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PubMed1992

Phase resetting and frequency entrainment of essential tremor.

Step and sinusoidal forcings were delivered to the wrists of 10 patients with advanced essential tremor using a computer-controlled torque motor. Consistent (type 0) phase resetting was produced in only 5 patients, whereas all 10 patients exhibited harmonic and 2:1 subharmonic entrainment of essential tremor. These results indicate that the oscillator of essential tremor is coupled to the stretch-reflex arc. Irregularity in the tremor rhythm and postperturbation mechanical-reflex oscillations obscured the phase of essential tremor, thereby impeding the computation of phase resetting curves. Sinusoidal forcings circumvented these problems, but frequency entrainment was produced only by forcings at frequencies within +/- 1 Hz of the tremor frequency and its second harmonic. Resonance accompanied frequency entrainment and probably plays a role in the clinical expression of tremor.

Adult↗
PubMed1991

Tail-tremor induced by exposure to cigarette smoke in rats.

Tremors appearing only in the tail (tail-tremor) induced by cigarette smoke and subcutaneous nicotine were investigated using a smoking machine and Wistar rats. Daily exposure (twice a day) to smokes of two commercial cigarettes (Mild-Seven Select for the first 7 days and Long-Peace for the next 6 days) caused the tail-tremor to appear even if it was slight. A single subcutaneous nicotine (0.5 mg/kg) administration to rats exposed to the cigarette smokes for 13 days markedly caused the tail-tremor. On the other hand, daily subcutaneous injection of nicotine (0.5 mg/kg/day) also caused the tail-tremor to appear beginning on the 4th day and the incidence of tremor increased to 100% by the 12th day. These results indicate that tail-tremor can be caused not only by daily subcutaneous administration of nicotine but also by daily exposure to cigarette smoke.

Animals↗
PubMed1990

Preliminary report: activation of the cerebellum in essential tremor.

Several images of cerebral blood flow were recorded during inhalation of carbon-15-labelled carbon dioxide by positron emission tomography in four patients with essential tremor and four normal controls. Unilateral involuntary postural tremor in essential tremor patients was associated with blood flow significantly greater than that at rest in the contralateral sensorimotor cortex, both lateral premotor regions, and both cerebellar hemispheres. Of these regions, only the cerebellum was not activated in normal controls holding a posture without tremor or in essential tremor patients undergoing passive wrist movement. The increased flow in the cerebellum therefore seems to represent neural activity involved in tremor generation. It is proposed that essential tremor is due to oscillation within cerebello-olivary pathways, relayed by way of the thalamus and motor cortex to the spinal cord.

Administration, Inhalation↗
PubMedDate not supplied

The role of aging in the clinical expression of essential tremor.

Essential tremor is the most common form of abnormal tremor. It is a monosymptomatic disorder characterized by action tremor but no other sign of motor dysfunction. More than half of all cases are inherited through a Mendelian dominant gene. Mild essential tremor is probably the cause of tremulousness that is frequently attributed to aging. The prevalence of essential tremor increases with age, and aging appears to have an independent effect on the clinical characteristics of essential tremor. Autopsies have revealed no discernible pathology. Essential tremor probably emerges from subtle pathologic transformation of a physiologic neuronal oscillator, possibly the inferior olive. A more complete characterization of the effects of aging on motor pathways may be necessary to fully understand the natural history and pathogenesis of this disorder.

Adolescent↗
PubMed1995

Reliability, specificity and sensitivity of long-term tremor recordings.

We have developed a method of long-term EMG recording that has proven suitable for the quantification of pathological tremor. In the present paper we show that the principal parameters of the method (tremor occurrence, tremor intensity, tremor frequency) are highly reproducible and that the method is specific and sensitive for detection of pathological tremor. Twelve patients with essential tremor (ET) and 13 patients with Parkinson's disease (PD) were recorded repeatedly on 3 successive days. For each patient group and for each parameter the intersubject variability was much larger than the intersubject variability. The intraclass correlation coefficient "R" was in the order of 0.9 for each parameter and the mean of Pearson's correlation coefficient between successive days was also approximately 0.9. Recordings from normal controls demonstrated that the method's specificity for pathological tremor is 94.1% and its sensitivity is 96%.

Adult↗
PubMed2006

Functional mobility and postural control in essential tremor.

OBJECTIVE: To evaluate functional mobility and postural control in participants with essential tremor (ET). DESIGN: Cross-sectional cohort study. SETTING: Motor performance research laboratory. PARTICIPANTS: Sixteen participants with ET including head tremor (age, 59.4+/-12.0 y), 14 participants with ET and no head tremor (age, 57.1+/-15.9 y), and 28 healthy controls (age, 58.4+/-12.4 y). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: We assessed the Timed Up & Go, time to ascend and descend stairs, Dynamic Gait Index, and Berg Balance Scale (BBS). Participants completed the Activities-specific Balance Confidence Scale and the Human Activity Profile. We assessed postural control using center-of-pressure measures from force platform recordings of quiet standing in 5 conditions. RESULTS: Participants with ET including head tremor performed worse than controls on all functional mobility performance and self-report measures (P<.05) except the BBS and stair descent time. Mean performance of ET participants without head tremor was intermediate between the other 2 groups. Sway speed measures of postural control showed similar patterns, but no significant group differences in post hoc analysis. There were no statistically significant or clinically important correlations between measures of tremor status and functional mobility status. CONCLUSIONS: Participants with ET show reduced functional mobility, especially those with head tremor.

Cohort Studies↗
PubMed2005

Olanzapine versus propranolol in essential tremor.

PURPOSE: In this study, we evaluated the anti-tremor effect of olanzapine in patients with essential tremor (ET). MATERIAL AND METHODS: Thirty-eight patients with ET affecting upper limbs underwent a randomized, crossover study with olanzapine (20 mg/day) and propranolol (120 mg/day). Evaluation (baseline and 1 month after each drug) was done by using the tremor clinical rating scale and a self-reported disability scale. RESULTS: We did not find statistical difference in all tremor parameters before treatment in two groups. Both drugs improved essential tremor parameters. However, olanzapine significantly improved all tremor parameters except hygiene as compared to propronalol. CONCLUSION: These results suggest that olanzapine might be efficacious for essential tremor. Further clinical trials are indicated to establish the efficacy of olanzapine in patients with ET.

Adrenergic beta-Antagonists↗
PubMed2005

Time-frequency analysis of transient neuromuscular events: dynamic changes in activity of the subthalamic nucleus and forearm muscles related to the intermittent resting tremor.

In order to investigate the dynamic change in transient neuromuscular events and the functional correlation between the neural and muscular activity, local field potentials (LFPs) of the subthalamic nucleus (STN) and surface electromyograms (sEMGs) over several episodes of transient resting tremor from a patient with Parkinson's disease were quantitatively characterised in time-frequency domain using short-time Fourier transform and continuous wavelet transform. Events of onset and cessation of the tremor-related activity in the STN and muscles were correlated to reveal the temporal relationship between the two signals. A significant suppression in the power of the STN LFPs in the beta band (10-30 Hz) preceded the onset of resting tremor, which was presented as the increases in the power at the tremor frequency (3.0-4.5 Hz) in both STN LFPs and surface EMGs. Over the episodes of the intermittent resting tremor, the power of the STN LFPs in the beta band and the power of sEMGs in the tremor frequency band change in an alternating pattern with a significant exponential correlation (P(STN) = 16.8+62.3 x exp(-P(EMG)/6270.7); R2 = 0.72; p < 0.05). Significant linear correlation in the power values at the tremor frequency appears between STN LFPs and sEMGs (P(STN) = 65.1 + 2.1 x 10(-4)P(EMG); R2 = 0.41; p < 0.05). In comparison with short-time Fourier transform, similar results could be achieved using continuous wavelet transform of an appropriate wavelet with a higher temporal resolution but larger distortion in the high frequency.

Electromyography↗
PubMed2005

Quality of life in Essential Tremor Questionnaire (QUEST): development and initial validation.

BACKGROUND/OBJECTIVE: Essential tremor (ET) can diminish functioning and quality of life (QOL) but generic QOL measures may be relatively insensitive to ET and its therapies. We sought to develop an ET-specific measure that might be more sensitive, acceptable to patients, relatively brief, and easily used. DESIGN/METHODS: A sample of 200 patients (average age 70 years, range 30-91; average disease duration 15 years) rated the extent to which tremor impacts a function or state, tremor severity in various body parts, perceived health, and overall QOL. Responses to this initial questionnaire were subjected to principal components analysis (PCA). Inspection of factor coordinates, Eigenvalues, variance accounted for, and correlation matrices were used to select items for confirmatory PCA. Final scale reliability was assessed using Cronbach's alpha. Validity was evaluated by correlations between QOL scales and self-rated tremor severity. RESULTS: PCA of 65 initial items yielded 11 factors accounting for 71% of variance. Six factors were discarded. Two items were eliminated for not loading on a factor and 33 for perceived redundancy. Confirmatory PCA of the retained 30 items yielded an almost identical factor structure (six factors, 70% of variance accounted for, and similar item loadings). Because two factors had very few items loading on them, these two factors were combined into one scale. The final measure has five scales: Physical, Psychosocial, Communication, Hobbies/Leisure, and Work/Finance. Reliability was excellent for the whole instrument and four scales (> or =0.89), and good for the Work/Finance scale (0.79). Severity of voice and head tremor were the best correlates of Communication (0.70 and 0.35), while the Physical scale was related to right and left upper extremity tremor (0.59 and 0.56). Scales correlated more highly with patients' rating of their overall QOL than their health perception. CONCLUSIONS: A brief, 30-item, ET-specific QOL scale with excellent reliability was developed. Preliminary validity data are encouraging. The Quality of Life in Essential Tremor Questionnaire (QUEST) promises to facilitate QOL measurement in ET.

Adult↗
PubMed1997

Involvement of nitric oxide in development of tail-tremor induced by repeated nicotine administration in rats.

Daily administration of nicotine (0.5 mg/kg per day s.c.) to rats caused a tremor that appeared only in the tail (tail-tremor) and which became more marked over 8 days. Nitric oxide (NO) synthase inhibitors, Nw-nitro-L-arginine (10 mg/kg per day i.p.) or Nw-nitro-L-arginine methyl ester (20 and 40 mg/kg per day i.p.), administered each day before nicotine attenuated the development of the tail-tremor. However, neither Nw-nitro-L-arginine (2-10 mg/kg i.p.) nor Nw-nitro-L-arginine methyl ester (10-40 mg/kg i.p.) affected the tail-tremor that developed after 14 days of repeated nicotine administration. The noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 ((+)-5-methyl-10,11,-dihydro-5H-dibenzo[a,b]cyclohepten-5,10-imine hydrogen maleate) at 0.2 mg/kg per day (i.p.), or competitive antagonist, CPP (3-[(+/-)-2-carboxypiperazin-4-yl] propyl-1-phosphonic acid) at 2 mg/kg per day (i.p.), administered each day before nicotine attenuated the development of the tail-tremor. MK-801 (0.01-0.2 mg/kg i.p.) but not CPP (0.5-4 mg/kg i.p.) suppressed the tail-tremor that developed after 14 days of repeated nicotine administration. These results suggest that NO formation mediated by NMDA receptors is involved in the mechanisms underlying the tail-tremor induced by the repeated administration of nicotine.

Animals↗
PubMed2002

Thalamic gray matter changes in unilateral Parkinsonian resting tremor: a voxel-based morphometric analysis of 3-dimensional magnetic resonance imaging.

The thalamus is assumed to be involved in the generation of Parkinsonian tremor. Ten patients with tremor-dominant idiopathic Parkinson's disease (IPD) and strictly unilateral resting tremor were investigated by cerebral high-resolution 3-dimensional magnetic resonance imaging (MRI). MRI data were analyzed by an observer-independent morphometric technique, voxel-based morphometry (VBM). For VBM, MRI data were automatically normalized and segmented, then gray matter volumes were analyzed on a voxel-by-voxel basis in comparison to an age-matched control group using Statistical Parametric Mapping (SPM99). Highly significant structural changes, i.e. locally increased gray matter concentrations (P<0.001), were found in the nucleus ventralis intermedius (VIM) of the thalamus contralateral to the tremor side and were significantly covariant with tremor amplitudes. On the one hand, these changes were localized in close vicinity to a thalamic focal hypermetabolism as revealed by a previous positron emission tomography study in unilateral Parkinsonian tremor patients. On the other hand, the localization of the focal structural changes in VIM corresponds with the generally accepted target area of tremor surgery in IPD.

Aged↗
PubMed2000

Effects of simulated source of tremor on acoustic and airflow voice measures.

To test the effects of different sources of tremor on the voice, tremor was simulated by external rhythmic perturbation of structures at the subglottal, glottal, and supraglottal levels in 10 healthy subjects. The acoustic and airflow signals simultaneously recorded during sustained phonation in the normal and the 3 simulated tremor conditions were analyzed and compared. Voice measures included: fundamental frequency, 2 short-term perturbation measures (jitter and shimmer), and 3 long-term tremor measures (prominence ratios of the spectral peaks of the acoustic frequency contour, acoustic amplitude contour, and airflow contour). Measures of fundamental frequency and percent shimmer were not significantly affected by the simulated tremors. Measures of percent jitter and the amplitudes of the long-term frequency and amplitude modulations were most prominently increased when respiratory drive was perturbed by simulated tremor. Spectral analysis of the acoustic amplitude contour was most useful in distinguishing the 3 sites of simulated tremor.

Adolescent↗
PubMed1996

The Parkinson larynx: tremor and videostroboscopic findings.

Patients with Parkinson's disease have a high incidence of speech, voice, and laryngeal abnormalities. To characterize laryngeal abnormalities, visual-perceptual ratings of endoscopic and stroboscopic examinations of 22 patients diagnosed with idiopathic Parkinson's disease and 7 patients with Parkinson's-plus syndromes were carried out by for trained viewers. Incidence of tremor, tremor location, phase closure, phase symmetry, amplitude, and mucosal waveform were scored. Tremor was observed in one or more of these conditions-rest, normal pitch and loudness, or loud phonation-for most of the 29 patients. Fifty-five percent of the idiopathic Parkinson's disease patients had tremor, with the primary location being vertical laryngeal tremor. Sixty-four percent of the Parkinson's-plus patients had tremor, with the arytenoid cartilages being the primary location. Laryngeal tremor was observed early in the disease in these Parkinson's disease patients. The most striking stroboscopic findings for the idiopathic Parkinson's disease patients were abnormal phase closure and phase asymmetry. Amplitude and mucosal wave-form were essentially within normal limits in the majority of the idiopathic Parkinson patients.

Aged↗
PubMed2002

Fluoxetine-induced tremor: clinical features in 21 patients.

We report a cohort of 21 patients (12 females and nine males), with a mean age of 42.4 years, who developed tremor after receiving fluoxetine at a mean dose of 25.7 mg per day. The mean latency period for tremor appearance was 54.3 days. Severity was found to be mild. In all patients, tremor was postural, with P<0.0005, compared to patients with rest tremor and P<0.05 compared to action/intention-tremor patients. The frequency range was 6-12 Hz/s. After fluoxetine was discontinued, tremor disappeared in 10 patients after a mean latency period of 35.5 days. In the remaining 11 patients, tremor persisted up to the end of the observation period (a mean of 449 days). We believe that this tremor phenomenon is due to the involvement of the red nucleus and the inferior olivary nucleus through their projections to the thalamus and the spinal cord.

Adult↗
PubMed2002

Kinetic tremor during tracking movements in patients with Parkinson's disease.

This study was undertaken to analyse kinetic tremor during a compensatory tracking task performed with the index fingers. Patients with Parkinson's disease (PD) (n=21) and control subjects (n=30) were tested using a laser system transducing displacement. All participants underwent a clinical examination. Nine characteristics quantifying the tracking task and tremor were applied to the processed displacement or velocity signal. The discriminating power of each characteristic was evaluated using differences between group means (p values), maximum percentage discrimination, and number of outliers in the patient group. All nine characteristics showed significant differences between means of the two groups using Welch-modified t-tests for unequal variances. The most discriminating characteristics reflected differences in the frequency distribution of the movement (proportional power in the 3-4Hz range, harmonicity and median frequency). These differences were rarely visible and did not correlate highly with tremor amplitude or with clinical ratings of tremor. Control subjects had residual spectral power from the tracking oscillations leaking above 3Hz, while most patients had a small 'kinetic tremor' in the 7-12Hz range. The maximum discrimination was moderate, 63% in the best case. Combining representative information about proportional power during posture (recorded in the same subjects) and tracking gave a much higher discrimination (90%) with respect to the 96.7th percentile of the control group. These results suggest that information coming from postural and kinetic tremors can be combined to isolate a subclinical feature of PD symptomatology. This feature could be used to re-evaluate the classic distinction made between the akineto-rigid and tremulous forms of PD and is independent of tremor amplitude.

Aged↗
PubMed2000

Tremor-correlated cortical activity detected by electroencephalography.

OBJECTIVE: In this study we investigated whether cortical activity related to Parkinsonian resting tremor can be detected by electroencephalography (EEG). METHODS: Seven patients with idiopathic Parkinson's disease suffering from unilateral tremor participated in the study. Electromyography (EMG) signals arising from the wrist extensor and flexor muscles as well as a high resolution EEG were recorded simultaneously. Coherencies between EEG and EMG were calculated. RESULTS: In all patients, we found highly significant coherencies at the tremor frequency or its first harmonic between the tremor EMG and contralateral EEG channels. There were no significant coherencies between the tremor EMG and ipsilateral EEG channels. Isocoherency maps illustrating the topography of the coherencies over the scalp showed that the maximum coherencies were situated over the cortical motor areas. In one case, a high coherency was also found over the parietal cortex. CONCLUSIONS: The results show for the first time that tremor-correlated cortical activity can be detected by electroencephalography. The findings underline that motor areas of the cerebral cortex are involved in the neuronal network generating resting tremor in Parkinson's disease.

Aged↗
PubMed2000

Modulation of symptomatic palatal tremor by magnetic stimulation of the motor cortex.

OBJECTIVES: Magnetic stimulation of the motor cortex can be used to determine the involvement of the cortex in rhythmic movement disorders. Symptomatic palatal tremor (SPT) is thought to come from a pacemaker that is relatively resistant to internal and external stimulation. In this study, we investigated the effect of magnetic stimulation of motor cortex on SPT. METHODS: Five male patients, aged 67-79 years, with SPT after brain stem infarction or hemorrhage, all had a synchronous mouth angle twitch with the palatal movement. Electromyographic activity was recorded with a monopolar needle electrode from orbicularis oris. In experiment 1, transcranial magnetic stimulation (TMS) was delivered at 200% motor threshold (MT) to reset SPT. In experiment 2, the effect of TMS intensities was studied at 80-240% MT in two SPT patients. To determine the influence of the TMS, we used the resetting index (RI). RESULTS: TMS reset the tremor in all 5 SPT patients at 200% MT with RIs of 0.86-0.96. The latency of the tremor reappearance after TMS was longer than the pre-stimulus tremor interval, and the intervals between the subsequent tremor bursts were also prolonged. The degree of tremor resetting was closely correlated with the magnetic stimulus intensity and the latency of the tremor reappearance after TMS. CONCLUSIONS: Stimulation of the motor cortex may modulate the generator of SPT.

Aged↗
PubMed2003

Dynamic synchronisation of central oscillators in essential tremor.

OBJECTIVE: Coherence analysis of electromyography (EMG) signals in essential tremor (ET) suggests that tremor in the right and left arm is induced by independent central oscillators. The sensorimotor cortex seems to be part of the tremor-generating neuronal network in ET. Here, we investigated using electroencephalography (EEG) whether the independence of central oscillators in ET is supported by the analysis of cortical activity. METHODS: In 8 patients with ET, bilateral hand tremor was activated by wrist extension. EMGs from the wrist flexors and extensors were recorded simultaneously with an EEG. EEG-EMG coherence was estimated for 74 epochs of 60 s duration. RESULTS: In 42.6% of the cases, EEG-EMG coherence at the tremor frequency existed only with the contralateral sensorimotor cortex. However, 21.6% of the tremor-EMGs were coherent with EEG activity over both the contralateral and ipsilateral sensorimotor cortex. Bilateral and exclusively contralateral EEG-EMG coherence could alternate within the same recording. Bilateral EEG-EMG coherence was associated with increased right-left EEG-EEG coherence, increased right-left EMG-EMG coherence as well as with increased tremor strength. CONCLUSIONS: In ET, central oscillators in the right and left brain are not entirely independent of each other. They may dynamically synchronise, presumably by interhemispheric coupling via the corpus callosum.

Adult↗