Writing tremor: its relationship to benign essential tremor

Long-term follow-up of task-specific tremor after thalamotomy: a retrospective observational study

OBJECTIVE

This study aimed to report the long-term results of thalamotomy in 23 patients with task-specific tremor.

METHODS

Data of 23 patients with task-specific tremor who underwent ventralis intermedius nucleus and posterior part of ventro-oral nucleus thalamotomy at the Tokyo Women's Medical University Hospital between 2010 and 2022 were retrospectively analyzed. To evaluate neurological conditions, the severity of task-specific tremor was divided into 0 (no tremor), 1 (slightly tremulous), 2 (moderately tremulous), 3 (accomplishing tasks with great difficulty), and 4 (unable to complete tasks). We also used the subscores "handwriting" (0-4) and "spiral drawing" (0-4) of the Clinical Rating Scales for Tremor. Evaluation scales were presented as medians and interquartile ranges.

RESULTS

The severities of task-specific tremor were 3.0 (3.0-4.0) preoperatively and 0.0 (0.0-0.0, p < 0.0001) at the last available evaluation. The writing and spiral drawing of the Clinical Rating Scales for Tremor significantly improved from 3.0 (3.0-4.0) and 3.0 (2.0-3.0) preoperatively, respectively, to 0.0 (0.0-0.0, p < 0.0001) and 0.0 (0.0-0.0, p < 0.0001) at the last available evaluation, respectively. The mean clinical follow-up period was 62.7 ± 26.0 months. Seven (30.4%) patients had focal hand dystonia, which newly developed on the ipsilateral side of the tremor at 2-45 months after the surgery. No serious complications were observed.

INTERPRETATION

Thalamotomy significantly improves task-specific tremor with high long-term efficacy, and long-term follow-up is important because focal hand dystonia can develop postoperatively.

Is essential tremor a family of diseases or a syndrome? A family of diseases

It is now well-established that essential tremor (ET) can manifest with different clinical presentations and progressions (i.e., upper limb tremor, head tremor, voice tremor, lower limb tremor, task- or position-specific tremor, or a combination of those). Common traits and overlaps are identifiable across these different subtypes of ET, including a slow rate of progression, a response to alcohol and a positive family history. At the same time, each of these manifestations are associated with specific demographic, clinical and treatment-response characteristics suggesting a family of diseases rather than a spectrum of a syndrome. Here we summarize the most important clinical, demographic, neuropathological and imagingfeatures of ET and of its subtypes to support ET as a family of identifiable conditions. This classification has relevance for counseling of patients with regard to disease progression and treatment response, as well as for the design of therapeutic clinical trials.

Primary Writing Tremor: Current Concepts

Primary Writing Tremor (PWT) is a type of task specific tremor which happens only while writing (Type A PWT) or assuming a writing position of the hand (Type B PWT). There is a considerable overlap of clinical features between PWT and writer's cramp which creates difficulty in diagnosing this condition in the clinic. PWT usually affects the dominant hand and is typically 5-7hz in frequency, worsened by anxiety, temporarily relieved by alcohol and associated with reduced writing speeds. There are a variety of hypotheses about the phenomenology of PWT (regarding whether it is a variant of essential tremor, focal dystonia or an independent entity). Unlike writer's cramp, PWT shows normal reciprocal inhibition of H reflex, does not exhibit excessive EMG activity in proximal muscles, and on fMRI shows underactivation of cingulum and overactivation of primary motor and supplementary areas. There are no randomised controlled trials currently for the treatment of PWT. Treatment modalities available are: medical treatment, botulinum toxin, surgical management (including DBS) as well as adaptive strategies and occupational therapy.

The Signature of Primary Writing Tremor Is Dystonic

BACKGROUND

It has been debated for decades whether primary writing tremor is a form of dystonic tremor, a variant of essential tremor, or a separate entity. We wished to test the hypothesis that primary writing tremor and dystonia share a common pathophysiology.

OBJECTIVES

The objective of the present study was to investigate the pathophysiological hallmarks of dystonia in patients affected by primary writing tremor.

METHODS

Ten patients with idiopathic dystonic tremor syndrome, 7 with primary writing tremor, 10 with essential tremor, and 10 healthy subjects were recruited. They underwent eyeblink classic conditioning, blink recovery cycle, and transcranial magnetic stimulation assessment, including motor-evoked potentials and short- and long-interval intracortical inhibition at baseline. Transcranial magnetic stimulation measures were also recorded after paired-associative plasticity protocol.

RESULTS

Primary writing tremor and dystonic tremor syndrome had a similar pattern of electrophysiological abnormalities, consisting of reduced eyeblink classic conditioning learning, reduced blink recovery cycle inhibition, and a lack of effect of paired-associative plasticity on long-interval intracortical inhibition. The latter 2 differ from those obtained in essential tremor and healthy subjects. Although not significant, slightly reduced short-interval intracortical inhibition and a larger effect of paired-associative plasticity in primary writing tremor and dystonic tremor syndrome, compared with essential tremor and healthy subjects, was observed.

CONCLUSIONS

Our initial hypothesis of a common pathophysiology between dystonia and primary writing tremor has been confirmed. Primary writing tremor might be considered a form of dystonic tremor. © 2021 International Parkinson and Movement Disorder Society.

Altered brain network measures in patients with primary writing tremor

PURPOSE

Primary writing tremor (PWT) is a rare task-specific tremor, which occurs only while writing or while adopting the hand in the writing position. The basic pathophysiology of PWT has not been fully understood. The objective of this study is to explore the alterations in the resting state functional brain connectivity, if any, in patients with PWT using graph theory-based analysis.

METHODS

This prospective case-control study included 10 patients with PWT and 10 age and gender matched healthy controls. All subjects underwent MRI in a 3-Tesla scanner. Several parameters of small-world functional connectivity were compared between patients and healthy controls by using graph theory-based analysis.

RESULTS

There were no significant differences in age, handedness (all right handed), gender distribution (all were males), and MMSE scores between the patients and controls. The mean age at presentation of tremor in the patient group was 51.7 ± 8.6 years, and the mean duration of tremor was 3.5 ± 1.9 years. Graph theory-based analysis revealed that patients with PWT had significantly lower clustering coefficient and higher path length compared to healthy controls suggesting alterations in small-world architecture of the brain. The clustering coefficients were lower in PWT patients in left and right medial cerebellum, right dorsolateral prefrontal cortex (DLPFC), and left posterior parietal cortex (PPC).

CONCLUSION

Patients with PWT have significantly altered small-world brain connectivity in bilateral medial cerebellum, right DLPFC, and left PPC. Further studies with larger sample size are required to confirm our results.

Research Priorities in Limb and Task-Specific Dystonias

Dystonia, which causes intermittent or sustained abnormal postures and movements, can present in a focal or a generalized manner. In the limbs, focal dystonia can occur in either the upper or lower limbs and may be task-specific causing abnormal motor performance for only a specific task, such as in writer’s cramp, runner’s dystonia, or musician’s dystonia. Focal limb dystonia can be non-task-specific and may, in some circumstances, be associated with parkinsonian disorders. The true prevalence of focal limb dystonia is not known and is likely currently underestimated, leaving a knowledge gap and an opportunity for future research. The pathophysiology of focal limb dystonia shares some commonalities with other dystonias with a loss of inhibition in the central nervous system and a loss of the normal regulation of plasticity, called homeostatic plasticity. Functional imaging studies revealed abnormalities in several anatomical networks that involve the cortex, basal ganglia, and cerebellum. Further studies should focus on distinguishing cause from effect in both physiology and imaging studies to permit focus on most relevant biological correlates of dystonia. There is no specific therapy for the treatment of limb dystonia given the variability in presentation, but off-label botulinum toxin therapy is often applied to focal limb and task-specific dystonia. Various rehabilitation techniques have been applied and rehabilitation interventions may improve outcomes, but small sample size and lack of direct comparisons between methods to evaluate comparative efficacy limit conclusions. Finally, non-invasive and invasive therapeutic modalities have been explored in small studies with design limitations that do not yet clearly provide direction for larger clinical trials that could support new clinical therapies. Given these gaps in our clinical, pathophysiologic, and therapeutic knowledge, we have identified priorities for future research including: the development of diagnostic criteria for limb dystonia, more precise phenotypic characterization and innovative clinical trial design that considers clinical heterogeneity, and limited available number of participants.

Epidemiology and treatment of 23 musicians with task specific tremor

BACKGROUND

Task specific tremors in musicians have been mainly described as primary bowing tremor in string instrumentalists in relatively small sample sizes. Our aim was to describe epidemiology, risk factors, phenomenology and treatment options of this disorder in 23 musicians of different instruments.

METHODS

We included 23 professional musicians (4 female, 19 male; mean age 51.5 ± 11.4 years) with a TSTM. During anamnesis, clinical examination, by mail or via telephone patients were asked for epidemiological, phenomenological information, risk factors and treatments. We then compared our findings to primary writing tremor, the most common task specific tremor.

RESULTS

Age at onset of the TST was 44.6 ± 13.6 years and tremor appeared 35.1 ± 13.5 years after beginning to play the instrument. The majority of patients were string instrumentalists, followed by woodwind instrumentalists. Other instrumentalists were a guitarist, pianist and percussionist respectively. In contrast to primary writing tremor, we also found proximal muscles of the upper extremity involved in tremor. A positive family history was found in Prior trauma was more common than in primary writing tremor. Treatment with a positive effect on tremor were in order of efficacy: Botulinumtoxin, Primidone, Propranolol, Trihexyphenidyl. No patient had undergone deep brain stimulation.

CONCLUSION

Task specific tremor in musicians is a heterogeneous disorder with a male gender predominance that shares many commonalities with PWT. The onset age as well as the time between starting to play the instrument and tremor onset has a wide range. Because previous trauma and overuse appear to be risk factors, preventive measures against playing related injuries are necessary. There appears to be a genetic predisposition for TST. No single beneficial medication exists and treatment of patients remains highly individual. It should be discussed, whether deep brain stimulation should be offered not only to patients that do not respond to any other medication but early in the course of the disease.

Task-specific tremor

Task-specific tremor is a form of action tremor that occurs only or mainly when a person is performing a specific skilled task. The most frequently encountered form of task-specific tremor is primary writing tremor (PWT). Currently, there is debate about whether PWT is a variant of essential tremor, writer's cramp (dystonia), a separate entity, or in some cases related to essential tremor and in others to dystonia. PWT typically occurs at a frequency of 5-7Hz and has been subdivided into to two types: Type A, task-induced tremor, and type B, positionally sensitive tremor. Temporary suppression of the tremor by alcohol is seen in about one-third of cases. There are no randomized controlled therapeutic studies involving patients with PWT, although anecdotal reports of beneficial responses to propranolol, primidone, anticholinergics, botulinum toxin treatment, and stereotactic surgery have been reported. Reciprocal inhibition of the H-reflex and intracortical excitability are normal in PWT, unlike writer's cramp. Hyperactivity in the cerebellar hemispheres has been demonstrated with positron emission tomography in PWT. Other task-specific tremors have been described but have not been studied in detail.

Primary writing tremor: Report of a case successfully treated with botulinum toxin A injections and discussion of underlying mechanism

Primary writing tremor (PWT) is a rare motor disorder of unknown etiology, where tremor is elicited primarily or exclusively with writing. We describe a patient with PWT, present a video before and after successful treatment with botulinum toxin type A injections, and discuss a possible underlying dystonic mechanism.

Primary writing tremor: motor cortex reorganisation and disinhibition

BACKGROUND

Primary writing tremor (PWT) is a task-specific tremor of uncertain origin. There has been debate as to whether PWT represents a variant of essential tremor or a tremulous form of focal dystonia related to writer's cramp. In writer's cramp there is evidence of changes in intracortical inhibition (ICI), as well as cortical motor reorganisation.

OBJECTIVE

To study corticomotor organisation and short-latency ICI in a patient with typical task-specific PWT.

METHODS

Transcranial magnetic stimulation mapping of the corticomotor representation of the hand and studies of ICI using paired-pulse stimulation were performed in a 47-year-old right-handed woman with a pure task-specific writing tremor.

RESULTS

The motor maps for the hand were displaced posteriorly on both sides and reverted to a normal position after treatment with botulinum toxin. Short-latency ICI was reduced for the dominant hand.

CONCLUSION

The findings indicate reorganisation and disinhibition of the corticomotor projection to the hand and point to the participation of cortical centres in the origin of PWT.

Neurophysiological investigations in patients with primary writing tremor

The pathophysiology of primary writing tremor (PWT) is still unknown: it has been classified as a focal form of essential tremor and as a tremulous form of writer's cramp. We studied cortical and spinal excitability in patients with PWT and compared the results with published data of patients with essential tremor, and writer's cramp. We used electrical stimulation of median and radial nerve to study reciprocal inhibition of forearm antagonist muscles and paired transcranial magnetic stimulation at short and long interstimulus intervals (ISIs) to assess intracortical excitability. Both studies were conducted on patients with PWT and on control subjects. The early (presynaptic) and late (disynaptic) phases of reciprocal inhibition were normal as was intracortical excitability at short and long ISIs. Our study suggests that the pathophysiology of PWT is different from that of writer's cramp and partially also from that of essential tremor.

Phenomenology and treatment of tremor disorders

Tremor is classified according to anatomic distribution among body parts, and by frequency and amplitude during rest, postural maintenance, movement, intention, and the performance of specific tasks. Key historical features include age at onset, progression over time, family history, exacerbating and remitting factors and behaviors, response to alcohol and medications, and additional neurological signs and symptoms. Accurate diagnosis is a critical factor in predicting the natural history and response to treatment.

Cerebral activation pattern in primary writing tremor

OBJECTIVE

To compare the cerebral activation pattern during writing of patients with writing tremor with healthy controls using functional MRI METHODS: Three patients with writing tremor and 10 healthy controls were examined using a 1.5 Tesla scanner. All subjects performed a paradigm of alternating 30 second periods of rest or writing. For functional imaging 60 EPI multislice data sets were acquired. All images were analyzed using SPM96 software. Data were analyzed for the group of patients with writing tremor and compared with those of the control group.

RESULTS

Both patients with writing tremor and controls showed a significant activation of the contralateral primary sensorimotor cortex, SMA, and area 44. By contrast, motor cortex activation in writing tremor also included the contralateral premotor area (area 6) and ipsilateral prefrontal area (inferior frontal gyrus; areas 10, 44, and 47). Only patients with writing tremor showed a bilateral activation of the parietal lobule (area 40) with a more pronounced activation on the contralateral side. Furthermore, there was a bilateral activation of the cerebellum with a more pronounced area of activation on the ipsilateral side.

CONCLUSIONS

Brain areas activated in writing tremor included activation patterns otherwise typical for both essential tremor and writer's cramp. Therefore a distinct category for writing tremor integrating hallmarks of essential tremor and writer's cramp is proposed.

[Neurophysiologic study of tremor]

Tremor is frequently encountered in neurologic practice. Clinical examination supplies information regarding its approximative frequency, regularity, amplitude, topography and activation conditions. The neurophysiological study helps in confirming the tremor, in differentiating it from other movement disorders like myoclonus, and may provide distinctive features which are important for the aetiological diagnosis. The neurophysiological investigation includes accelerometry, which analyses the mechanics of the movement. Spectral analysis with FFT allows the determination of frequency and amplitude. Accelerometry is always associated with surface EMG of at least two antagonistic muscles. It may show rhythmic bursts, their frequency, duration and activation pattern (alternating or synchronous). This neurophysiological approach to tremor has multiple interests. It may help in differentiating a true rest tremor from a postural tremor seemingly persisting at rest. Brief interruptions or rhythm breaks during distraction manoeuvers are seen in psychogenic tremors. Surface EMG may also demonstrate positive myoclonic bursts, or brief silent periods corresponding to negative myoclonus, sometimes pseudorhythmic, thus appearing clinically like a tremor, but investigations, aetiologies and treatment are different. Several features, especially slow frequency, may suggest a midbrain tremor, thus requiring brain imagery centered around the posterior fossa. Finally, the neurophysiological examination is the only way to demonstrate a primary writing tremor, or a primary orthostatic tremor, the frequency of which is pathognomonic while clinical symptoms are rather misleading.

Effect of Hand Posture on the Temporal and Kinematic Properties of Pointing and Drawing Movements Executed by Healthy Subjects and by a Patient With Primary Writing Tremor

Healthy individuals (n = 6) and a patient with "pure" primary writing tremor executed pointing and drawing movements while adopting different hand postures. The control subjects and the patient exhibited similar kinematics for most conditions. The patient displayed a severe right hand 4- to 6-Hz tremor and prolonged movements only when drawing with his normal hand posture. His tremor was manifested after a ready cue, in anticipation of a go command. The premovement tremor was abolished when the authors simply eliminated the ready cue and instructed the patient to relax and not think about drawing until he heard the go cue. Thus, the patient's writing tremor depended not only upon the writing or drawing act but also upon the hand position adopted and the intent to write, even in the absence of movement. The present results suggest that (a) similar high-level control mechanisms exist for pointing and drawing in healthy subjects and (b) the patient's deficits are compatible with a higher motor defect in central nervous system structures involved in the control of pointing and drawing movements.

Consensus statement of the Movement Disorder Society on Tremor. Ad Hoc Scientific Committee

This is a proposal of the Movement Disorder Society for a clinical classification of tremors. The classification is based on the distinction between rest, postural, simple kinetic, and intention tremor (tremor during target-directed movements). Additional data from a medical history and the results of a neurologic examination can be combined into one of the following clinical syndromes defined in this statement: enhanced physiologic tremor, classical essential tremor (ET), primary orthostatic tremor, task- and position-specific tremors, dystonic tremor, tremor in Parkinson's disease (PD), cerebellar tremor, Holmes' tremor, palatal tremor, drug-induced and toxic tremor, tremor in peripheral neuropathies, or psychogenic tremor. Conditions such as asterixis, epilepsia partialis continua, clonus, and rhythmic myoclonus can be misinterpreted as tremor. The features distinguishing these conditions from tremor are described. Controversial issues are outlined in a comment section for each item and thus reflect the open questions that at present cannot be answered on a scientific basis. We hope that this statement provides a basis for better communication among clinicians working in the field and stimulates tremor research.

Bilateral primary writing tremor

Primary writing tremor is a task-specific tremor that is considered to be unilateral. We report a 59-year-old man with a 5-year history of a typical primary writing tremor in the right hand who developed similar symptoms in the left hand. Copyright 1998 Lippincott Williams & Wilkins

Agreement among movement disorder specialists on the clinical diagnosis of essential tremor

Even though essential tremor (ET) is the most prevalent movement disorder, there has been little agreement in the neurologic literature regarding diagnostic criteria for ET. The authors attempted to determine the extent and source of agreement and disagreement among neurologists regarding diagnostic criteria for clinically definite ET. The authors designed and mailed a semistructured questionnaire to 160 neurologists who specialize in movement disorders in 24 countries. The questionnaire included three sections: a list of inclusion criteria, a list of exclusion criteria, and a list of potential clinical scenarios (for example, isolated site-specific tremor and primary orthostatic tremor). The questionnaire was completed by 98 (61%) of 160 targeted neurologists. There was greater consensus regarding features considered unnecessary inclusion criteria for clinically definite ET (extent of disability, disease duration, and positive family history) than for those considered necessary inclusion criteria (postural versus action tremor). With regard to exclusion criteria, there was some consensus in terms of the presence of Parkinson's disease, dystonia, history of hyperthyroidism or concurrent use of tremor-inducing medications, and cerebellar signs. The majority of neurologists would diagnose ET in the setting of isolated head or voice tremor. There are areas of both consensus and divergence among neurologists with regard to diagnostic criteria for ET. The choice of diagnostic criteria may vary depending on the intended use of the criteria (that is, clinical versus genetic studies). Hopefully, this study will foster further discussion to achieve a more general consensus.

Focal task-specific tremors

Focal task-specific tremors besides primary writing tremor have rarely been reported in the literature. We describe nine cases of focal tremors induced by different specific tasks, involving a repetitive and frequently performed movement. Only one of these patients had a family history of any similar disorders. There was no overt dystonia in any of the cases, but these tremors may be forms of focal dystonia, rather than a manifestation of essential tremor.

Prevalence of focal dystonias in the western area of Tottori Prefecture in Japan

We evaluated the prevalence of focal dystonias in the western area of Tottori Prefecture in Japan. The population of the area was 244,935 on October 1, 1992. Because four patients with blepharospasm and three patients with writer's cramp did not visit any hospitals or clinics in 1993 and did not reply to our question letter, we could not confirm their present condition: with or without focal dystonia in 1993. Four patients with facial dystonia including blepharospasm and oromandibular dystonia, seven with spasmodic torticollis, and four with writer's cramp were observed. The prevalence of focal dystonias was 6.12 per 100,000 persons, which may be lower than that in western countries. Although the reasons for this difference are still unclear, a genetic factor may be one implication.

[Writing tremor: report of a case]

Primary writing tremor is induced by a specific motor activity, generally the handwriting. The case is analyzed under clinic and therapeutic points of view. The patient had a tremor elicited by handwriting without any other concurrent neurologic alteration. He neither presented familiar antecedents nor metabolic, endocrine, iatrogenic, toxic and traumatic ones. As to the therapeutic approach, the tremor did not respond satisfactorily neither to propranolol nor to primidone. But with anticholinergics improvement of the tremor was verified.

Effect of vigabatrin on sedation and cognitive function in patients with refractory epilepsy

Twenty-four patients with refractory epilepsy on one or more antiepileptic drugs were given additional vigabatrin (1 g twice daily for six weeks, followed by 1.5 g twice daily for a further six weeks) and matched placebo in a double blind, randomised, crossover study. A battery of neuropsychological tests was administered at baseline and at weeks two, six and 12 of both treatment periods. No significant differences were found between vigabatrin and placebo at any time point for any of the objective tests of cognitive function. Patients, however, reported a greater degree of sedation after two and six weeks on vigabatrin than during the equivalent placebo phase (p < 0.01), although no such difference was apparent at 12 weeks. Follow up over a mean of 14.75 months in 12 responders, who continued on vigabatrin, revealed a significant improvement (all p < 0.01) on each of three composite scales (three psychomotor tests, four memory tests, three self rating scales) compared with their scores during the double blind trial. Vigabatrin did not cause cognitive impairment either acutely or in the long term. Phased introduction, however, seems a prudent policy to allow tolerance to early subjective sedation.

Assessing the impact of essential tremor on upper limb function

We compared the impact of essential tremor on the performance of three manual tasks: drawing spirals, holding a cup full of water and a joystick-controlled tracking test. Tremor amplitude and frequency were measured by accelerometry during the tracking test, when holding the cup and whilst a standard posture was maintained. The inter-relationships between tremor amplitude, frequency and task impairment were then examined. The results showed that the amplitude and frequency of essential tremor (measured from the principal spectral peak) changed with different activities, with the mildest postural tremors changing most in frequency (by up to 4-5 Hz). The amplitude of tremor decreased in almost every case during the tasks, relative to posture, and this decrement was greatest for the most severe tremors. We also demonstrate that for practical purposes, such as routine clinical situations and therapeutic trails, the effect of essential tremor upon upper limb function can be usefully assessed by two simple complementary techniques: rating spirals and measuring the volume of water split from a cup. The impairments in carrying out these tasks and the tracking test were highly correlated with one another and also with the amplitude and frequency of postural tremor. The concept of tremor "suppressability" is introduced: the relative percentage decrease in the amplitude of a particular tremor during the performance of a specific task compared to that recorded whilst holding a standard posture.

Linkage analysis with chromosome 9 markers in hereditary essential tremor

Hereditary essential tremor (ET) is an autosomal dominant disorder with variable expression and reduced penetrance. A tremor indistinguishable from ET may be observed in patients with autosomal dominant idiopathic torsion dystonia (ITD), in which the disease locus has been mapped to 9q32-34 in some kindreds, tightly linked to the argininosuccinate synthetase (ASS) locus. We performed linkage analysis in 15 families with ET containing 60 definitely affected individuals, using dinucleotide repeat polymorphisms at the ASS locus and the Abelson locus (ABL). Cumulative lod scores were -19.5 for ASS and -10.8 for ABL at a recombination fraction of 0.01, and tight linkage to ASS was excluded individually in 11 of the families. These data indicate that the ET gene is not allelic to that causing ITD.

A new method for the measurement of tremor at rest

This paper establishes a standard method for measuring human tremor. The electronic instrument described is an application of this method. It solves the need for an effective and simple tremor-measuring instrument fit for wide distribution. This instrument consists of a piezoelectric accelerometer connected to an electronic circuit and to an LCD display. The signal is also analysed by a computer after accelerometer analogic/digital conversion in order to test the method. The tremor of 1079 healthy subjects was studied. Spectral analysis showed frequency peaks between 5.85 and 8.80 Hz. Chronic cigarette-smoking and coffee drinking did not modify the tremor as compared with controls. Relaxation session decreased tremor significantly in healthy subjects (P less than 0.01). This new tremor-measuring method opens new horizons in the understanding of physiological and pathological tremor, stress, anxiety and in the means to avoid or compensate them.

Primary writing tremor. A form of focal dystonia?

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, high-frequency 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.

A single family with writer's cramp, essential tremor, and primary writing tremor

We studied seven members of a family who had different types of movement disorders: Two had typical essential tremor, two (twins) had typical writer's cramp, one had both essential tremor and writer's cramp, one had primary writing tremor, and one (deceased) had uncharacterized tremor. This appears to be the first report of writer's cramp in twins and in so many family members. This family links together primary writing tremor, essential tremor, and writer's cramp and may help resolve the apparent controversy about the relationship of primary writing tremor to essential tremor and writer's cramp.