity of CTS (analyses of variance, Kruskal–Wallis test, regression analysis, and Spearman correlation, all P , 0.05, Fig. 2). In the multivariate regression analysis, the MCV, SCV f-w, TLI, and MFR showed significant correlations with the clinical severity of CTS irrespective of age and sex (Table 2).
TABLE 1.
DISCUSSION Carpal tunnel syndrome is the most common entrapment neuropathy, with a 10% lifetime risk in the general population (American Academy of Neurology, 1993a, 1993b; Aygul et al., 2009; Duncan et al., 1987; Jablecki et al., 1993; Katz et al., 1998; Padua et al., 1997; Spitzer, 1996; Wilson and Sumner, 1995; You et al., 1999). Carpal tunnel syndrome results from compression of the median nerve during passage through the carpal tunnel under the transverse carpal ligament. The Boston questionnaire (BQ) including symptoms severity score and functional severity score is the most commonly used tool to assess the clinical feature of CTS (Greenslade et al., 2004; Heybeli et al., 2002; Levine et al., 1993; Mondelli et al., 2000; Sezgin et al., 2006).
Age, Sex, and Electrophysiological Parameters With Different Severity Groups of Carpal Tunnel Syndrome
Age, year Sex (M/F), n DML‡, millisecond MCV§, cm/second SNCV f-w¶, cm/second SNCV‡ p-w, cm/second F-diff M-U¶, millisecond TLI¶ RL‡, millisecond MFR#
Asymptomatic
Mild CTS
Moderate CTS
Severe CTS
P
51.0 (25–70) 8:32 3.05 (2.40–3.90) 57.2 6 2.8 43.8 6 4.4 36.5 (27.6–50.3) 0.15 (21.30 to 3.05) 0.35 6 0.04 2.95 (2.30–3.79) 2.06 6 0.29
53.0 (25–70) 22:81 3.45 (2.36–5.95) 56.8 6 3.0 39.2 6 6.4 31.7 (17.6–45.3) 0.9 (21.60 to 6.25) 0.31 6 0.05 3.34 (2.25–5.83) 1.92 6 0.35
54.0 (32–69) 4:39 4.85 (2.80–6.35) 54.7 6 3.6 30.1 6 5.7 24.1 (17–41) 3.50 (20.3 to 10.55) 0.23 6 0.04 4.74 (2.71–6.25) 1.47 6 0.31
51 (39–67) 8:18 6.63 (4.80–8.35) 49.3 6 5.6 24.4 6 5.0 19.4 (12.7–29) 7.55 (3.80–16.25) 0.19 6 0.06 6.51 (3.34–13.31) 1.26 6 0.49
0.36* 0.16† ,0.01* ,0.01k ,0.01k ,0.01* ,0.01* ,0.01k ,0.01* ,0.01k
CTS, carpal tunnel syndrome; DML, distal motor latency of median nerve; F-diff MU, difference of minimal F-wave latency between median and ulnar nerves; MCV, distal motor conduction velocity of median nerve; MFR, modified F-wave latency ratio; RL, residual latency of median nerve; SNCV f-w, sensory nerve conduction velocity at finger–wrist segment of median nerve; SNCV p-w, sensory nerve conduction velocity at palm–wrist segment of median nerve; TLI, terminal latency index of median nerve. *Kruskal–Wallis test. †Chi-square test. ‡P , 0.05 in comparison between asymptomatic and mild and mild and moderate CTS. §P , 0.05 in comparison between mild and moderate and moderate and severe CTS. kAVOVAs, post-hoc comparison analysis (Scheffe test). ¶P , 0.05 in comparison between asymptomatic and mild, mild and moderate, and moderate and severe CTS. #P , 0.05 in comparison between mild and moderate CTS.
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Usefulness of Terminal Latency Index
FIG. 2. Correlation of DML, SNCV p-w, F-diff M-U, and RL according to the groups of hand with asymptomatic, mild, moderate, or severe CTS. CTS, carpal tunnel syndrome; DML, distal motor latency of median nerve; SNCV p-w, sensory nerve conduction velocity in palm–wrist segment of median nerve; F-diff M-U, difference of minimal F-wave latencies between median and ulnar nerves; RL, residual latency of median nerve (Spearman correlation; DML, coefficient of correlation: 0.73, P , 0.01; SNCV p-w, coefficient of correlation: 20.67, P , 0.01; F-diff M-U, coefficient of correlation: 0.72, P , 0.01; RL, coefficient of correlation: 0.73, P , 0.01). The disability of arm, shoulder, and hand sore (Greenslade et al., 2004; Hudak et al., 1996) and Michigan hand outcomes questionnaire (Chung et al., 1998; Kotsis and Chung, 2005) are other tools to evaluate the functional status of upper extremity. However, these self-administered questionnaires have some disadvantages. They do not sufficiently reflect the objective neurologic signs because they mainly reflect the subjective symptoms and functional hand capacities of CTS patients. Moreover, the current physical, psycholgical, and emotional states of CTS patients may affect their results. These questionnaires mainly evaluate the bimanual function of CTS patients. Therefore, they are limited in separately evaluating the function of each side hand. These selfadministered questionnaires provide clinical diagnostic certainty of CTS, such as classic, probable, possible, and unlikely instead of defining the clinical severity of CTS. Copyright 2014 by the American Clinical Neurophysiology Society
We applied the Hi-Ob scale to the classification of CTS hands according to the clinical severity (Giannini et al., 2002). The Hi-Ob parameter was positively related to the neurophysiological classification and BQ in the validation test of Hi-Ob scale (Giannini et al., 2002). Caliandro et al. (2010) proposed the historical-objectivedistribution (Hi-Ob-Db) scale, which added the Hi-Ob scale to distribution of paresthesia. The Hi-Ob-Db was significantly correlated to the sensory nerve conduction velocity, DML, neurophysiological classification, and BQ scores. Presently, we divided the CTS patients into four severity groups according to the objective neurologic sign. We simplified the six stages of the original Hi-Ob scale into four (asymptomatic, mild, moderate, and severe CTS) because the boundaries between stages 1 and 2 and stages 4 and 5 were obscure in some cases. Asymptomatic is the normal hand of the unilateral CTS 165
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FIG. 3. Correlation of MCV, SNCV f-w, TLI, and MFR according to the groups of hand with asymptomatic, mild, moderate, or severe CTS. CTS, carpal tunnel syndrome; MCV, distal motor nerve conduction velocity of median nerve; SNCV f-w, sensory nerve conduction velocity in finger–wrist segment of median nerve; TLI, terminal latency index of median nerve; MFR, modified F ratio of median nerve (regression analysis; MCV, R2 ¼ 0.25, P , 0.01; SNCV f-w, R2 ¼ 0.47, P , 0.01; TLI, R2 ¼ 0.52, P , 0.01; MFR, R2 ¼ 0.35, P , 0.01).
patients. Mild CTS is indicated when the patient complains of the typical symptoms of CTS and shows Tinel sign or positive Phalene maneuver (inclusion of the aforementioned American Academy of Neurology practice parameters criteria 1 and 4), but the sensory and motor function tests of the affected hand are normal (exclusion of criteria 2 and 3). Moderate CTS is indicated when the patient complains of the typical symptoms of CTS and the sensory deficit in the median nerve territory of the affected hand is observed (inclusion of criteria 1, 2, and 4), but the motor function is normal (exclusion of criterion 3). Severe CTS is indicated when the patient complains of the typical symptoms of CTS, the sensory deficit and motor weakness, and atrophy in the median nerve territory of the affected hand are observed (inclusion of criteria 1, 2, 3, and 4). The classification is based on the clinical observations and scientific investigations that 166
nerve entrapment of CTS affects earlier sensory nerve than motor nerve (American Academy of Neurology, 1993a, 1993b; Aygul et al., 2009; Heybeli et al., 2002; Jablecki et al., 1993; Katz et al., 1998; Levine et al., 1993; Padua et al., 1997; Spitzer, 1996; You et al., 1999). The NCS findings show the following progression in pacing with the clinical progression of CTS: (1) abnormalities of segmental sensory NCT such as disto-proximal ratio (R); (2) SNCV slowing in digit–wrist segments; (3) increased DML; (4) disappearance of digit–wrist SNAPs; and (5) disappearance of motor response (Padua et al., 1997). In this study, the electrophysiological classification and each parameter showed a significant correlation with the clinical severity. This is consistent with the previous studies using the Hi-Ob and Hi-Ob-Db scales (Caliandro et al., 2010; Giannini et al., 2002). Especially, the TLI, F-diff M-U, and SNCV f-w Copyright 2014 by the American Clinical Neurophysiology Society
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TABLE 2. Analysis)
Usefulness of Terminal Latency Index
Correlation of MCV, SNCV f-w, TLI, and MFR According to Age, Sex, and CTS Severity (Multivariate Regression Unstandardized Coefficients
MCV
SNCV f-w
TLI
MFR
CTS severity Age Sex CTS severity Age Sex CTS severity Age Sex CTS severity Age Sex
Unstandardized Coefficients
Beta
Standard Error
Beta
t
P
22.226 20.840 1.668 26.698 20.141 21.359 20.055 20.001 0.012 20.289 20.005 20.050
0.273 0.023 0.592 0.508 0.039 1.039 0.004 0.000 0.008 0.028 0.002 0.061
20.474 20.213 0.162 20.668 20.184 20.066 20.705 20.117 1.463 20.578 20.128 20.046
28.156 23.668 2.819 213.172 23.625 21.307 214.641 22.432 1.463 210.306 22.287 20.829
,0.01 ,0.01 ,0.01 ,0.01 ,0.01 0.19 ,0.01 0.02 0.15 ,0.01 0.02 0.41
MCV, motor nerve conduction velocity of median nerve; MFR, modified F ratio of median nerve; SNCV f-w, sensory nerve conduction velocity of median nerve; TLI, terminal latency index of median nerve.
showed a significant difference among all groups of CTS severity. The TLI of median nerve and the F-diff M-U are well-known calculated electrophysiological parameters used to diagnose the early stage of CTS, although its sensitivity and specificity is variable according to investigations (Aygul et al., 2009; Cevik et al., 2012; Simovic and Weinberg, 1997; Uzar et al., 2011). We found that TLI and F-diff M-U can be used to assess the stages of CTS severity. We also calculated the sensitivity, specificity, and cutoff value of these parameters among groups with asymptomatic, mild, moderate, and severe CTS. The cut-off value between asymptomatic and mild CTS group may indicate a point of diagnosis of early stage of CTS. The cut-off value between mild and moderate CTS group may indicate a point of surgical treatment in CTS patients. The cut-off value between moderate and severe CTS group may indicate a point of poor outcome of treatment in CTS patients. The limitations of this study are its retrospective nature with small study sample size. As well, sometimes the boundary among the groups of each CTS severity was not clear-cut. We did not perform the NCS in normal controls. The NCS findings of asymptomatic hand of unilateral CTS patients and hands of normal control may differ.
TABLE 3. Results of Receiver Operating Characteristic Curve Analysis of SNCV, TLI, and F-diff M-U Between Asymptomatic and Mild, Mild and Moderate, and Moderate and Severe CTS Cut-off Value Sensitivity/ Asymptomatic Specificity and Mild SNCV f-w, cm/second, % TLI, ratio, % F-diff M-U, %
Mild and Moderate
Moderate and Severe
40.0, 60.2/85.0
34.8, 90.5/79.6
26.4, 75.0/73.8
0.33, 68.0/67.5 0.3, 68.0/57.5
0.27, 74.4/77.2 2.3, 81.4/85.4
0.20, 52.2/83.7 4.2, 96.2/76.7
F-diff M-U, difference of minimal F-wave latencies between median and ulnar nerves; SNCV f-w, sensory nerve conduction velocity in finger–wrist segment of median nerve; TLI, terminal latency index of median nerve.
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