- Email: [email protected]
Correlations between MUNE obtained by the intraneural microstimulation technique and the Appel clinical rating scale
Motor Unit Number Estimation (Supplements to Clinical Neurophysiology Vol. 55) Editor: M.B. Bromberg ß 2003 Elsevier Science B.V. All rights reserved.
253
Chapter 27
Correlations between MUNE obtained by the intraneural microstimulation technique and the Appel clinical rating scale Keisuke Arasaki* EMG/EEG Laboratory, Department of Neurology, NTT East Kanto Medical Center, 5-9-22 Higashi-Gotanda, Shinagawa-ku, Tokyo 141-0022, Japan
Introduction
Methods
The time course of functional spinal alpha motor neuron loss in ALS should provide insight into the natural course of the disease (Dantes and McComas, 1991). Clinical rating scales (Appel et al., 1987; ACTS Group, 1996) are used in current therapeutic trials to document the course of ALS and the eects of drugs, but changes in MUNE values may be a more sensitive outcome measure of this disease (Yuen and Olney, 1997; Olney et al., 1999). Consistent with this idea are the results of our previous study (Arasaki and Tamaki, 1998), in which ALS patients who lost about 70% of their functional SA motor neurons showed only a 15% increase in their Appel ALS scores (Appel et al., 1987). Thus, our present study was aimed at delineating the time course of functional spinal alpha motor neuron loss and changes in a clinical rating scale in ALS patients. Detailed results of the present study are in press (Arasaki et al., 2002).
We obtained a series of MUNE values for each of ten patients, 36±85 years of age, who were diagnosed with de®nite ALS according to the El Escorial criteria (WFN Research Group, 1994). The time of testing was between 10 and 12, 16 and 18, and 22 and 24 months after the onset of symptoms. At the time of testing, we also examined the patients clinically to obtain their Appel scores (Appel et al., 1987). The Appel score is the sum of ®ve groups of functional scores: medullary functions, respiration, muscle strength, upper extremity functions, and lower extremity functions. The normal score for each functional group is six, making the Appel score for a completely normal person equal to 30. As a patient's condition worsens, the score becomes higher, and the worst score is 164. The control subjects were 20 patients, 36±80 years of age, with headaches but no other neurological symptoms or signs. In each subject of the control group, MUNEs were obtained twice with an interval of one week in order to document their reproducibility. Before testing, we discussed the procedure with both groups of subjects and obtained their informed consent. Their medical
*Correspondence to: Dr. Keisuke Arasaki, EMG/EEG Laboratory, Department of Neurology, NTT East Kanto Medical Center, 5-9-22 Higashi-Gotanda, Shinagawa-ku, Tokyo 141-0022, Japan. Tel.: 81-3-3448-6455, Fax: 81-3-3448-6458. e-mail: [email protected] doi: 10.1016/S1567-424X(03)00027-8
254
records were reviewed. Our study was approved by the Committee for the Assurance of Clinical Study Quality in our institution. Our current methods of performing MUNE is dierent from those described elsewhere (Arasaki and Tamaki, 1998) in that data acquisition and analysis were done using Neuropack MEB-2200 (Nihon Kohden, Tokyo, Japan). We recorded the maximal compound muscle action potentials (CMAPs) and at least ten unitary muscle action potentials (MAPs) from hypothenar and EDB muscles. For the microstimulation of motor axons, ®ne tungsten-needle electrodes with a tip impedance of 9±13 M at 1000 Hz and 10 8 A (Frederick Haer & Co., Brunswick, ME, USA) were inserted into the ulnar and peroneal nerves at the wrist and ankle, respectively. While keeping the same insertion point, we manipulated the needle electrode manually, placing its tip at dierent points in the nerve trunk to stimulate dierent single motor axons with an electric square pulse of 0.5±8.0 mA and a duration of 10±50 ms. Using an MEB-2200 with an integration algorithm installed6, the area of the negative portion of the maximal CMAP was measured. In order to obtain the mean unitary MAP waveform, at least ten unitary MAP waveforms were recorded and averaged by an o-line computer. An exception to this was that fewer than ten dierent motor units could be sampled successfully in some patients with advanced ALS and the mean unitary MAP waveform was determined using only those sampled (see below). A MUNE was then calculated by dividing the area of the negative portion of the CMAP by that of the digitally averaged unitary MAP.
Results The Appel score in the group of patients with headaches was 32 2 (mean SD, n=20), whereas that in the ALS patient group (n=10) was 47 9 at 12 months after onset, 72 15 at 18 months, and 117 20 at 24 months (Fig. 1A). The rate of progression of the disease in each of the ALS patient group was highly variable. As shown in Fig. 1B, the rate of progression was slow in two cases, whereas it
Fig. 1. Changes in Appel's scores. In A, each box and bar indicate the mean and SD of the scores, respectively, at 12, 18, and 24 months after onset of symptoms. In B, the scores of each ALS patient are plotted in the same manner as in A. Individual patients were represented by different symbols.
was relatively fast in ®ve. The score included lateral pinch power (see above), which represented the motor strength of intrinsic hand muscles. As we measured the hypothenar MUNE, we paid particular attention to pinch power, which was 5.9 1.6 kg at 12 months after onset (n=10), 4.3 2.5 kg at 18 months (n=10), and 1.4 0.8 kg at 24 months (n=8).
255
MUNE values from the hypothenar muscle in the control group of patients was 247 94, whereas that of the EDB muscle was 107 56 (n=20). In the ALS patient group, MUNE values of the hypothenar and EDB muscles decreased to 62 30 (a range of 22±100) and 22 14 (5±48) at 12 months after onset (n=10), 30 14 (15±58) and 12 18 (3±32) at 18 months (n=10), and 11 12 (2±40) and 4 5 (0± 16) at 24 months (n=8), respectively (Fig. 2A). As shown in Fig. 2B and C, MUNE values were also variable according to each patient, but what was remarkable was the similarity between changes in the Appel scores and those in the MUNEs. Two ALS patients with slow clinical progression showed a slow decrease in their MUNE values, whereas four ALS patients with a rapid clinical progression showed a similar rapid decrease in their MUNE values. The relationship between Appel scores and MUNE values is shown in Fig. 3. MUNE values of the hypothenar and EDB muscles of each patient with ALS plotted against Appel scores were variable but seemed to have a negative correlation. In fact, the means of these MUNE values showed a negative hyperbolic correlation with Appel scores, and the decrease in the hypothenar MUNE was steeper than that in the EDB MUNE (Fig. 3C).
Discussion The present study was a longitudinal assessment, in which we followed ten patients with ALS and performed MUNE studies in each patient at 12, 18, and 24 months after the onset of symptoms. As the patients became more disabled, their Appel scores increased. Although the rate of progression in the scores of individual ALS patients was highly variable, as shown in Fig. 1B, the mean values of the rates showed a slower increase 12±18 months after onset than 18±24 months after onset (Fig. 1A). As the patients became more disabled, their MUNE values decreased. In ALS patients with severe muscular atrophy, however, we were not always able to sample at least ten motor units, but the number of motor units recorded was consistently equal to the number of remaining functional
Fig. 2. MUNEs of the hypothenar and EDB muscles in patients with ALS. In A, filled triangles and open circles indicate MUNEs of the hypothenar and EDB muscles, respectively, obtained from ALS patients at 12, 18, and 24 months after onset. B and C show changes in MUNEs of the hypothenar and EDB muscles, respectively, in each ALS patient obtained at 12, 18, and 24 months after onset. Individual patients were represented by different symbols.
256
Fig. 3. Relationship between Appel's scores and MUNEs of the hypothenar and EDB muscles in patients with ALS. A and B show the hypothenar and EDB MUNEs, respectively, of each ALS patient plotted against his/her Appel's scores. Three points in each patient's plot represent data obtained at 12, 18, and 24 months after onset. Individual patients were represented by different symbols. In C, filled triangles and open circles indicate the means of the MUNEs of the hypothenar and EDB muscles, respectively, obtained 12, 18, and 24 months after onset. In each figure, the abscissa is Appel's scores, whereas the ordinate is MUNEs.
motor units. It has also been recognized by other authors (Armon et al., 1997; Shefner, 2001) that the fewer the remaining motor units there are, the more consistent are the resulting MUNE values. Therefore, we conclude that MUNE values obtained with our methodology should represent the number of functional motor units in a muscle in a wide range of states, from normal to severe atrophy. Although the rate of decrease in MUNE values in the ALS patient group was highly variable, as shown in Fig. 3B and C, the mean MUNE values showed a steeper decrease at 12±18 months after onset than at 18±24 months after onset. Although we now use clinical rating scales (ACTS Group, 1996) for the clinical assessment of ALS patients in therapeutic trials, MUNE should have a major impact because such rating scales may not be sensitive enough to detect early changes in ALS (Yuen and Olney, 1997). Rating scales such as Appel scores show composite and average bodily changes in order to de®ne disability. Although a direct comparison between Appel scores and MUNE might seem irrational, changes in the rating scale result from a loss of motor neurons supplying the bulbar, truncal, and limb muscles in ALS patients. Accordingly, a MUNE of a single muscle may well be compared to the part of a scale that is functionally related to that particular muscle, and such a relationship between the MUNE values of a proximal muscle and their isometric strength has already been studied (Bromberg and Larson, 1996). As clinical rating scales in ALS patients re¯ect a loss of upper and lower motor neurons, such scales may theoretically be substituted for MUNE of all muscles in the regions being studied. This is technically impractical, but it is interesting to speculate on how many muscles should be tested to obtain a composite MUNE score that may be comparable to the rating scale. In the present study; we suggest that MUNE of the hypothenar and EDB muscles might be sucient for this purpose. Furthermore, the MUNE values were distributed hyperbolically against Appel scores in Fig. 3C, which means that the former seems more sensitive than the latter in detecting early changes in ALS. Thus, considering the importance of initiating therapeutic
257
intervention as early as possible in the course of ALS, the use of MUNE in the early assessment of a patient's condition may be a better parameter than clinical rating scales. Despite technical variability, MUNE values obtained using dierent methods show a close agreement in studies of normal subjects and patients with neurological disorders (Shefner, 2001). The occurrence of signi®cant changes in MUNE in the early stage of ALS has already been reported by previous authors (Brown and Jaatool, 1974; Dantes and McComas, 1991). In these reports, however, MUNE was performed by a manual incremental technique that is subject to technical pitfalls (McComas, 1998), whereas in the present study we used the microstimulation method, the validity of which has been proven by an animal study (Arasaki et al., 1997). Our present data, therefore, strengthen the reliability of the ®nding that changes in MUNE are more signi®cant than changes in rating scale in patients with early ALS.
References Appel, V., Stewart, S.S., Smith, G. and Appel, S.H. A rating scale for amyotrophic lateral sclerosis: description and preliminary experience. Ann. Neurol., 1987, 22: 328±333. Arasaki, K. and Tamaki, M. A loss of functional spinal alpha motor neurons in amyotrophic lateral sclerosis. Neurology, 1998, 51: 603±605.
Arasaki, K., Tamaki, M., Hosoya, Y. and Kudo, N. Validity of electromyograms and tension as a means of motor unit number estimation. Muscle Nerve, 1997, 20: 552±560. Arasaki, K, Kato, Y, Hyodo, A, Ushijima, R and Tamaki, M. Longitudinal study of functional spinal alpha motor neuron loss in amyotrophic lateral sclerosis. Muscle Nerve, 2002, 25: 520±526. Armon, C., Brandstater, M.E. and Peterson, G.W. Motor unit number estimates and quantitative muscle strength measurements of distal muscles in patients with amyotrophic lateral sclerosis. Muscle Nerve, 1997, 20: 499±501. Bromberg, M. and Larson, W.L. Relationship between motorunit number estimates and isometric strength in distal muscles in ALS/MND. J. Neurol. Sci., 1996, 139(Suppl.): 38±42. Brown, W.F. and Jaatool, N. Amyotrophic lateral sclerosis. Electrophysiological study. Arch. Neurol., 1974, 31: 242±248. Dantes, M. and McComas, A. The extent and time course of motoneuron involvement in amyotrophic lateral sclerosis. Muscle Nerve, 1991, 14: 416±421. McComas, A.J. Motor units: how many, how large, what kind? J. Electromyogr. Kinesiol., 1998, 8: 391±402. Olney, R.K., Yen, E.C. and Engstrom, J.W. The rate of changes in motor unit number estimates predicts survival in patients with amyotrophic lateral sclerosis. Neurology, 1999, 52 (Suppl. 2): A3. Shefner, J.M. Motor unit number estimation in human neurological diseases and animal models. Clin. Neurophysiol., 2001, 112: 955±964. The ALS CNTF treatment study (ACTS) phase 1-II Study Group. The amyotrophic lateral sclerosis functional rating scale. Arch. Neurol., 1996, 53: 141±147. World Federation of Neurology Research Group on Neuromuscular Diseases. El Escorial World Federation of Neurology criteria for the diagnosis of amyotrophic lateral sclerosis. J. Neurol. Sci., 1994, 124: 96±107. Yuen, E.C. and Olney, R.K. Longitudinal study of fiber density and motor unit number estimate in patients with amyotrophic lateral sclerosis. Neurology, 1997, 49: 573±578.
253
Chapter 27
Correlations between MUNE obtained by the intraneural microstimulation technique and the Appel clinical rating scale Keisuke Arasaki* EMG/EEG Laboratory, Department of Neurology, NTT East Kanto Medical Center, 5-9-22 Higashi-Gotanda, Shinagawa-ku, Tokyo 141-0022, Japan
Introduction
Methods
The time course of functional spinal alpha motor neuron loss in ALS should provide insight into the natural course of the disease (Dantes and McComas, 1991). Clinical rating scales (Appel et al., 1987; ACTS Group, 1996) are used in current therapeutic trials to document the course of ALS and the eects of drugs, but changes in MUNE values may be a more sensitive outcome measure of this disease (Yuen and Olney, 1997; Olney et al., 1999). Consistent with this idea are the results of our previous study (Arasaki and Tamaki, 1998), in which ALS patients who lost about 70% of their functional SA motor neurons showed only a 15% increase in their Appel ALS scores (Appel et al., 1987). Thus, our present study was aimed at delineating the time course of functional spinal alpha motor neuron loss and changes in a clinical rating scale in ALS patients. Detailed results of the present study are in press (Arasaki et al., 2002).
We obtained a series of MUNE values for each of ten patients, 36±85 years of age, who were diagnosed with de®nite ALS according to the El Escorial criteria (WFN Research Group, 1994). The time of testing was between 10 and 12, 16 and 18, and 22 and 24 months after the onset of symptoms. At the time of testing, we also examined the patients clinically to obtain their Appel scores (Appel et al., 1987). The Appel score is the sum of ®ve groups of functional scores: medullary functions, respiration, muscle strength, upper extremity functions, and lower extremity functions. The normal score for each functional group is six, making the Appel score for a completely normal person equal to 30. As a patient's condition worsens, the score becomes higher, and the worst score is 164. The control subjects were 20 patients, 36±80 years of age, with headaches but no other neurological symptoms or signs. In each subject of the control group, MUNEs were obtained twice with an interval of one week in order to document their reproducibility. Before testing, we discussed the procedure with both groups of subjects and obtained their informed consent. Their medical
*Correspondence to: Dr. Keisuke Arasaki, EMG/EEG Laboratory, Department of Neurology, NTT East Kanto Medical Center, 5-9-22 Higashi-Gotanda, Shinagawa-ku, Tokyo 141-0022, Japan. Tel.: 81-3-3448-6455, Fax: 81-3-3448-6458. e-mail: [email protected] doi: 10.1016/S1567-424X(03)00027-8
254
records were reviewed. Our study was approved by the Committee for the Assurance of Clinical Study Quality in our institution. Our current methods of performing MUNE is dierent from those described elsewhere (Arasaki and Tamaki, 1998) in that data acquisition and analysis were done using Neuropack MEB-2200 (Nihon Kohden, Tokyo, Japan). We recorded the maximal compound muscle action potentials (CMAPs) and at least ten unitary muscle action potentials (MAPs) from hypothenar and EDB muscles. For the microstimulation of motor axons, ®ne tungsten-needle electrodes with a tip impedance of 9±13 M at 1000 Hz and 10 8 A (Frederick Haer & Co., Brunswick, ME, USA) were inserted into the ulnar and peroneal nerves at the wrist and ankle, respectively. While keeping the same insertion point, we manipulated the needle electrode manually, placing its tip at dierent points in the nerve trunk to stimulate dierent single motor axons with an electric square pulse of 0.5±8.0 mA and a duration of 10±50 ms. Using an MEB-2200 with an integration algorithm installed6, the area of the negative portion of the maximal CMAP was measured. In order to obtain the mean unitary MAP waveform, at least ten unitary MAP waveforms were recorded and averaged by an o-line computer. An exception to this was that fewer than ten dierent motor units could be sampled successfully in some patients with advanced ALS and the mean unitary MAP waveform was determined using only those sampled (see below). A MUNE was then calculated by dividing the area of the negative portion of the CMAP by that of the digitally averaged unitary MAP.
Results The Appel score in the group of patients with headaches was 32 2 (mean SD, n=20), whereas that in the ALS patient group (n=10) was 47 9 at 12 months after onset, 72 15 at 18 months, and 117 20 at 24 months (Fig. 1A). The rate of progression of the disease in each of the ALS patient group was highly variable. As shown in Fig. 1B, the rate of progression was slow in two cases, whereas it
Fig. 1. Changes in Appel's scores. In A, each box and bar indicate the mean and SD of the scores, respectively, at 12, 18, and 24 months after onset of symptoms. In B, the scores of each ALS patient are plotted in the same manner as in A. Individual patients were represented by different symbols.
was relatively fast in ®ve. The score included lateral pinch power (see above), which represented the motor strength of intrinsic hand muscles. As we measured the hypothenar MUNE, we paid particular attention to pinch power, which was 5.9 1.6 kg at 12 months after onset (n=10), 4.3 2.5 kg at 18 months (n=10), and 1.4 0.8 kg at 24 months (n=8).
255
MUNE values from the hypothenar muscle in the control group of patients was 247 94, whereas that of the EDB muscle was 107 56 (n=20). In the ALS patient group, MUNE values of the hypothenar and EDB muscles decreased to 62 30 (a range of 22±100) and 22 14 (5±48) at 12 months after onset (n=10), 30 14 (15±58) and 12 18 (3±32) at 18 months (n=10), and 11 12 (2±40) and 4 5 (0± 16) at 24 months (n=8), respectively (Fig. 2A). As shown in Fig. 2B and C, MUNE values were also variable according to each patient, but what was remarkable was the similarity between changes in the Appel scores and those in the MUNEs. Two ALS patients with slow clinical progression showed a slow decrease in their MUNE values, whereas four ALS patients with a rapid clinical progression showed a similar rapid decrease in their MUNE values. The relationship between Appel scores and MUNE values is shown in Fig. 3. MUNE values of the hypothenar and EDB muscles of each patient with ALS plotted against Appel scores were variable but seemed to have a negative correlation. In fact, the means of these MUNE values showed a negative hyperbolic correlation with Appel scores, and the decrease in the hypothenar MUNE was steeper than that in the EDB MUNE (Fig. 3C).
Discussion The present study was a longitudinal assessment, in which we followed ten patients with ALS and performed MUNE studies in each patient at 12, 18, and 24 months after the onset of symptoms. As the patients became more disabled, their Appel scores increased. Although the rate of progression in the scores of individual ALS patients was highly variable, as shown in Fig. 1B, the mean values of the rates showed a slower increase 12±18 months after onset than 18±24 months after onset (Fig. 1A). As the patients became more disabled, their MUNE values decreased. In ALS patients with severe muscular atrophy, however, we were not always able to sample at least ten motor units, but the number of motor units recorded was consistently equal to the number of remaining functional
Fig. 2. MUNEs of the hypothenar and EDB muscles in patients with ALS. In A, filled triangles and open circles indicate MUNEs of the hypothenar and EDB muscles, respectively, obtained from ALS patients at 12, 18, and 24 months after onset. B and C show changes in MUNEs of the hypothenar and EDB muscles, respectively, in each ALS patient obtained at 12, 18, and 24 months after onset. Individual patients were represented by different symbols.
256
Fig. 3. Relationship between Appel's scores and MUNEs of the hypothenar and EDB muscles in patients with ALS. A and B show the hypothenar and EDB MUNEs, respectively, of each ALS patient plotted against his/her Appel's scores. Three points in each patient's plot represent data obtained at 12, 18, and 24 months after onset. Individual patients were represented by different symbols. In C, filled triangles and open circles indicate the means of the MUNEs of the hypothenar and EDB muscles, respectively, obtained 12, 18, and 24 months after onset. In each figure, the abscissa is Appel's scores, whereas the ordinate is MUNEs.
motor units. It has also been recognized by other authors (Armon et al., 1997; Shefner, 2001) that the fewer the remaining motor units there are, the more consistent are the resulting MUNE values. Therefore, we conclude that MUNE values obtained with our methodology should represent the number of functional motor units in a muscle in a wide range of states, from normal to severe atrophy. Although the rate of decrease in MUNE values in the ALS patient group was highly variable, as shown in Fig. 3B and C, the mean MUNE values showed a steeper decrease at 12±18 months after onset than at 18±24 months after onset. Although we now use clinical rating scales (ACTS Group, 1996) for the clinical assessment of ALS patients in therapeutic trials, MUNE should have a major impact because such rating scales may not be sensitive enough to detect early changes in ALS (Yuen and Olney, 1997). Rating scales such as Appel scores show composite and average bodily changes in order to de®ne disability. Although a direct comparison between Appel scores and MUNE might seem irrational, changes in the rating scale result from a loss of motor neurons supplying the bulbar, truncal, and limb muscles in ALS patients. Accordingly, a MUNE of a single muscle may well be compared to the part of a scale that is functionally related to that particular muscle, and such a relationship between the MUNE values of a proximal muscle and their isometric strength has already been studied (Bromberg and Larson, 1996). As clinical rating scales in ALS patients re¯ect a loss of upper and lower motor neurons, such scales may theoretically be substituted for MUNE of all muscles in the regions being studied. This is technically impractical, but it is interesting to speculate on how many muscles should be tested to obtain a composite MUNE score that may be comparable to the rating scale. In the present study; we suggest that MUNE of the hypothenar and EDB muscles might be sucient for this purpose. Furthermore, the MUNE values were distributed hyperbolically against Appel scores in Fig. 3C, which means that the former seems more sensitive than the latter in detecting early changes in ALS. Thus, considering the importance of initiating therapeutic
257
intervention as early as possible in the course of ALS, the use of MUNE in the early assessment of a patient's condition may be a better parameter than clinical rating scales. Despite technical variability, MUNE values obtained using dierent methods show a close agreement in studies of normal subjects and patients with neurological disorders (Shefner, 2001). The occurrence of signi®cant changes in MUNE in the early stage of ALS has already been reported by previous authors (Brown and Jaatool, 1974; Dantes and McComas, 1991). In these reports, however, MUNE was performed by a manual incremental technique that is subject to technical pitfalls (McComas, 1998), whereas in the present study we used the microstimulation method, the validity of which has been proven by an animal study (Arasaki et al., 1997). Our present data, therefore, strengthen the reliability of the ®nding that changes in MUNE are more signi®cant than changes in rating scale in patients with early ALS.
References Appel, V., Stewart, S.S., Smith, G. and Appel, S.H. A rating scale for amyotrophic lateral sclerosis: description and preliminary experience. Ann. Neurol., 1987, 22: 328±333. Arasaki, K. and Tamaki, M. A loss of functional spinal alpha motor neurons in amyotrophic lateral sclerosis. Neurology, 1998, 51: 603±605.
Arasaki, K., Tamaki, M., Hosoya, Y. and Kudo, N. Validity of electromyograms and tension as a means of motor unit number estimation. Muscle Nerve, 1997, 20: 552±560. Arasaki, K, Kato, Y, Hyodo, A, Ushijima, R and Tamaki, M. Longitudinal study of functional spinal alpha motor neuron loss in amyotrophic lateral sclerosis. Muscle Nerve, 2002, 25: 520±526. Armon, C., Brandstater, M.E. and Peterson, G.W. Motor unit number estimates and quantitative muscle strength measurements of distal muscles in patients with amyotrophic lateral sclerosis. Muscle Nerve, 1997, 20: 499±501. Bromberg, M. and Larson, W.L. Relationship between motorunit number estimates and isometric strength in distal muscles in ALS/MND. J. Neurol. Sci., 1996, 139(Suppl.): 38±42. Brown, W.F. and Jaatool, N. Amyotrophic lateral sclerosis. Electrophysiological study. Arch. Neurol., 1974, 31: 242±248. Dantes, M. and McComas, A. The extent and time course of motoneuron involvement in amyotrophic lateral sclerosis. Muscle Nerve, 1991, 14: 416±421. McComas, A.J. Motor units: how many, how large, what kind? J. Electromyogr. Kinesiol., 1998, 8: 391±402. Olney, R.K., Yen, E.C. and Engstrom, J.W. The rate of changes in motor unit number estimates predicts survival in patients with amyotrophic lateral sclerosis. Neurology, 1999, 52 (Suppl. 2): A3. Shefner, J.M. Motor unit number estimation in human neurological diseases and animal models. Clin. Neurophysiol., 2001, 112: 955±964. The ALS CNTF treatment study (ACTS) phase 1-II Study Group. The amyotrophic lateral sclerosis functional rating scale. Arch. Neurol., 1996, 53: 141±147. World Federation of Neurology Research Group on Neuromuscular Diseases. El Escorial World Federation of Neurology criteria for the diagnosis of amyotrophic lateral sclerosis. J. Neurol. Sci., 1994, 124: 96±107. Yuen, E.C. and Olney, R.K. Longitudinal study of fiber density and motor unit number estimate in patients with amyotrophic lateral sclerosis. Neurology, 1997, 49: 573±578.