- Email: [email protected]
Polymyography in the diagnosis of childhood onset movement disorders
ARTICLE IN PRESS E U R O P E A N J O U R N A L O F PA E D I AT R I C N E U R O L O G Y
12 (2008) 480 – 483
Official Journal of the European Paediatric Neurology Society
Original article
Polymyography in the diagnosis of childhood onset movement disorders C. Canavesea, C. Cianob, G. Zorzia, F. Zibordia, C. Costaa, N. Nardoccia, a
UO Neuropsichiatria Infantile, Fondazione I.R.C.C.S. Istituto Neurologico Carlo Besta, Milano, Italy UO Neurofisiologia Clinica, Fondazione I.R.C.C.S. Istituto Neurologico Carlo Besta, Milano, Italy
b
ar t ic l e i n f o
abs tra ct
Article history:
We report on the results of a clinical and polymyographic retrospective study of 61
Received 24 July 2007
paediatric patients with tremor, dystonia and/or myoclonus. Aim of the study was to verify
Received in revised form
the contribution of polymyography in the classification of these movement disorders and
18 December 2007
in their aetiological definition. Methods: The movement disorders were clinically classified by two experts, based on
Accepted 25 December 2007
clinical and videotape recordings evaluation; all patients underwent standardized Keywords: Paediatric movement disorders Clinical classification Psychogenic movement disorders Polymyography
polymyographic evaluation; aetiological diagnosis was performed according to diagnostic protocols for dystonia, myoclonus, tremor and psychogenic movement disorders. The polymyographic features were summarized in five different patterns (dystonia, subcortical myoclonus, myoclonic dystonia, tremor, normal) and compared with the clinical classification and with aetiological diagnosis.
Results: In more than 70% of the patients the polymyographic features were in accordance with the clinical classification; in 31% the polymyographic features allowed to identify a clinically unclassified movement disorder and in 19.6% disclosed a not clinically evident associated movement disorder. The polymyographic study did not contribute to the aetiological diagnosis, but was useful in supporting the clinical diagnosis of psychogenic movement disorder. & 2008 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
Some movement disorders (MDs) (tremor, dystonia, myoclonus) are rare in paediatric pathology and may sometimes be misdiagnosed. The clinical classification of the different types of MDs is an important and problematic issue; it is rather subjective, based on experts consensus. A correct definition is anyway crucial for a rationale diagnostic workup. Little is known about polymyographic features of MD in paediatric patients. Some neurophysiologic studies, such as
polymyography, revealed to be a useful tool in adults pathology, providing neurophysiologic criteria supporting the diagnosis of dystonia,1–3 myoclonus4 and tremor.5–7 Aim of the study was to describe polymyographic features of tremor, dystonia and myoclonus observed in a series of paediatric patients and to verify if polymyography contributed to the classification of these rare MD and to their aetiological definition. We report on the results of a clinical and polymyographic retrospective study of 61 paediatric patients with tremor, dystonia and/or myoclonus.
Corresponding author. Tel.: +39 0223942223.
E-mail address: [email protected] (N. Nardocci). 1090-3798/$ - see front matter & 2008 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ejpn.2007.12.007
ARTICLE IN PRESS E U R O P E A N J O U R N A L O F PA E D I AT R I C N E U R O L O G Y
2.
Patients and methods
Sixty one children, admitted to the National Neurological Institute ‘‘C. Besta’’ of Milan from 2000 to 2005, for a diagnosis of MD were evaluated. Patients affected by chorea or tics were excluded. The MD was classified by at least two MDs experts based on clinical and videotape recordings evaluations. Videotape recording was performed according to a standardized protocol:
Lying at rest (1500 ). Sitting at rest (1500 ). Speech (week days and months of the year). Postural maintenance (arms and hands outstretched). Finger to nose movements, rapid alternating movements of hands, voluntary movements (pouring water, threading beadsy). Standing (1500 ). Walking (normal, tip-toe walk, tandem walk, backwards walk, running). Writing and drawing (Archimedes spiral).
Polymyographic study was performed in all patients. EMG activity was recorded with surface electrodes from at least one pair of antagonist muscles, chosen on the basis of clinical features of the patient. The most studied pairs of muscles were wrist flexor/extensor, fingers flexor/ extensor and biceps/triceps. The electrodes were positioned 3 cm apart, following the direction of the muscle fibres. The high-pass filter was set at 20 Hz–1 kHz. The study was performed at rest, in postural maintenance, during goaldirected movements and during specific tasks (writing, drawing). EMG bursts (tonic activity, clonic jerks or tremor) correlating with involuntary movements were measured in terms of amplitude, frequency, rhythmic or arrhythmic occurrence, duration, synchronism or asynchronism on antagonist muscles (co-contraction) and diffusion of muscular activity to muscles normally not involved in the specific movement (overflow). Modifications of EMG activity (frequency, amplitude and distribution) related to distracting manoeuvres (e.g. counting backwards or performing rapid alternating movements of opposite limb) were considered. The results of polymyographic studies were summarized, according to the literature,1–7 in five patterns:
‘‘Dystonia’’: Prolonged tonic activity during postural main-
tenance and voluntary movements associated or not with co-contraction of agonist and antagonist muscles, or overflow of activity to remote muscle groups that are not normally implicated in the movement. ‘‘Subcortical myoclonus’’: Bursts of EMG activity, synchronous on agonists and antagonists, lasting more than 50 ms recorded at rest, during postural maintenance and voluntary movements. ‘‘Myoclonic dystonia’’: Dystonia pattern with superimposed bursts of irregular, arrhythmic, synchronous or asynchronous EMG activity, lasting more than 50 ms.
12 (2008) 480 – 483
481
‘‘Tremor’’: Tremor activity with frequency 3–11 Hz alternat-
ing on antagonists, evident at rest, during postural maintenance and/or voluntary movements. ‘‘Normal’’.
All patients with myoclonus polymyographic pattern, both ‘‘subcortical myoclonus’’ and ‘‘myoclonic dystonia’’, underwent an EEG-polygraphy recording in which no EEG correlate was disclosed. Aetiological diagnosis, based on diagnostic protocols for dystonia,8 myoclonus,9 tremor 10 and psychogenic MD,11 was reached in 55 patients: in the 37 patients with dystonia (13 primary non-DYT 1; 18 inherited myoclonus-dystonia syndrome: 10 positive for DYT 11 mutations and 8 negative; 4 secondary; 2 heredodegenerative), tremor in eight patients (four essential; three secondary; one heredodegenerative), subcortical myoclonus in four patients (two secondary, two heredodegenerative), psychogenic MD in six patients. In six patients the aetiological diagnosis was not reached (undiagnosed).
3.
Results
3.1.
Clinical results
Thirty-two males and twenty-nine females with a mean age at polymyographic study of 12.2 years (SD:5.8; median:12; range:1–25). Clinical evaluation allowed classification of the MD in 48 patients: upper limbs tremor (10), dystonic movements and/or postures (16), arrhythmic myoclonic jerks (7), mixed MD (15 patients: dystonic movements and/or postures+ unclassified MD in six, dystonic movements and/or postures+ upper limbs tremor in one and dystonic movements and/or postures+myoclonic jerks in eight). In 13 patients the MD remained clinically unclassified as the two experts did not reach a consensus (11 isolated MD and 2 associated with ataxia).
3.2.
Polymyographic results
The ‘‘Dystonia’’ pattern (7 patients) was characterized by: prolonged tonic activity lasting from 1 to 2 s during postural maintenance and voluntary movements in all patients; cocontraction of agonist and antagonist muscles in six cases; overflow of activity to remote muscle groups that are not normally implicated in the movement in four cases. The ‘‘Subcortical Myoclonus’’ pattern (15 patients) was characterized by: myoclonic bursts synchronous on agonists and antagonists, lasting 60–600 ms, evident during postural maintenance and voluntary movements, also at rest in eight cases. The ‘‘Myoclonic Dystonia’’ pattern (24 patients) was characterized by: tonic activity lasting from 1 to 2 s during postural maintenance and voluntary movements; co-contraction in 17 cases; overflow in 9 cases and superimposed myoclonic bursts mainly synchronous on agonists and antagonists, lasting 100–600 ms, evident during postural maintenance and voluntary movements.
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E U R O P E A N J O U R N A L O F PA E D I AT R I C N E U R O L O G Y
The ‘‘Tremor’’ pattern (20 patients) was characterized by: tremor activity with low frequency (o4 Hz) in two patients, medium frequency (4–7 Hz) in eleven patients and high frequency (47 Hz) in seven patients, mainly alternating on antagonists, evident during postural maintenance and voluntary movements, also at rest in six cases. In one patient the polymyographic study was normal. In six patients more than one polymyographic pattern was disclosed leading to the definition of ‘‘Mixed’’ pattern (dystonia+tremor in two; subcortical myoclonus+tremor in two; myoclonic dystonia+tremor in two).
3.3.
Clinical–polymyographic comparison
Polymyographic features were compared with clinical classification in order to evaluate the role of polymyography in the identification of MD: I. Patients in which polymyography confirmed the clinically classified MD 25 patients: five dystonia, four myoclonic-dystonia, five subcortical myoclonus, ten tremors and one dystonia+tremor. II. Patients in which polymyography disclosed an associated MD not clinically evident 12 patients: subcortical myoclonus in seven patients with dystonia, tremor in three patients with dystonia, dystonia in two patients with myoclonus. III. Patients in which polymyography permitted to characterize the clinically unclassified MD (isolated or associated to a definite MD) 17 patients: five myoclonic dystonia (one of them with associated ataxia), six subcortical myoclonus (four associated with dystonia and one associated with ataxia), four tremor and two subcortical myoclonus+tremor. IV. Others Seven patients clinically defined as having dystonia (isolated in one, associated with myoclonus in four or with unclassified MD in two): polymyographic findings of subcortical myoclonus in six, normal in one.
3.4.
Aetiological–polymyographic comparison
The polymyographic features of our patients did not result specific for any aetiological MD subgroup (primary, secondary or heredodegenerative) except for the psychogenic one. In five patients with psychogenic tremor polymyography showed a tremor activity with variable frequency and amplitude, that tended to decrease with distracting manoeuvres, as reported by Brown.12 In one patient with psychogenic dystonia polymyography was normal.
4.
Discussion
The polymyographic findings of our paediatric patients were concordant with literature data about dystonia,1–3 myoclonus4,9 and tremor5–7 in adults.
12 (2008) 480 – 483
Prolonged tonic activity during postural maintenance and voluntary movements was present in all patients with dystonia in our series resulting the cardinal polymyographic pattern. Cocontraction, classically considered to be a typical feature of dystonia, was absent in 7 of our 30 patients affected by dystonia. This finding is concordant with a recent study that disclosed co-contraction only in 48.7% of 179 dystonic patients.3 Another study did not show higher levels of co-contraction in a series of dystonic in comparison to healthy children, during voluntary movements, confirming that co-contraction should not be considered a mandatory neurophysiologic feature of dystonia.13 The Authors, after examining the EMG patterns throughout the complete movement cycle, observed a delay between movements in opposite directions in subjects with dystonia as a result of a defect of agonist/antagonist muscle activation; in particular activation of the agonist remained inappropriately constant during the movement and EMG activity in the antagonist muscle was not properly built up to prepare for smooth movement reversal.13 Overflow was absent in more than half of our patients with dystonia, confirming the results observed in the series of Delval. Polymyography played a key role in the diagnostic work-up allowing to identify a MD not clinically evident (12 patients) or unclassified (19 patients) in more than a half of the patients of our series (50.8%). Interestingly in the majority of the clinically unclassified MD polymyography demonstrated the presence of more than one MD: mainly dystonia and subcortical myoclonus. Group IV (others) includes seven patients clinically classified as suffering from pure dystonia or dystonia associated with myoclonus or unclassified MD. In these patients polymyography failed to demonstrate dystonia pattern only disclosing a subcortical myoclonus pattern (six patients) or a normal pattern (one patient). This fact is reasonably explainable by the fact that polymyography was oriented towards the characterization of rapid, arrhythmic hyperkinesias and not of dystonic phenomenology. Furthermore Delval et al. found 14.7% of dystonic patients with no EMG abnormalities and adduced these findings to limitations of exploration (intermittent symptoms, dystonia involving deep muscles which were not recorded by surface EMG, difficulties to reproduce the conditions of apparition of the dystonic symptoms during examination). As already reported in literature3,14–16 a high number of dystonic patients of our series (22 patients; 59%) showed clinical or polymyographic evidence of an associated MD: subcortical myoclonus in 18 patients, tremor in 2 patients, and both in 2 patients. In the Consensus Statement of the Movement Disorder Society the tremor is classified as ‘‘dystonic tremor’’ when It affects a body part affected by dystonia, and ‘‘tremor associated with dystonia’’ when It occurs in a body part not affected by dystonia.10 All the patients of our series showing dystonia and tremor fulfilled the diagnostic criteria for ‘‘dystonic tremor’’. The polymyographic features were of a postural and kinetic activity characterized by irregular amplitude and variable frequency mainly less than 7 Hz. Delval et al. reported a sensitivity (number of true positive/ number of true positives+number of false negatives) of polymyographic studies of 84% (88% for primary dystonia
ARTICLE IN PRESS E U R O P E A N J O U R N A L O F PA E D I AT R I C N E U R O L O G Y
and 81% for secondary dystonia).3 Myoclonic dystonia was not mentioned in their series. We found a sensitivity of 100% for tremor and subcortical myoclonus and a sensitivity of 72.2% for dystonia; specifically 100% for non-DYT 1 primary dystonia, 100% for secondary/heredodegenerative dystonia and 44% for myoclonic dystonia. The latter low sensitivity is reasonably due to the exiguity of dystonia in patients with inherited myoclonus-dystonia syndrome: in 10 patients out of 18 (five positive and five negative for DYT 11 mutations) we found a polymyographic pattern of isolated subcortical myoclonus. Moreover the myoclonic dystonia pattern was disclosed in 10 patients with non-DYT 1 primary dystonia, confirming that this pattern is not specific of inherited myoclonus-dystonia syndrome.14,15 Polymyography did not supply any evidence for aetiology, except for psychogenic tremor. The diagnosis of definite psychogenic MD may be difficult. Fahn et al.11 proposed clinical criteria based on history, physical examination and response to treatment for the classification in ‘‘documented psychogenic MD’’, ‘‘clinically established psychogenic MD’’, ‘‘probable psychogenic MD’’ and ‘‘possible psychogenic MD’’. Similar classification was also used by Kirsch to categorize psychogenic MD in children.17 In our series polymyography was useful in supporting the clinical diagnosis of psychogenic MD; the results of polymyographic examination should be added among the criteria for the diagnosis of psychogenic tremor and dystonia. In conclusion, according to our study, polymyography plays a key role in the diagnostic work-up of MD: both from a clinical point of view, allowing to identify not clinically evident or unclassified MD, and from an aetiological point of view, supporting the diagnosis of psychogenic MD. R E F E R E N C E S
1. Marsden CD, Rothwell JC. The physiology of idiopathic dystonia. Can J Neurol Sci 1987;14:521–7.
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483
2. Berardelli A, Rothwell JC, Hallett M, Thompson PD, Manfredi M, Marsden CD. The pathophysiology of primary dystonia. Brain 1998;121:1195–212. 3. Delval A, Krystkowiak P, Cassim F, Skrzypzak L, Destee A, et al. Usefulness and limitations of polymyographic recordings in dystonia. Rev Neurol 2004;160:547–53. 4. Shibasaki H, Hallett M. Electrophysiological studies of myoclonus. Muscle Nerve 2005;31:157–74. 5. Deuschl G, Krack P, Lauk M, Timmer J. Clinical neurophysiology of tremor. J Clin Neurophysiol 1996;13:110–21. 6. Milanov I. Electromyographic differentiation of tremors. Clin Neurophysiol 2001;112:1626–32. 7. Gironell A, Kulisevsky J, Pascual-Sedano B, Barbanoj M. Routine neurophysiologic tremor analysis as a diagnostic tool for essential tremor: a prospective study. J Clin Neurophysiol 2004;21:446–50. 8. Fahn S, Bressman S, Marsden CD. Classification of dystonia. Adv Neurol 1998;78:1–10. 9. Caviness J, Brown P. Myoclonus: current concepts and recent advances. Lancet Neurol 2004;3:598–607. 10. Deuschl G, Bain P, Brin M. Ad hoc scientific committee, consensus statement of the movement disorder society on tremor. Mov Disord 1998;13(Suppl. 3):2–23 [review]. 11. Fahn S, Williams D. Psychogenic dystonia. Adv Neurol 1988;50:431–55. 12. Brown P, Thompson PD. Electrophysiological aids to the diagnosis of psychogenic jerks, spasms and tremor. Mov Disord 2001;16:595–9. 13. Malfait N, Sanger TD. Does dystonia always include cocontraction? A study of unconstrained reaching in children with primary and secondary dystonia. Exp Brain Res 2006; e-pub ahead of print. 14. Obeso JA, Rothwell JC, Lang AE, Marsden CD. Myoclonic dystonia. Neurology 1983;33:825–30. 15. Quinn NP, Rothwell JC, Thomson PD, Marsden CD. Hereditary myoclonic dystonia, hereditary torsion dystonia and hereditary essential myoclonus: an area of confusion. In: Stanley F, et al., editors. Advances in neurology, vol. 50: dystonia 2. New York: Raven Press; 1988. 16. Jedynak CP, Bonnet AM, Agid Y. Tremor and idiopathic dystonia. Mov Disord 1991;6(3):230–6. 17. Kirsch DB, Mink JW. Psychogenic movement disorders in children. Ped Neurol 2004;30:1–6.
12 (2008) 480 – 483
Official Journal of the European Paediatric Neurology Society
Original article
Polymyography in the diagnosis of childhood onset movement disorders C. Canavesea, C. Cianob, G. Zorzia, F. Zibordia, C. Costaa, N. Nardoccia, a
UO Neuropsichiatria Infantile, Fondazione I.R.C.C.S. Istituto Neurologico Carlo Besta, Milano, Italy UO Neurofisiologia Clinica, Fondazione I.R.C.C.S. Istituto Neurologico Carlo Besta, Milano, Italy
b
ar t ic l e i n f o
abs tra ct
Article history:
We report on the results of a clinical and polymyographic retrospective study of 61
Received 24 July 2007
paediatric patients with tremor, dystonia and/or myoclonus. Aim of the study was to verify
Received in revised form
the contribution of polymyography in the classification of these movement disorders and
18 December 2007
in their aetiological definition. Methods: The movement disorders were clinically classified by two experts, based on
Accepted 25 December 2007
clinical and videotape recordings evaluation; all patients underwent standardized Keywords: Paediatric movement disorders Clinical classification Psychogenic movement disorders Polymyography
polymyographic evaluation; aetiological diagnosis was performed according to diagnostic protocols for dystonia, myoclonus, tremor and psychogenic movement disorders. The polymyographic features were summarized in five different patterns (dystonia, subcortical myoclonus, myoclonic dystonia, tremor, normal) and compared with the clinical classification and with aetiological diagnosis.
Results: In more than 70% of the patients the polymyographic features were in accordance with the clinical classification; in 31% the polymyographic features allowed to identify a clinically unclassified movement disorder and in 19.6% disclosed a not clinically evident associated movement disorder. The polymyographic study did not contribute to the aetiological diagnosis, but was useful in supporting the clinical diagnosis of psychogenic movement disorder. & 2008 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
Some movement disorders (MDs) (tremor, dystonia, myoclonus) are rare in paediatric pathology and may sometimes be misdiagnosed. The clinical classification of the different types of MDs is an important and problematic issue; it is rather subjective, based on experts consensus. A correct definition is anyway crucial for a rationale diagnostic workup. Little is known about polymyographic features of MD in paediatric patients. Some neurophysiologic studies, such as
polymyography, revealed to be a useful tool in adults pathology, providing neurophysiologic criteria supporting the diagnosis of dystonia,1–3 myoclonus4 and tremor.5–7 Aim of the study was to describe polymyographic features of tremor, dystonia and myoclonus observed in a series of paediatric patients and to verify if polymyography contributed to the classification of these rare MD and to their aetiological definition. We report on the results of a clinical and polymyographic retrospective study of 61 paediatric patients with tremor, dystonia and/or myoclonus.
Corresponding author. Tel.: +39 0223942223.
E-mail address: [email protected] (N. Nardocci). 1090-3798/$ - see front matter & 2008 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ejpn.2007.12.007
ARTICLE IN PRESS E U R O P E A N J O U R N A L O F PA E D I AT R I C N E U R O L O G Y
2.
Patients and methods
Sixty one children, admitted to the National Neurological Institute ‘‘C. Besta’’ of Milan from 2000 to 2005, for a diagnosis of MD were evaluated. Patients affected by chorea or tics were excluded. The MD was classified by at least two MDs experts based on clinical and videotape recordings evaluations. Videotape recording was performed according to a standardized protocol:
Lying at rest (1500 ). Sitting at rest (1500 ). Speech (week days and months of the year). Postural maintenance (arms and hands outstretched). Finger to nose movements, rapid alternating movements of hands, voluntary movements (pouring water, threading beadsy). Standing (1500 ). Walking (normal, tip-toe walk, tandem walk, backwards walk, running). Writing and drawing (Archimedes spiral).
Polymyographic study was performed in all patients. EMG activity was recorded with surface electrodes from at least one pair of antagonist muscles, chosen on the basis of clinical features of the patient. The most studied pairs of muscles were wrist flexor/extensor, fingers flexor/ extensor and biceps/triceps. The electrodes were positioned 3 cm apart, following the direction of the muscle fibres. The high-pass filter was set at 20 Hz–1 kHz. The study was performed at rest, in postural maintenance, during goaldirected movements and during specific tasks (writing, drawing). EMG bursts (tonic activity, clonic jerks or tremor) correlating with involuntary movements were measured in terms of amplitude, frequency, rhythmic or arrhythmic occurrence, duration, synchronism or asynchronism on antagonist muscles (co-contraction) and diffusion of muscular activity to muscles normally not involved in the specific movement (overflow). Modifications of EMG activity (frequency, amplitude and distribution) related to distracting manoeuvres (e.g. counting backwards or performing rapid alternating movements of opposite limb) were considered. The results of polymyographic studies were summarized, according to the literature,1–7 in five patterns:
‘‘Dystonia’’: Prolonged tonic activity during postural main-
tenance and voluntary movements associated or not with co-contraction of agonist and antagonist muscles, or overflow of activity to remote muscle groups that are not normally implicated in the movement. ‘‘Subcortical myoclonus’’: Bursts of EMG activity, synchronous on agonists and antagonists, lasting more than 50 ms recorded at rest, during postural maintenance and voluntary movements. ‘‘Myoclonic dystonia’’: Dystonia pattern with superimposed bursts of irregular, arrhythmic, synchronous or asynchronous EMG activity, lasting more than 50 ms.
12 (2008) 480 – 483
481
‘‘Tremor’’: Tremor activity with frequency 3–11 Hz alternat-
ing on antagonists, evident at rest, during postural maintenance and/or voluntary movements. ‘‘Normal’’.
All patients with myoclonus polymyographic pattern, both ‘‘subcortical myoclonus’’ and ‘‘myoclonic dystonia’’, underwent an EEG-polygraphy recording in which no EEG correlate was disclosed. Aetiological diagnosis, based on diagnostic protocols for dystonia,8 myoclonus,9 tremor 10 and psychogenic MD,11 was reached in 55 patients: in the 37 patients with dystonia (13 primary non-DYT 1; 18 inherited myoclonus-dystonia syndrome: 10 positive for DYT 11 mutations and 8 negative; 4 secondary; 2 heredodegenerative), tremor in eight patients (four essential; three secondary; one heredodegenerative), subcortical myoclonus in four patients (two secondary, two heredodegenerative), psychogenic MD in six patients. In six patients the aetiological diagnosis was not reached (undiagnosed).
3.
Results
3.1.
Clinical results
Thirty-two males and twenty-nine females with a mean age at polymyographic study of 12.2 years (SD:5.8; median:12; range:1–25). Clinical evaluation allowed classification of the MD in 48 patients: upper limbs tremor (10), dystonic movements and/or postures (16), arrhythmic myoclonic jerks (7), mixed MD (15 patients: dystonic movements and/or postures+ unclassified MD in six, dystonic movements and/or postures+ upper limbs tremor in one and dystonic movements and/or postures+myoclonic jerks in eight). In 13 patients the MD remained clinically unclassified as the two experts did not reach a consensus (11 isolated MD and 2 associated with ataxia).
3.2.
Polymyographic results
The ‘‘Dystonia’’ pattern (7 patients) was characterized by: prolonged tonic activity lasting from 1 to 2 s during postural maintenance and voluntary movements in all patients; cocontraction of agonist and antagonist muscles in six cases; overflow of activity to remote muscle groups that are not normally implicated in the movement in four cases. The ‘‘Subcortical Myoclonus’’ pattern (15 patients) was characterized by: myoclonic bursts synchronous on agonists and antagonists, lasting 60–600 ms, evident during postural maintenance and voluntary movements, also at rest in eight cases. The ‘‘Myoclonic Dystonia’’ pattern (24 patients) was characterized by: tonic activity lasting from 1 to 2 s during postural maintenance and voluntary movements; co-contraction in 17 cases; overflow in 9 cases and superimposed myoclonic bursts mainly synchronous on agonists and antagonists, lasting 100–600 ms, evident during postural maintenance and voluntary movements.
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E U R O P E A N J O U R N A L O F PA E D I AT R I C N E U R O L O G Y
The ‘‘Tremor’’ pattern (20 patients) was characterized by: tremor activity with low frequency (o4 Hz) in two patients, medium frequency (4–7 Hz) in eleven patients and high frequency (47 Hz) in seven patients, mainly alternating on antagonists, evident during postural maintenance and voluntary movements, also at rest in six cases. In one patient the polymyographic study was normal. In six patients more than one polymyographic pattern was disclosed leading to the definition of ‘‘Mixed’’ pattern (dystonia+tremor in two; subcortical myoclonus+tremor in two; myoclonic dystonia+tremor in two).
3.3.
Clinical–polymyographic comparison
Polymyographic features were compared with clinical classification in order to evaluate the role of polymyography in the identification of MD: I. Patients in which polymyography confirmed the clinically classified MD 25 patients: five dystonia, four myoclonic-dystonia, five subcortical myoclonus, ten tremors and one dystonia+tremor. II. Patients in which polymyography disclosed an associated MD not clinically evident 12 patients: subcortical myoclonus in seven patients with dystonia, tremor in three patients with dystonia, dystonia in two patients with myoclonus. III. Patients in which polymyography permitted to characterize the clinically unclassified MD (isolated or associated to a definite MD) 17 patients: five myoclonic dystonia (one of them with associated ataxia), six subcortical myoclonus (four associated with dystonia and one associated with ataxia), four tremor and two subcortical myoclonus+tremor. IV. Others Seven patients clinically defined as having dystonia (isolated in one, associated with myoclonus in four or with unclassified MD in two): polymyographic findings of subcortical myoclonus in six, normal in one.
3.4.
Aetiological–polymyographic comparison
The polymyographic features of our patients did not result specific for any aetiological MD subgroup (primary, secondary or heredodegenerative) except for the psychogenic one. In five patients with psychogenic tremor polymyography showed a tremor activity with variable frequency and amplitude, that tended to decrease with distracting manoeuvres, as reported by Brown.12 In one patient with psychogenic dystonia polymyography was normal.
4.
Discussion
The polymyographic findings of our paediatric patients were concordant with literature data about dystonia,1–3 myoclonus4,9 and tremor5–7 in adults.
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Prolonged tonic activity during postural maintenance and voluntary movements was present in all patients with dystonia in our series resulting the cardinal polymyographic pattern. Cocontraction, classically considered to be a typical feature of dystonia, was absent in 7 of our 30 patients affected by dystonia. This finding is concordant with a recent study that disclosed co-contraction only in 48.7% of 179 dystonic patients.3 Another study did not show higher levels of co-contraction in a series of dystonic in comparison to healthy children, during voluntary movements, confirming that co-contraction should not be considered a mandatory neurophysiologic feature of dystonia.13 The Authors, after examining the EMG patterns throughout the complete movement cycle, observed a delay between movements in opposite directions in subjects with dystonia as a result of a defect of agonist/antagonist muscle activation; in particular activation of the agonist remained inappropriately constant during the movement and EMG activity in the antagonist muscle was not properly built up to prepare for smooth movement reversal.13 Overflow was absent in more than half of our patients with dystonia, confirming the results observed in the series of Delval. Polymyography played a key role in the diagnostic work-up allowing to identify a MD not clinically evident (12 patients) or unclassified (19 patients) in more than a half of the patients of our series (50.8%). Interestingly in the majority of the clinically unclassified MD polymyography demonstrated the presence of more than one MD: mainly dystonia and subcortical myoclonus. Group IV (others) includes seven patients clinically classified as suffering from pure dystonia or dystonia associated with myoclonus or unclassified MD. In these patients polymyography failed to demonstrate dystonia pattern only disclosing a subcortical myoclonus pattern (six patients) or a normal pattern (one patient). This fact is reasonably explainable by the fact that polymyography was oriented towards the characterization of rapid, arrhythmic hyperkinesias and not of dystonic phenomenology. Furthermore Delval et al. found 14.7% of dystonic patients with no EMG abnormalities and adduced these findings to limitations of exploration (intermittent symptoms, dystonia involving deep muscles which were not recorded by surface EMG, difficulties to reproduce the conditions of apparition of the dystonic symptoms during examination). As already reported in literature3,14–16 a high number of dystonic patients of our series (22 patients; 59%) showed clinical or polymyographic evidence of an associated MD: subcortical myoclonus in 18 patients, tremor in 2 patients, and both in 2 patients. In the Consensus Statement of the Movement Disorder Society the tremor is classified as ‘‘dystonic tremor’’ when It affects a body part affected by dystonia, and ‘‘tremor associated with dystonia’’ when It occurs in a body part not affected by dystonia.10 All the patients of our series showing dystonia and tremor fulfilled the diagnostic criteria for ‘‘dystonic tremor’’. The polymyographic features were of a postural and kinetic activity characterized by irregular amplitude and variable frequency mainly less than 7 Hz. Delval et al. reported a sensitivity (number of true positive/ number of true positives+number of false negatives) of polymyographic studies of 84% (88% for primary dystonia
ARTICLE IN PRESS E U R O P E A N J O U R N A L O F PA E D I AT R I C N E U R O L O G Y
and 81% for secondary dystonia).3 Myoclonic dystonia was not mentioned in their series. We found a sensitivity of 100% for tremor and subcortical myoclonus and a sensitivity of 72.2% for dystonia; specifically 100% for non-DYT 1 primary dystonia, 100% for secondary/heredodegenerative dystonia and 44% for myoclonic dystonia. The latter low sensitivity is reasonably due to the exiguity of dystonia in patients with inherited myoclonus-dystonia syndrome: in 10 patients out of 18 (five positive and five negative for DYT 11 mutations) we found a polymyographic pattern of isolated subcortical myoclonus. Moreover the myoclonic dystonia pattern was disclosed in 10 patients with non-DYT 1 primary dystonia, confirming that this pattern is not specific of inherited myoclonus-dystonia syndrome.14,15 Polymyography did not supply any evidence for aetiology, except for psychogenic tremor. The diagnosis of definite psychogenic MD may be difficult. Fahn et al.11 proposed clinical criteria based on history, physical examination and response to treatment for the classification in ‘‘documented psychogenic MD’’, ‘‘clinically established psychogenic MD’’, ‘‘probable psychogenic MD’’ and ‘‘possible psychogenic MD’’. Similar classification was also used by Kirsch to categorize psychogenic MD in children.17 In our series polymyography was useful in supporting the clinical diagnosis of psychogenic MD; the results of polymyographic examination should be added among the criteria for the diagnosis of psychogenic tremor and dystonia. In conclusion, according to our study, polymyography plays a key role in the diagnostic work-up of MD: both from a clinical point of view, allowing to identify not clinically evident or unclassified MD, and from an aetiological point of view, supporting the diagnosis of psychogenic MD. R E F E R E N C E S
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