| | Functional Mobility and Postural Control in Essential TremorPresented in part to the Society for Neuroscience, November 12–16, 2005, Washington, DC. Abstract Parisi SL, Héroux ME, Culham EG, Norman KE. Functional mobility and postural control in essential tremor. ObjectiveTo evaluate functional mobility and postural control in participants with essential tremor (ET). DesignCross-sectional cohort study. SettingMotor performance research laboratory. ParticipantsSixteen participants with ET including head tremor (age, 59.4±12.0y), 14 participants with ET and no head tremor (age, 57.1±15.9y), and 28 healthy controls (age, 58.4±12.4y). InterventionsNot applicable. Main Outcome MeasuresWe 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. ResultsParticipants 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. ConclusionsParticipants with ET show reduced functional mobility, especially those with head tremor. ESSENTIAL TREMOR (ET) is the most common neurologically based movement disorder.1 It is estimated to affect between 0.4% and 3.9% of the population1 and, although it can become symptomatic at any age,2 there is general agreement that prevalence increases with age.1, 2 Population-based studies have estimated the prevalence of ET in people over 70 to be 5% to 7%.3, 4 ET is characterized primarily by hand tremor; however, tremor of the head, legs, voice, or trunk may also occur.5 A diagnosis of ET may be given when visible and persistent postural or kinetic tremor is observed in the hands or forearms (with or without other limbs affected) or in the head,6 and other neurologic disorders with similar tremor features (eg, Parkinson’s or cerebellar disease) have been ruled out. However, the vast majority of people with ET do not seek specialist medical attention and many remain undiagnosed.1, 3, 4, 7 Because hand tremor is the main feature of classic ET, studies of activity limitations in this population have principally focused on hand function.8, 9, 10, 11, 12 Nevertheless, limitations in whole body movements have also been reported in people with ET. Bain et al13 reported that many ET respondents to a survey reported difficulty with stairs. Furthermore, tandem gait abnormalities in people with ET have been reported14, 15 and recently have been shown to be similar to tandem gait abnormalities of people with cerebellar disease.16 These reports led us to hypothesize that there are movement performance impairment and activity limitations in many people with ET. Specifically, we hypothesized that people with ET have altered balance and limitations in functional mobility compared with age-matched control participants. Our primary objective was to determine if people with ET perform differently than a control group on a wide array of measures of functional mobility and postural control. Because ET is primarily a disorder of older adults, we considered it relevant to include measures that are associated with fall risk. Postural control in ET has recently been examined,17 but no previous studies of people with ET have investigated any of the other measures we used in this study. Although strength is neither reported nor suspected to be affected in ET, we measured participants’ strength in major lower-limb muscle groups because a decrement in lower-limb strength would be a confounding variable in functional mobility tasks. If people with ET have functional mobility limitations, it is clinically relevant to determine whether the severity of limitations is associated with tremor status. Our secondary objective was therefore to determine—for any measures of functional mobility in which the ET and control groups differed—whether outcomes on such measures correlated with measures of tremor or disease state. Our study was thus designed as a comparison of 2 groups. However, as participant testing and data processing proceeded, we noted that approximately half of our ET participants demonstrated head tremor. Head tremor may be hypothesized to have a deleterious effect on functional mobility and postural control based on how the head is normally controlled in walking and turning18 and the fact that extra head motion is likely to render more complicated the task of integrating visual and vestibular inputs for balance. In addition, there has been a recent report17 of postural control abnormalities in ET participants with head tremor. We therefore expanded our primary objective to perform a 3-group comparison: that is, whether there were differences between control participants, ET participants without head tremor and ET participants with head tremor on the aforementioned measures of functional mobility and postural control. Methods  Participants We recruited community-dwelling persons with ET through the local movement disorders clinic as well as through community advertisements for people with tremor. Prospective participants recruited through the latter route who had not been formally diagnosed with ET had other causes of tremor (eg, hyperthyroidism, medication) ruled out by their physician prior to inclusion. Control participants were recruited through community advertisement and through acquaintances of the investigators. Exclusion criteria for both groups included presence of other neurologic disorders, major musculoskeletal abnormalities or pain, and visual or cognitive impairments severe enough to render a participant unable to read the questionnaires or follow the instructions for the other measures. For the ET group, the use of medications known to affect tremor, other than β-adrenergic antagonists which are commonly prescribed and unlikely to affect coordination, was also an exclusion criterion. A pilot study on hand tremor and postural control showed statistically significant differences in groups with a sample size of 16 per group. To improve generalizability of the results, we aimed to recruit 30 subjects with ET and 30 without. All participants provided informed consent to the protocol that had been approved by the Health Sciences Research Ethics Board of Queen’s University and its affiliated hospitals. Procedures Intake interview and tremor assessment We interviewed participants to obtain demographic and relevant medical information, and history of falls or near-misses—the latter defined as the participant’s having felt that he/she was going to fall but did not actually do so—in the previous year. In addition, ET participants were questioned about features of their tremor including age of onset and which body parts were currently affected. We quantified hand tremor by measuring, using laser displacement sensors, the oscillations of a light box held in front of the body as described in a previous publication.19 In ET participants, we expected to find a predominant peak frequency and a concentration of power in the typical interval for this disorder between 4 and 9Hz; this was used as a confirmation of diagnosis and an inclusion criterion. While physiologic tremor at the wrist in this task will also include power in this frequency interval, it is without any predominant peak having a high concentration of power. Based on methods also described previously,19 a measure of postural tremor amplitude was calculated based on the highest summed power in a 1-Hz window surrounding the peak frequency in the power spectrum calculated from the acceleration time series. This was done for each hand, measuring both horizontal and vertical displacement of the box in each of 2 trials, for a total of 8 such values for each participant, the highest of which was used as our measure of tremor severity. We quantified disability associated with tremor by using the Tremor Disability Questionnaire (TDQ), which has shown to be a valid and reliable tool with people with ET.12 It was modified so that participants could self-administer the questionnaire and was subsequently scored by the investigators. A total tremor disability score out of 100 was assessed from answers to 36 questions, 31 of which relate almost entirely to the impact of tremor on hand function, and the remainder to tremor in other body parts and overall embarrassment from tremor. Higher scores represent greater disability. Clinical measures of functional mobility and balance We used 5 performance-based clinical measures. The Timed Up & Go (TUG) test requires the participant to rise from sitting, walk 3m, turn, and return to sitting.20 A mean time of 2 trials was our outcome measure. The Dynamic Gait Index (DGI) is an 8-item test designed to assess maintenance of balance during gait, each performed while walking down a hallway of 6.1m (20ft).21 All DGI items are scored 0, 1, 2, or 3 by an observer; the best possible score is 24. Tasks included items such as turning one’s head from side to side and stepping over an obstacle. The Berg Balance Scale (BBS) is a 14-item test in which participants are rated on ability to maintain balance while performing tasks such as standing with eyes closed, turning 360°, and standing on 1 foot.22 All BBS items are scored 0, 1, 2, 3, or 4 by an observer; the best possible score is 56. These 3 measures have demonstrated adequate interrater reliability in other studies.20, 23, 24 In addition, we developed timed tests of stair performance, one each of ascent and descent on a standard flight of 10 stairs, because of the earlier survey report of “difficulty with stairs.”13 For each test, participants were instructed to “go (up/down) as quickly as you safely can,” and participants were free to use the handrails located on either side. A short rest period was provided between the ascent and descent tests. Reliability was not determined for these timed stair tests. For all 5 of these clinical measures, testing was performed in the same settings—that is, same room for the TUG and BBS, same corridor for the DGI, same stairway for stair ascent and descent. All measures were timed or rated by 1 of 3 investigators using a standardized protocol. Blinding to group was not possible. We asked participants to complete 2 self-report measures. The Activities-specific Balance Confidence (ABC) scale consists of a list of 16 activities.25 For each activity, participants rated on a visual scale between 0% and 100% how confident they felt that they would not lose their balance or become unsteady. The outcome score of the ABC is the mean of all 16 ratings such that 100 is the maximum score and represents high balance confidence. The Human Activity Profile (HAP) is designed to determine a participant’s level of physical activity and consists of a list of 94 activities related to self-care, mobility, household tasks, or recreation listed in order of increasing metabolic cost.26, 27 Participants were assigned an “adjusted activity score” which is the difference between the rank of the most advanced activity reported as “still doing” and the number of activities reported as “have stopped doing” that are lower on the scale.26 The maximum score is 94 and indicates a high activity level. Both the ABC and HAP have demonstrated good test-retest reliability.25, 28 Postural control measures We obtained postural control measures from recordings of participants standing barefoot on a force platform.a Four 60-second trials were collected at a sampling rate of 500Hz under each of the following conditions: feet apart with eyes open, feet apart with eyes closed, feet together with eyes open, and feet together with eyes closed. The distance between a participant’s feet in the “feet apart” conditions was standardized according to height, with a maximum distance of 30cm between the bases of the fifth metatarsal bones. Subsequently, tandem stance trials of 30-second duration were recorded, 1 each of right-foot-ahead and left-foot-ahead. Center of pressure (COP) time series were calculated from the force platform outputs and were filtered with a 20Hz low-pass filter (Butterworth zero-lag, 10th order, in Matlab softwareb). Standard deviation (SD) of the COP in both the right-left and anteroposterior (AP) directions was calculated, and used as the outcome measures of overall displacement of the COP. Sway speed of the COP was also calculated based on the total path length of the COP and duration of the trial. For tandem stance the mean values from the 2 trials were calculated as the outcome measures. We attempted to develop a measure of head tremor using laser displacement sensors during recording of the first 4 stance conditions; however, a reliable method was not achieved. Therefore, participants were classified as having head tremor at least intermittently, or not having head tremor, based on visual observation or participant’s self-report. Strength measures We acquired strength data using a Biodex isokinetic dynamometer.c Peak torque during each of concentric flexion and extension was collected bilaterally from reciprocal motions at 60°/s about the knees, ankles, and hips. Each testing set consisted of 1 practice repetition, followed by 5 recorded repetitions. Data were sampled at 100Hz and processed off-line. Torque data were filtered with a 6-Hz low-pass filter (Butterworth, zero-lag, 4th order). Peak torque, from among the torque values created within 5% of the desired isokinetic speed, was obtained for both movement directions in each repetition. The mean of the 3 highest torque values was computed to provide 1 value for each joint in each direction. Preliminary analysis showed no significant difference between values from the left and right sides, and thus the mean of values from both sides was computed to create 1 score for each participant for each of extension and flexion of the ankle, knee, and hip. Values were then normalized to the participant’s body weight. Statistical Analysis Our recruitment of ET participants was such that approximately half of them had head tremor. As well, a preliminary inspection of the data indicated that ET participants with head tremor generally performed more poorly than ET participants without head tremor. Therefore, we elected to divide the ET group into 2 subgroups for analysis of dependent measures after verifying that relevant independent measures such as age and height did not differ across groups. We chose a value of .05 as the level of significance for all tests. Statistical analysis of all data was performed with SPSS software.d All clinical measures were tested for normal distribution using a Kolmogorov-Smirnov test. For normally distributed data, a multivariate analysis of variance (MANOVA) was performed. Because of small and unequal sample sizes, the Pillai trace statistic rather than the more commonly reported Wilks λ was examined. When a significant result was obtained, 1-way analysis of variance (ANOVA) tests were employed for each clinical measure to test whether there was a difference between the 3 groups and homogeneity of variance was tested with the Levene statistic. Where applicable, post hoc analyses were performed to determine differences between groups, using the Tukey honestly significant difference test for data with equal variances and the Dunnett test for data without equal variances. For ordinal data (BBS, DGI), Kruskal-Wallis tests were used to compare groups and, where applicable, post hoc analyses were performed using a Mann-Whitney U analysis. For postural control, we examined data from the first 4 stance conditions in a repeated-measures ANOVA, 2-within (foot position, vision), 1-between (group) design for each of the 3 dependent measures. Sphericity was confirmed using the Mauchly test. For tandem stance, 1-way ANOVAs were used to compare data between groups. Post hoc (Dunnett) testing was conducted where appropriate. Strength data were examined in a MANOVA. For clinical measures on which differences were found between groups, we entered scores for each of the ET groups into partial correlation matrices, controlling for age, with 4 variables representing disease status; that is, TDQ score, age of tremor onset, disease duration, and hand tremor severity. The tremor severity values were log transformed, to achieve a normal distribution, before being entered in the correlation calculations. Results Participants and Tremor Characteristics Thirty community-dwelling participants with ET participated. Further detail about the results of participant recruitment was described in a previous study of these participants’ performance in upper-limb function measures.19 Five of the ET participants had isolated head tremor; 11 had head tremor in addition to limb tremor. The other 14 ET participants had only upper-limb tremor. The control group was composed of 28 participants of similar age, height, and weight. Characteristics of the participant groups are shown in table 1. There were no significant differences between groups in age, height, weight, or body mass index. There was no significant difference between the 2 ET groups for any of the tremor characteristics. Clinical Measures of Functional Mobility and Balance Results for clinical scores with normally distributed data (TUG, stair ascent, stair descent, ABC, HAP) are shown in figure 1. The MANOVA revealed a significant difference between groups (Pillai trace, .393; F10,104=2.546, P=.009). The univariate ANOVAs revealed significant differences between groups on all 5 measures: TUG (F2,57=3.99, P=.024), stair ascent (F2,57=3.56, P=.035), stair descent (F2,57=3.36, P=.042), ABC (F2,57=8.34, P=.001), and HAP (F2,57=3.73, P=.030). All group means showed that the participants with ET with head tremor had the poorest performance. Mean scores from ET participants without head tremor were intermediate between those of controls and those of ET participants with head tremor. Post hoc analyses revealed statistically significant differences only between the controls and the ET group with head tremor for 4 of the 5 measures: TUG (mean difference, 1.43s; 95% confidence interval [CI], 0.11–2.75s), stair ascent (mean difference, .72s; 95% CI, 0.07–1.37s), ABC (mean difference, 10.5; 95% CI, 1.3–19.6), and HAP (mean difference, 6.8; 95% CI, 0.1–13.5). The scores on the DGI and BBS did not follow a normal distribution because of a ceiling effect for both scales among participants in all groups. The median, minimum, and maximum of scores from the 3 groups on the DGI and BBS are shown in table 2. The Kruskal-Wallis test revealed a significant difference between groups for DGI score (χ2 test=9.34, P=.009) and no difference for the BBS score. Post hoc Mann-Whitney U analysis for the DGI scores revealed a significant difference between the control group and the ET group with head tremor (P=.002). Although the median, minimum, and maximum of scores are similar across groups, the significant difference reflects the difference in distribution. Most control participants (n=22 [71%]) received the maximum score of 24 on the DGI and the remainder scored 23 (n=5 [18%]) or 21 (n=1), whereas among ET participants with head tremor, 6 (38%) scored 24, 3 (19%) scored 23, 4 (25%) scored 22, 2 (13%) scored 21, and 1 scored 20. The items on which ET participants most frequently did not attain maximum score were maintaining smooth gait while performing horizontal head turns and performing stairs, the latter always because of the need to use the handrail. | | |  | Measures | Control Participants | ET Participants Without Head Tremor | ET Participants With Head Tremor | |
|---|
| DGI (/24) | 24 (21–24) | 24(20–24) | 23(20–24) | | | BBS (/56) | 56(54–56) | 55.5(48–56) | 56(49–56) | | | | |
Postural Control Measures Values for right-left and AP sway displacement and sway speed in all stance conditions are shown in table 3. All participants were able to independently remain standing in all of the first 4 conditions, although many participants reported that the 4th task (feet together, eyes closed) was difficult. As expected, repeated-measures ANOVA on these 4 stance conditions showed a main effect of stance position (ie, feet apart or together) and a main effect of vision (ie, eyes open or closed) for all 3 dependent measures. No main effect of group was found for right-left sway or AP sway. There was, however, a main effect of group for sway speed (F2,57=3.81, P=.028). There were no interaction effects between group and other variables. Post hoc analysis revealed no significant difference between any 2 groups. All control participants and all but 2 ET participants (1 without head tremor, 1 with head tremor) were able to complete the 30-second tandem stance conditions, although many participants required additional trials. Similar to the results above, a between-group difference was found for sway speed (F2,57=4.24, P=.020) but post hoc analysis revealed no significant difference between any 2 groups. As in the other stance conditions, there were no significant differences between the groups for either right-left or AP sway. Among individual data, we noted that none of the ET participants without head tremor had discernible leg tremor, whereas 2 of the ET participants with head tremor had clearly visible leg tremor. One of these participants had the study’s greatest sway speed value in 4 of the 5 conditions. The other had the greatest sway speed in 1 condition and the second greatest value in 3 other conditions. The ANOVAs were therefore repeated after omitting data from these 2 participants. There was no longer any significant effect of group for sway speed. Strength Measures The control group’s mean peak torque value was higher than the other groups’ mean values for all measures (3 joints, 2 directions) but the variability was also high. The MANOVA revealed no effect of group (Pillai trace, .235; F12,102=1.129, P=.345). Correlation Analysis Between group differences were revealed on the TUG, ABC, HAP, stair ascent, stair descent, and DGI tests, as described previously, and they were thus examined in the partial correlation analysis, controlling for age, with measures of disease status. In the ET group with head tremor, no correlation coefficient was greater than r equal to .269 (P=.333) in absolute value. In the ET group without head tremor, the greatest (absolute value) correlation coefficient was r equal to −.555 (P=.049) between stair ascent time and disease duration. After adjusting the level of significance to reflect the multiple correlation analysis, none of these correlations was statistically significant. Discussion Functional Mobility Deficits in People With ET Our findings show that people with ET have reduced functional mobility, revealed by both performance-based measures and self-report measures, in comparison to a control group. The clinical importance of these findings should be interpreted in light of how much our sample of ET participants is typical of the ET population, and the magnitude of the difference between groups. In many respects, the ET participants in this study are typical of other ET samples reported. The tremor can manifest at any age, but the prevalence is higher in older adults. Our sample’s rates of positive family history and of tremor reduction from alcohol are intermediate in comparison to other reports.3, 13, 29, 30, 31, 32 Our sample’s rate of head tremor is somewhat higher than other reports,3, 4, 13, 14, 17, 30, 33 but can be explained by the presence of more women in our sample, among whom a higher prevalence of head tremor is reported.14, 33 Our sample’s mean, minimum, and maximum for age and tremor duration is very similar to the samples in other reports of tandem gait and postural control findings in ET.14, 16, 17 In 1 important respect, however, our ET sample was different from other ET samples, in having generally mild disease status, as shown by the low scores on the TDQ and the low percentage of participants using tremor-reducing medication. We attribute the relatively mild disease status of the ET participants to our recruitment via community advertisements, because community samples of people with ET generally have less severe tremor than clinic-based samples.34, 35 Having relatively mild ET cases makes the group differences in functional mobility status all the more striking. In hindsight, the ordinal scales we selected were relatively insensitive to potential deficits in our participants because these scales were designed for people with less mobility, especially the BBS. Although there was a significant group difference for DGI score, all participants scored above the proposed threshold of 19 seconds reported to be associated with falls in the elderly.36, 37 Similarly, the TUG performance of all participants was well below the threshold for risk of falls of 20 seconds proposed by the test developers20; only 1 ET participant’s TUG performance was above the more conservative threshold of 12 seconds proposed more recently.38 Nevertheless, the mean TUG time was 18% (ET without head tremor) to 23% (ET with head tremor) longer among ET participants than controls. Our findings for stair ascent and descent times were similar to our TUG findings, and are consistent with the previous report of “difficulty with stairs.”13 In self-report measures, the ET participants scored far above the mean reported for a “low mobility group” on the ABC25 and in the “average and above” category reported for the HAP.27 Based on these findings, we cannot conclude that any of our sample of ET participants are currently at high risk of falls. However, their performance on measures associated with fall risk is poorer than control participants of comparable age. Moreover, the findings on self-report measures corroborate the performance-based measures. Our findings indicate that head tremor, more than simply having ET, is associated with reduced performance and self-perceived mobility status. The between-group differences were small in our functional mobility measures, but it is important to note that the head tremor itself was small and intermittent in our ET participants. Many ET participants with head tremor reported that they first learned they had head tremor because they were told by others. In addition, many of them reported that they generally were not aware of it unless other people told them or interpreted their head movement to be that they were nodding “yes” or shaking their head “no” to an implicit question. Presumably, vestibulo-ocular reflexes stabilize vision sufficiently for small head tremor to remain largely sub-threshold for self-perception. However, head tremor will likely complicate the task of moving the head and stabilizing vision during tasks such as the sit-to-stand, turn and stand-to-sit transitions of the TUG, the head-turning tasks of the DGI and many of the items of the ABC. Head tremor—perhaps especially fluctuating, intermittent head tremor—creates a situation in which the visual and vestibular inputs that normally contribute to balance have more “noise” in the sense of a greater proportion of signal that is not related to whole body movement. Head tremor could thus lead to reduced mobility in either or both of the following ways. First, a person susceptible to head tremor may have developed a strategy of generally slowing down for safety (TUG, stairs) or being more cautious in vigorous or potentially destabilizing activities (HAP, ABC). Second, at least to explain the findings for TUG and stairs, the occurrence of tremor itself may result in slowness in specific components of the movements. Any explanation for why people with ET who have head tremor have reduced functional performance must also take into account that people with ET who do not have head tremor have a generally intermediate performance between control participants and ET participants with head tremor. It is possible but unlikely that they have head tremor that no one has yet noticed. It is also unlikely that weakness is an important contributor as it is in many neurologic disease groups. It is more likely that there is a more general change in movement ability associated with ET. We speculate that the general change in movement ability includes altered movement coordination, consistent with hypotheses proposed by others that at least some and perhaps all people with ET are developing coordination problems resembling cerebellar ataxia.16, 39, 40 These hypotheses are further supported by evidence from imaging studies that cerebellar function is altered in ET.41, 42, 43, 44, 45, 46 In the detailed study of tandem gait abnormalities in people with ET,16 a positive association was found between ordinal scale ratings of observed intention tremor of the hands, self-reported disability from tremor, and measures of tandem gait abnormalities similar to those seen in people with cerebellar ataxia.16 We did not find such an association between tremor and functional mobility measures, possibly due to inadequate measures of disease severity or due to the predominance of mild cases of tremor in our sample. Postural Control in ET There was a significant difference between groups in sway speed, but not for other measures of COP movement, in quiet standing under various conditions. These findings are highly consistent with a recent report that several postural sway variables did not differ in ET participants compared with controls, and only when ET participants with head tremor were separated from the rest was a difference found for COP path (directly related to mean sway speed).17 This report does not specify whether leg tremor was a feature of any of their ET participants with head tremor. However, our significant findings for sway speed appeared to be substantially influenced by outliers from 2 participants with leg tremor. These participants did not have outlying values from the rest of their group for sway excursion in the AP or right-left directions (nor for the functional mobility tests). Their sway speed values thus imply many small displacements of the COP within an overall area no different than that of other participants. We interpret our findings to mean that people with ET are not generally abnormal in their control of standing quietly, in contrast to their reduced performance and self-report status in more dynamic tasks. We acknowledge, however, that other postural control measures, or ET participants with more severe disease, might have led us to different conclusions. Nonetheless, it seems that postural control abnormalities do not necessarily precede alterations in functional mobility. Study Limitations and Needs for Future Research We cannot rule out that expectation bias may have contributed to our findings in performance-based measures, because the investigators conducting the tests were aware of the hypotheses. However, expectation bias does not seem to us a convincing explanation for the reduction in ET participants’ self-reported balance confidence and activity levels. Moreover, the hypothesis that ET participants with head tremor would have more reduced performance than ET participants without head tremor was developed after testing was completed. The design change from a 2-group to a 3-group comparison, however, reduced our power to detect statistically significant differences. In particular, for none of the measures were we able to determine if the ET participants without head tremor were different from either the control group or ET participants with head tremor. In addition, the late development of the hypothesis regarding head tremor meant that we did not obtain detailed information from participants regarding the status of their visual and vestibular systems. Such information would have been useful in relation to our speculations about how head tremor may be related to reduced functional performance. Arising from our findings, we see needs for future research that can be divided into 2 general categories: (1) the mechanism of head tremor’s effect on functional mobility and (2) the clinical implications of functional decline in older adults with ET. A method of quantifying head tremor is needed that captures the subtle tremor seen in most people with ET who have head tremor and that can be used in conjunction with functional tasks such as those in the measures we used. With such a method, hypotheses can be tested regarding the specific components of the tasks that head tremor affects and thus how head tremor may lead to reduced performance. The implication of our findings that ET may be associated with risk of greater functional decline than is typical for age needs to be evaluated in a study focused on older adults rather than the wide age range of our participants. It may then be important to determine if people with ET can benefit from the same types of interventions to reduce fall risk as other older adults with similar functional decline arising from other conditions. Conclusions On performance-based and self-report measures of functional mobility, participants with ET show poorer performance than control participants. The mean scores of participants with ET who have head tremor are poorer than those of ET participants without head tremor. The group differences are unlikely to be due to age or strength because these characteristics were similar across groups. The extent of the functional mobility reduction did not correlate with disease duration or severity of hand tremor. Thus, in this highly prevalent and mostly undiagnosed condition, people have reductions in functional mobility for reasons that appear unrelated to hand tremor but may be, at least in some cases, related to head tremor. Suppliers Acknowledgments We thank Juliana Larocerie-Salgado, BOT, and Daphne Pala, BSc, for their assistance in conducting the evaluation of participants. References 1. 1Louis ED. Essential tremor. Lancet Neurol. 2005;4:100–110. Abstract | Full Text |
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46. 46Pagan FL, Butman JA, Dambrosia JM, Hallett M. Evaluation of essential tremor with multi-voxel magnetic resonance spectroscopy. Neurology. 2003;60:1344–1347. School of Rehabilitation Therapy, Queen’s University, Kingston, ON, Canada.  Reprint requests to Kathleen E. Norman, PhD, PT, School of Rehabilitation Therapy, Queen’s University, 31 George St, Kingston, ON K7L 3N6, Canada
Supported by the Ministry of Colleges and Universities of Ontario (graduate scholarship), a Carmichael Scholarship, the Canadian Institutes of Health Research (grant no. MOP67044). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. PII: S0003-9993(06)00841-0 doi:10.1016/j.apmr.2006.07.255 © 2006 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved. | |
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