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NeuroRehabilitation 35 (2014) 543–552 DOI:10.3233/NRE-141150 IOS Press
Relationship between Semmes-Weinstein Monofilaments perception Test and sensory nerve conduction studies in Carpal Tunnel Syndrome Parvin Rajia , Noureddin Nakhostin Ansarib , Soofia Naghdib,∗ , Bijan Foroghc and Scott Hassond a Department
of Occupational Therapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran b Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran c Department of Physical Medicine and Rehabilitation, Firoozgar University Hospital, Iran University of Medical Sciences, Tehran, Iran d Department of Physical Therapy, Georgia Regents University, Augusta, GA, USA Abstract. BACKGROUND: The Semmes-Weinstein Monofilament Test (SWMT) is a clinical widely used test to quantify the sensibility in patients with Carpal Tunnel Syndrome (CTS). No study has investigated the relationship between the SWMT and sensory nerve conduction studies (SNCS) in patients with CTS. OBJECTIVE: To assess the relationship between the SWMT and SNCS findings in patients with CTS. METHODS: This cross-sectional clinical measurement study included 35 patients with CTS (55 hands) with a mean age of 45 ± 12 years. The outcome measures were the SWMT and SNCS measures of distal latency (DLs), amplitude (AMPs), and nerve conduction velocity (NCV). The median innervated fingers were tested using SWMT and electrodiagnostic tests. The primary outcome was the correlations between the SWMTs and NCS measures. RESULTS: All of the patients/hands had abnormal NCS findings. When looking at the three digits of interest (thumb, index and middle), the thumb SWMTs had the highest number of abnormal findings (58.2%), with the middle digit having the lowest (45.5%). All NCS findings were statistically different between abnormal and normal thumb SWMTs and abnormal and normal total summed SWMTs. There were significant moderate correlations between thumb SWMT scores and all NCS outcomes. CONCLUSIONS: Although only approximately 50% of the CTS diagnosed through NCS are corroborated through SWMT; the significant associations between SWMT and NCS measures suggest that SWMT is a valid test for assessing sensations in patients with CTS. Keywords: Carpal Tunnel Syndrome, Semmes-Weinstein Monofilament Test, nerve conduction study
1. Introduction Carpal Tunnel Syndrome (CTS) is the most common entrapment neuropathy with median nerve compression in the wrist (Wilson & Sevier, 2003). The classic ∗ Address
for correspondence: Dr. Soofia Naghdi, Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Enghelab Ave, Pitch-e-shemiran, Tehran 11489, Iran. Tel.: +98 21 77533939; Fax: +98 21 77727009; E-mail: naghdi@ sina.tums.ac.ir.
symptoms of CTS are sensory in nature with diurnal parasthesia, burning pain, numbness, and tingling (Giersiepen & Spallek, 2011; Huisstede et al., 2010; Arrori & Spence, 2008). Estimates suggest that prevalence of CTS in the general population is 14.4% (Atroshi et al., 1999), and women are more affected than men (23:1 to 3:1) (Geoghegan, Clark, Bainbridge, Smith, & Hubbard, 2004; Ahn, Yoon, Koo, & Park, 2000). The cause of about 90% of all entrapment neuropathies is CTS, and health care costs due to CTS is high (Arrori & Spence, 2008).
1053-8135/14/$27.50 © 2014 – IOS Press and the authors. All rights reserved
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The exact pathogenesis of CTS is not known (Werner & Andary, 2002). While no clear cause can be identified in 50% of patients with CTS, there are local, regional, and systematic causes for CTS (Arrori & Spence, 2008). Mechanical pressure, raised intracarpal canal pressure and ischemic changes have been suggested as possible mechanisms to explain the nerve injury, symptoms, and impaired nerve conduction studies (Wilson & Sevier, 2003; Arrori & Spence, 2008; Zyluk, 2013; Bland, 2005). CTS diagnosis is usually made clinically based on history, symptoms, and bedside diagnostic tests. However, a combination of clinical symptoms, signs and electrodiagnostic tests are used as the most valid approach for diagnosing CTS (Arrori & Spence, 2008; Alfonso, Jann, Massa, & Torreggiani, 2010; Ansari, Adelmanesh, Naghdi, & Mousavi, 2009; Walker-Bone, Palmer, Reading, & Cooper, 2003). In CTS, both sensory and motor components of the median nerve are affected, and the sensory component is involved much earlier than the motor component (Arrori & Spence, 2008). Nerve conduction studies (NCS) are objective measures to quantify sensory and motor nerve conduction velocity. In CTS, both sensory and motor latencies of the median nerve are prolonged (Williams et al., 2005; Stevens, 1997). Although median NCS have been shown to be sensitive and specific and are considered the gold standard diagnostic tests, they require equipment, are expensive, and are time consuming (Arrori & Spence, 2008; Ansari, Adelmanesh, Naghdi, & Mousavi, 2009; Stevens, 1997; Walters & Muuray, 2001). There are various techniques that may be used to assess sensory impairments in clinical and research settings including Semmes-Weinstein Monofilament Test (SWMT). The SWMT is one neurophysiological technique to document CTS (Werner & Andary, 2002). The SWMT, also referred to as the touch threshold test, is widely used by clinicians as it is simple, inexpensive, reliable and valid (Tan, 2010; Schreuders, Selles, van Ginneken, Janssen, & Stam, 2008; Jerosch-Herold, 2003; Mayfield & Sugarman, 2000; Bell-Krotoski, 1990). A review article to identify the usefulness of the monofilaments found that the monofilament is a beneficial clinical instrument for detecting severe neuropathy and identifying patients at risk of ulceration and amputation (Tan, 2010). In a study by Schreuders, Selles, van Ginneken, Janssen, and Stam (2008) the reliability of the SWMTs was investigated in 15 patients with Charcot-Marie-Tooth. They found good intra- and interobserver reliability for SWMT with
ICCs of 0.91 and 0.86, respectively. Jerosch-Herold (2003) conducted a longitudinal dynamic cohort study on patients with median nerve injuries to evaluate the relative responsiveness of sensibility tests and reported that the monofilaments to test touch threshold exhibited the highest degree of responsiveness indicating the validity of the monofilaments. In a review by Mayfield and Sugarman (2000) to evaluate the usefulness of the SWMT and other tests for preventing ulcers and amputation in subjects with diabetes, the authors concluded that the SWMT is the best test for screening patients with neuropathy because it provides good predictive ability for the risk of ulceration and amputation. A review by Bell-Krotoski (1990) found that the SWMT is a reliable tool and can demonstrate changes in nerve status and is correlated with treatment effects. It has been shown that the SWMT is one of the standardized tests for tactile testing which has quantified psychometric properties, and should be included as an outcome measure in assessing patients with median nerve injury (Jerosch-Herold, 2003, 2005). The SWMT is used to quantify the smallest force at which tactile point pressure can be detected. Szabo, Slater, Farver, Stanton, and Sharman (1999) examined several clinical tools/tests to determine the validity to diagnose CTS and found a sensitivity of 83% for SWMT and concluded that CTS will be diagnosed correctly 86% of the time with abnormal SWMT combined with abnormal hand diagram, positive Durkan’s test, and night pain. NCS is one of the major components in electrodiagnostic examinations which can provide objective evidence of nerve abnormalities. NCS can aid in the diagnosis of nerve entrapments, and can be used to detect nerve lesions and to monitor re-innervation after a nerve repair (Slutsky, 2003). Electrodiagnostic studies are reliable and valid, and also highly sensitive and specific for diagnosing CTS (Lew et al., 2005; American Association of Electrodiagnostic Medicine, American Academy of Neurology, and American Academy of Physical Medicine and Rehabilitation, 2002). NCS techniques involve stimulating sensory, motor, or mixed nerves at given sites and recording the time taken for the stimulus to be detected by recording electrodes (Wilbourn, 2002). Parameters of amplitude, duration, latency, and conduction velocity can be obtained from a NCS. In this study, NCS tests have been used as the criterion gold standard to evaluate the validity of the SWMT. There are mixed results on the usefulness of SWMT in patients with CTS. While several studies found
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SWMT useful for identifying peripheral and entrapment neuropathies (Tan, 2010; Schreuders, Selles, van Ginneken, Janssen, & Stam, 2008; Jerosch-Herold, 2003; Mayfield & Sugarman, 2000; Bell-Krotoski, 1990; Szabo, Slater, Farver, Stanton, & Sharman, 1999; Dioquino, Dellosa, Reyes, & Panganiban, 2009; MacDermid, Kramer, & Roth, 1994). Pagel, Kaul, and Dryden (2002) examined the value of SWMT in patients with electrodiagnostically confirmed CTS and found that the SWMT did not have utility in diagnosing patients with electrodiagnostically confirmed carpal CTS. However, no study has investigated the relationship between the SWMT and SNCS standard tests in patients with CTS. The major objective of this study was to address this deficit by assessing the relationship between the SWMT and SNCS findings in patients with CTS. In order to meet this objective there were three purposes for this study: 1) to determine if patients with CTS having abnormal SNCS outcomes also have SWMT that correspond to these abnormal findings; 2) to determine if hands or digits rated abnormal and normal through SWMT are different when comparing distal latency, amplitude, and nerve conduction velocity; and 3) to determine if there are associations between SWMT and NCS findings to evaluate concurrent criterion validity for SWMT.
2. Materials and methods 2.1. Patients Patients were recruited from the University, orthopedic, neurology, and rehabilitation clinics. The patients with CTS included in this study had the following criteria: 1) age 18 years or older; 2) diurnal parasthesia, burning pain, numbness, and tingling in the median nerve area; and 3) a positive Tinel and/or Phalen sign. Patients with previous wrist trauma or surgery as well as patients with diabetes mellitus, pregnancy, or polyneuropathy were excluded. Patients were referred by orthopedist, neurologist, or physiatrist from the clinics. The eligibility of patients was assessed again by the first author using the same criteria as described above. Approval of the Research Council of the Rehabilitation School and the Ethical Committee was obtained. The study participants gave their written informed consent to participate in the study with the right to withdraw from the study.
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2.2. Outcome measures The outcome measures were the SWMT and NCS tests of sensory distal latency (DLs), sensory amplitude (AMPs), and nerve conduction velocity (NCV). 2.3. Anthropometric measurements Anthropometric measurements including body weight and height were measured. Body Mass Index (BMI) was calculated as body weight (kilograms) divided by the squared value of bodyheight (meters). 2.4. Nerve conduction and Semmes-Weinstein Monofilament studies The collection and interpretation of the NCS data was performed by a physiatrist who was blinded to the clinical data. The SWMT was performed by an occupational therapist (OT) who was blinded to the NCS findings. This was done to reduce assessor bias. The examiners were not allowed to access the NCS or SWMT data during the study. The NCS was performed first before SWMT evaluation. The patients rested for 5 minutes before the SWMT evaluation was performed. In the case of a bilateral hand involvement, the order of hand evaluations was randomized. A Cadwell electromyography Unit (model Excel, Cadwell Laboratories, Inc., Kennewick, WA) was used to perform the NCS. Surface stimulating, recording, and ground electrodes were used for performing antidromic sensory NCS. The area and skin of the electrode location was cleaned. The NCS were performed in a room with temperature ranging from 26◦ C to 28◦ C. The temperature of the hand skin was maintained at 32◦ C with an infrared lamp and was checked using an Omron 3way digital thermometer (model MC-600). 2.5. Median sensory NCS Patients were positioned in supine with the forearm in supination. Sensitivity was set at 5–20 V/div, lowhigh frequency filter at 20 Hz–2 kHz, and sweep speed at 2 msec/div. The median sensory NCS (SNCS) were recorded from 1st, 2nd, and 3rd digits antidromically with standard distance of 10 cm (thumb) and 14 cm (2nd and 3rd digits) between stimulation and recording electrodes. The median nerve was stimulated at the wrist and at the palm to calculate the sensory NCV (SNCV) such that the distance between stimulation sites (wrist, palm) was 8 cm. The active recording
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electrode was placed at the middle finger for the SNCV. For SNCS, distal latency, sensory nerve action potential (SNAP) amplitude and SNCV were measured. The peak latency and peak to peak amplitude were calculated. Normal mean values include onset latency 3.4 ± 0.3 msec, amplitude 63.0 ± 33.0 V, and NCV 56.2 ± 5.8 m/s (Buschbacher, 1999). The distal latency and amplitude data from thumb, index and middle fingers were averaged to obtain total DLs and total AMPs.
Table 1 The grades of Semmes-Weinstein Monofilament Test Grades Monofilament Target size force (gm) 6 5 4
1.65–2.83 3.22–3.61 3.84–4.31
0.008–0.07 0.16–0.4 0.6–2
3 2 1
4.56–4.93 5.07–5.88 6.10–6.65
4–8 10–60 100–300
0
–
–
Interpretation Normal Diminished light touch Diminished protective sensation Loss of protective sensation Loss of protective sensation/ Deep pressure sensation only Loss of sensation
2.6. Semmes-Weinstein Monofilament testing The Semmes-Weinstein Monofilament test kit (North Coast Medical, Inc, USA) was used to evaluate sensory thresholds of the tips of the thumb, the index, and the middle fingers. The kit consists of 20 flexible nylon monofilaments of varying diameter and length to measure the level of skin touch sensation. The monofilaments have log numbers from 1.65 to 6.65 which begins with the light filaments (1.65–3.61) and progresses to heavy filaments of increasing diameter (3.84–6.65). Heavy filaments need increased pressure for touch to be recognized by patients. The tester applies each monofilament to the surface area of the skin with a perpendicular angle, then applies slight and steady pressure until the monofilament begins to bend, which is the end point of the test. The monofilament number 2.83 was defined as cut-off for normal sensation (Schreuders, Selles, van Ginneken, Janssen, & Stam, 2008).
was recorded that the patient had abnormal sensation for the specific digit (Table 1). Monofilament testing was applied three times. If the patient responded positive to one of the stimuli, this monofilament was recorded indicating that the stimulus was detected. The order and time intervals were randomized. The data from thumb, index and middle fingers were pooled to obtain total frequency of normal and abnormal SWMT. To calculate the direct correlation between the SWMT and NCS findings, the values of log numbers were grouped to produce a scale from 0–6 in which 6 indicates normal and 0 indicates loss of sensation (Table 1). The SWMT scores obtained for the thumb, index and middle fingers were summated to obtain a total SWMT score (range 0–18).
2.7. Procedure
Statistical analysis was carried out using SPSS software 18.0 for Windows (SPSS Inc., Chicago, USA) package. The monofilament numbers ≤2.83 and >2.83 were recoded as normal and abnormal, respectively. The chi-square test was used to determine whether there were equal proportions of normal and abnormal SWMTs for each digit tested and for pooled values. Inter-group differences for NCS findings between digits with abnormal and normal SWMT were analyzed using an Independent Samples t-Test. Additionally, an analysis was performed to evaluate concurrent criterion validity between the SWMT and the NCS findings and identify the level of correlation with the use of standard Pearson correlation test for interval data or Spearman’s rank correlation test for ordinal variables. The interpretation of correlation coefficients was as follows: low (0.00–0.39), moderate (0.40–0.59), moderately high (0.60–0.79), high (0.80–1.00) (Feinstein, 1987). A p value of ≤0.05 was defined statistically significant.
All patients were tested by the first author, an experienced OT, in a quiet room. This procedure was followed to avoid inter-rater reliability problems. She explained the procedure of assessing cutaneous touch threshold of the hand to the patient before beginning the test. Patients were seated at the table opposite of the examiner. The hand being tested was placed on a towel and was hidden behind a screen with the forearm in supination. Patients were asked to verbally respond (saying ‘yes’) when they felt that they were being touched by the monofilaments. The monofilament number of 2.83 was used first in order to establish if the patient had normal or abnormal tactile sensation. If the patient perceived the stimulus, then lighter monofilaments were applied to record the lightest possible monofilament for the patient. If the patient was not able to perceive the 2.83 monofilament, a thicker filament was used, and it
2.8. Statistical analysis
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Table 2 Frequency of normal/abnormal SWMT Fingers Thumb (n = 55) Index (n = 55) Middle (n = 55) Total (n = 165)
Normal No/%
Abnormal No/%
Chi-Square test P value
23/41.8% 26/47.3% 30/54.5% 79/47.9%
32/58.2% 29/52.7% 25/45.5% 86/52.1%
0.23 0.69 0.50 0.59
Abbreviations; SWMT, Semmes-Weinstein Monofilament Test.
3. Results Thirty five patients with CTS (32 women and 3 men; mean age 45 ± 12 years, range 20–73; BMI, 25.39 ± 4.25, range 16.00–36.84) participated in the study. The mean duration of disease was 30 months [standard deviation (SD) 36.8; range 1–120]. The CTS was bilateral in 20 patients. Fifty five hands were included for evaluations (33 on the right side and 22 on the left side). The right hand was dominant in 32 patients. Table 2 and Fig. 1 show the frequency of abnormal and normal sensory findings using SWMT obtained for digits tested and for all SWMT. The SWMT revealed that 58.2% of tests were abnormal for the thumb, 52.7% for the index, 45.5% for the middle digit, and 52.1% for all SWMT. In fact, 48% of all SWMTs were within normal range (indicating sensation detected at monofilament size ≤2.83). There were no statistical differences for the proportions of normal and abnormal SWMT (p > 0.05). The median (interquartile range, IQR) for SWMT scores were similar for thumb and index being 5 (5-6). For the middle finger, median was 6 (IQR 5-6). The mean (SD) of the total SWMT score was 16.1 (1.7, range 12–18). Table 3 summarizes the results of the sensory NCS found in this study. The mean scores for all NCS variables for all of the digits fell outside of the normal values. The physician indicated that all patients had abnormal NCS tests, suggesting the likely presence of CTS. The results of NCS for fingers with abnormal and normal SWMTs are presented in Table 4. The differences for both DLs and AMPs were statistically different between thumbs with abnormal and normal SWMTs (p < 0.05). However, the DLs and AMPs were not statistically different between index and middle fingers with abnormal and normal SWMTs (p > 0.05). The total DLs and the total AMPs both were statistically different between fingers with the total abnormal (n = 86) and normal (n = 79) SWMT (p < 0.05). The NCV differences were statistically significant only between thumbs with abnormal and normal SWMT (p = 0.001)
Fig. 1. Frequency of Semmes-Weinstein Monofilament Test (SWMT) grades for (A) thumb, (B) index, and (C) middle digits.
and between fingers with total abnormal and normal SWMT (t = 3.33, df = 163, p = 0.001). The Spearman’s rho coefficients found between the SWMT scores and NCS findings are illustrated in Table 5 and scatterplots for the significant correlations are indicated in Fig. 2. There were significant correlations between the thumb SWMT scores and all
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P. Raji et al. / Relationship between SWMT and SNCS in Carpal Tunnel Syndrome Table 3 NCS findings (n = 55)
Variables Thumb Index Middle Total
nificant correlation between the SWMT scores and the amplitude. The total SWMT score demonstrated significant correlations with the total AMPs (Pearson coefficient 0.30, p = 0.02) and the NCV (Pearson coefficient 0.33, p = 0.006). There was no significant correlation between the total SWMT score and the total DLs (Pearson coefficient −0.16, p = 0.12).
Mean Standard Maximum Minimum deviation DL (msec) Amp (V) DL (msec) Amp (V) DL (msec) Amp (V) DL (msec) Amp (V)
NCV (m/s)
3.8 44.0 4.1 45.6 4.4 37.6 4.1 42.4 31.6
0.6 16.2 0.6 17.8 0.1 21.1 0.8 18.7 7.9
5.4 102.0 5.9 95.0 7.9 94.0 7.9 102.0 46.0
1.4 8.0 2.9 12.0 3.5 5.0 1.4 5.0 13.0
4. Discussion
Abbreviations; NCS, nerve conduction study, DL, distal latency, AMP, amplitude, NCV, nerve conduction velocity.
In this study, we aimed to explore: if patients with CTS having abnormal NCS outcomes also have SWMT that correspond to these abnormal findings; if hands or digits rated abnormal and normal through SWMT are different when comparing sensory distal latency, amplitude, and sensory nerve conduction velocity; and
NCS measures. For the index, the correlation between the SWMT scores and the NCV was not statistically significant. For the middle digit, there was only a sig-
Table 4 NCS findings for hands with normal and abnormal SWMTs Variables Thumb
DL (msec)
Normal SWMT, n = 23 Abnormal SWMT, n = 32 Normal SWMT, n = 23 Abnormal SWMT, n = 32 Normal SWMT, n = 26 Abnormal SWMT, n = 29 Normal SWMT, n = 26 Abnormal SWMT, n = 29 Normal SWMT, n = 30 Abnormal SWMT, n = 25 Normal SWMs, n = 30 Abnormal SWMT, n = 25 Normal SWMT, n = 79 Abnormal SWMT, n = 86 Normal SWMT, n = 79 Abnormal SWMT, n = 86 Normal SWMT, n = 23 Abnormal SWMT, n = 32
Amp(V) Index
DL (msec) Amp (V)
Middle
DL (msec) Amp (V)
Total
DL (msec) Amp (V)
NCV (m/s)
Mean
SD
t-Test
3.6 3.9 50.8 39.1 4.0 4.3 49.2 42.4 4.3 4.6 41.7 32.6 4.0 4.3 46.8 38.3 35.7 28.7
0.6 0.5 17.0 13.9 0.6 0.7 17.3 17.9 0.7 1.2 22.0 19.2 0.7 0.9 19.3 17.2 6.4 7.6
t = −2.53, df = 53, p = 0.01 t = 2.81, df = 53, p = 0.007 t = −1.89, df = 53, p = 0.06 t = 1.43, df = 53, p = 0.16 t = −1.38, df = 53, p = 0.17 t = 1.62, df = 53, p = 0.11 t = −2.44, df = 163, p = 0.02 t = 2.99, df = 163, p = 0.003 t = 3.6, df = 53, p = 0.001
Abbreviations; SD, Standard Deviation; NCS, nerve conduction study; DL, distal latency; AMP, amplitude; NCV, nerve conduction velocity; SWMT, Semmes-Weinstein Monofilament Test. Table 5 Spearman’s correlation coefficients between the SWMT scores and the sensory NCS findings SWMT score
Thumb DL
Thumb p Index p Middle p Total SWMT score
–0.42∗ 0.001
Index
Amp
NCV
0.44∗ middle). Although there were no significant differences for the proportions of normal/abnormal SWMT, these findings may indicate that the thumb is likely the most sensitive digit for the SWMT and better able to demonstrate loss of sensation in patients with CTS (Slutsky, 2003). Our results contradict the findings of Elfar, Yassen, Stern, & Kiefhaber, (2010), in 35 patients (40 hands) with CTS evaluated preoperatively on the day of surgery. They reported that the SWMT showed the middle digit as the most symptomatic compared to the thumb and index digits, and concluded that the middle digit, and to a slightly lesser extent the thumb being more sensitive than the others in the hand using SWMT to confirm CTS (Elfar, Yassen, Stern, & Kiefhaber, 2010). The seemingly contradictory findings might be due to differences in the characteristics of patients and the study protocol. In the present study, the sensory profile of patients with CTS were mostly within the diminished light touch range. We recommend further investigations with a larger sample size and patients with greater loss of sensation to confirm the results.
The thumb sensory DLs, AMPs, and NCV were all statistically different between thumbs with abnormal and normal SWMTs. Total NCS findings (DLs, AMPs, and NCV) were also statistically different between abnormal and normal SWMTs. However, the NCS of index and middle digits were not significantly different between the index and middle digits with abnormal and normal SWMTs. Nevertheless, all mean NCS results for the abnormal SWMT were impaired to a greater degree than the NCS findings of the normal SWMT. In summary for the discriminative testing portion of this investigation we suggest the thumb SWMT and the summative total SWMT for the hand as both measurement protocols demonstrate the ability to detect a difference between abnormal and normal sensation in patients with CTS, and thus support the validity of using SWMT. Furthermore just testing the thumb requires a shorter time period than testing all three digits, so if there is a time constraint we recommend just examining SWMT for the thumb for patients with CTS. In the present study, there were negative, inverse correlations between the SWMT scores and sensory distal latency. This indicates that when the SWMT score increases, we can expect the distal latency to decline indicating an improvement in sensibility. The correlations between the SWMT scores and sensory amplitude and the NCV were positive. This indicates that an increase or decrease of SWMT scores can predict accordingly the same directional changes of the amplitude and the NCV. Thus, we can expect that as the SWMT score increases or improves, both the amplitude and the NCV improve. There were significant moderate correlations between the thumb SWMT scores and all sensory findings. Although the standard NCS includes sensory latencies of the thumb, index, and middle fingers (Slutsky, 2003), the correlations between the thumb SWMT score and the sensory NCS findings suggest that when using the thumb SWMT for testing sensibility in patients with CTS, the thumb sensory NCS may be sufficient to confirm the CTS. In antidromic sensory studies of fingers performed on 59 patients with CTS, Kothari et al. (1995), reported that in milder cases of CTS, the thumb was the most sensitive in identifying abnormality of sensory conduction across the wrist. In the present study, the index and middle SWMT scores as well as the total SWMT score did not show consistent correlations with all SNCS measures. While the index SWMT score had significant low correlations with the DLs and AMPs, the middle finger had low
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correlation with only the AMPs. This indicates that the index may be a more sensitive indicator than the middle finger. Our findings are not in agreement with the results reported by other investigators (Elfar, Yassen, Stern, & Kiefhaber, 2010; Kothari et al., 1995), which could be due to the differences in the study protocol and objectives, differences in characteristics of patient populations, NCS protocols, the outcome measures, and even statistical methodology and tests utilized. The discrepancies in the correlation coefficients found between the individual fingers and the NCS measures may indicate that the CTS affects the fingers differentially (Elfar, Yassen, Stern, & Kiefhaber, 2010). The total SWMT score also had low correlations with the total AMPs and the NCV. When comparing the thumb SWMT and the total SWMT correlations with the SNCS measures, we may suggest the thumb SWMT score as a more valid test for examining sensibility in CTS. In this study, the significant correlations between the SWMT and the NCS were not strong ranging from 0.24 up to 0.44 (low to moderate agreement). This is in agreement with others (Bregar, 1987; Elfar, Yassen, Stern, & Kiefhaber, 2010). Bregar (1987) found low correlations between the SWMTs and the NCS tests in patients with Hansen disease, and discussed that there is no direct correlation between the clinical test (SWMT) and the NCS tests because they assess different problems of the nerves. Elfar, Yassen, Stern, and Kiefhaber (2010) found no significant correlations between SWMTs and electrodiagnostic results. The low correlations between the SWMT and the NCS may be explained in part by the fact that they may be measuring different phenomena and thus cannot be expected to correlate directly and strongly. Another possible explanation for the low correlations could be the small number of patients included in the study. For future studies, more patients representing a wide distribution of CTS involvement from normal to severe loss of sensation compared with control healthy subjects are required. However, the correlations of thumb SWMT scores with the NCS indicators were stronger than the other digits. In summary for the correlational portion of this investigation we suggest the thumb SWMT is valid when compared to the criterion of sensory NCS and NCV as evidenced by the significant moderate correlations. When combined with the discriminative portion of the study these findings demonstrate differences among the individual digits that suggest the thumb as the best digit for testing sensibility compared to the index and middle digits, and the total SWMT score.
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Overall, the thumb SWMT and the total SWMT were able to detect differences in NCS findings between digits with abnormal and normal sensations. The thumb SWMT scores were moderately correlated with all SNCS measures. Although only approximately 50% of the CTS diagnosed through NCS are corroborated through SWMT; the significant associations between SWMT and NCS measures suggest that SWMT is a valid test for assessing sensations in patients with CTS, but that caution should be taken as it is clear SWMT and NCS do not fully represent the same construct. Acknowledgments The authors greatly thank all patients, and staff at the Department of Physical Medicine and Rehabilitation. References Ahn, D. S., Yoon, E. S., Koo, S. H., & Park, S. H. (2000). A prospective study of the anatomic variations of the median nerve in the carpal tunnel in Asians. Annals of Plastic Surgery, 44, 282-287. Alfonso, C., Jann, S., Massa, R., & Torreggiani, A. (2010). Diagnosis, treatment and follow-up of the carpal tunnel syndrome: A review. Neurological Sciences, 31, 243-252. American Association of Electrodiagnostic Medicine., American Academy of Neurology., & American Academy of Physical Medicine and Rehabilitation. (2002). Practice parameter for electrodiagnostic studies in carpal tunnel syndrome: Summary statement. Muscle & Nerve, 25, 918-922. Ansari, N. N., Adelmanesh, F., Naghdi, S., & Mousavi, S. (2009). The relationship between symptoms, clinical tests and nerve conduction study findings in carpal tunnel syndrome. Electromyography and Clinical Neurophysiology, 49, 53-57. Arrori, S., & Spence, R. A. (2008). Carpal tunnel syndrome. Ulster Medical Journal, 77, 6-17. Atroshi, I., Gummesson, C., Johnsson, R., Ornstein, E., Ranstam, J., & Rosen, I. (1999). Prevalence of carpal tunnel syndrome in a general population. JAMA, 281, 153-158. Bell-Krotoski, J. (1990). Pocket filaments and specifications for the Semmes-Weinstein Monofilaments. Journal of Hand Therapy, 3, 26-31. Bland, J. D. (2005). Carpal tunnel syndrome. Current Opinion in Neurology, 18, 581-585. Bregar, D. (1987). Correlating Semmes-Weinstein Monofilament mappings with sensory nerve conduction parameters in Hansen’s disease patients: An update. Journal of Hand Therapy, 1, 33-37. Buschbacher, R. M. (1999). Median 14 cm and 7 cm antidromic sensory studies to digits 2 and 3. American Journal of Physical Medicine & Rehabilitation, 78, S53-S62. D’Arcy, C. A., & McGee, S. (2000). The rational clinical examination. Does this patient have carpal tunnel syndrome? JAMA, 283, 31103117. Erratum in: JAMA, 284, 1383. Dioquino, C. P., Dellosa, M. A., Reyes, J. P., & Panganiban, L. C. (2009). Usefulness of monofilament testing for detecting peripheral neuropathy I. Acta Medica Philippina, 43, 4-8.
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Elfar, J. C., Yassen, Z., Stern, P. J., & Kiefhaber, T. R. (2010). Individual finger sensibility in carpal tunnel syndrome. Journal of Hand Surgery, 35, 1807-1812. Feinstein, A. R. (1987). Clinimetrics. New Haven, CT, Yale University Press. Feng, Y., Schlosser, F. J., & Sumpio, B. E. (2009). The Semmes Weinstein monofilament examination as a screening tool for diabetic peripheral neuropathy. Journal of Vascular Surgery, 50, 675-682. Geoghegan, J. M., Clark, D. I., Bainbridge, L. C., Smith, C., & Hubbard, R. (2004). Risk factors in carpal tunnel syndrome. Journal of Hand Surgery, 29, 315-320. Giersiepen, K., & Spallek, M. (2011). Carpal tunnel syndrome as ¨ an occupational disease. Deutsches Arzteblatt International, 23, 238-242. Huisstede, B. M., Hoogvliet, P., Randsdorp, M. S., Glerum, S., van Middelkoop, M., & Koes, B. W. (2010). Carpal tunnel syndrome. Part I: Effectiveness of nonsurgical treatments-a systematic review. Archives of Physical Medicine and Rehabilitation, 91, 981-1004. Jerosch-Herold, C. (2005). Assessment of sensibility after nerve injury and repair: A systematic review of evidence for validity, reliability and responsiveness of tests. Journal of Hand Surgery, 30, 252-264. Jerosch-Herold, C. (2003). A study of the relative responsiveness of five sensibility tests for assessment of recovery after median nerve injury and repair. Journal of Hand Surgery, 28, 255-260. Kothari, M. J., Rutkove, S. B., Caress, J. B., Hinchey, J., Logigian, E. L., & Preston, D. C. (1995). Comparison of digital sensory studies in patients with carpal tunnel syndrome. Muscle & Nerve, 18, 1272-1276. Lew, H. L., Date, E. S., Pan, S. S., Wu, P., Ware, P. F., & Kingery, W. S. (2005). Sensitivity, specificity, and variability of nerve conduction velocity measurements in carpal tunnel syndrome. Archives of Physical Medicine and Rehabilitation, 86, 12-16. MacDermid, J. C., Kramer, J. F., & Roth, J. H. (1994). Decision making in detecting abnormal Semmes-Weinstein monofilament thresholds in carpal tunnel syndrome. Journal of Hand Therapy, 7, 158-162. Mayfield, J. A., & Sugarman, J. R. (2000). The use of the Semmes– Weinstein monofilament and other threshold tests for preventing foot ulceration and amputation in persons with diabetes. Journal of Family Practice, 49, S17-S29.
Pagel, K. J., Kaul, M. P., & Dryden, J. D. (2002). Lack of utility of Semmes-Weinstein Monofilament testing in suspected carpal tunnel syndrome. American Journal of Physical Medicine & Rehabilitation, 81, 597-600. Schreuders, T. A., Selles, R. W., van Ginneken, B. T., Janssen, W. G., & Stam, H. J. (2008). Sensory evaluation of the hands in patients with Charcot-Marie-Tooth disease using SemmesWeinstein Monofilaments. Journal of Hand Therapy, 21, 28-34. Slutsky, D. J. (2003). Nerve Conduction studies in hand surgery. Journal of the American Society for Surgery of the Hand, 3, 152-169. Stevens, J. C. (1997). AAEM minimonograph #26: The electrodiagnosis of carpal tunnel syndrome. American Association of Electrodiagnostic Medicine. Muscle & Nerve, 20, 1477-1486. Szabo, R. M., Slater, R. R., Farver, T. B., Stanton, D. B., & Sharman, W. K. (1999). The value of diagnostic testing in carpal tunnel syndrome. Journal of Hand Surgery, 24, 704-714. Tan, L. S. (2010). The clinical use of the 10g monofilament and its limitations: A review. Diabetes Research and Clinical Practice, 90, 1-7. Walker-Bone, K. E., Palmer, K. T., Reading, I., & Cooper, C. (2003). Criteria for assessing pain and nonarticular soft-tissue rheumatic disorders of the neck and upper limb. Seminars in Arthritis and Rheumatism, 33, 168-184. Walters, R. J., & Murray, N. M. (2001). Transcarpal motor conduction velocity in carpal tunnel syndrome. Muscle & Nerve, 24, 966-968. Werner, R. A., & Andary, M. (2002). Carpal tunnel syndrome: Pathophysiology and clinical neurophysiology. Clinical Neurophysiology, 113, 1373-1381. Wilbourn, A. J. (2002). Nerve conduction studies. Types components, abnormalities, and value in localization. Neurologic Clinics, 20, 305-338. Williams, F. H., Johns, J. S., Weiss, J. M., Weis, L. D., Kim, C. T., Strommen, J. A., & Rashbaum, I. G. (2005). Neuromuscular Rehabilitation and Electrodiagnosis.1. Mononeuropathy. Archives of Physical Medicine & Rehabilitation, 86, S3-S10. Wilson, J. K., & Sevier, T. L. (2003). A review of treatment for carpal tunnel syndrome. Disability and Rehabilitation, 25, 113-119. Zyluk, A. (2013). Is carpal tunnel syndrome an occupational disease? A review. Polish Orthopedics and Traumatology, 78, 121-126.
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NeuroRehabilitation 35 (2014) 543–552 DOI:10.3233/NRE-141150 IOS Press
Relationship between Semmes-Weinstein Monofilaments perception Test and sensory nerve conduction studies in Carpal Tunnel Syndrome Parvin Rajia , Noureddin Nakhostin Ansarib , Soofia Naghdib,∗ , Bijan Foroghc and Scott Hassond a Department
of Occupational Therapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran b Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran c Department of Physical Medicine and Rehabilitation, Firoozgar University Hospital, Iran University of Medical Sciences, Tehran, Iran d Department of Physical Therapy, Georgia Regents University, Augusta, GA, USA Abstract. BACKGROUND: The Semmes-Weinstein Monofilament Test (SWMT) is a clinical widely used test to quantify the sensibility in patients with Carpal Tunnel Syndrome (CTS). No study has investigated the relationship between the SWMT and sensory nerve conduction studies (SNCS) in patients with CTS. OBJECTIVE: To assess the relationship between the SWMT and SNCS findings in patients with CTS. METHODS: This cross-sectional clinical measurement study included 35 patients with CTS (55 hands) with a mean age of 45 ± 12 years. The outcome measures were the SWMT and SNCS measures of distal latency (DLs), amplitude (AMPs), and nerve conduction velocity (NCV). The median innervated fingers were tested using SWMT and electrodiagnostic tests. The primary outcome was the correlations between the SWMTs and NCS measures. RESULTS: All of the patients/hands had abnormal NCS findings. When looking at the three digits of interest (thumb, index and middle), the thumb SWMTs had the highest number of abnormal findings (58.2%), with the middle digit having the lowest (45.5%). All NCS findings were statistically different between abnormal and normal thumb SWMTs and abnormal and normal total summed SWMTs. There were significant moderate correlations between thumb SWMT scores and all NCS outcomes. CONCLUSIONS: Although only approximately 50% of the CTS diagnosed through NCS are corroborated through SWMT; the significant associations between SWMT and NCS measures suggest that SWMT is a valid test for assessing sensations in patients with CTS. Keywords: Carpal Tunnel Syndrome, Semmes-Weinstein Monofilament Test, nerve conduction study
1. Introduction Carpal Tunnel Syndrome (CTS) is the most common entrapment neuropathy with median nerve compression in the wrist (Wilson & Sevier, 2003). The classic ∗ Address
for correspondence: Dr. Soofia Naghdi, Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Enghelab Ave, Pitch-e-shemiran, Tehran 11489, Iran. Tel.: +98 21 77533939; Fax: +98 21 77727009; E-mail: naghdi@ sina.tums.ac.ir.
symptoms of CTS are sensory in nature with diurnal parasthesia, burning pain, numbness, and tingling (Giersiepen & Spallek, 2011; Huisstede et al., 2010; Arrori & Spence, 2008). Estimates suggest that prevalence of CTS in the general population is 14.4% (Atroshi et al., 1999), and women are more affected than men (23:1 to 3:1) (Geoghegan, Clark, Bainbridge, Smith, & Hubbard, 2004; Ahn, Yoon, Koo, & Park, 2000). The cause of about 90% of all entrapment neuropathies is CTS, and health care costs due to CTS is high (Arrori & Spence, 2008).
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The exact pathogenesis of CTS is not known (Werner & Andary, 2002). While no clear cause can be identified in 50% of patients with CTS, there are local, regional, and systematic causes for CTS (Arrori & Spence, 2008). Mechanical pressure, raised intracarpal canal pressure and ischemic changes have been suggested as possible mechanisms to explain the nerve injury, symptoms, and impaired nerve conduction studies (Wilson & Sevier, 2003; Arrori & Spence, 2008; Zyluk, 2013; Bland, 2005). CTS diagnosis is usually made clinically based on history, symptoms, and bedside diagnostic tests. However, a combination of clinical symptoms, signs and electrodiagnostic tests are used as the most valid approach for diagnosing CTS (Arrori & Spence, 2008; Alfonso, Jann, Massa, & Torreggiani, 2010; Ansari, Adelmanesh, Naghdi, & Mousavi, 2009; Walker-Bone, Palmer, Reading, & Cooper, 2003). In CTS, both sensory and motor components of the median nerve are affected, and the sensory component is involved much earlier than the motor component (Arrori & Spence, 2008). Nerve conduction studies (NCS) are objective measures to quantify sensory and motor nerve conduction velocity. In CTS, both sensory and motor latencies of the median nerve are prolonged (Williams et al., 2005; Stevens, 1997). Although median NCS have been shown to be sensitive and specific and are considered the gold standard diagnostic tests, they require equipment, are expensive, and are time consuming (Arrori & Spence, 2008; Ansari, Adelmanesh, Naghdi, & Mousavi, 2009; Stevens, 1997; Walters & Muuray, 2001). There are various techniques that may be used to assess sensory impairments in clinical and research settings including Semmes-Weinstein Monofilament Test (SWMT). The SWMT is one neurophysiological technique to document CTS (Werner & Andary, 2002). The SWMT, also referred to as the touch threshold test, is widely used by clinicians as it is simple, inexpensive, reliable and valid (Tan, 2010; Schreuders, Selles, van Ginneken, Janssen, & Stam, 2008; Jerosch-Herold, 2003; Mayfield & Sugarman, 2000; Bell-Krotoski, 1990). A review article to identify the usefulness of the monofilaments found that the monofilament is a beneficial clinical instrument for detecting severe neuropathy and identifying patients at risk of ulceration and amputation (Tan, 2010). In a study by Schreuders, Selles, van Ginneken, Janssen, and Stam (2008) the reliability of the SWMTs was investigated in 15 patients with Charcot-Marie-Tooth. They found good intra- and interobserver reliability for SWMT with
ICCs of 0.91 and 0.86, respectively. Jerosch-Herold (2003) conducted a longitudinal dynamic cohort study on patients with median nerve injuries to evaluate the relative responsiveness of sensibility tests and reported that the monofilaments to test touch threshold exhibited the highest degree of responsiveness indicating the validity of the monofilaments. In a review by Mayfield and Sugarman (2000) to evaluate the usefulness of the SWMT and other tests for preventing ulcers and amputation in subjects with diabetes, the authors concluded that the SWMT is the best test for screening patients with neuropathy because it provides good predictive ability for the risk of ulceration and amputation. A review by Bell-Krotoski (1990) found that the SWMT is a reliable tool and can demonstrate changes in nerve status and is correlated with treatment effects. It has been shown that the SWMT is one of the standardized tests for tactile testing which has quantified psychometric properties, and should be included as an outcome measure in assessing patients with median nerve injury (Jerosch-Herold, 2003, 2005). The SWMT is used to quantify the smallest force at which tactile point pressure can be detected. Szabo, Slater, Farver, Stanton, and Sharman (1999) examined several clinical tools/tests to determine the validity to diagnose CTS and found a sensitivity of 83% for SWMT and concluded that CTS will be diagnosed correctly 86% of the time with abnormal SWMT combined with abnormal hand diagram, positive Durkan’s test, and night pain. NCS is one of the major components in electrodiagnostic examinations which can provide objective evidence of nerve abnormalities. NCS can aid in the diagnosis of nerve entrapments, and can be used to detect nerve lesions and to monitor re-innervation after a nerve repair (Slutsky, 2003). Electrodiagnostic studies are reliable and valid, and also highly sensitive and specific for diagnosing CTS (Lew et al., 2005; American Association of Electrodiagnostic Medicine, American Academy of Neurology, and American Academy of Physical Medicine and Rehabilitation, 2002). NCS techniques involve stimulating sensory, motor, or mixed nerves at given sites and recording the time taken for the stimulus to be detected by recording electrodes (Wilbourn, 2002). Parameters of amplitude, duration, latency, and conduction velocity can be obtained from a NCS. In this study, NCS tests have been used as the criterion gold standard to evaluate the validity of the SWMT. There are mixed results on the usefulness of SWMT in patients with CTS. While several studies found
P. Raji et al. / Relationship between SWMT and SNCS in Carpal Tunnel Syndrome
SWMT useful for identifying peripheral and entrapment neuropathies (Tan, 2010; Schreuders, Selles, van Ginneken, Janssen, & Stam, 2008; Jerosch-Herold, 2003; Mayfield & Sugarman, 2000; Bell-Krotoski, 1990; Szabo, Slater, Farver, Stanton, & Sharman, 1999; Dioquino, Dellosa, Reyes, & Panganiban, 2009; MacDermid, Kramer, & Roth, 1994). Pagel, Kaul, and Dryden (2002) examined the value of SWMT in patients with electrodiagnostically confirmed CTS and found that the SWMT did not have utility in diagnosing patients with electrodiagnostically confirmed carpal CTS. However, no study has investigated the relationship between the SWMT and SNCS standard tests in patients with CTS. The major objective of this study was to address this deficit by assessing the relationship between the SWMT and SNCS findings in patients with CTS. In order to meet this objective there were three purposes for this study: 1) to determine if patients with CTS having abnormal SNCS outcomes also have SWMT that correspond to these abnormal findings; 2) to determine if hands or digits rated abnormal and normal through SWMT are different when comparing distal latency, amplitude, and nerve conduction velocity; and 3) to determine if there are associations between SWMT and NCS findings to evaluate concurrent criterion validity for SWMT.
2. Materials and methods 2.1. Patients Patients were recruited from the University, orthopedic, neurology, and rehabilitation clinics. The patients with CTS included in this study had the following criteria: 1) age 18 years or older; 2) diurnal parasthesia, burning pain, numbness, and tingling in the median nerve area; and 3) a positive Tinel and/or Phalen sign. Patients with previous wrist trauma or surgery as well as patients with diabetes mellitus, pregnancy, or polyneuropathy were excluded. Patients were referred by orthopedist, neurologist, or physiatrist from the clinics. The eligibility of patients was assessed again by the first author using the same criteria as described above. Approval of the Research Council of the Rehabilitation School and the Ethical Committee was obtained. The study participants gave their written informed consent to participate in the study with the right to withdraw from the study.
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2.2. Outcome measures The outcome measures were the SWMT and NCS tests of sensory distal latency (DLs), sensory amplitude (AMPs), and nerve conduction velocity (NCV). 2.3. Anthropometric measurements Anthropometric measurements including body weight and height were measured. Body Mass Index (BMI) was calculated as body weight (kilograms) divided by the squared value of bodyheight (meters). 2.4. Nerve conduction and Semmes-Weinstein Monofilament studies The collection and interpretation of the NCS data was performed by a physiatrist who was blinded to the clinical data. The SWMT was performed by an occupational therapist (OT) who was blinded to the NCS findings. This was done to reduce assessor bias. The examiners were not allowed to access the NCS or SWMT data during the study. The NCS was performed first before SWMT evaluation. The patients rested for 5 minutes before the SWMT evaluation was performed. In the case of a bilateral hand involvement, the order of hand evaluations was randomized. A Cadwell electromyography Unit (model Excel, Cadwell Laboratories, Inc., Kennewick, WA) was used to perform the NCS. Surface stimulating, recording, and ground electrodes were used for performing antidromic sensory NCS. The area and skin of the electrode location was cleaned. The NCS were performed in a room with temperature ranging from 26◦ C to 28◦ C. The temperature of the hand skin was maintained at 32◦ C with an infrared lamp and was checked using an Omron 3way digital thermometer (model MC-600). 2.5. Median sensory NCS Patients were positioned in supine with the forearm in supination. Sensitivity was set at 5–20 V/div, lowhigh frequency filter at 20 Hz–2 kHz, and sweep speed at 2 msec/div. The median sensory NCS (SNCS) were recorded from 1st, 2nd, and 3rd digits antidromically with standard distance of 10 cm (thumb) and 14 cm (2nd and 3rd digits) between stimulation and recording electrodes. The median nerve was stimulated at the wrist and at the palm to calculate the sensory NCV (SNCV) such that the distance between stimulation sites (wrist, palm) was 8 cm. The active recording
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electrode was placed at the middle finger for the SNCV. For SNCS, distal latency, sensory nerve action potential (SNAP) amplitude and SNCV were measured. The peak latency and peak to peak amplitude were calculated. Normal mean values include onset latency 3.4 ± 0.3 msec, amplitude 63.0 ± 33.0 V, and NCV 56.2 ± 5.8 m/s (Buschbacher, 1999). The distal latency and amplitude data from thumb, index and middle fingers were averaged to obtain total DLs and total AMPs.
Table 1 The grades of Semmes-Weinstein Monofilament Test Grades Monofilament Target size force (gm) 6 5 4
1.65–2.83 3.22–3.61 3.84–4.31
0.008–0.07 0.16–0.4 0.6–2
3 2 1
4.56–4.93 5.07–5.88 6.10–6.65
4–8 10–60 100–300
0
–
–
Interpretation Normal Diminished light touch Diminished protective sensation Loss of protective sensation Loss of protective sensation/ Deep pressure sensation only Loss of sensation
2.6. Semmes-Weinstein Monofilament testing The Semmes-Weinstein Monofilament test kit (North Coast Medical, Inc, USA) was used to evaluate sensory thresholds of the tips of the thumb, the index, and the middle fingers. The kit consists of 20 flexible nylon monofilaments of varying diameter and length to measure the level of skin touch sensation. The monofilaments have log numbers from 1.65 to 6.65 which begins with the light filaments (1.65–3.61) and progresses to heavy filaments of increasing diameter (3.84–6.65). Heavy filaments need increased pressure for touch to be recognized by patients. The tester applies each monofilament to the surface area of the skin with a perpendicular angle, then applies slight and steady pressure until the monofilament begins to bend, which is the end point of the test. The monofilament number 2.83 was defined as cut-off for normal sensation (Schreuders, Selles, van Ginneken, Janssen, & Stam, 2008).
was recorded that the patient had abnormal sensation for the specific digit (Table 1). Monofilament testing was applied three times. If the patient responded positive to one of the stimuli, this monofilament was recorded indicating that the stimulus was detected. The order and time intervals were randomized. The data from thumb, index and middle fingers were pooled to obtain total frequency of normal and abnormal SWMT. To calculate the direct correlation between the SWMT and NCS findings, the values of log numbers were grouped to produce a scale from 0–6 in which 6 indicates normal and 0 indicates loss of sensation (Table 1). The SWMT scores obtained for the thumb, index and middle fingers were summated to obtain a total SWMT score (range 0–18).
2.7. Procedure
Statistical analysis was carried out using SPSS software 18.0 for Windows (SPSS Inc., Chicago, USA) package. The monofilament numbers ≤2.83 and >2.83 were recoded as normal and abnormal, respectively. The chi-square test was used to determine whether there were equal proportions of normal and abnormal SWMTs for each digit tested and for pooled values. Inter-group differences for NCS findings between digits with abnormal and normal SWMT were analyzed using an Independent Samples t-Test. Additionally, an analysis was performed to evaluate concurrent criterion validity between the SWMT and the NCS findings and identify the level of correlation with the use of standard Pearson correlation test for interval data or Spearman’s rank correlation test for ordinal variables. The interpretation of correlation coefficients was as follows: low (0.00–0.39), moderate (0.40–0.59), moderately high (0.60–0.79), high (0.80–1.00) (Feinstein, 1987). A p value of ≤0.05 was defined statistically significant.
All patients were tested by the first author, an experienced OT, in a quiet room. This procedure was followed to avoid inter-rater reliability problems. She explained the procedure of assessing cutaneous touch threshold of the hand to the patient before beginning the test. Patients were seated at the table opposite of the examiner. The hand being tested was placed on a towel and was hidden behind a screen with the forearm in supination. Patients were asked to verbally respond (saying ‘yes’) when they felt that they were being touched by the monofilaments. The monofilament number of 2.83 was used first in order to establish if the patient had normal or abnormal tactile sensation. If the patient perceived the stimulus, then lighter monofilaments were applied to record the lightest possible monofilament for the patient. If the patient was not able to perceive the 2.83 monofilament, a thicker filament was used, and it
2.8. Statistical analysis
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Table 2 Frequency of normal/abnormal SWMT Fingers Thumb (n = 55) Index (n = 55) Middle (n = 55) Total (n = 165)
Normal No/%
Abnormal No/%
Chi-Square test P value
23/41.8% 26/47.3% 30/54.5% 79/47.9%
32/58.2% 29/52.7% 25/45.5% 86/52.1%
0.23 0.69 0.50 0.59
Abbreviations; SWMT, Semmes-Weinstein Monofilament Test.
3. Results Thirty five patients with CTS (32 women and 3 men; mean age 45 ± 12 years, range 20–73; BMI, 25.39 ± 4.25, range 16.00–36.84) participated in the study. The mean duration of disease was 30 months [standard deviation (SD) 36.8; range 1–120]. The CTS was bilateral in 20 patients. Fifty five hands were included for evaluations (33 on the right side and 22 on the left side). The right hand was dominant in 32 patients. Table 2 and Fig. 1 show the frequency of abnormal and normal sensory findings using SWMT obtained for digits tested and for all SWMT. The SWMT revealed that 58.2% of tests were abnormal for the thumb, 52.7% for the index, 45.5% for the middle digit, and 52.1% for all SWMT. In fact, 48% of all SWMTs were within normal range (indicating sensation detected at monofilament size ≤2.83). There were no statistical differences for the proportions of normal and abnormal SWMT (p > 0.05). The median (interquartile range, IQR) for SWMT scores were similar for thumb and index being 5 (5-6). For the middle finger, median was 6 (IQR 5-6). The mean (SD) of the total SWMT score was 16.1 (1.7, range 12–18). Table 3 summarizes the results of the sensory NCS found in this study. The mean scores for all NCS variables for all of the digits fell outside of the normal values. The physician indicated that all patients had abnormal NCS tests, suggesting the likely presence of CTS. The results of NCS for fingers with abnormal and normal SWMTs are presented in Table 4. The differences for both DLs and AMPs were statistically different between thumbs with abnormal and normal SWMTs (p < 0.05). However, the DLs and AMPs were not statistically different between index and middle fingers with abnormal and normal SWMTs (p > 0.05). The total DLs and the total AMPs both were statistically different between fingers with the total abnormal (n = 86) and normal (n = 79) SWMT (p < 0.05). The NCV differences were statistically significant only between thumbs with abnormal and normal SWMT (p = 0.001)
Fig. 1. Frequency of Semmes-Weinstein Monofilament Test (SWMT) grades for (A) thumb, (B) index, and (C) middle digits.
and between fingers with total abnormal and normal SWMT (t = 3.33, df = 163, p = 0.001). The Spearman’s rho coefficients found between the SWMT scores and NCS findings are illustrated in Table 5 and scatterplots for the significant correlations are indicated in Fig. 2. There were significant correlations between the thumb SWMT scores and all
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P. Raji et al. / Relationship between SWMT and SNCS in Carpal Tunnel Syndrome Table 3 NCS findings (n = 55)
Variables Thumb Index Middle Total
nificant correlation between the SWMT scores and the amplitude. The total SWMT score demonstrated significant correlations with the total AMPs (Pearson coefficient 0.30, p = 0.02) and the NCV (Pearson coefficient 0.33, p = 0.006). There was no significant correlation between the total SWMT score and the total DLs (Pearson coefficient −0.16, p = 0.12).
Mean Standard Maximum Minimum deviation DL (msec) Amp (V) DL (msec) Amp (V) DL (msec) Amp (V) DL (msec) Amp (V)
NCV (m/s)
3.8 44.0 4.1 45.6 4.4 37.6 4.1 42.4 31.6
0.6 16.2 0.6 17.8 0.1 21.1 0.8 18.7 7.9
5.4 102.0 5.9 95.0 7.9 94.0 7.9 102.0 46.0
1.4 8.0 2.9 12.0 3.5 5.0 1.4 5.0 13.0
4. Discussion
Abbreviations; NCS, nerve conduction study, DL, distal latency, AMP, amplitude, NCV, nerve conduction velocity.
In this study, we aimed to explore: if patients with CTS having abnormal NCS outcomes also have SWMT that correspond to these abnormal findings; if hands or digits rated abnormal and normal through SWMT are different when comparing sensory distal latency, amplitude, and sensory nerve conduction velocity; and
NCS measures. For the index, the correlation between the SWMT scores and the NCV was not statistically significant. For the middle digit, there was only a sig-
Table 4 NCS findings for hands with normal and abnormal SWMTs Variables Thumb
DL (msec)
Normal SWMT, n = 23 Abnormal SWMT, n = 32 Normal SWMT, n = 23 Abnormal SWMT, n = 32 Normal SWMT, n = 26 Abnormal SWMT, n = 29 Normal SWMT, n = 26 Abnormal SWMT, n = 29 Normal SWMT, n = 30 Abnormal SWMT, n = 25 Normal SWMs, n = 30 Abnormal SWMT, n = 25 Normal SWMT, n = 79 Abnormal SWMT, n = 86 Normal SWMT, n = 79 Abnormal SWMT, n = 86 Normal SWMT, n = 23 Abnormal SWMT, n = 32
Amp(V) Index
DL (msec) Amp (V)
Middle
DL (msec) Amp (V)
Total
DL (msec) Amp (V)
NCV (m/s)
Mean
SD
t-Test
3.6 3.9 50.8 39.1 4.0 4.3 49.2 42.4 4.3 4.6 41.7 32.6 4.0 4.3 46.8 38.3 35.7 28.7
0.6 0.5 17.0 13.9 0.6 0.7 17.3 17.9 0.7 1.2 22.0 19.2 0.7 0.9 19.3 17.2 6.4 7.6
t = −2.53, df = 53, p = 0.01 t = 2.81, df = 53, p = 0.007 t = −1.89, df = 53, p = 0.06 t = 1.43, df = 53, p = 0.16 t = −1.38, df = 53, p = 0.17 t = 1.62, df = 53, p = 0.11 t = −2.44, df = 163, p = 0.02 t = 2.99, df = 163, p = 0.003 t = 3.6, df = 53, p = 0.001
Abbreviations; SD, Standard Deviation; NCS, nerve conduction study; DL, distal latency; AMP, amplitude; NCV, nerve conduction velocity; SWMT, Semmes-Weinstein Monofilament Test. Table 5 Spearman’s correlation coefficients between the SWMT scores and the sensory NCS findings SWMT score
Thumb DL
Thumb p Index p Middle p Total SWMT score
–0.42∗ 0.001
Index
Amp
NCV
0.44∗ middle). Although there were no significant differences for the proportions of normal/abnormal SWMT, these findings may indicate that the thumb is likely the most sensitive digit for the SWMT and better able to demonstrate loss of sensation in patients with CTS (Slutsky, 2003). Our results contradict the findings of Elfar, Yassen, Stern, & Kiefhaber, (2010), in 35 patients (40 hands) with CTS evaluated preoperatively on the day of surgery. They reported that the SWMT showed the middle digit as the most symptomatic compared to the thumb and index digits, and concluded that the middle digit, and to a slightly lesser extent the thumb being more sensitive than the others in the hand using SWMT to confirm CTS (Elfar, Yassen, Stern, & Kiefhaber, 2010). The seemingly contradictory findings might be due to differences in the characteristics of patients and the study protocol. In the present study, the sensory profile of patients with CTS were mostly within the diminished light touch range. We recommend further investigations with a larger sample size and patients with greater loss of sensation to confirm the results.
The thumb sensory DLs, AMPs, and NCV were all statistically different between thumbs with abnormal and normal SWMTs. Total NCS findings (DLs, AMPs, and NCV) were also statistically different between abnormal and normal SWMTs. However, the NCS of index and middle digits were not significantly different between the index and middle digits with abnormal and normal SWMTs. Nevertheless, all mean NCS results for the abnormal SWMT were impaired to a greater degree than the NCS findings of the normal SWMT. In summary for the discriminative testing portion of this investigation we suggest the thumb SWMT and the summative total SWMT for the hand as both measurement protocols demonstrate the ability to detect a difference between abnormal and normal sensation in patients with CTS, and thus support the validity of using SWMT. Furthermore just testing the thumb requires a shorter time period than testing all three digits, so if there is a time constraint we recommend just examining SWMT for the thumb for patients with CTS. In the present study, there were negative, inverse correlations between the SWMT scores and sensory distal latency. This indicates that when the SWMT score increases, we can expect the distal latency to decline indicating an improvement in sensibility. The correlations between the SWMT scores and sensory amplitude and the NCV were positive. This indicates that an increase or decrease of SWMT scores can predict accordingly the same directional changes of the amplitude and the NCV. Thus, we can expect that as the SWMT score increases or improves, both the amplitude and the NCV improve. There were significant moderate correlations between the thumb SWMT scores and all sensory findings. Although the standard NCS includes sensory latencies of the thumb, index, and middle fingers (Slutsky, 2003), the correlations between the thumb SWMT score and the sensory NCS findings suggest that when using the thumb SWMT for testing sensibility in patients with CTS, the thumb sensory NCS may be sufficient to confirm the CTS. In antidromic sensory studies of fingers performed on 59 patients with CTS, Kothari et al. (1995), reported that in milder cases of CTS, the thumb was the most sensitive in identifying abnormality of sensory conduction across the wrist. In the present study, the index and middle SWMT scores as well as the total SWMT score did not show consistent correlations with all SNCS measures. While the index SWMT score had significant low correlations with the DLs and AMPs, the middle finger had low
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correlation with only the AMPs. This indicates that the index may be a more sensitive indicator than the middle finger. Our findings are not in agreement with the results reported by other investigators (Elfar, Yassen, Stern, & Kiefhaber, 2010; Kothari et al., 1995), which could be due to the differences in the study protocol and objectives, differences in characteristics of patient populations, NCS protocols, the outcome measures, and even statistical methodology and tests utilized. The discrepancies in the correlation coefficients found between the individual fingers and the NCS measures may indicate that the CTS affects the fingers differentially (Elfar, Yassen, Stern, & Kiefhaber, 2010). The total SWMT score also had low correlations with the total AMPs and the NCV. When comparing the thumb SWMT and the total SWMT correlations with the SNCS measures, we may suggest the thumb SWMT score as a more valid test for examining sensibility in CTS. In this study, the significant correlations between the SWMT and the NCS were not strong ranging from 0.24 up to 0.44 (low to moderate agreement). This is in agreement with others (Bregar, 1987; Elfar, Yassen, Stern, & Kiefhaber, 2010). Bregar (1987) found low correlations between the SWMTs and the NCS tests in patients with Hansen disease, and discussed that there is no direct correlation between the clinical test (SWMT) and the NCS tests because they assess different problems of the nerves. Elfar, Yassen, Stern, and Kiefhaber (2010) found no significant correlations between SWMTs and electrodiagnostic results. The low correlations between the SWMT and the NCS may be explained in part by the fact that they may be measuring different phenomena and thus cannot be expected to correlate directly and strongly. Another possible explanation for the low correlations could be the small number of patients included in the study. For future studies, more patients representing a wide distribution of CTS involvement from normal to severe loss of sensation compared with control healthy subjects are required. However, the correlations of thumb SWMT scores with the NCS indicators were stronger than the other digits. In summary for the correlational portion of this investigation we suggest the thumb SWMT is valid when compared to the criterion of sensory NCS and NCV as evidenced by the significant moderate correlations. When combined with the discriminative portion of the study these findings demonstrate differences among the individual digits that suggest the thumb as the best digit for testing sensibility compared to the index and middle digits, and the total SWMT score.
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