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The correlation between muscle and nerve fiber conduction velocities in thenar muscle is lost in case of carpal tunnel syndrome
Clinical Neurophysiology 113 (2002) 1121–1124 www.elsevier.com/locate/clinph
The correlation between muscle and nerve fiber conduction velocities in thenar muscle is lost in case of carpal tunnel syndrome Mohamad El Dassouki, Jean-Pascal Lefaucheur* Service de Physiologie – Explorations Fonctionnelles, CHU Henri Mondor, Assistance Publique Hopitaux de Paris, 51 avenue de-Lattre-de-Tassigny, 94010 Creteil, France Accepted 10 April 2002
Abstract Objective and methods: This study investigated the relationship between muscle fiber conduction velocity (MFCV) and motor nerve conduction velocity (MNCV) in thenar muscle of 20 normal subjects and of 20 patients suffering from a moderate carpal tunnel syndrome. Our goal was to confirm the positive correlation between MFCV and MNCV and to assess the influence of carpal tunnel syndrome on this relationship. MFCV was calculated in voluntarily contracted thenar muscle using a multi-channel surface recording and a spike-triggered averaging technique. Results: MFCV values ranged between 2.6 and 7.2 m/s (mean ^ SEM: 4.5 ^ 0.3) in normal subjects and between 3.5 and 6.9 m/s (4.7 ^ 0.2) in patients. Subjects and patients did not differ regarding MFCV values, but a correlation between MFCV and MNCV was found in normal subjects (P ¼ 0:0005) and not in patients (P ¼ 0:54). Conclusions: A correlation between muscle and nerve conduction velocities existed in healthy subjects but was lost in case of moderate carpal tunnel syndrome. MFCV appeared to be insensitive to focal nerve conduction slowing. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Carpal tunnel syndrome; Motor nerve conduction velocity; Motor unit action potential; Muscle fiber conduction velocity; Spike-triggered averaging
1. Introduction Muscle fiber conduction velocity (MFCV) was found to correlate with motor nerve conduction velocity (MNCV) in single motor units of thenar muscle in a recent study that used a collision technique for MNCV measurement (Okajima et al., 1998). Our first goal was to confirm this correlation, using a standard procedure of nerve conduction study to determine MNCV and the spike-triggered averaging (STA) method to calculate MFCV (Nishizono et al., 1979; Fang et al., 1996). MFCV can be measured in humans as the velocity of propagation of motor unit action potentials (MUAPs) along muscle fibers (Arendt-Nielsen and Zwarts, 1989; Zwarts, 1989), and the MUAPs are recorded with a series of surface electrodes during voluntary muscle contraction (Nishizono et al., 1979; Sadoyama et al., 1983; Masuda et al., 1985; Yamada et al., 1987; Nishizono et al., 1989). STA method allows calculating MFCV by dividing inter-electrode distance with the propagation * Corresponding author. Tel.: 133-1-4981-2694; fax: 133-1-4981-4660. E-mail address: [email protected] (J.-P. Lefaucheur).
delay of an averaged MUAP detected by two consecutive recording electrodes. Our second goal was to assess the relationship between MFCV and MNCV in a pathological demyelinating condition. As we studied thenar muscle, we compared MFCV and MNCV obtained in normal subjects to those obtained in case of a moderate carpal tunnel syndrome, which is the most frequent demyelinating disease affecting the median nerve distal territory.
2. Patients and methods Electrophysiological recordings were performed unilaterally in the right hand, in 20 healthy subjects and in 20 patients suffering from clinically symptomatic carpal tunnel syndrome. All subjects and patients were right-handed. The 20 healthy subjects, 12 females and 8 males, aged 24–78 years (mean ^ SEM: 45.6 ^ 3.4 years) had no history of neuromuscular disease, no clinical sign of carpal tunnel syndrome and were included after verifying that the right median nerve conduction was normal across the carpal tunnel. The conduction of median sensory nerve fibers
1388-2457/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S 1388-245 7(02)00118-9
CLINPH 2001710
1122
M. El Dassouki, J.-P. Lefaucheur / Clinical Neurophysiology 113 (2002) 1121–1124
was orthodromically studied by performing a mixed nerve stimulation at the palm: for a palm-to-wrist segment of 8 cm in length, lower limits of normal are 45 m/s for velocity and 50 mV for amplitude (Liveson and Ma, 1990). To study motor conduction parameters, the median nerve was stimulated at the second crease of the wrist with surface recording realized over the abductor pollicis brevis muscle. All subjects had normal distal motor onset latency shorter than 4 ms (Liveson and Ma, 1990). Twenty patients, 8 females and 12 males, aged 30–76 years (mean ^ SEM: 48.1 ^ 3.3 years), were included in this study among the cohort of patients referred in our laboratory for a clinical suspicion of carpal tunnel syndrome. They were included if a moderate, but not a severe carpal tunnel syndrome was proved by the following electrophysiological features: a median sensory nerve action potential which was present but of reduced amplitude together with a palm-towrist conduction velocity slowing, a prolonged distal motor latency ranging between 4 and 6 ms and the absence of denervation in needle electromyographic (EMG) examination of abductor pollicis brevis muscle. The recording was performed with a Phasis II EMG machine (EsaOte, Florence, Italy). Palm skin temperatures were maintained between 30 and 358C throughout the recording period. For MNCV measurement, the median nerve was stimulated at the wrist (second crease) and at the elbow, and motor responses were recorded over the abductor pollicis brevis muscle. A ground electrode was placed on the anterior face of the forearm. The stimulus duration was 0.5 ms and the bandpass ranged from 20 to 2000 Hz. Only two parameters of motor nerve conduction were analyzed: the distal motor latency (DML) at wrist stimulation and the MNCV between wrist and elbow. Other parameters of median nerve conduction study, e.g. palm-to-wrist conduction velocity, were not taken any further into account. For MFCV measurement, we used a multi-electrode arrangement derived from previously published works (Masuda et al., 1985; Masuda and Sadoyama, 1986; Yamada et al., 1987; Yamada et al., 1991). The recording multi-electrode was arranged on a flexible gum board and consisted in two linear arrays of 8 electrodes that were 2 mm in diameter and spaced at 5-mm intervals (PMT Corporation, Chanhassen, USA) (Fig. 1). This multi-electrode was placed longitudinally over the abductor pollicis brevis muscle belly in parallel with muscle fiber axis, between the motor endplate zone and the proximal tendon. Recordings were performed with electrodes assembled as a cascade formation, each electrode being connected to the active input of a separate channel and to the reference input of the next channel (Fang et al., 1996) (Fig. 1). With such an arrangement, the propagation of muscle potentials between two consecutive channels could be assessed. Subjects were asked to develop voluntary muscle contraction (thumb abduction) sufficient to obtain a single MUAP, that was triggered using a threshold amplitude of 1 mV, averaged and analyzed by means of the STA technique. MFCV was
calculated by dividing the distance between two electrodes (5 mm) with the propagation delay (time interval) of an averaged MUAP detected on two consecutive channels (Fig. 1). The bandpass ranged from 20 to 2000 Hz. The sweep was of 5 ms per division with a 3-division delay. We studied the relationship between motor nerve conduction parameters (DML and MNCV), MFCV and age by using the Spearman correlation test. The values obtained in patients and in controls were compared using the Mann–Whitney U test. A P value less than 0.05 was considered significant.
3. Results MUAP recording in three consecutive channels is illustrated in Fig. 2. In normal subjects, MFCV values ranged between 2.6 and 7.2 m/s (mean ^ SEM: 4.5 ^ 0.3), DML between 3.2 and 3.9 ms (3.6 ^ 0.05) and MNCV between 48 and 68 m/s (56.1 ^ 1.5). In patients with carpal tunnel syndrome, MFCV values ranged between 3.5 and 6.9 m/s (mean ^ SEM: 4.7 ^ 0.2), DML between 4.1 and 5.7 ms (4.5 ^ 0.1) and MNCV between 40 and 62 m/s (52.2 ^ 1.6). No difference was found between subjects and patients regarding age, MFCV or MNCV (Mann–Whitney U test, P ¼ 0:75, 0.84 and 0.16, respectively). Only DML differed (P , 0:0001). A correlation was found between MFCV and DML or MNCV (Spearman test, r ¼
Fig. 1. Schema of the recording arrangement to measure MFCV. The recording multi-electrode consisted in two linear arrays of 8 electrodes which were 2 mm in diameter and spaced at 5-mm intervals. Each electrode was connected to the active input of a separate channel and to the reference input of the next channel. The multi-electrode was placed longitudinally over the abductor pollicis brevis muscle and subjects were asked to abduct the thumb. MFCV was calculated by dividing the distance between two electrodes (dist) with the propagation delay (D lat) of an averaged MUAP triggered and detected on two consecutive channels.
M. El Dassouki, J.-P. Lefaucheur / Clinical Neurophysiology 113 (2002) 1121–1124
1123
4. Discussion
Fig. 2. Traces showing the propagation an averaged MUAP in three consecutive channels. The muscle fiber conduction velocity was 4.2 m/s. Sweep: 5 ms/division; and sensitivity: 1 mV/division.
20:50 and 0.71, P ¼ 0:025 and 0.0005, respectively) in normal subjects, but not in patients (r ¼ 0:10 and 0.14 with P ¼ 0:68 and 0.54, respectively) (Fig. 3). In contrast, MFCV correlated negatively with age, both in controls and in patients (r ¼ 20:47 and 20.50, P ¼ 0:04 and 0.03, respectively). Finally, MNCV correlated also with age, both in controls and in patients (r ¼ 20:56 and 20.72, P ¼ 0:009 and 0.0004, respectively).
The purpose of the present study was to assess the relationship between muscle fiber and motor nerve fiber conduction velocities in thenar muscle, and to appraise the influence of a carpal tunnel syndrome on this relationship. Since MFCV was found to correlate with MNCV, it could be assumed that MFCV reflected some features of motor nerve fibers involved in nerve conduction and that both MFCV and MNCV measurements were influenced by the size principle introduced by Hennemann et al., 1965. Such an influence is supported by various experimental results. First, the electrical stimulation of motor nerves was found to recruit motor units in the same order than voluntary contraction (Knaflitz et al., 1990; Feiereisen et al., 1997). Second, MFCV was showed to increase in parallel with contraction force (Sadoyama et al., 1983; Nishizono et al., 1990; Yamada et al., 1991), due to the recruitment of faster motor units following the size principle (Andreassen and Arendt-Nielsen, 1987; Sadoyama and Masuda, 1987; Masuda and De Luca, 1991). However, a theoretical concern could be raised regarding the effect of size principle on the correlation found in the present study between MFCV and MNCV. MFCV was determined by single MUAP analysis at weak contraction, when the recruited muscle fibers are slow conducting ones.
Fig. 3. Relationship between muscle MFCV and DML or MNCV in normal subjects (left column) and in patients with moderate carpal tunnel syndrome (right column).
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M. El Dassouki, J.-P. Lefaucheur / Clinical Neurophysiology 113 (2002) 1121–1124
In contrast, DML and MNCV were measured from compound muscle action potential recorded at supra-maximal stimulus intensity, exploring a pool of large, fastconducting nerve fibers. Therefore, additional mechanisms other than size principle may be involved, like the influence of age which correlated both with MFCV and MNCV. However, MFCV and MNCV related to age both in healthy subjects and in patients, while the correlation between MFCV and MNCV was lost in patients with moderate carpal tunnel syndrome. In patients compared to controls, DML was significantly prolonged and MNCV tended to be reduced, but MFCV did not change. MFCV remained unaffected by the occurrence of a moderate carpal tunnel syndrome, which results primarily in segmental demyelination (Ross and Kimura, 1995; Kerwin et al., 1996). Secondarily, when median nerve entrapment becomes severe, a motor axonal loss occurs, but this was not the case in our patients, as showed by normal EMG examination of thenar muscles. Therefore, we conclude that focal demyelination does not modify MFCV. However, since MFCV has been reported to be reduced in the case of axonal neuropathy (Van der Hoeven et al., 1993; Huppertz et al., 1997; Cruz-Martinez and Arpa, 1999), further studies should be performed in cases of carpal tunnel syndrome with a significant degree of axonal loss. Acknowledgements The authors would like to thank Ms Isabelle Me´ nard for her valuable technical support. References Andreassen S, Arendt-Nielsen L. Muscle fibre conduction velocity in motor units of the human anterior tibial muscle: a new size principle parameter. J Physiol (Lond) 1987;391:561–571. Arendt-Nielsen L, Zwarts M. Measurement of muscle fiber conduction velocity in humans: techniques and applications. J Clin Neurophysiol 1989;6:173–190. Cruz-Martinez A, Arpa J. Muscle fiber conduction velocity in situ (MFCV) in denervation, reinnervation and disuse atrophy. Acta Neurol Scand 1999;100:337–340. Fang J, Shahani BT, Dhand UK. Measurement of muscle fiber conduction velocity by surface electromyograph triggered averaging technique. Muscle Nerve 1996;19:918–919. Feiereisen P, Duchateau J, Hainaut K. Motor unit recruitment order during voluntary and electrically induced contractions in the tibialis anterior. Exp Brain Res 1997;114:117–123.
Hennemann E, Somjen G, Carpenter DO. Functional significance of cell size in spinal motoneurons. J Neurophysiol 1965;28:560–580. Huppertz HJ, Disselhorst-Klug C, Silny J, Rau G, Heimann G. Diagnostic yield of non-invasive high spatial resolution electromyography in neuromuscular diseases. Muscle Nerve 1997;20:1360–1370. Kerwin G, Williams CS, Seiler III JG. The pathophysiology of carpal tunnel syndrome. Hand Clin 1996;12:243–251. Knaflitz M, Merletti R, De Luca CJ. Influence of motor unit recruitment order in voluntary and electrically elicited contractions. J Appl Physiol 1990;68:1657–1667. Liveson JA, Ma DM. Laboratory reference for clinical neurophysiology. Philadelphia: F.A. Davis Company, 1990. p. 83, 117. Masuda T, De Luca CJ. Recruitment threshold and muscle fiber conduction velocity of single motor units. J Electromyogr Kinesiol 1991;1:116– 123. Masuda T, Sadoyama T. The propagation of single motor unit action potentials detected by a surface electrode array. Electroenceph clin Neurophysiol 1986;63:590–598. Masuda T, Miyano H, Sadoyama T. A surface electrode array for detecting action potential trains of single motor units. Electroenceph clin Neurophysiol 1985;60:435–443. Nishizono H, Saito Y, Miyashita M. The estimation of conduction velocity in human skeletal muscles in situ with surface electrodes. Electroenceph clin Neurophysiol 1979;46:659–664. Nishizono H, Kurata H, Miyashita M. Muscle fiber conduction velocity related to stimulation rate. Electroenceph clin Neurophysiol 1989;72:529–534. Nishizono H, Jujimoto T, Ohtake H, Miyashita M. Muscle fiber conduction velocity and contractile properties estimated from surface electrode arrays. Electroenceph clin Neurophysiol 1990;75:75–81. Okajima Y, Toikawa H, Hanayama K, Ohtsuka T, Kimura A, Chino N. Relationship between nerve and muscle fiber conduction velocities of the same motor unit in man. Neurosci Lett 1998;253:65–67. Ross MA, Kimura J. AAEM case report #2: the carpal tunnel syndrome. Muscle Nerve 1995;18:567–573. Sadoyama T, Masuda T. Changes of the average muscle fiber conduction velocity during a varying force contraction. Electroenceph clin Neurophysiol 1987;67:495–497. Sadoyama T, Masuda T, Miyano H. Relationships between muscle fiber conduction velocity and frequency parameters of surface EMG during sustained contraction. Eur J Appl Physiol 1983;51:247–256. Van der Hoeven JH, Zwarts MJ, Van Weerden TW. Muscle fiber conduction velocity in amyotrophic lateral sclerosis and traumatic lesions of the plexus brachialis. Electroenceph clin Neurophysiology 1993;89:304–310. Yamada M, Kumagai K, Uchiyama A. The distribution and propagation pattern of motor unit action potentials studied multi-channel surface EMG. Electroenceph clin Neurophysiol 1987;67:395–401. Yamada M, Kumagai K, Uchiyama A. Muscle fiber conduction velocity studied by the multi-channel surface EMG. Electromyogr Clin Neurophysiol 1991;31:251–256. Zwarts M. Evaluation of the estimation of muscle fiber conduction velocity. Surface versus needle method. Electroenceph clin Neurophysiol 1989;73:544–548.
The correlation between muscle and nerve fiber conduction velocities in thenar muscle is lost in case of carpal tunnel syndrome Mohamad El Dassouki, Jean-Pascal Lefaucheur* Service de Physiologie – Explorations Fonctionnelles, CHU Henri Mondor, Assistance Publique Hopitaux de Paris, 51 avenue de-Lattre-de-Tassigny, 94010 Creteil, France Accepted 10 April 2002
Abstract Objective and methods: This study investigated the relationship between muscle fiber conduction velocity (MFCV) and motor nerve conduction velocity (MNCV) in thenar muscle of 20 normal subjects and of 20 patients suffering from a moderate carpal tunnel syndrome. Our goal was to confirm the positive correlation between MFCV and MNCV and to assess the influence of carpal tunnel syndrome on this relationship. MFCV was calculated in voluntarily contracted thenar muscle using a multi-channel surface recording and a spike-triggered averaging technique. Results: MFCV values ranged between 2.6 and 7.2 m/s (mean ^ SEM: 4.5 ^ 0.3) in normal subjects and between 3.5 and 6.9 m/s (4.7 ^ 0.2) in patients. Subjects and patients did not differ regarding MFCV values, but a correlation between MFCV and MNCV was found in normal subjects (P ¼ 0:0005) and not in patients (P ¼ 0:54). Conclusions: A correlation between muscle and nerve conduction velocities existed in healthy subjects but was lost in case of moderate carpal tunnel syndrome. MFCV appeared to be insensitive to focal nerve conduction slowing. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Carpal tunnel syndrome; Motor nerve conduction velocity; Motor unit action potential; Muscle fiber conduction velocity; Spike-triggered averaging
1. Introduction Muscle fiber conduction velocity (MFCV) was found to correlate with motor nerve conduction velocity (MNCV) in single motor units of thenar muscle in a recent study that used a collision technique for MNCV measurement (Okajima et al., 1998). Our first goal was to confirm this correlation, using a standard procedure of nerve conduction study to determine MNCV and the spike-triggered averaging (STA) method to calculate MFCV (Nishizono et al., 1979; Fang et al., 1996). MFCV can be measured in humans as the velocity of propagation of motor unit action potentials (MUAPs) along muscle fibers (Arendt-Nielsen and Zwarts, 1989; Zwarts, 1989), and the MUAPs are recorded with a series of surface electrodes during voluntary muscle contraction (Nishizono et al., 1979; Sadoyama et al., 1983; Masuda et al., 1985; Yamada et al., 1987; Nishizono et al., 1989). STA method allows calculating MFCV by dividing inter-electrode distance with the propagation * Corresponding author. Tel.: 133-1-4981-2694; fax: 133-1-4981-4660. E-mail address: [email protected] (J.-P. Lefaucheur).
delay of an averaged MUAP detected by two consecutive recording electrodes. Our second goal was to assess the relationship between MFCV and MNCV in a pathological demyelinating condition. As we studied thenar muscle, we compared MFCV and MNCV obtained in normal subjects to those obtained in case of a moderate carpal tunnel syndrome, which is the most frequent demyelinating disease affecting the median nerve distal territory.
2. Patients and methods Electrophysiological recordings were performed unilaterally in the right hand, in 20 healthy subjects and in 20 patients suffering from clinically symptomatic carpal tunnel syndrome. All subjects and patients were right-handed. The 20 healthy subjects, 12 females and 8 males, aged 24–78 years (mean ^ SEM: 45.6 ^ 3.4 years) had no history of neuromuscular disease, no clinical sign of carpal tunnel syndrome and were included after verifying that the right median nerve conduction was normal across the carpal tunnel. The conduction of median sensory nerve fibers
1388-2457/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S 1388-245 7(02)00118-9
CLINPH 2001710
1122
M. El Dassouki, J.-P. Lefaucheur / Clinical Neurophysiology 113 (2002) 1121–1124
was orthodromically studied by performing a mixed nerve stimulation at the palm: for a palm-to-wrist segment of 8 cm in length, lower limits of normal are 45 m/s for velocity and 50 mV for amplitude (Liveson and Ma, 1990). To study motor conduction parameters, the median nerve was stimulated at the second crease of the wrist with surface recording realized over the abductor pollicis brevis muscle. All subjects had normal distal motor onset latency shorter than 4 ms (Liveson and Ma, 1990). Twenty patients, 8 females and 12 males, aged 30–76 years (mean ^ SEM: 48.1 ^ 3.3 years), were included in this study among the cohort of patients referred in our laboratory for a clinical suspicion of carpal tunnel syndrome. They were included if a moderate, but not a severe carpal tunnel syndrome was proved by the following electrophysiological features: a median sensory nerve action potential which was present but of reduced amplitude together with a palm-towrist conduction velocity slowing, a prolonged distal motor latency ranging between 4 and 6 ms and the absence of denervation in needle electromyographic (EMG) examination of abductor pollicis brevis muscle. The recording was performed with a Phasis II EMG machine (EsaOte, Florence, Italy). Palm skin temperatures were maintained between 30 and 358C throughout the recording period. For MNCV measurement, the median nerve was stimulated at the wrist (second crease) and at the elbow, and motor responses were recorded over the abductor pollicis brevis muscle. A ground electrode was placed on the anterior face of the forearm. The stimulus duration was 0.5 ms and the bandpass ranged from 20 to 2000 Hz. Only two parameters of motor nerve conduction were analyzed: the distal motor latency (DML) at wrist stimulation and the MNCV between wrist and elbow. Other parameters of median nerve conduction study, e.g. palm-to-wrist conduction velocity, were not taken any further into account. For MFCV measurement, we used a multi-electrode arrangement derived from previously published works (Masuda et al., 1985; Masuda and Sadoyama, 1986; Yamada et al., 1987; Yamada et al., 1991). The recording multi-electrode was arranged on a flexible gum board and consisted in two linear arrays of 8 electrodes that were 2 mm in diameter and spaced at 5-mm intervals (PMT Corporation, Chanhassen, USA) (Fig. 1). This multi-electrode was placed longitudinally over the abductor pollicis brevis muscle belly in parallel with muscle fiber axis, between the motor endplate zone and the proximal tendon. Recordings were performed with electrodes assembled as a cascade formation, each electrode being connected to the active input of a separate channel and to the reference input of the next channel (Fang et al., 1996) (Fig. 1). With such an arrangement, the propagation of muscle potentials between two consecutive channels could be assessed. Subjects were asked to develop voluntary muscle contraction (thumb abduction) sufficient to obtain a single MUAP, that was triggered using a threshold amplitude of 1 mV, averaged and analyzed by means of the STA technique. MFCV was
calculated by dividing the distance between two electrodes (5 mm) with the propagation delay (time interval) of an averaged MUAP detected on two consecutive channels (Fig. 1). The bandpass ranged from 20 to 2000 Hz. The sweep was of 5 ms per division with a 3-division delay. We studied the relationship between motor nerve conduction parameters (DML and MNCV), MFCV and age by using the Spearman correlation test. The values obtained in patients and in controls were compared using the Mann–Whitney U test. A P value less than 0.05 was considered significant.
3. Results MUAP recording in three consecutive channels is illustrated in Fig. 2. In normal subjects, MFCV values ranged between 2.6 and 7.2 m/s (mean ^ SEM: 4.5 ^ 0.3), DML between 3.2 and 3.9 ms (3.6 ^ 0.05) and MNCV between 48 and 68 m/s (56.1 ^ 1.5). In patients with carpal tunnel syndrome, MFCV values ranged between 3.5 and 6.9 m/s (mean ^ SEM: 4.7 ^ 0.2), DML between 4.1 and 5.7 ms (4.5 ^ 0.1) and MNCV between 40 and 62 m/s (52.2 ^ 1.6). No difference was found between subjects and patients regarding age, MFCV or MNCV (Mann–Whitney U test, P ¼ 0:75, 0.84 and 0.16, respectively). Only DML differed (P , 0:0001). A correlation was found between MFCV and DML or MNCV (Spearman test, r ¼
Fig. 1. Schema of the recording arrangement to measure MFCV. The recording multi-electrode consisted in two linear arrays of 8 electrodes which were 2 mm in diameter and spaced at 5-mm intervals. Each electrode was connected to the active input of a separate channel and to the reference input of the next channel. The multi-electrode was placed longitudinally over the abductor pollicis brevis muscle and subjects were asked to abduct the thumb. MFCV was calculated by dividing the distance between two electrodes (dist) with the propagation delay (D lat) of an averaged MUAP triggered and detected on two consecutive channels.
M. El Dassouki, J.-P. Lefaucheur / Clinical Neurophysiology 113 (2002) 1121–1124
1123
4. Discussion
Fig. 2. Traces showing the propagation an averaged MUAP in three consecutive channels. The muscle fiber conduction velocity was 4.2 m/s. Sweep: 5 ms/division; and sensitivity: 1 mV/division.
20:50 and 0.71, P ¼ 0:025 and 0.0005, respectively) in normal subjects, but not in patients (r ¼ 0:10 and 0.14 with P ¼ 0:68 and 0.54, respectively) (Fig. 3). In contrast, MFCV correlated negatively with age, both in controls and in patients (r ¼ 20:47 and 20.50, P ¼ 0:04 and 0.03, respectively). Finally, MNCV correlated also with age, both in controls and in patients (r ¼ 20:56 and 20.72, P ¼ 0:009 and 0.0004, respectively).
The purpose of the present study was to assess the relationship between muscle fiber and motor nerve fiber conduction velocities in thenar muscle, and to appraise the influence of a carpal tunnel syndrome on this relationship. Since MFCV was found to correlate with MNCV, it could be assumed that MFCV reflected some features of motor nerve fibers involved in nerve conduction and that both MFCV and MNCV measurements were influenced by the size principle introduced by Hennemann et al., 1965. Such an influence is supported by various experimental results. First, the electrical stimulation of motor nerves was found to recruit motor units in the same order than voluntary contraction (Knaflitz et al., 1990; Feiereisen et al., 1997). Second, MFCV was showed to increase in parallel with contraction force (Sadoyama et al., 1983; Nishizono et al., 1990; Yamada et al., 1991), due to the recruitment of faster motor units following the size principle (Andreassen and Arendt-Nielsen, 1987; Sadoyama and Masuda, 1987; Masuda and De Luca, 1991). However, a theoretical concern could be raised regarding the effect of size principle on the correlation found in the present study between MFCV and MNCV. MFCV was determined by single MUAP analysis at weak contraction, when the recruited muscle fibers are slow conducting ones.
Fig. 3. Relationship between muscle MFCV and DML or MNCV in normal subjects (left column) and in patients with moderate carpal tunnel syndrome (right column).
1124
M. El Dassouki, J.-P. Lefaucheur / Clinical Neurophysiology 113 (2002) 1121–1124
In contrast, DML and MNCV were measured from compound muscle action potential recorded at supra-maximal stimulus intensity, exploring a pool of large, fastconducting nerve fibers. Therefore, additional mechanisms other than size principle may be involved, like the influence of age which correlated both with MFCV and MNCV. However, MFCV and MNCV related to age both in healthy subjects and in patients, while the correlation between MFCV and MNCV was lost in patients with moderate carpal tunnel syndrome. In patients compared to controls, DML was significantly prolonged and MNCV tended to be reduced, but MFCV did not change. MFCV remained unaffected by the occurrence of a moderate carpal tunnel syndrome, which results primarily in segmental demyelination (Ross and Kimura, 1995; Kerwin et al., 1996). Secondarily, when median nerve entrapment becomes severe, a motor axonal loss occurs, but this was not the case in our patients, as showed by normal EMG examination of thenar muscles. Therefore, we conclude that focal demyelination does not modify MFCV. However, since MFCV has been reported to be reduced in the case of axonal neuropathy (Van der Hoeven et al., 1993; Huppertz et al., 1997; Cruz-Martinez and Arpa, 1999), further studies should be performed in cases of carpal tunnel syndrome with a significant degree of axonal loss. Acknowledgements The authors would like to thank Ms Isabelle Me´ nard for her valuable technical support. References Andreassen S, Arendt-Nielsen L. Muscle fibre conduction velocity in motor units of the human anterior tibial muscle: a new size principle parameter. J Physiol (Lond) 1987;391:561–571. Arendt-Nielsen L, Zwarts M. Measurement of muscle fiber conduction velocity in humans: techniques and applications. J Clin Neurophysiol 1989;6:173–190. Cruz-Martinez A, Arpa J. Muscle fiber conduction velocity in situ (MFCV) in denervation, reinnervation and disuse atrophy. Acta Neurol Scand 1999;100:337–340. Fang J, Shahani BT, Dhand UK. Measurement of muscle fiber conduction velocity by surface electromyograph triggered averaging technique. Muscle Nerve 1996;19:918–919. Feiereisen P, Duchateau J, Hainaut K. Motor unit recruitment order during voluntary and electrically induced contractions in the tibialis anterior. Exp Brain Res 1997;114:117–123.
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