- Email: [email protected]
A comparison of concentric needle electromyography, quantitative EMG and single fibre EMG in the diagnosis of neuromuscular diseases
Electroencephalography and clinical Neurophysiology, 1984, 58:220-225 Elsevier Scientific Publishers Ireland, Ltd.
220
A C O M P A R I S O N O F C O N C E N T R I C N E E D L E E L E C T R O M Y O G R A P H Y , QUANTITATIVE E M G A N D S I N G L E F I B R E E M G IN T H E D I A G N O S I S O F N E U R O M U S C U L A R D I S E A S E S i Y.L. YU 2 and N.M.F. MURRAY
3
Department of Clinical Neurophysiology, The National Hospital, Queen Square, London WCIN 3BG (England) (Accepted for publication: May 17, 1984)
Concentric needle electromyography (CNEMG) is limited by lack of sensitivity and specificity in mild or early cases of neuromuscular disease and by difficulty in objective evaluation and documentation. An early method of quantifying findings was the examination of twenty or more motor unit potentials elicited by weak effort and the measurement of various parameters including duration, number of phases and amplitude (Kugelberg 1949; Pinelli and Buchthal 1953). This method increases the diagnostic yield of C N E M G and provides numerical data necessary for progress studies but is time consuming. Another approach to quantifying the E M G is assessment of the interference pattern. Willison's method of quantitative E M G (Quant-EMG) measures the potential direction changes or turns and the amplitudes of potential changes between turns (Willison 1964). Different sites in the muscle are sampled with a concentric needle during a constant load. Analysis was initially by a mechanical counting system but has been greatly simplified by development of an electronic analyser. Characteristically there is elevation in the mean turns count in primary muscle disease whereas evaluation of the mean amplitude occurs in chronic partial denervation (Hayward and Willison 1973, 1977). Reproducible data are available for follow-up purposes. Various modifications such as fractional load
1 Read in part at the 5th International Congress on Neuromuscular Diseases, Marseilles, September 1982. 2 Present address: University Medical Unit, Tung Wah Hospital, 12 Po Yan Street, Hong Kong. 3 Address for correspondence: Dr. N.M.F. Murray, The National Hospital, Queen Square, London WC1N 3BG, England.
(Fuglsang-Frederiksen et al. 1976) and the ratio of turns to average amplitude (Haridasan et al. 1980) have been shown to increase sensitivity without undue increase in technical complexity but the requirement for a constant load is a drawback of all these techniques of interference pattern analysis. Single fibre electromyography (SFEMG) (St~lberg and Trontelj 1977) uses a needle with a small recording surface (25/tm) and a high-pass filter of 500 Hz to record single muscle fibre action potentials within 300/~m of the recording surface. Various parameters affected by diseases of the motor unit can be measured and quantified, including jitter, fibre density (FD) and mean interspike interval (MISI). The jitter is calculated as the mean of consecutive interpotential differences and in the normal muscle it mainly reflects variability in transmission time at the neuromuscular junction but can also be affected by conduction along reinnervating nerve fibres and diseased muscle fibres. Fibre density is the mean number of muscle fibres belonging to the same motor unit in each of at least 20 recording sites. It is typically increased in neurogenic conditions due to reinnervation but may also increase in myopathy due to fibre splitting, fibre shrinkage or regeneration after necrosis of the muscle fibre (Sthlberg et al. 1975; Sthlberg 1977). Patients were selected for the study who had neuromuscular disorders which were likely sooner or later to become generalised and thus to produce abnormalities in the right biceps, whether or not this muscle was clinically affected at the time of the study. The aim was to examine the relative contribution of routine concentric needle EMG,
0013-4649/84/$03.00 © 1984 Elsevier Scientific Publishers Ireland, Ltd.
COMPARISON OF EMG TECHNIQUES
221
C N E M G was performed on the biceps and other muscles. Spontaneous activity, motor unit size and configuration, and the density and amplitude of the interference pattern on maximum voluntary contraction were recorded. Formal measurement of 20 individual motor unit potentials was not performed. An APA6 analyser was used for Quant-EMG; 16 sites were examined under a 2 kg load for 5 sec runs. Recording techniques were as described by Hayward (1977) as were the control values (mean amplitude 0.35 mV, S.D. 0.07, mean turns count 371/sec, S.D. 89). SFEMG was performed with a Medelec SF-25 electrode; 20 sites in the biceps were examined. Fibre density and MISI were calculated as described by StMberg and Trontelj (1977) and the presence of abnormal jitter or component blocking was noted in the 20 sites studied. Normal age-related values for fibre density in biceps were provided by Professor StMberg (personal communication).
intereference pattern analysis by Willison's method and S F E M G in neurogenic and myopathic disorders. We were interested in both the rate of abnormality detection by the 3 techniques and whether the abnormalities demonstrated were of help in differentiating a neurogenic process from primary muscle disease. Heterogeneity of cases was not considered a disadvantage since the purpose was not to identify changes specific to a particular neuromuscular disease.
Patients and Methods
The 3 techniques, viz. CNEMG, Quant-EMG and SFEMG, were performed in 10 patients with anterior horn cell disease (motor neurone disease, MND, 8, spinal muscular atrophy, SMA, 2) and 20 patients with primary muscle disease (polymyositis 11, muscular dystrophy 5, mitochondrial myopathy 3, acid maltase deficiency 1). Diagnoses were firmly established on clinical grounds including follow-up of subsequent developments and other relevant investigations including muscle biopsy for those with myopathic disorders. The right biceps muscle was used for comparison of the techniques and was graded clinically according to the Medical Research Council (MRC) scale.
Results
Neurogenic disorders Clinical and electromyographic data are summarised in Table I. In all 10 cases routine C N E M G was abnormal in biceps and adequate for the
TABLE I Clinical a n d e l e c t r o m y o g r a p h i c d a t a in p a t i e n t s with a n t e r i o r h o r n cell diseases. Case
Disease
Age
Duration
Biceps s t r e n g t h
CNEMG
(years)
(months)
( M R C grade)
SA
Units
IP
Quant-EMG Turns/sec
SFEMG A m p (mV)
FD
MISI
Jitter
1
MND
67
24
4
+
+
+
(324)
0.57
2.65
(0.70)
+
2 3
MND MND
69 45
12 3
5 4
+ +
+
+
(372) (303)
(0.48) 0.62
2.20 2.65
(0.75) 0.94
+ + B
4 5 6
MND MND MND
66 49 61
7 3 7
4 4 5
+ + +
+ -
-
(454) (363) (491)
(0.42) (0.34) 0.52
1.85 2.00 1.85
0.99 0.85 (0.58)
+ + B +
7 8 9 10
MND MND SMA SMA
66 52 42 20
30 60 72 108
4 5 4 5 Individual abnormality Overall abnormality
+ -
+ + + +
+ + +
(508) 614 (374) (304)
0.67 0.53 0.87 0.94
2.75 1.80 2.36 1.95
0.97 1.0 1.28 1.39
+ B + +
7
7
5
'
~ 10
1 / ~
7 " - - ~ 7
10 ~
7 " 10
9
SA = s p o n t a n e o u s activity; I P = i n t e r f e r e n c e p a t t e r n ; F D = fibre density; M I S I = m e a n i n t e r s p i k e interval; B = blocking p h e n o m e n o n ; M N D = m o t o r n e u r o n e disease; S M A = spinal m u s c u l a r a t r o p h y ; + = a b n o r m a l ; - a n d ( ) = n o r m a l .
Y.L. Y U , N.M.F. M U R R A Y
222
T A B L E II C l i n i c a l a n d e l e c t r o m y o g r a p h i c d a t a in p a t i e n t s with p o l y m y o s i t i s . Case
Age (years)
Duration
Biceps s t r e n g t h ( M R C grade)
CNEMG
1 2 3 4 5 6 7 8 9 10 11
55 33 77 47 50 30 55 69 72 34 65
3m 6 m 6 m 4 m 18 m 18 m 6.5 y 6y 25 y 4y 35 y
4 5 4 4 4 4 4 4 4 4 4 Individual abnormality Overall abnormality
+ + + + + + + + +
+ = abnormal; - and (
Quant-EMG
SFEMG
Turns/sec
A m p (mV)
FD
MISI
Jitter
606 (503) 880 (472) 696 857 945 554 1002 567 719
(0.32) (0.22) (0.39) (0.38) (0.46) (0.34) (0.49) (0.40) 0.64 (0.38) (0.47)
1.75 (1.40) 2.45 1.70 1.75 1.85 2.40 (1.75) 1.75 1.95 (1.75)
(0.77) 1.72 1.36 1.04 1.36 2.74 1.06 (0.56) 0.85 0.87 (0.77)
+ + + + + + + + +
9
9
1
8
x.
/
8
;
9
9
~,
lO
) = normal.
individual units or the interference pattern was noted. Quant-EMG showed increased mean amplitudes in 7 subjects, highest in the 2 patients with spinal muscular atrophy of more than 5 years duration. Case 8 was the only one in whom the mean turns count was increased. Fibre density was
diagnosis of a neurogenic process in 9. In case 8 the only abnormality was a non-specific increase in polyphasic units but sampling of other muscles revealed clear evidence of chronic partial denervation. In 3 cases (2, 4 and 6) fibrillation and fasciculations were seen but no definite abnormality of T A B L E III
C l i n i c a l a n d e l e c t r o m y o g r a p h i c d a t a in p a t i e n t s w i t h n o n - i n f l a m m a t o r y muscle disease. Case
1 2 3
5 6 7 8 9
Disease
Scapulo-peroneal dystrophy Limb-girdle dystrophy Becker dystrophy FSH FSH CPEO CPEO CPEO Acid-maltase deficiency
Age
Duration
Biceps s t r e n g t h
(years)
(years)
( M R C grade)
+ = abnormal;
-
and (
Quant-EMG Turns/sec
SFEMG A m p (mV)
FD
MISI
Jitter
56
2
4
+
568
(0.48)
1.74
0.93
+
36
1.5
4
+
947
0.56
(1.50)
2.42
+
4 5 4 4 5 4 4
+ + +
682 (438) 555 643 580 654 726
0.56 0.50 0.73 (0.41) (0.42) (0.44) (0.47)
1.79 1.55 2.15 1.60 (1.35) 1.65 1.75
2.06 0.62 1.00 (0.64) (0.77) 0.80 (0.65)
+ + + -
23 25 24 22 58 58 56
20 20 9 12 5 12 5
Individual abnormality Overall abnormality
moplegia.
CNEMG
)= normal;
-
+ --
6
8 ~
6
FSH = facioscapulohumeral dystrophy;
4 -,~ 9
7 ~
~
6 -' 8
C P E O = chronic progressive e x t e r n a l o p h t h a i -
COMPARISON
223
OF EMG TECHNIQUES
increased in all subjects, with abnormal jitter in 9 and intermittent component blocking in 3.
Myopathic disorders The findings in cases of polymyositis and noninflammatory muscle disease are summarised in Tables II and III respectively. Conventional C N E M G was typical of a myopathy in 9 out of 11 patients with polymyositis, and fibrillations suggesting an active inflammatory process were present in the 6 cases of acute polymyositis. There were minor non-specific abnormalities in two cases of chronic polymyositis (8 and 11). An abnormal turns count was recorded in 9 cases, in one of whom the mean amplitude was increased. At least one S F E M G parameter was abnormal in 10 cases and often all three. Five patients with muscular dystrophy all had a myopathic C N E M G and abnormal interference pattern analysis and SFEMG, whereas turns counts and S F E M G were more sensitive indices of abnormality than routine C N E M G in the cases of chronic progressive external ophthalmoplegia and acid maltase deficiency. Three of the dystrophy patients were found to have raised mean amplitude and turns counts on Q u a n t - E M G ; examination of the intereference pattern during C N E M G revealed brief spikes of large amplitude, up to 10 mV in case 3 and 8 mV in case 5, though the great majority of components were of normal or small amplitude.
Discussion
In this study 3 different electromyographic techniques were used to examine the right biceps muscle, irrespective of whether the biceps was clinically abnormal. We found that analysis of the interference pattern by Willison's technique and examination of neuromuscular transmission and local concentration of fibres by S F E M G were only slightly more sensitive than routine C N E M G in detecting abnormality. Overall, diagnostically helpful changes were detected by C N E M G in 24 of the 30 subjects with non-specific abnormalities in 3 others, whereas Q u a n t - E M G was abnormal in 25 and S F E M G in 28. The muscle examined was clinically normal in only 7 of the patients in this series though this does not take into account the possibility of weak-
T A B L E IV S u m m a r y of E M G findings in p a t i e n t s with clinically n o r m a l biceps. Disease
CNEMG
Quant-EMG
SFEMG
MND
+ (SA only)
-
+
MND MND
+ (SA only) + (NS)
+ +
+ +
SMA
+
+
+
Polymyositis FSH
+ +
+
+ +
CPEO
-
+
-
Total abnormal
6
5
6
+ = a b n o r m a l ; - = n o r m a l ; SA = s p o n t a n e o u s activity; N S = non-specific a b n o r m a l i t y .
ness in M N D cases being of upper motor neurone origin. Of the 7, the routine E M G was abnormal in 6, Q u a n t - E M G in 5 and S F E M G in 6 (Table IV). A study comparing frequency of abnormality detection in clinically unaffected muscles by these techniques in a larger number of subjects would be of interest and ideally would include more detailed measurement of individual motor units with a concentric needle electrode. Both Willison's technique and S F E M G provide information about the pathophysiology of the disease process as it affects the motor units. In anterior horn cell disease increase in mean amplitude and in fibre density reflect increase in the density of muscle fibres in the motor unit due to reinnervation. In this study Q u a n t - E M G findings were comparable to those previously reported whereas fibre density values though abnormal were consistently lower than those found by others in anterior horn cell disease (St~lberg et al. 1975; Schwartz and Swash 1982). The reasons for this disparity are not apparent as the same techniques and criteria were employed and patients had comparable biceps strength, illness duration and ages. Nevertheless similar trends are seen. In cases with rapid progression of M N D fibre density tends to be less elevated as reinnervation is overshadowed by progressive denervation. Jitter and component blocking tend to be more prominent in these cases, where S F E M G provides information on prognosis as well as diagnosis. In the patients with primary muscle disease there was little difference between Q u a n t - E M G and S F E M G in the rate of detection of abnormality. However, increase in the turns count, docu-
224 menting as it does the characteristic recruitment pattern of myopathy was of more help in diagnosis than the equally frequent but less specific S F E M G abnormalities. Quant-EMG findings typical of myopathy were present in 2 cases where routine C N E M G showed a non-specific abnormality. S F E M G findings in this study are in general agreement with previous reports (StMberg 1977; Sthlberg and Trontelj 1977; Henriksson and StMberg 1978), but we found that S F E M G was often technically difficult in myopathy where weak contraction can be accompanied by much recruitment. In contrast Quant-EMG was easy to perform even with limited patient cooperation. Four patients with myopathy showed the unusual Quant-EMG finding of increased mean amplitude as well as increased turns count. While it has been noted that reduction in amplitude is less specific than increase in turns count (FuglsangFrederiksen et al. 1976), raised amplitude has not previously been emphasised in myopathy. Large amplitude potentials of up to 10 mV with brief rise times (0.2 msec) consistent with single muscle fibre spikes were seen on concentric needle electromyography as well as S F E M G and in these patients muscle biopsy demonstrated some grossly hypertrophied fibres, up to 200 #m. These findings suggest that the brief large amplitude potentials and increased mean amplitude sometimes found in myopathy are from hypertrophied fibres rather than from reinnervation or from closely packed fibres that have arisen from splitting of a large fibre. Such fibres would provide sources of current large relative to the recording area. Each of the 3 electromyographic methods examined in this study has its own place in the assessment of neuromuscular disorders. C N E M G has the advantages of convenience and rapidity of performance and, particularly when the presence of spontaneous activity is taken into account, it loses little in terms of diagnostic yield to the other techniques. Quantitative analysis of the interference pattern using a constant load provides numerical data invaluable for assessment of response to treatment or progression of a disorder and is particularly helpful in primary muscle disease. S F E M G is a highly sensitive technique which may provide the earliest evidence of disease affecting the motor unit and in certain cases the stability of components is of value in estimating prognosis.
Y.L. YU, N.M.F. MURRAY Summary Conventional concentric needle electromyography, quantitative electromyography using automatic analysis (Quant-EMG) and single fibre electromyography (SFEMG) were compared in the right biceps muscle of 10 patients with anterior horn cell disease and 20 patients with primary muscle disease. Abnormalities were demonstrable by all 3 techniques in the majority of cases irrespective of whether the biceps was weak. SFEMG was found to be more sensitive than Quant-EMG in neurogenic cases and it also provided an indication of disease activity. In cases of myopathy Quant-EMG was of more diagnostic help and was easier to perform than SFEMG. Large amplitude potentials found in some cases of myopathy were associated with increase in the mean amplitude on Quant-EMG and these probably emanate from hypertrophied muscle fibres.
R6sum6
Comparaison entre blectromyographie avec blectrode concentrique, E M G quantitatif et E M G de fibre unitaire duns le diagnostic des maladies neuromusculaires
L'61ectromyographie conventionnelle h 61ectrode concentrique, l'61ectromyographie quantitative utilisant une m6thode d'analyse automatique (EMG-Quant) et l'dectromyographie de la fibre isol6e (EMGFI) ont 6t6 compar6es duns le biceps droit de 10 patients pr6sentant un trouble des neurones des comes ant6rieures et 20 patients pr6sentant un d6sordre primaire des muscles. Dans la majorit6 des cas, et ind6pendamment du fait que le muscle soit faible ou non, des anomalies furent d6montr6es par les 3 techniques utilis6es. Dans les cas neurog6nes, I'EMGFI a 6t6 plus efficace que l'EMG-Quant e t a 6galement donn6 une indication sur l'activit6 de la maladie. Duns les cas de myopathie, l'EMG-Quant a avantag6 le diagnostic et fut plus facile h r6aliser que I'EMGFI. Des potentiels de grandes amplitudes trouv6s dans certains cas de myopathie furent associ6s avec une augmentation de l'amplitude moyenne du EMGQuant, ceux-ci provenant probablement des fibres musculaires hypertrophiques.
COMPARISON OF EMG TECHNIQUES We wish to thank Professor E. Sthlberg for providing us with fibre density values in control subjects and Dr. R.G. Willison for helpful discussion. We also thank Miss Alison Polglase for preparing the manuscript.
References Fuglsang-Frederiksen, A., Scheel, U. and Buchthal, F. Diagnostic yield of analysis of the pattern of electrical activity and of individual motor unit potentials in myopathy. J. Neurol. Neurosurg. Psychiat., 1976, 39: 742-750. Haridasan, G., Sanghivi, S.H., Joshi, V.M., Pandya, S.S. and Desai, A.D. Quantitative electromyography using automatic analysis, J. neurol. Sci., 1980, 48: 353-365. Hayward, M. Automatic analysis of the electromyogram in healthy subjects of different ages. J. neurol., Sci., 1977, 33: 397-413. Hayward, M. and Willison, R.G. The recognition of myogenic and neurogenic lesions by quantitative EMG. In: J.E. Desmedt (Ed.), New Developments in Electromyography and Clinical Neurophysiology, Vol. 2. Karger, Basel, 1973: 448-453. Hayward, M. and Willison, R.G. Automatic analysis of the electromyogram in patients with chronic partial denervation. J. neurol. Sci., 1977, 33: 415-423.
225 Henriksson, K.G. and St/dberg, E. The terminal innervation pattern in polymyositis: a histochemical and SFEMG study. Muscle Nerve, 1978, 1: 3-13. Kugelberg, E. Electromyography in muscular dystrophies and chronic lower motor neurone lesions. J. Neurol. Neurosurg. Psychiat., 1949, 12: 129-136. Pinelli, P. and Buchthal, F. Muscle action potentials in myopathies with special regard to progressive muscular dystrophy. Neurology (Minneap.), 1953, 3: 347-359. Schwartz, M.S. and Swash, M. Pattern of involvement in the early stages of motor neurone disease: a single fibre EMG study. Acta neurol, scand., 1982, 65: 424-431. Sthlberg, E. Electrogenesis in human muscular dystrophy. In: L.P. Rowland (Ed.), Pathogenesis of Human Muscular Dystrophies. Proc. 5th Int. Conf. of the Muscular Dystrophy Ass. Excerpta Medica, Amsterdam, 1977: 560-587. Sthlberg, E. and Trontelj, J.V. Single Fibre Electromyography. Miravelle Press, Old Woking, 1977. Sthlberg, E., Schwarz, M.S. and Trontelj, J.V. Single fibre electromyography in various processes affecting the anterior horn cell. J. neurol. Sci., 1975, 24: 403-415. Willison, R.G. Analysis of electrical activity in healthy and dystrophic muscle in man. J. Neurol. Neurosurg. Psychiat., 1964, 27: 386-394.
220
A C O M P A R I S O N O F C O N C E N T R I C N E E D L E E L E C T R O M Y O G R A P H Y , QUANTITATIVE E M G A N D S I N G L E F I B R E E M G IN T H E D I A G N O S I S O F N E U R O M U S C U L A R D I S E A S E S i Y.L. YU 2 and N.M.F. MURRAY
3
Department of Clinical Neurophysiology, The National Hospital, Queen Square, London WCIN 3BG (England) (Accepted for publication: May 17, 1984)
Concentric needle electromyography (CNEMG) is limited by lack of sensitivity and specificity in mild or early cases of neuromuscular disease and by difficulty in objective evaluation and documentation. An early method of quantifying findings was the examination of twenty or more motor unit potentials elicited by weak effort and the measurement of various parameters including duration, number of phases and amplitude (Kugelberg 1949; Pinelli and Buchthal 1953). This method increases the diagnostic yield of C N E M G and provides numerical data necessary for progress studies but is time consuming. Another approach to quantifying the E M G is assessment of the interference pattern. Willison's method of quantitative E M G (Quant-EMG) measures the potential direction changes or turns and the amplitudes of potential changes between turns (Willison 1964). Different sites in the muscle are sampled with a concentric needle during a constant load. Analysis was initially by a mechanical counting system but has been greatly simplified by development of an electronic analyser. Characteristically there is elevation in the mean turns count in primary muscle disease whereas evaluation of the mean amplitude occurs in chronic partial denervation (Hayward and Willison 1973, 1977). Reproducible data are available for follow-up purposes. Various modifications such as fractional load
1 Read in part at the 5th International Congress on Neuromuscular Diseases, Marseilles, September 1982. 2 Present address: University Medical Unit, Tung Wah Hospital, 12 Po Yan Street, Hong Kong. 3 Address for correspondence: Dr. N.M.F. Murray, The National Hospital, Queen Square, London WC1N 3BG, England.
(Fuglsang-Frederiksen et al. 1976) and the ratio of turns to average amplitude (Haridasan et al. 1980) have been shown to increase sensitivity without undue increase in technical complexity but the requirement for a constant load is a drawback of all these techniques of interference pattern analysis. Single fibre electromyography (SFEMG) (St~lberg and Trontelj 1977) uses a needle with a small recording surface (25/tm) and a high-pass filter of 500 Hz to record single muscle fibre action potentials within 300/~m of the recording surface. Various parameters affected by diseases of the motor unit can be measured and quantified, including jitter, fibre density (FD) and mean interspike interval (MISI). The jitter is calculated as the mean of consecutive interpotential differences and in the normal muscle it mainly reflects variability in transmission time at the neuromuscular junction but can also be affected by conduction along reinnervating nerve fibres and diseased muscle fibres. Fibre density is the mean number of muscle fibres belonging to the same motor unit in each of at least 20 recording sites. It is typically increased in neurogenic conditions due to reinnervation but may also increase in myopathy due to fibre splitting, fibre shrinkage or regeneration after necrosis of the muscle fibre (Sthlberg et al. 1975; Sthlberg 1977). Patients were selected for the study who had neuromuscular disorders which were likely sooner or later to become generalised and thus to produce abnormalities in the right biceps, whether or not this muscle was clinically affected at the time of the study. The aim was to examine the relative contribution of routine concentric needle EMG,
0013-4649/84/$03.00 © 1984 Elsevier Scientific Publishers Ireland, Ltd.
COMPARISON OF EMG TECHNIQUES
221
C N E M G was performed on the biceps and other muscles. Spontaneous activity, motor unit size and configuration, and the density and amplitude of the interference pattern on maximum voluntary contraction were recorded. Formal measurement of 20 individual motor unit potentials was not performed. An APA6 analyser was used for Quant-EMG; 16 sites were examined under a 2 kg load for 5 sec runs. Recording techniques were as described by Hayward (1977) as were the control values (mean amplitude 0.35 mV, S.D. 0.07, mean turns count 371/sec, S.D. 89). SFEMG was performed with a Medelec SF-25 electrode; 20 sites in the biceps were examined. Fibre density and MISI were calculated as described by StMberg and Trontelj (1977) and the presence of abnormal jitter or component blocking was noted in the 20 sites studied. Normal age-related values for fibre density in biceps were provided by Professor StMberg (personal communication).
intereference pattern analysis by Willison's method and S F E M G in neurogenic and myopathic disorders. We were interested in both the rate of abnormality detection by the 3 techniques and whether the abnormalities demonstrated were of help in differentiating a neurogenic process from primary muscle disease. Heterogeneity of cases was not considered a disadvantage since the purpose was not to identify changes specific to a particular neuromuscular disease.
Patients and Methods
The 3 techniques, viz. CNEMG, Quant-EMG and SFEMG, were performed in 10 patients with anterior horn cell disease (motor neurone disease, MND, 8, spinal muscular atrophy, SMA, 2) and 20 patients with primary muscle disease (polymyositis 11, muscular dystrophy 5, mitochondrial myopathy 3, acid maltase deficiency 1). Diagnoses were firmly established on clinical grounds including follow-up of subsequent developments and other relevant investigations including muscle biopsy for those with myopathic disorders. The right biceps muscle was used for comparison of the techniques and was graded clinically according to the Medical Research Council (MRC) scale.
Results
Neurogenic disorders Clinical and electromyographic data are summarised in Table I. In all 10 cases routine C N E M G was abnormal in biceps and adequate for the
TABLE I Clinical a n d e l e c t r o m y o g r a p h i c d a t a in p a t i e n t s with a n t e r i o r h o r n cell diseases. Case
Disease
Age
Duration
Biceps s t r e n g t h
CNEMG
(years)
(months)
( M R C grade)
SA
Units
IP
Quant-EMG Turns/sec
SFEMG A m p (mV)
FD
MISI
Jitter
1
MND
67
24
4
+
+
+
(324)
0.57
2.65
(0.70)
+
2 3
MND MND
69 45
12 3
5 4
+ +
+
+
(372) (303)
(0.48) 0.62
2.20 2.65
(0.75) 0.94
+ + B
4 5 6
MND MND MND
66 49 61
7 3 7
4 4 5
+ + +
+ -
-
(454) (363) (491)
(0.42) (0.34) 0.52
1.85 2.00 1.85
0.99 0.85 (0.58)
+ + B +
7 8 9 10
MND MND SMA SMA
66 52 42 20
30 60 72 108
4 5 4 5 Individual abnormality Overall abnormality
+ -
+ + + +
+ + +
(508) 614 (374) (304)
0.67 0.53 0.87 0.94
2.75 1.80 2.36 1.95
0.97 1.0 1.28 1.39
+ B + +
7
7
5
'
~ 10
1 / ~
7 " - - ~ 7
10 ~
7 " 10
9
SA = s p o n t a n e o u s activity; I P = i n t e r f e r e n c e p a t t e r n ; F D = fibre density; M I S I = m e a n i n t e r s p i k e interval; B = blocking p h e n o m e n o n ; M N D = m o t o r n e u r o n e disease; S M A = spinal m u s c u l a r a t r o p h y ; + = a b n o r m a l ; - a n d ( ) = n o r m a l .
Y.L. Y U , N.M.F. M U R R A Y
222
T A B L E II C l i n i c a l a n d e l e c t r o m y o g r a p h i c d a t a in p a t i e n t s with p o l y m y o s i t i s . Case
Age (years)
Duration
Biceps s t r e n g t h ( M R C grade)
CNEMG
1 2 3 4 5 6 7 8 9 10 11
55 33 77 47 50 30 55 69 72 34 65
3m 6 m 6 m 4 m 18 m 18 m 6.5 y 6y 25 y 4y 35 y
4 5 4 4 4 4 4 4 4 4 4 Individual abnormality Overall abnormality
+ + + + + + + + +
+ = abnormal; - and (
Quant-EMG
SFEMG
Turns/sec
A m p (mV)
FD
MISI
Jitter
606 (503) 880 (472) 696 857 945 554 1002 567 719
(0.32) (0.22) (0.39) (0.38) (0.46) (0.34) (0.49) (0.40) 0.64 (0.38) (0.47)
1.75 (1.40) 2.45 1.70 1.75 1.85 2.40 (1.75) 1.75 1.95 (1.75)
(0.77) 1.72 1.36 1.04 1.36 2.74 1.06 (0.56) 0.85 0.87 (0.77)
+ + + + + + + + +
9
9
1
8
x.
/
8
;
9
9
~,
lO
) = normal.
individual units or the interference pattern was noted. Quant-EMG showed increased mean amplitudes in 7 subjects, highest in the 2 patients with spinal muscular atrophy of more than 5 years duration. Case 8 was the only one in whom the mean turns count was increased. Fibre density was
diagnosis of a neurogenic process in 9. In case 8 the only abnormality was a non-specific increase in polyphasic units but sampling of other muscles revealed clear evidence of chronic partial denervation. In 3 cases (2, 4 and 6) fibrillation and fasciculations were seen but no definite abnormality of T A B L E III
C l i n i c a l a n d e l e c t r o m y o g r a p h i c d a t a in p a t i e n t s w i t h n o n - i n f l a m m a t o r y muscle disease. Case
1 2 3
5 6 7 8 9
Disease
Scapulo-peroneal dystrophy Limb-girdle dystrophy Becker dystrophy FSH FSH CPEO CPEO CPEO Acid-maltase deficiency
Age
Duration
Biceps s t r e n g t h
(years)
(years)
( M R C grade)
+ = abnormal;
-
and (
Quant-EMG Turns/sec
SFEMG A m p (mV)
FD
MISI
Jitter
56
2
4
+
568
(0.48)
1.74
0.93
+
36
1.5
4
+
947
0.56
(1.50)
2.42
+
4 5 4 4 5 4 4
+ + +
682 (438) 555 643 580 654 726
0.56 0.50 0.73 (0.41) (0.42) (0.44) (0.47)
1.79 1.55 2.15 1.60 (1.35) 1.65 1.75
2.06 0.62 1.00 (0.64) (0.77) 0.80 (0.65)
+ + + -
23 25 24 22 58 58 56
20 20 9 12 5 12 5
Individual abnormality Overall abnormality
moplegia.
CNEMG
)= normal;
-
+ --
6
8 ~
6
FSH = facioscapulohumeral dystrophy;
4 -,~ 9
7 ~
~
6 -' 8
C P E O = chronic progressive e x t e r n a l o p h t h a i -
COMPARISON
223
OF EMG TECHNIQUES
increased in all subjects, with abnormal jitter in 9 and intermittent component blocking in 3.
Myopathic disorders The findings in cases of polymyositis and noninflammatory muscle disease are summarised in Tables II and III respectively. Conventional C N E M G was typical of a myopathy in 9 out of 11 patients with polymyositis, and fibrillations suggesting an active inflammatory process were present in the 6 cases of acute polymyositis. There were minor non-specific abnormalities in two cases of chronic polymyositis (8 and 11). An abnormal turns count was recorded in 9 cases, in one of whom the mean amplitude was increased. At least one S F E M G parameter was abnormal in 10 cases and often all three. Five patients with muscular dystrophy all had a myopathic C N E M G and abnormal interference pattern analysis and SFEMG, whereas turns counts and S F E M G were more sensitive indices of abnormality than routine C N E M G in the cases of chronic progressive external ophthalmoplegia and acid maltase deficiency. Three of the dystrophy patients were found to have raised mean amplitude and turns counts on Q u a n t - E M G ; examination of the intereference pattern during C N E M G revealed brief spikes of large amplitude, up to 10 mV in case 3 and 8 mV in case 5, though the great majority of components were of normal or small amplitude.
Discussion
In this study 3 different electromyographic techniques were used to examine the right biceps muscle, irrespective of whether the biceps was clinically abnormal. We found that analysis of the interference pattern by Willison's technique and examination of neuromuscular transmission and local concentration of fibres by S F E M G were only slightly more sensitive than routine C N E M G in detecting abnormality. Overall, diagnostically helpful changes were detected by C N E M G in 24 of the 30 subjects with non-specific abnormalities in 3 others, whereas Q u a n t - E M G was abnormal in 25 and S F E M G in 28. The muscle examined was clinically normal in only 7 of the patients in this series though this does not take into account the possibility of weak-
T A B L E IV S u m m a r y of E M G findings in p a t i e n t s with clinically n o r m a l biceps. Disease
CNEMG
Quant-EMG
SFEMG
MND
+ (SA only)
-
+
MND MND
+ (SA only) + (NS)
+ +
+ +
SMA
+
+
+
Polymyositis FSH
+ +
+
+ +
CPEO
-
+
-
Total abnormal
6
5
6
+ = a b n o r m a l ; - = n o r m a l ; SA = s p o n t a n e o u s activity; N S = non-specific a b n o r m a l i t y .
ness in M N D cases being of upper motor neurone origin. Of the 7, the routine E M G was abnormal in 6, Q u a n t - E M G in 5 and S F E M G in 6 (Table IV). A study comparing frequency of abnormality detection in clinically unaffected muscles by these techniques in a larger number of subjects would be of interest and ideally would include more detailed measurement of individual motor units with a concentric needle electrode. Both Willison's technique and S F E M G provide information about the pathophysiology of the disease process as it affects the motor units. In anterior horn cell disease increase in mean amplitude and in fibre density reflect increase in the density of muscle fibres in the motor unit due to reinnervation. In this study Q u a n t - E M G findings were comparable to those previously reported whereas fibre density values though abnormal were consistently lower than those found by others in anterior horn cell disease (St~lberg et al. 1975; Schwartz and Swash 1982). The reasons for this disparity are not apparent as the same techniques and criteria were employed and patients had comparable biceps strength, illness duration and ages. Nevertheless similar trends are seen. In cases with rapid progression of M N D fibre density tends to be less elevated as reinnervation is overshadowed by progressive denervation. Jitter and component blocking tend to be more prominent in these cases, where S F E M G provides information on prognosis as well as diagnosis. In the patients with primary muscle disease there was little difference between Q u a n t - E M G and S F E M G in the rate of detection of abnormality. However, increase in the turns count, docu-
224 menting as it does the characteristic recruitment pattern of myopathy was of more help in diagnosis than the equally frequent but less specific S F E M G abnormalities. Quant-EMG findings typical of myopathy were present in 2 cases where routine C N E M G showed a non-specific abnormality. S F E M G findings in this study are in general agreement with previous reports (StMberg 1977; Sthlberg and Trontelj 1977; Henriksson and StMberg 1978), but we found that S F E M G was often technically difficult in myopathy where weak contraction can be accompanied by much recruitment. In contrast Quant-EMG was easy to perform even with limited patient cooperation. Four patients with myopathy showed the unusual Quant-EMG finding of increased mean amplitude as well as increased turns count. While it has been noted that reduction in amplitude is less specific than increase in turns count (FuglsangFrederiksen et al. 1976), raised amplitude has not previously been emphasised in myopathy. Large amplitude potentials of up to 10 mV with brief rise times (0.2 msec) consistent with single muscle fibre spikes were seen on concentric needle electromyography as well as S F E M G and in these patients muscle biopsy demonstrated some grossly hypertrophied fibres, up to 200 #m. These findings suggest that the brief large amplitude potentials and increased mean amplitude sometimes found in myopathy are from hypertrophied fibres rather than from reinnervation or from closely packed fibres that have arisen from splitting of a large fibre. Such fibres would provide sources of current large relative to the recording area. Each of the 3 electromyographic methods examined in this study has its own place in the assessment of neuromuscular disorders. C N E M G has the advantages of convenience and rapidity of performance and, particularly when the presence of spontaneous activity is taken into account, it loses little in terms of diagnostic yield to the other techniques. Quantitative analysis of the interference pattern using a constant load provides numerical data invaluable for assessment of response to treatment or progression of a disorder and is particularly helpful in primary muscle disease. S F E M G is a highly sensitive technique which may provide the earliest evidence of disease affecting the motor unit and in certain cases the stability of components is of value in estimating prognosis.
Y.L. YU, N.M.F. MURRAY Summary Conventional concentric needle electromyography, quantitative electromyography using automatic analysis (Quant-EMG) and single fibre electromyography (SFEMG) were compared in the right biceps muscle of 10 patients with anterior horn cell disease and 20 patients with primary muscle disease. Abnormalities were demonstrable by all 3 techniques in the majority of cases irrespective of whether the biceps was weak. SFEMG was found to be more sensitive than Quant-EMG in neurogenic cases and it also provided an indication of disease activity. In cases of myopathy Quant-EMG was of more diagnostic help and was easier to perform than SFEMG. Large amplitude potentials found in some cases of myopathy were associated with increase in the mean amplitude on Quant-EMG and these probably emanate from hypertrophied muscle fibres.
R6sum6
Comparaison entre blectromyographie avec blectrode concentrique, E M G quantitatif et E M G de fibre unitaire duns le diagnostic des maladies neuromusculaires
L'61ectromyographie conventionnelle h 61ectrode concentrique, l'61ectromyographie quantitative utilisant une m6thode d'analyse automatique (EMG-Quant) et l'dectromyographie de la fibre isol6e (EMGFI) ont 6t6 compar6es duns le biceps droit de 10 patients pr6sentant un trouble des neurones des comes ant6rieures et 20 patients pr6sentant un d6sordre primaire des muscles. Dans la majorit6 des cas, et ind6pendamment du fait que le muscle soit faible ou non, des anomalies furent d6montr6es par les 3 techniques utilis6es. Dans les cas neurog6nes, I'EMGFI a 6t6 plus efficace que l'EMG-Quant e t a 6galement donn6 une indication sur l'activit6 de la maladie. Duns les cas de myopathie, l'EMG-Quant a avantag6 le diagnostic et fut plus facile h r6aliser que I'EMGFI. Des potentiels de grandes amplitudes trouv6s dans certains cas de myopathie furent associ6s avec une augmentation de l'amplitude moyenne du EMGQuant, ceux-ci provenant probablement des fibres musculaires hypertrophiques.
COMPARISON OF EMG TECHNIQUES We wish to thank Professor E. Sthlberg for providing us with fibre density values in control subjects and Dr. R.G. Willison for helpful discussion. We also thank Miss Alison Polglase for preparing the manuscript.
References Fuglsang-Frederiksen, A., Scheel, U. and Buchthal, F. Diagnostic yield of analysis of the pattern of electrical activity and of individual motor unit potentials in myopathy. J. Neurol. Neurosurg. Psychiat., 1976, 39: 742-750. Haridasan, G., Sanghivi, S.H., Joshi, V.M., Pandya, S.S. and Desai, A.D. Quantitative electromyography using automatic analysis, J. neurol. Sci., 1980, 48: 353-365. Hayward, M. Automatic analysis of the electromyogram in healthy subjects of different ages. J. neurol., Sci., 1977, 33: 397-413. Hayward, M. and Willison, R.G. The recognition of myogenic and neurogenic lesions by quantitative EMG. In: J.E. Desmedt (Ed.), New Developments in Electromyography and Clinical Neurophysiology, Vol. 2. Karger, Basel, 1973: 448-453. Hayward, M. and Willison, R.G. Automatic analysis of the electromyogram in patients with chronic partial denervation. J. neurol. Sci., 1977, 33: 415-423.
225 Henriksson, K.G. and St/dberg, E. The terminal innervation pattern in polymyositis: a histochemical and SFEMG study. Muscle Nerve, 1978, 1: 3-13. Kugelberg, E. Electromyography in muscular dystrophies and chronic lower motor neurone lesions. J. Neurol. Neurosurg. Psychiat., 1949, 12: 129-136. Pinelli, P. and Buchthal, F. Muscle action potentials in myopathies with special regard to progressive muscular dystrophy. Neurology (Minneap.), 1953, 3: 347-359. Schwartz, M.S. and Swash, M. Pattern of involvement in the early stages of motor neurone disease: a single fibre EMG study. Acta neurol, scand., 1982, 65: 424-431. Sthlberg, E. Electrogenesis in human muscular dystrophy. In: L.P. Rowland (Ed.), Pathogenesis of Human Muscular Dystrophies. Proc. 5th Int. Conf. of the Muscular Dystrophy Ass. Excerpta Medica, Amsterdam, 1977: 560-587. Sthlberg, E. and Trontelj, J.V. Single Fibre Electromyography. Miravelle Press, Old Woking, 1977. Sthlberg, E., Schwarz, M.S. and Trontelj, J.V. Single fibre electromyography in various processes affecting the anterior horn cell. J. neurol. Sci., 1975, 24: 403-415. Willison, R.G. Analysis of electrical activity in healthy and dystrophic muscle in man. J. Neurol. Neurosurg. Psychiat., 1964, 27: 386-394.