Movement Disorders Vol. 5 , No. 2, 1990, pp. 118-126. 0 1990 Movement Disorder Society
Primary Writing Tremor A Form of Focal Dystonia? Rodger J. Elble, Charles Moody, and Constance Higgins Department of Medicine, Division of Neurology, Southern Illinois University School of Medicine, Springfield, Illinois, U.S.A.
Summary: Five patients exhibited severe tremor in the upper extremity, primarily when attempting to write or draw. Electromyography was performed to determine the patterns of muscle activity that were responsible for this tremor. Tremor was measured with an accelerometer and with a digitizing tablet. Two patients had postural tremor that was indistinguishable from mild, highfrequency essential tremor. All patients exhibited a severe 5-7-Hz tremor during the acts of writing and drawing. Muscles throughout the affected extremity exhibited rhythmic 5-7-Hz bursts of motor unit discharge, and the average level of motor unit activity was tonically increased in antagonistic muscles. This abnormal coactivation of antagonistic muscles produced subtle dystonic posturing of the affected limb that was overshadowed by severe tremor. Electromyography was useful in confirming the coexistence of tremor and dystonia in our patients. The nonspecificity of dystonia and postural tremor must be considered when discussing the nosology and pathophysiology of primary writing tremor. Key Words: Tremor-Dystonia-Electromyography-Writer’s crampPrimary writing tremor.
been reported by several authors (2-7). In general, there has been a variable response to ethanol, propranolol, primidone, and anticholinergic agents. Anticholinergic agents are most frequently beneficial, but they are often poorly tolerated. Most patients have no family history of tremor or other movement disorders, but Rosenbaum and Jankovic (7) elicited a family history of tremor in seven of 19 patients with task-specific tremor. Stretch-reflex amplitudes and latencies are normal in nearly all patients (2,6).Stereotactic thdamotomy in ventralis intermedius suppresses this tremor, but the burst discharges in this nucleus are not time-locked to tremor (5). Therefore, thalamotomy probably exerts an indirect effect on the tremor oscillator, possibly by transcortical reflex pathways (8)+ NOautopsy studies have been performed, and consequently, the pathologic characteristics of primary writing tremor are unknown. The proper nosologic classification of primary
Rothwell and co-workers (1) described a 20year-old man who exhibited bursts of 4-6-Hz tremor with pronation of the forearm, particularly during the act of writing. Electromyograms (EMGs) revealed tremor in muscles throughout the forearm and arm, but the authors observed no dystonia. During its early stages, this tremor was suppressed by the ingestion of ethanol, but ethanol subsequently lost its effectiveness. Injection of local anesthetic into the motor point of the pronator teres abolished the tremor. Rothwell and colleagues named this condition primary writing tremor. Other cases of primary writing tremor have since
__ A videotape segment accompanies this article. Address correspondence and reprint requests to Dr. Rodger J. Elble, Department of Medicine, Southern Illinois University School of Medicine, P.O. BOX 19230, Springfield, IL 62794-9230, U.S.A. This work was presented in part at the 1987 annual meeting of the American Academy of Neurology.
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PRIMARY WRITING TREMOR
writing tremor is also unknown. Several authors have argued that primary writing tremor is a variant of essential tremor because it shares some of the neurophysiologic and clinical characteristics of essential tremor (2,4,7). Other authors have emphasized a possible relationship to focal dystonia (6,7). Cohen and co-workers (9) studied a family in which there appeared to be a genetic link between essential tremor, primary writing tremor, and writer’s cramp, a form of focal dystonia. However, while essential tremor is commonly inherited, primary writing tremor and focal dystonias are usually sporadic (2,3,5,6,9-11). Furthermore, the frequently beneficial response of primary writing tremor to anticholinergic medications (3,6) is more characteristic of dystonia (1 1) than essential tremor (12). We describe five patients who complained of incapacitating tremor during the act of writing. All five exhibited evidence of focal dystonia with prolonged writing, but this dystonia was overshadowed by severe tremor. The nosology of primary writing tremor is discussed. METHODS The conditions of five patients were evaluated after they gave informed consent (Table 1). Six normal adults (three men and three women aged 40-51 years) were also observed. Description of Patients Patient 1 A 51-year-old right-handed male cabinet maker complained of a 3-year history of tremor in the right upper extremity when writing or drawing. The tremor was first noticed during a 2-week hospitalization for an uncomplicated myocardial infarction, during which he received quinidine and meperidine. Although he noticed tremor while writing and while drawing lines on cabinets, he had no difficulty using other tools. With prolonged writing, his right wrist fluctuated between exaggerated extension and flexion. He exhibited no postural tremor, and the fre-
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quency of his writing tremor was 5-7 Hz. Neurological examination revealed no other abnormal findings. A computed tomography head scan 3 years after the onset of tremor was normal. There was no family history of tremor. He rarely drank ethanol and noticed no effect of ethanol on his tremor. Diphenhydramine, 100 mg four times daily, suppressed the tremor but gradually lost much of its effectiveness. The patient retired and refused other medications. Patient 2 At age 40, this 61-year-old right-handed male insurance agent first noticed hand tremor and “soreness” in the right index finger while writing. This problem began insidiously. He noticed that 1 oz of ethanol suppressed his tremor long enough for him to write a paragraph or two. However, he rarely drank, and the benefit derived from ethanol disappeared as his tremor advanced. At age 41, he was examined by a neurologist who observed mild tremor while writing. Benzodiazepines were prescribed and provided subjective relief. The patient continued to work, but by age 57, his tremor had progressed to such an extent that writing was nearly impossible. He also began experiencing a “cramping discomfort” in his arm while writing and described rare, intermittent “voice spasms” that caused transient loss of voice when he became excited. There was no family history of neurological disease. Neurological examination revealed no abnormalities except when he attempted to write. Any attempt to write or draw produced a severe 5-7-Hz tremor that began in the wrist and spread proximally to involve the muscles of the arm and shoulder. Excessive coactivation of muscles throughout the right upper extremity was associated with abnormal abduction of the arm and flexion of the wrist and fingers. We have not observed his voice spasms despite having observed this patient for 4 years. Trihexyphenidyl, 5 mg three times daily; amantadine, 100 mg three times daily; propranolol sustained-release capsules, 240 mg/day ; and primi-
TABLE 1. Clinical characteristics of the five patients Patienttsexiage, yr
Tremor frequency, Hz
1/M/51 2lM161
5-1
3lFl64
5-7 5-1 5-1
4/M/44 5 M 61
5-1
Duration, yr
Postural tremor, Hz
Family history
3 21
-
-
14 13
7-9
45
8-10
-
-
+
Dystonia
+ + + + +
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done, 250 mg three times daily, each produced no beneficial effect. Patient 3 A 64-year-old female restaurant owner complained of a 14-year history of tremor only when writing with the dominant right hand. This problem began insidiously and progressed slowly. She rarely drank 1 or 2 oz. of ethanol, but noticed no effect on her tremor. During the past few years, she had also noticed a tendency for the muscles of the arm and forearm to “tense up” while writing. Her mother had mild hand tremor late in life, but the patient’s four siblings and other family members had no history of neurological disease. Neurological examination results were normal except for an incapacitating tremor when writing or drawing. This tremor was associated with an abnormal coactivation of muscles throughout the right upper extremity, resulting in dystonic posturing of the hand, particularly after writing several lines of text (Fig. 1). Propranolol and primidone did not help. Benadryl, 100 mg orally three times daily, produced substantial reduction in tremor and dystonia, but the beneficial
effect of this medication gradually dissipated over a few months. Trihexyphenidyl, 4 mg three times daily and benztropine, 2 mg twice daily, produced questionable improvement and were discontinued because of side effects. Patient 4 A 44-year-old right-handed man described a 13year history of tremor in the right upper extremity, primarily when writing. There was no family history of neurological disease. The tremor began insidiously and slowly progressed. As the tremor became more severe, he noticed a tendency for the muscles of his right upper extremity to become uncomfortably tense while writing. He discovered that repeated modification of writing posture produced significant but short-lasting improvement. He occasionally drank ethanol without a noticeable effect on his tremor. Examination revealed a very mild, rapid postural tremor in the fingers of both hands. During writing and drawing, there was a large and somewhat paroxysmal tremor of the right upper extremity that was associated with dystonic extension of the wrist and flexion of the fingers with the
FIG. 1. All five patients exhibited dystonic posturing of the hand while writing (left). The forearm pronated excessively, and the wrist exhibited exaggerated extension and, at times, flexion. The fingers flexed excessively, making it difficult to hold the pen. Examples of handwriting and an Archimedes spiral are shown for patient 3 (right).
Movement Disorders, Vol. 5 , No. 2 , 1990
PRIMARY WRITING TREMOR spread of abnormal coactivation of antagonistic muscles throughout the right upper extremity. Neurological examination revealed no other abnormalities. He refused trials of medications. Patient 5 A 61-year-old man complained of a 45-year history of tremor when writing. This began insidiously, and his script gradually became illegible, causing him to resort to printing. His problem was initially confined to writing, but over the course of many years, he began to notice mild tremor during other fine motor activities. There was no family history of tremor or other neurological disease. His consumption of ethanol was usually limited to 2 or 3 oz of wine per day, which had no effect on his tremor. However, he recalled one occasion at age 43 when he drank to the point of intoxication and noticed nearly total suppression of his tremor. Neurological examination revealed no abnormalities until he was asked to write. The first few words were written with little difficulty. As he continued to write, he gripped his pen with excessive pressure, and a pronounced 5-7-Hz tremor ensued. His fingers flexed excessively, making it difficult for him to hold his pen. His wrist fluctuated between excessive extension and flexion, and dystonic co-contraction of antagonist muscles developed throughout the upper extremity. Haloperidol, propranolol, clorazepate, diazepam, clonazepam, doxepin, amitriptyline, and benztropine produced no objective improvement. Measurement of Tremor and EMG Postural tremor and writing tremor were recorded from the dominant hand of all five patients. Postural tremor was recorded using a 5-g piezoresistive accelerometer that was taped to the dorsum of the hand between the second and third metacarpal bones, just proximal to the metacarpophalangeal joints. The hand was extended horizontally against gravity, with the forearm pronated and supported to the wrist. This method of recording tremor provides an accurate measure of extension-flexion movement about the wrist (13). However, writing is a twodimensional movement produced by motion about the shoulder, elbow, and wrist (14). A one-dimensional accelerometer was useful for recording the frequency of writing tremor but provided only a rough approximation of its amplitude. We therefore devised an alternative method of recording writing tremor using a digitizing tablet
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(15) and an International Business Machinescompatible personal computer. This method and its technical limitations will be addressed in another publication. Briefly, patients and controls were required to write a series of cursive letters “err across one line of 8.5 x 11-in paper mounted on the tablet. They were also required to draw and trace a standard Archimedes spiral. With our tablet and its electronic pen, we were able to digitize tremor at a rate of 169 samplesh and with a resolution of 0.005 in. The vertical and horizontal components of handwriting and drawing were thereby recorded. Each component was double-differentiated using numerical methods (16) to provide a measure of acceleration. In so doing, the lower-frequency voluntary movements were readily separated from tremor. Electromyograms were recorded from extensors digitorum communis and carpi radialis brevis, flexor carpi radialis, deltoid, biceps brachii, and triceps brachii using 0.7-cm Ag-AgC1 skin electrodes that were mounted 2 cm apart, longitudinally over the muscle belly in a bipolar configuration. Prior to spectral analysis, all EMGs were full-wave rectified and low-pass filtered (- 3 dB at 30 Hz) as described in our previous work (13,17). The accelerometer signal, rectified-filtered EMG, and the tablet acceleration data were subjected to spectral analysis to determine the frequency and amplitude of tremor (13,17). The timing relationships (phase) between bursts of tremor in the EMGs were determined by performing cross-spectral analysis on pairs of rectified-filtered EMGs, as previously described (13,17). Included in this analysis is the computation of coherency, which is the squared correlation between two signals at a given frequency (13,17). Values of coherency range from 0 to 1. In general, tremor produces a prominent spectral peak in the acceleration spectrum and in the rectified-filtered EMG spectra. A high coherency between the spectral peaks of two signals suggests a causal relationship. For our data, coherencies greater than 0.2 and spectral peak-to-valley ratios of 2:l are significant at the p = 0.01 level. RESULTS Three of five patients had no postural tremor other than physiologic tremor (Fig. 2). Patients 4 and 5 exhibited abnormal postural tremor in the hand. The frequency of this tremor was 7-9 Hz and 8-10 Hz, respectively. The associated rhythmic bursts of EMG in forearm antagonists fluctuated between the alternating and synchronous patterns,
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WRITING TREMOR
POSTURAL TREMOR NO MASS LOAD
""1
TREMOR
1 00
SOOGRAM LOAD
TREMOR
_I
EDC
EDC
/k
450
2
4
6
8
0
1 0 1 2 114
0
1 0
2
4
6
8 1 0 1 2 1 4
1.01
l.O
.75-
.75
.75 >
>
u
35 5 0 -
Y 2
8
0
0
E
t
0
5 5
50-
0 .25
25 -
- 0
0
2
4
6
8
10
FREOUENCV l H z l
.so
I
0
2
4
6
8
1 0 1 2 1 4
12 14 FREOUENCY (HI)
2
4
6
8 1 0 1 2
1I
LJL
0 0
2
4
6
6
1012
FREOUENCY (HZ1
FIG. 2. Power spectra of wrist tremor and rectified-filtered electromyography (EMG) extensor digitorurn cornmunis (EDC) are shown for patient 1. During steady, horizontal extension of the wrist, this patient exhibited normal mechanical-reflex tremor with no evidence of tremor in the EMG (hence, a flat EMG spectrum). Loading the hand with 500 g produced a normal reduction in tremor frequency. Severe 5-7-Hz tremor and bursts of EMG occurred during writing.
in a manner similar to that seen in essential tremor (13). Application of a 0.5-kg load to the hand had no effect on the frequency of tremor, which is also characteristic of essential tremor (13,lg). All five patients exhibited dystonic co-con-
Movement Disorders, Vol. 5 , N o . 2 , 1990
traction of antagonistic muscles in the forearm, which produced dystonic flexion and at times extension of the fingers and wrist. The dystonia was initially subtle in all patients, but it increased and spread to muscles of the arm and shoulder as writ-
PRIMARY WRITING TREMOR
123
ECRb I
1
200p
1
FIG. 3. Spectral, coherency, and phase analysis of rectified-filtered electromyography (EMG) revealed that bursts of tremor in the arm (e.g., triceps) were usually phase-locked to those of the forearm [e.g., extensor carpi radialis brevis (ECRb)]. Note the excessive degree of sustained motor unit activation in the triceps.
oowv
1
1-
TRICEPS
100 msec
ECRb SPECTRUM
ECRb vs TRICEPS
TRICEPS SPECTRUM 400
Bool
1.0,
Phase = 2 8 ? 4 deg.
300 >
0
2 4 6 8 1 0 1 2 FREOUENCY (Hz)
0
2
4
6
8
10
FREOUENCY ( H z )
ing continued (Fig. 3). Abnormal coactivation of muscles in the arm and shoulder was evident in the EMG of all patients. Muscles in the arm and shoulder of our controls were only intermittently active and of low amplitude. Sustained co-contraction was not observed in the arms and shoulders of our controls. The frequency of writing tremor in each patient was 5-7 Hz (Figs. 2-4). Alternating bursts of EMG were usually recorded in antagonistic muscles of the arm and forearm (Fig. 4),but the actual phase measurements varied between 0-180". The mechanism of this phase variability was not systematically investigated but seemed to relate to the posture of the extremity. Rhythmic bursts of EMG in the arm were often phase-locked with those of the forearm (Fig. 3).
12
FREOUENCY (HA
DISCUSSION The characteristics of writing tremor in our patients closely resemble those described by previous authors (3,6,7). Primary writing tremor is induced primarily by the act of writing, but its task specificity is not absolute. Patients exhibit little or no tremor during other fine motor activities. The frequency of primary writing tremor is 5-7 Hz. Both alternating and roughly synchronous patterns of EMG activity are observed in antagonistic muscles, but the alternating pattern is more common. The effects of therapeutic drugs and ethanol were not studied systematically in our patients, but our clinical observations are in line with those of other authors (1-7). Two of our patients exhibited mild postural tremor that was indistinguishable from mild high-
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FCR
1
200pv
1
10opv
FIG. 4. Coherency and phase analysis of rectifiedfiltered electromyography (EMG) usually revealed a reciprocal pattern of EMG bursts in antagonistic muscles of the forearm [extensor carpi radialis brevis (ECRb);flexor carpi radialis (FCR)]. There was also an abnormally sustained mean level of motor unit activation in both muscles ( i . e . , cocontraction).
1-
ECRb
100 msec
ECRb vs FCR
FCR SPECTRUM 1000
Phase = 156 5 6 deg.
800 700
> V
N
> 600
z
W
U
w
I 0
400
u
:~~L 100
00
0
2
6 8 1 0 1 2 FREOUENCY (Hr) 4
2
4
8 1 0 1 2
0
FREOUENCY (Hz!
frequency essential tremor (13). Kachi and coworkers (2) found a tendency for primary writing tremor to spill over into other motor activities and found that many patients benefit from ethanol and propranolol. Consequently, they and other authors (4,7) speculated that primary writing tremor might be a variant of essential tremor. However, essential tremor and primary writing tremor differ in their response to anticholinergic agents and frequency of genetic inheritance. Furthermore, the clinical and neurophysiologic characteristics of essential tremor are too varied, nonspecific, and poorly characterized to distinguish essential tremor from many other forms of action tremor. Action tremors of similar frequency, EMG patterns, and pharmacologic response (e.g., to ethanol and propranolol) are not necessarily of the same disease.
Movement Disorders, Vol. 5 , N o . 2, 1990
6
2
4 6 8 1 0 1 2 FREOUENCY (Hz)
All of our patients exhibited incapacitating tremor while writing and drawing. They also experienced an inappropriate, involuntary co-contraction of antagonistic muscles that spread to neighboring muscles, resulting in contortions of the affected extremity. The abnormal co-contraction of antagonistic muscles in our patients produced only subtle dystonic contortions of the upper extremity, and these contortions were overshadowed by severe tremor. We did not fully appreciate the degree of dystonia in our patients until electromyography was performed. Other authors (6,10,19) also found that the coexistence of tremor and dystonia may not be appreciated without electromyography . Electromyographic evidence of tremor (i.e., rhythmic bursts of motor unit activity) is often present in patients with
PRIMARY WRITING TREMOR generalized and focal dystonia (10,19). These patients have little or no external evidence of tremor when the frequency of tremor is greater than 7 Hz, and without electromyography , such tremor may not be recognized (10,19). Conversely, we found that dystonia can be difficult to appreciate in patients with severe writing tremor. Electromyographic evidence of sustained coactivation of antagonistic muscles is a characteristic sign of dystonia (10,19). However, coactivation of antagonistic muscles is also a normal mechanism by which the healthy nervous system controls the stiffness of joints (20). Increased joint stiffness is useful in limiting undesirable involuntary movement (20), and Feldman (21) demonstrated that co-contraction of antagonistic muscles is also a normal component of rapid, voluntary, rhythmic movements. Normal handwriting consists of roughly orthogonal oscillations with frequencies that approach those of primary writing tremor (22). Therefore, some degree of co-contraction should be expected in normal volunteers, particularly in the forearm and hand, and mild dystonia may be difficult or impossible to distinguish electromyographically from the “voluntary” dystonic postures observed by Rosenbaum and Jankovic (7) in some patients with writing tremor. These limitations of electromyography notwithstanding, sustained co-contraction in the arm and shoulder was observed only in our patients, and this co-contraction was clearly beyond their control. It could be argued that our patients have writer’s cramp and not a unique form of tremor. Other authors have also described patients with coexisting dystonia and writing tremor (6,7) and have suggested that primary writing tremor is a tremulous variety of writer’s cramp (6). The clinical characteristics of primary writing tremor and writer’s cramp are similar in several respects. Both conditions are more or less task specific, uncommonly inherited, and frequently responsive to anticholinergic medications (1-8), and nearly half of patients with writer’s cramp exhibit a superimposed tremor that may be severe (11). Therefore, in many patients, primary writing tremor may be a manifestation of focal dystonia. In conclusion, patients with writing tremor may exhibit varying proportions of tremor and focal dystonia, and electromyography is useful in identifying subtle components of both disorders of movement. Our patients and those of other authors illustrate the uncertain nosologic relationships among essen-
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tial tremor, primary writing tremor, and writer’s cramp (23). When grappling with these observations, one should remain mindful that clinical similarities do not prove identity in nosologic or pathophysiologic terms (24). Acknowledgment: We gratefully acknowledge our typist, Faye Shaw. This work was supported by grant NS20973 from the National Institute of Neurological Disorders and Stroke and by Biomedical Research Support Grant S07RR05843 from the National Institutes of Health.
LEGENDS TO THE VIDEOTAPE SEGMENT 1. Patient 2 exhibited no abnormal postural tremor or kinetic tremor in the upper extremities during finger-to-nose testing, but severe tremor occurred when he attempted to write or draw. Note the tremulous contraction of the distal and proximal muscles of the right upper extremity, and note the mild dystonia of the hand and wrist. SEGMENT 2. Patient 3 exhibited severe tremor and mild dystonia of the right upper extremity during writing and drawing but not during steady posture and finger-to-nose testing. REFERENCES 1. Rothwell JC, Traub MM, Marsden CD. Primary writing tremor. J Neurol Neurosurg Psychiatry 1979;42:1106-1114. 2. Kachi T, Rothwell JC, Cowan JMA, Marsden CD. Writing tremor: its relationship to benign essential tremor. J Neurol Neurosurg Psychiatry 1985;48:545-550.
3. Klawans HL, Glantz R, Tanner CM, Goetz CG. Primary writing tremor: a selective action tremor. Neurology 1982; 32:203-206. 4. Koller WC, Martyn B. Writing tremor: its relationship to essential tremor. J Neurol Neurosurg Psychiatry 1986;49: 220. 5 . Ohye C, Miyazaki M, Hirai T, Shibazaki T, Nakajima H,
Nagaseki Y. Primary writing tremor treated by stereotactic selective thalamotomy. J Neurol Neurosurg Psychiatry 1982;45:988-997. 6. Ravits J, Hallett M, Baker M, Wilkins D. Primary writing tremor and myoclonic writer‘s cramp. Neurology 1985;35: 1387-1391. 7. Rosenbaum F, Jankovic J. Focal task-specific tremor and
dystonia: categorization of occupational movement disorders. Neurology 1 988 ;38 :522-527. 8. Ohye C, Shibazaki T, Hirai T, Wada H, Hirato M, Kawashima Y.Further physiological observations on the ventralis intermedius neurons in the human thalamus. J Neurophysiol 1989;61:488-500. 9. Cohen LG, Hallett M, Sudarsky L. A single family with
writer’s cramp, essential tremor, and primary writing tremor. Movement Dis 1987;2: 10P-116. 10. Cohen LG, Hallett M. Hand cramps: clinical features and electromyographic patterns in a focal dystonia. Neurology 1988;38: 1005-10 12. 11. Sheehy MP, Marsden CD. Writer’s c r a m p a focal dystonia. Brain 1982;105:461-480.
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12. Findley LJ, Koller WC. Essential tremor: a review. Neurology 1987;37:1194-1197. 13. Elble RJ. Physiologic and essential tremor. Neurology 1986; 36~225-231. 14. Lacquaniti F, Femgno G , Pedotti A, Soechting JF, Terzuolo C . Changes in spatial scale in drawing and handwriting: kinematic contributions by proximal and distal joints. J Neurosci 1987;7:819-828. 15. Diehl S, Apiki S . Graphic details. Byte 1989;14:162-174. 16. Savitzky A, Golay MJE. Smoothing and differentiation of data by simplified least squares procedures. Anal Chem 1964;36:1627-1639. 17. Elble W ,Randall JE. Motor-unit activity responsible for 8to 12-Hz component of human physiological finger tremor. J Neurophysiol 1976;39:37@383. 18. Homberg V, Hefter H, Reiners K, Freund H-J. Differential effects of changes in mechanical limb properties on physio-
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19. 20.
21. 22. 23. 24.
logic and pathologic tremor. J Neurol Neurosurg Psychiatry 1987 ;50:56&579. Yanagisawa N, Goto A. Dystonia musculorum deformans: analysis with electromyography. J Neurol Sci 3971;13:3965. Humphrey DR, Reed DJ. Separate cortical systems for control of joint movement and joint stiffness: reciprocal activation and coactivation of antagonist muscles. In: Desmedt JE, ed. Motor control mechanisms in health and disease. New York: Raven Press, 1983:347-372. Feldman AG. Superposition of motor programs. I. Rhythmic forearm movements in man. Neuroscience 1980;5:81-90. Hollerbach JM. An oscillation theory of handwriting. Biol Cybern 1981;39:139-156. Elble RJ, Moody C , Higgins C. Primary writing tremor. Neurology 1987;37(suppl):283. Hudgson P. Writer’s cramp. Br Med J 1983;286:585-586.
Primary Writing Tremor A Form of Focal Dystonia? Rodger J. Elble, Charles Moody, and Constance Higgins Department of Medicine, Division of Neurology, Southern Illinois University School of Medicine, Springfield, Illinois, U.S.A.
Summary: Five patients exhibited severe tremor in the upper extremity, primarily when attempting to write or draw. Electromyography was performed to determine the patterns of muscle activity that were responsible for this tremor. Tremor was measured with an accelerometer and with a digitizing tablet. Two patients had postural tremor that was indistinguishable from mild, highfrequency essential tremor. All patients exhibited a severe 5-7-Hz tremor during the acts of writing and drawing. Muscles throughout the affected extremity exhibited rhythmic 5-7-Hz bursts of motor unit discharge, and the average level of motor unit activity was tonically increased in antagonistic muscles. This abnormal coactivation of antagonistic muscles produced subtle dystonic posturing of the affected limb that was overshadowed by severe tremor. Electromyography was useful in confirming the coexistence of tremor and dystonia in our patients. The nonspecificity of dystonia and postural tremor must be considered when discussing the nosology and pathophysiology of primary writing tremor. Key Words: Tremor-Dystonia-Electromyography-Writer’s crampPrimary writing tremor.
been reported by several authors (2-7). In general, there has been a variable response to ethanol, propranolol, primidone, and anticholinergic agents. Anticholinergic agents are most frequently beneficial, but they are often poorly tolerated. Most patients have no family history of tremor or other movement disorders, but Rosenbaum and Jankovic (7) elicited a family history of tremor in seven of 19 patients with task-specific tremor. Stretch-reflex amplitudes and latencies are normal in nearly all patients (2,6).Stereotactic thdamotomy in ventralis intermedius suppresses this tremor, but the burst discharges in this nucleus are not time-locked to tremor (5). Therefore, thalamotomy probably exerts an indirect effect on the tremor oscillator, possibly by transcortical reflex pathways (8)+ NOautopsy studies have been performed, and consequently, the pathologic characteristics of primary writing tremor are unknown. The proper nosologic classification of primary
Rothwell and co-workers (1) described a 20year-old man who exhibited bursts of 4-6-Hz tremor with pronation of the forearm, particularly during the act of writing. Electromyograms (EMGs) revealed tremor in muscles throughout the forearm and arm, but the authors observed no dystonia. During its early stages, this tremor was suppressed by the ingestion of ethanol, but ethanol subsequently lost its effectiveness. Injection of local anesthetic into the motor point of the pronator teres abolished the tremor. Rothwell and colleagues named this condition primary writing tremor. Other cases of primary writing tremor have since
__ A videotape segment accompanies this article. Address correspondence and reprint requests to Dr. Rodger J. Elble, Department of Medicine, Southern Illinois University School of Medicine, P.O. BOX 19230, Springfield, IL 62794-9230, U.S.A. This work was presented in part at the 1987 annual meeting of the American Academy of Neurology.
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PRIMARY WRITING TREMOR
writing tremor is also unknown. Several authors have argued that primary writing tremor is a variant of essential tremor because it shares some of the neurophysiologic and clinical characteristics of essential tremor (2,4,7). Other authors have emphasized a possible relationship to focal dystonia (6,7). Cohen and co-workers (9) studied a family in which there appeared to be a genetic link between essential tremor, primary writing tremor, and writer’s cramp, a form of focal dystonia. However, while essential tremor is commonly inherited, primary writing tremor and focal dystonias are usually sporadic (2,3,5,6,9-11). Furthermore, the frequently beneficial response of primary writing tremor to anticholinergic medications (3,6) is more characteristic of dystonia (1 1) than essential tremor (12). We describe five patients who complained of incapacitating tremor during the act of writing. All five exhibited evidence of focal dystonia with prolonged writing, but this dystonia was overshadowed by severe tremor. The nosology of primary writing tremor is discussed. METHODS The conditions of five patients were evaluated after they gave informed consent (Table 1). Six normal adults (three men and three women aged 40-51 years) were also observed. Description of Patients Patient 1 A 51-year-old right-handed male cabinet maker complained of a 3-year history of tremor in the right upper extremity when writing or drawing. The tremor was first noticed during a 2-week hospitalization for an uncomplicated myocardial infarction, during which he received quinidine and meperidine. Although he noticed tremor while writing and while drawing lines on cabinets, he had no difficulty using other tools. With prolonged writing, his right wrist fluctuated between exaggerated extension and flexion. He exhibited no postural tremor, and the fre-
119
quency of his writing tremor was 5-7 Hz. Neurological examination revealed no other abnormal findings. A computed tomography head scan 3 years after the onset of tremor was normal. There was no family history of tremor. He rarely drank ethanol and noticed no effect of ethanol on his tremor. Diphenhydramine, 100 mg four times daily, suppressed the tremor but gradually lost much of its effectiveness. The patient retired and refused other medications. Patient 2 At age 40, this 61-year-old right-handed male insurance agent first noticed hand tremor and “soreness” in the right index finger while writing. This problem began insidiously. He noticed that 1 oz of ethanol suppressed his tremor long enough for him to write a paragraph or two. However, he rarely drank, and the benefit derived from ethanol disappeared as his tremor advanced. At age 41, he was examined by a neurologist who observed mild tremor while writing. Benzodiazepines were prescribed and provided subjective relief. The patient continued to work, but by age 57, his tremor had progressed to such an extent that writing was nearly impossible. He also began experiencing a “cramping discomfort” in his arm while writing and described rare, intermittent “voice spasms” that caused transient loss of voice when he became excited. There was no family history of neurological disease. Neurological examination revealed no abnormalities except when he attempted to write. Any attempt to write or draw produced a severe 5-7-Hz tremor that began in the wrist and spread proximally to involve the muscles of the arm and shoulder. Excessive coactivation of muscles throughout the right upper extremity was associated with abnormal abduction of the arm and flexion of the wrist and fingers. We have not observed his voice spasms despite having observed this patient for 4 years. Trihexyphenidyl, 5 mg three times daily; amantadine, 100 mg three times daily; propranolol sustained-release capsules, 240 mg/day ; and primi-
TABLE 1. Clinical characteristics of the five patients Patienttsexiage, yr
Tremor frequency, Hz
1/M/51 2lM161
5-1
3lFl64
5-7 5-1 5-1
4/M/44 5 M 61
5-1
Duration, yr
Postural tremor, Hz
Family history
3 21
-
-
14 13
7-9
45
8-10
-
-
+
Dystonia
+ + + + +
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done, 250 mg three times daily, each produced no beneficial effect. Patient 3 A 64-year-old female restaurant owner complained of a 14-year history of tremor only when writing with the dominant right hand. This problem began insidiously and progressed slowly. She rarely drank 1 or 2 oz. of ethanol, but noticed no effect on her tremor. During the past few years, she had also noticed a tendency for the muscles of the arm and forearm to “tense up” while writing. Her mother had mild hand tremor late in life, but the patient’s four siblings and other family members had no history of neurological disease. Neurological examination results were normal except for an incapacitating tremor when writing or drawing. This tremor was associated with an abnormal coactivation of muscles throughout the right upper extremity, resulting in dystonic posturing of the hand, particularly after writing several lines of text (Fig. 1). Propranolol and primidone did not help. Benadryl, 100 mg orally three times daily, produced substantial reduction in tremor and dystonia, but the beneficial
effect of this medication gradually dissipated over a few months. Trihexyphenidyl, 4 mg three times daily and benztropine, 2 mg twice daily, produced questionable improvement and were discontinued because of side effects. Patient 4 A 44-year-old right-handed man described a 13year history of tremor in the right upper extremity, primarily when writing. There was no family history of neurological disease. The tremor began insidiously and slowly progressed. As the tremor became more severe, he noticed a tendency for the muscles of his right upper extremity to become uncomfortably tense while writing. He discovered that repeated modification of writing posture produced significant but short-lasting improvement. He occasionally drank ethanol without a noticeable effect on his tremor. Examination revealed a very mild, rapid postural tremor in the fingers of both hands. During writing and drawing, there was a large and somewhat paroxysmal tremor of the right upper extremity that was associated with dystonic extension of the wrist and flexion of the fingers with the
FIG. 1. All five patients exhibited dystonic posturing of the hand while writing (left). The forearm pronated excessively, and the wrist exhibited exaggerated extension and, at times, flexion. The fingers flexed excessively, making it difficult to hold the pen. Examples of handwriting and an Archimedes spiral are shown for patient 3 (right).
Movement Disorders, Vol. 5 , No. 2 , 1990
PRIMARY WRITING TREMOR spread of abnormal coactivation of antagonistic muscles throughout the right upper extremity. Neurological examination revealed no other abnormalities. He refused trials of medications. Patient 5 A 61-year-old man complained of a 45-year history of tremor when writing. This began insidiously, and his script gradually became illegible, causing him to resort to printing. His problem was initially confined to writing, but over the course of many years, he began to notice mild tremor during other fine motor activities. There was no family history of tremor or other neurological disease. His consumption of ethanol was usually limited to 2 or 3 oz of wine per day, which had no effect on his tremor. However, he recalled one occasion at age 43 when he drank to the point of intoxication and noticed nearly total suppression of his tremor. Neurological examination revealed no abnormalities until he was asked to write. The first few words were written with little difficulty. As he continued to write, he gripped his pen with excessive pressure, and a pronounced 5-7-Hz tremor ensued. His fingers flexed excessively, making it difficult for him to hold his pen. His wrist fluctuated between excessive extension and flexion, and dystonic co-contraction of antagonist muscles developed throughout the upper extremity. Haloperidol, propranolol, clorazepate, diazepam, clonazepam, doxepin, amitriptyline, and benztropine produced no objective improvement. Measurement of Tremor and EMG Postural tremor and writing tremor were recorded from the dominant hand of all five patients. Postural tremor was recorded using a 5-g piezoresistive accelerometer that was taped to the dorsum of the hand between the second and third metacarpal bones, just proximal to the metacarpophalangeal joints. The hand was extended horizontally against gravity, with the forearm pronated and supported to the wrist. This method of recording tremor provides an accurate measure of extension-flexion movement about the wrist (13). However, writing is a twodimensional movement produced by motion about the shoulder, elbow, and wrist (14). A one-dimensional accelerometer was useful for recording the frequency of writing tremor but provided only a rough approximation of its amplitude. We therefore devised an alternative method of recording writing tremor using a digitizing tablet
121
(15) and an International Business Machinescompatible personal computer. This method and its technical limitations will be addressed in another publication. Briefly, patients and controls were required to write a series of cursive letters “err across one line of 8.5 x 11-in paper mounted on the tablet. They were also required to draw and trace a standard Archimedes spiral. With our tablet and its electronic pen, we were able to digitize tremor at a rate of 169 samplesh and with a resolution of 0.005 in. The vertical and horizontal components of handwriting and drawing were thereby recorded. Each component was double-differentiated using numerical methods (16) to provide a measure of acceleration. In so doing, the lower-frequency voluntary movements were readily separated from tremor. Electromyograms were recorded from extensors digitorum communis and carpi radialis brevis, flexor carpi radialis, deltoid, biceps brachii, and triceps brachii using 0.7-cm Ag-AgC1 skin electrodes that were mounted 2 cm apart, longitudinally over the muscle belly in a bipolar configuration. Prior to spectral analysis, all EMGs were full-wave rectified and low-pass filtered (- 3 dB at 30 Hz) as described in our previous work (13,17). The accelerometer signal, rectified-filtered EMG, and the tablet acceleration data were subjected to spectral analysis to determine the frequency and amplitude of tremor (13,17). The timing relationships (phase) between bursts of tremor in the EMGs were determined by performing cross-spectral analysis on pairs of rectified-filtered EMGs, as previously described (13,17). Included in this analysis is the computation of coherency, which is the squared correlation between two signals at a given frequency (13,17). Values of coherency range from 0 to 1. In general, tremor produces a prominent spectral peak in the acceleration spectrum and in the rectified-filtered EMG spectra. A high coherency between the spectral peaks of two signals suggests a causal relationship. For our data, coherencies greater than 0.2 and spectral peak-to-valley ratios of 2:l are significant at the p = 0.01 level. RESULTS Three of five patients had no postural tremor other than physiologic tremor (Fig. 2). Patients 4 and 5 exhibited abnormal postural tremor in the hand. The frequency of this tremor was 7-9 Hz and 8-10 Hz, respectively. The associated rhythmic bursts of EMG in forearm antagonists fluctuated between the alternating and synchronous patterns,
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WRITING TREMOR
POSTURAL TREMOR NO MASS LOAD
""1
TREMOR
1 00
SOOGRAM LOAD
TREMOR
_I
EDC
EDC
/k
450
2
4
6
8
0
1 0 1 2 114
0
1 0
2
4
6
8 1 0 1 2 1 4
1.01
l.O
.75-
.75
.75 >
>
u
35 5 0 -
Y 2
8
0
0
E
t
0
5 5
50-
0 .25
25 -
- 0
0
2
4
6
8
10
FREOUENCV l H z l
.so
I
0
2
4
6
8
1 0 1 2 1 4
12 14 FREOUENCY (HI)
2
4
6
8 1 0 1 2
1I
LJL
0 0
2
4
6
6
1012
FREOUENCY (HZ1
FIG. 2. Power spectra of wrist tremor and rectified-filtered electromyography (EMG) extensor digitorurn cornmunis (EDC) are shown for patient 1. During steady, horizontal extension of the wrist, this patient exhibited normal mechanical-reflex tremor with no evidence of tremor in the EMG (hence, a flat EMG spectrum). Loading the hand with 500 g produced a normal reduction in tremor frequency. Severe 5-7-Hz tremor and bursts of EMG occurred during writing.
in a manner similar to that seen in essential tremor (13). Application of a 0.5-kg load to the hand had no effect on the frequency of tremor, which is also characteristic of essential tremor (13,lg). All five patients exhibited dystonic co-con-
Movement Disorders, Vol. 5 , N o . 2 , 1990
traction of antagonistic muscles in the forearm, which produced dystonic flexion and at times extension of the fingers and wrist. The dystonia was initially subtle in all patients, but it increased and spread to muscles of the arm and shoulder as writ-
PRIMARY WRITING TREMOR
123
ECRb I
1
200p
1
FIG. 3. Spectral, coherency, and phase analysis of rectified-filtered electromyography (EMG) revealed that bursts of tremor in the arm (e.g., triceps) were usually phase-locked to those of the forearm [e.g., extensor carpi radialis brevis (ECRb)]. Note the excessive degree of sustained motor unit activation in the triceps.
oowv
1
1-
TRICEPS
100 msec
ECRb SPECTRUM
ECRb vs TRICEPS
TRICEPS SPECTRUM 400
Bool
1.0,
Phase = 2 8 ? 4 deg.
300 >
0
2 4 6 8 1 0 1 2 FREOUENCY (Hz)
0
2
4
6
8
10
FREOUENCY ( H z )
ing continued (Fig. 3). Abnormal coactivation of muscles in the arm and shoulder was evident in the EMG of all patients. Muscles in the arm and shoulder of our controls were only intermittently active and of low amplitude. Sustained co-contraction was not observed in the arms and shoulders of our controls. The frequency of writing tremor in each patient was 5-7 Hz (Figs. 2-4). Alternating bursts of EMG were usually recorded in antagonistic muscles of the arm and forearm (Fig. 4),but the actual phase measurements varied between 0-180". The mechanism of this phase variability was not systematically investigated but seemed to relate to the posture of the extremity. Rhythmic bursts of EMG in the arm were often phase-locked with those of the forearm (Fig. 3).
12
FREOUENCY (HA
DISCUSSION The characteristics of writing tremor in our patients closely resemble those described by previous authors (3,6,7). Primary writing tremor is induced primarily by the act of writing, but its task specificity is not absolute. Patients exhibit little or no tremor during other fine motor activities. The frequency of primary writing tremor is 5-7 Hz. Both alternating and roughly synchronous patterns of EMG activity are observed in antagonistic muscles, but the alternating pattern is more common. The effects of therapeutic drugs and ethanol were not studied systematically in our patients, but our clinical observations are in line with those of other authors (1-7). Two of our patients exhibited mild postural tremor that was indistinguishable from mild high-
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FCR
1
200pv
1
10opv
FIG. 4. Coherency and phase analysis of rectifiedfiltered electromyography (EMG) usually revealed a reciprocal pattern of EMG bursts in antagonistic muscles of the forearm [extensor carpi radialis brevis (ECRb);flexor carpi radialis (FCR)]. There was also an abnormally sustained mean level of motor unit activation in both muscles ( i . e . , cocontraction).
1-
ECRb
100 msec
ECRb vs FCR
FCR SPECTRUM 1000
Phase = 156 5 6 deg.
800 700
> V
N
> 600
z
W
U
w
I 0
400
u
:~~L 100
00
0
2
6 8 1 0 1 2 FREOUENCY (Hr) 4
2
4
8 1 0 1 2
0
FREOUENCY (Hz!
frequency essential tremor (13). Kachi and coworkers (2) found a tendency for primary writing tremor to spill over into other motor activities and found that many patients benefit from ethanol and propranolol. Consequently, they and other authors (4,7) speculated that primary writing tremor might be a variant of essential tremor. However, essential tremor and primary writing tremor differ in their response to anticholinergic agents and frequency of genetic inheritance. Furthermore, the clinical and neurophysiologic characteristics of essential tremor are too varied, nonspecific, and poorly characterized to distinguish essential tremor from many other forms of action tremor. Action tremors of similar frequency, EMG patterns, and pharmacologic response (e.g., to ethanol and propranolol) are not necessarily of the same disease.
Movement Disorders, Vol. 5 , N o . 2, 1990
6
2
4 6 8 1 0 1 2 FREOUENCY (Hz)
All of our patients exhibited incapacitating tremor while writing and drawing. They also experienced an inappropriate, involuntary co-contraction of antagonistic muscles that spread to neighboring muscles, resulting in contortions of the affected extremity. The abnormal co-contraction of antagonistic muscles in our patients produced only subtle dystonic contortions of the upper extremity, and these contortions were overshadowed by severe tremor. We did not fully appreciate the degree of dystonia in our patients until electromyography was performed. Other authors (6,10,19) also found that the coexistence of tremor and dystonia may not be appreciated without electromyography . Electromyographic evidence of tremor (i.e., rhythmic bursts of motor unit activity) is often present in patients with
PRIMARY WRITING TREMOR generalized and focal dystonia (10,19). These patients have little or no external evidence of tremor when the frequency of tremor is greater than 7 Hz, and without electromyography , such tremor may not be recognized (10,19). Conversely, we found that dystonia can be difficult to appreciate in patients with severe writing tremor. Electromyographic evidence of sustained coactivation of antagonistic muscles is a characteristic sign of dystonia (10,19). However, coactivation of antagonistic muscles is also a normal mechanism by which the healthy nervous system controls the stiffness of joints (20). Increased joint stiffness is useful in limiting undesirable involuntary movement (20), and Feldman (21) demonstrated that co-contraction of antagonistic muscles is also a normal component of rapid, voluntary, rhythmic movements. Normal handwriting consists of roughly orthogonal oscillations with frequencies that approach those of primary writing tremor (22). Therefore, some degree of co-contraction should be expected in normal volunteers, particularly in the forearm and hand, and mild dystonia may be difficult or impossible to distinguish electromyographically from the “voluntary” dystonic postures observed by Rosenbaum and Jankovic (7) in some patients with writing tremor. These limitations of electromyography notwithstanding, sustained co-contraction in the arm and shoulder was observed only in our patients, and this co-contraction was clearly beyond their control. It could be argued that our patients have writer’s cramp and not a unique form of tremor. Other authors have also described patients with coexisting dystonia and writing tremor (6,7) and have suggested that primary writing tremor is a tremulous variety of writer’s cramp (6). The clinical characteristics of primary writing tremor and writer’s cramp are similar in several respects. Both conditions are more or less task specific, uncommonly inherited, and frequently responsive to anticholinergic medications (1-8), and nearly half of patients with writer’s cramp exhibit a superimposed tremor that may be severe (11). Therefore, in many patients, primary writing tremor may be a manifestation of focal dystonia. In conclusion, patients with writing tremor may exhibit varying proportions of tremor and focal dystonia, and electromyography is useful in identifying subtle components of both disorders of movement. Our patients and those of other authors illustrate the uncertain nosologic relationships among essen-
125
tial tremor, primary writing tremor, and writer’s cramp (23). When grappling with these observations, one should remain mindful that clinical similarities do not prove identity in nosologic or pathophysiologic terms (24). Acknowledgment: We gratefully acknowledge our typist, Faye Shaw. This work was supported by grant NS20973 from the National Institute of Neurological Disorders and Stroke and by Biomedical Research Support Grant S07RR05843 from the National Institutes of Health.
LEGENDS TO THE VIDEOTAPE SEGMENT 1. Patient 2 exhibited no abnormal postural tremor or kinetic tremor in the upper extremities during finger-to-nose testing, but severe tremor occurred when he attempted to write or draw. Note the tremulous contraction of the distal and proximal muscles of the right upper extremity, and note the mild dystonia of the hand and wrist. SEGMENT 2. Patient 3 exhibited severe tremor and mild dystonia of the right upper extremity during writing and drawing but not during steady posture and finger-to-nose testing. REFERENCES 1. Rothwell JC, Traub MM, Marsden CD. Primary writing tremor. J Neurol Neurosurg Psychiatry 1979;42:1106-1114. 2. Kachi T, Rothwell JC, Cowan JMA, Marsden CD. Writing tremor: its relationship to benign essential tremor. J Neurol Neurosurg Psychiatry 1985;48:545-550.
3. Klawans HL, Glantz R, Tanner CM, Goetz CG. Primary writing tremor: a selective action tremor. Neurology 1982; 32:203-206. 4. Koller WC, Martyn B. Writing tremor: its relationship to essential tremor. J Neurol Neurosurg Psychiatry 1986;49: 220. 5 . Ohye C, Miyazaki M, Hirai T, Shibazaki T, Nakajima H,
Nagaseki Y. Primary writing tremor treated by stereotactic selective thalamotomy. J Neurol Neurosurg Psychiatry 1982;45:988-997. 6. Ravits J, Hallett M, Baker M, Wilkins D. Primary writing tremor and myoclonic writer‘s cramp. Neurology 1985;35: 1387-1391. 7. Rosenbaum F, Jankovic J. Focal task-specific tremor and
dystonia: categorization of occupational movement disorders. Neurology 1 988 ;38 :522-527. 8. Ohye C, Shibazaki T, Hirai T, Wada H, Hirato M, Kawashima Y.Further physiological observations on the ventralis intermedius neurons in the human thalamus. J Neurophysiol 1989;61:488-500. 9. Cohen LG, Hallett M, Sudarsky L. A single family with
writer’s cramp, essential tremor, and primary writing tremor. Movement Dis 1987;2: 10P-116. 10. Cohen LG, Hallett M. Hand cramps: clinical features and electromyographic patterns in a focal dystonia. Neurology 1988;38: 1005-10 12. 11. Sheehy MP, Marsden CD. Writer’s c r a m p a focal dystonia. Brain 1982;105:461-480.
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12. Findley LJ, Koller WC. Essential tremor: a review. Neurology 1987;37:1194-1197. 13. Elble RJ. Physiologic and essential tremor. Neurology 1986; 36~225-231. 14. Lacquaniti F, Femgno G , Pedotti A, Soechting JF, Terzuolo C . Changes in spatial scale in drawing and handwriting: kinematic contributions by proximal and distal joints. J Neurosci 1987;7:819-828. 15. Diehl S, Apiki S . Graphic details. Byte 1989;14:162-174. 16. Savitzky A, Golay MJE. Smoothing and differentiation of data by simplified least squares procedures. Anal Chem 1964;36:1627-1639. 17. Elble W ,Randall JE. Motor-unit activity responsible for 8to 12-Hz component of human physiological finger tremor. J Neurophysiol 1976;39:37@383. 18. Homberg V, Hefter H, Reiners K, Freund H-J. Differential effects of changes in mechanical limb properties on physio-
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21. 22. 23. 24.
logic and pathologic tremor. J Neurol Neurosurg Psychiatry 1987 ;50:56&579. Yanagisawa N, Goto A. Dystonia musculorum deformans: analysis with electromyography. J Neurol Sci 3971;13:3965. Humphrey DR, Reed DJ. Separate cortical systems for control of joint movement and joint stiffness: reciprocal activation and coactivation of antagonist muscles. In: Desmedt JE, ed. Motor control mechanisms in health and disease. New York: Raven Press, 1983:347-372. Feldman AG. Superposition of motor programs. I. Rhythmic forearm movements in man. Neuroscience 1980;5:81-90. Hollerbach JM. An oscillation theory of handwriting. Biol Cybern 1981;39:139-156. Elble RJ, Moody C , Higgins C. Primary writing tremor. Neurology 1987;37(suppl):283. Hudgson P. Writer’s cramp. Br Med J 1983;286:585-586.
