| | Upper-Extremity Disability in Essential TremorPresented in part to the Society for Neuroscience, November 12–16, 2005, Washington, DC. Accepted 10 January 2006. Abstract Héroux ME, Parisi SL, Larocerie-Salgado J, Norman KE. Upper-extremity disability in essential tremor. ObjectiveTo determine the extent of disability in subjects with essential tremor (ET) using time-based, standardized measures of upper-extremity function. DesignDescriptive case series. SettingMotor performance research laboratory. ParticipantsThirty subjects with ET (mean age, 58.3±13.7y) and 28 healthy controls (mean age, 58.4±12.4y). InterventionsNot applicable. Main Outcome MeasuresWe assessed upper-extremity function using the Box and Block Test, Purdue Pegboard Test (PPT), and Test Évaluant la performance des Membres supérieurs des Personnes Âgées (TEMPA). We measured tremor severity with laser displacement sensors. ResultsSubjects with ET-type tremor in 1 or both hands performed significantly worse than controls on all unilateral and bilateral tasks (P range, .038–.001) except on the PPT for the dominant side. ET subjects without ET-type tremor in the dominant hand also performed significantly worse than controls on the TEMPA unilateral tasks (P=.043). Performance on the 3 functional measures correlated moderately with tremor severity for the nondominant hand. ConclusionsSubjects with ET show measurable disability on time-based measures of upper-extremity function. However, our findings are consistent with other reports that tremor severity does not correlate well with disability, especially with regard to the dominant upper extremity.
ESSENTIAL TREMOR (ET) IS THE MOST common tremor disorder and ranks among the most common neurologic movement disorders.1 Because the tremor persists, there is a much higher prevalence of ET in older adults, estimated at 4.0% to 37% in people older than 40 to 55 years,2, 3, 4, 5, 6 many of whom are never formally diagnosed.4, 7, 8 The principal criterion for diagnosing ET is the clinical observation of postural or kinetic tremor involving the hands and forearms that is visible and persistent; additional or isolated tremor of the head may also be present.9, 10, 11 There may also be tremor in the voice, jaw, or lower extremities. In addition, other common causes of tremor—enhanced physiologic tremor, altered thyroid function, Parkinson’s disease, dystonia, or other neurologic disorders—must be ruled out.12
The rhythmic, involuntary muscle activity that is characteristic of ET is thought to be primarily responsible for the functional deficits present in this patient population.13, 14, 15 Approximately 75% of those diagnosed with ET present with some form of activity limitation (ie, disability) in tasks such as feeding, drinking, writing, fine object manipulation, and body care.7, 8, 16, 17 In addition, 53% to 63% of subjects with previously undiagnosed ET report some form of activity limitation due to tremor.7, 8 To date, however, activity limitations in people with ET have been assessed primarily with nonstandard questionnaires and functional tests,13, 18, 19 and condition-specific (ET or Parkinson’s disease) or symptom-specific (tremor) ordinal scale performance-based measures and questionnaires.15, 17, 18, 20, 21, 22, 23 Similar to the use of ordinal scales to rate tremor severity,8, 13, 17 ordinal scale questionnaires and performance-based measures are prone to floor and ceiling effects, especially in mild tremor cases.13, 19 With these measures, therefore, it is not possible to adequately assess functional deficits in subjects with mild ET. Recent reports also indicate that ET is not a monosymptomatic condition in light of the evidence for impaired ballistic movements,24, 25 coordination deficits,26 and eye movement abnormalities,27 in addition to other nonmotor abnormalities.28, 29, 30, 31 Thus, condition- and symptom-specific performance-based measures and questionnaires may not capture the extent of activity limitations present in ET.
There is, therefore, a dearth of information regarding the level of disability in people with ET as assessed by standardized measures commonly used in the rehabilitation science literature. The use of valid and reliable standardized measures of upper-extremity function would permit disability associated with ET to be compared with population norms and with data from other populations with upper-extremity disability. The primary objective of this study was to determine the extent of disability in subjects with ET as assessed by time-based, standardized, performance-based measures of upper-extremity function. We also examined the relation between performance on these standardized measures and both tremor severity and self-reported tremor-related disability.
Methods  Participants We recruited community-dwelling subjects with ET from the local movement disorders clinic and from community advertisements for people with tremor. For prospective subjects who had not been formally diagnosed with ET, causes of tremor other than ET were ruled out by each person’s family physician. We recruited control subjects from community advertisements and acquaintances of the investigators. Exclusion criteria for both ET and control subjects included other neurologic disorders, the use of psychotropic medications or medications known to affect tremor (excluding β-adrenergic antagonists), and factors that may have confounded the measurement of disability: major musculoskeletal abnormalities or pain or severe visual impairments. The rationale for including subjects taking β-adrenergic antagonists was that these medications, based on their mechanism, were unlikely to affect coordination.32 Moreover, they are the most common category of medication prescribed for ET; therefore, excluding such subjects would have reduced both the sample size and the generalizability of results to the ET population. All subjects 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. Procedure Subjective assessment We interviewed subjects to obtain demographic data and we determined how long they had been aware of their tremor, what body parts were affected, whether any relatives showed tremor, and whether they took any medications to reduce tremor. To assess ET subjects’ perceived functional limitations due to tremor, we administered the Tremor Disability Questionnaire (TDQ),33 which has been shown to be a valid and reliable measurement tool in this patient population.20 The TDQ consists of a total of 36 items; however, we focused on the first 31 items because they are used to tabulate a total hand tremor disability score. It was modified from its original form to make it a questionnaire completed by subjects and scored subsequently by investigators, rather than administered by interview. Hand tremor testing We quantified subjects’ hand tremor by measuring the oscillations of a light object held in front of the body in a posture like that of holding a cup of liquid—a task that is reported to be problematic for many people with tremor. Each subject was seated without back support, holding a styrofoam box (mass, 44g) approximately 40 to 50cm in front of the lower chest, with the shoulder slightly abducted and flexed and the elbow flexed approximately 80° (fig 1). The box had a recessed handle permitting a grip (width, 3.5cm) between the thumb and first 2 to 3 fingers. The movement of the box was measured with 2 high-precision laser displacement sensorsa positioned such that vertical movement corresponded approximately to wrist ulnar-radial deviation and horizontal movement to wrist flexion and extension. Two 30-second trials were recorded for each hand, starting with the dominant hand, with a break of approximately 60 seconds between successive trials. Signals were sampled at 1000Hz and stored on a computer for off-line analysis. Upper-extremity function testing We quantified subjects’ upper-extremity functional status using 3 measures of upper-extremity function widely used in the rehabilitation literature: the Box and Block Test (BBT),34, 35 the Test Évaluant la performance des Membres supérieurs des Personnes Âgées (TEMPA),36 and the Purdue Pegboard Test (PPT).37, 38 These valid and reliable measures were selected because they are time-based measures, they focus on different aspects of upper-extremity function, they have published norms, and they are not symptom or condition specific. The BBT consists of moving, one by one, the maximum number of blocks (2.5cm3) from 1 compartment of a box to another of equal size within 60 seconds and thus provides 2 outcome measures: number of blocks transferred with each of the dominant and nondominant hands. The PPT consists of placing the maximum amount of pegs into slots on a board—done unilaterally and bilaterally—and a bilateral assembly task with pegs, washers, and collars. The PPT provides 4 outcome measures: number of pegs placed with each of the dominant and nondominant hands in separate 30-second trials; number of pairs of pegs placed using both hands in 30 seconds; and number of component parts placed during the assembly task in 60 seconds. The TEMPA is composed of 9 standardized tasks representing daily activities that require varying degrees of fine- and gross-motor function of the upper extremities. Four tasks are unilateral and are done with the dominant hand first (pick up and move a jar; pick up a pitcher and pour water into a glass; manipulate coins; pick up and move small objects), whereas the other 5 tasks are bilateral (open a jar and take a spoonful of coffee; unlock a cabinet and open a pill container; write on an envelope and stick on a stamp; tie a scarf around one’s neck; shuffle and deal playing cards). Scoring for the TEMPA is based on the time to perform tasks and an ordinal rating (0–4) of functional performance; only the time was used in our analyses. The total time was summed for each of the dominant and nondominant hands’ performance on the 4 unilateral tasks and the 5 bilateral tasks. The grand total of time for all TEMPA tasks was also summed. Data Processing Hand tremor recordings were low-pass filtered (Butterworth zero-lag, fourth-order) at 20Hz and differentiated twice to produce time series in acceleration units. In ET subjects, we expected to find a predominant peak frequency and a concentration of power in the typical range for this disorder of 4 to 9Hz.1, 39 Physiologic tremor at the wrist in this task will also include power in this frequency range but without any predominant concentration of power. From each acceleration time series, we calculated a power spectrum with a frequency resolution of 0.1Hz and then determined the peak frequency in the 4-to-9Hz range. Next we determined the sum of power within all windows of 1-Hz width that included the peak frequency and retained the largest of these summed power values. Thus, for each hand of ET and control subjects, we obtained 4 values of postural tremor (2 trials, 2 directions of movement recorded). We used the highest of these 4 values in the categorization process described as follows and in the correlation analysis described subsequently. The categorization of ET subjects as having ET-type tremor in the dominant or nondominant hands was based on a comparison with data from control subjects. The maximal postural tremor amplitude values for the dominant and nondominant hands were averaged across control subjects and were used to construct 99% confidence intervals for physiologic tremor. Each hand of each ET subject was classified as having ET-type tremor (ie, greater amplitude than physiologic tremor) if at least 1 of their 4 postural tremor amplitude values was greater than the upper limit of the corresponding 99% confidence intervals for control subjects for either the dominant or nondominant hand. Data Analysis For the PPT, BBT, and TEMPA scores, we calculated z scores for control subjects who were in age and sex categories for which published norms are available.35, 36, 38, 40 We examined the mean and distribution of all calculable z scores to verify that our control group was reasonably comparable with other healthy comparison groups. Furthermore, all of the timed task measures, TDQ scores, and tremor severity measures were examined with Kolmogorov-Smirnov tests to verify Gaussian distribution. Measures for which the raw scores were not normally distributed were log-transformed, and we verified that this transformation resulted in a distribution adequately close to Gaussian (ie, nonsignificant Kolmogorov-Smirnov statistic) for performance of parametric inferential statistics. We performed analyses of variance (ANOVAs) to determine if there were differences in performance on the timed tasks in control subjects compared with 2 subgroups of ET subjects: those with and those without measurable ET-type tremor in the hand(s) used for the timed task. When a significant F value was found, post hoc comparisons were performed using the Tukey honestly significant difference method. The associations between measured tremor severity and unilateral PPT, BBT, and TEMPA scores from control subjects and ET subjects with and without tremor were examined using the Pearson product-moment correlation coefficient. In the correlation matrices for ET subjects, the TDQ score was also included. The level of significance was set at P less than .05 for all tests; significance for correlation analysis was adjusted for multiple comparisons using a Bonferroni adjustment. All statistical analyses were performed in SPSS, version 12.0,b for Windows. Results Thirty-one community-dwelling subjects with ET were recruited: 8 from the local movement disorders clinic and 23 from community advertisements. One prospective ET subject who had not been formally diagnosed did not show head tremor or ET-type hand tremor during testing, and his data were excluded from subsequent analysis. The data from the remaining 30 ET subjects were used for analysis. The control group was composed of 28 subjects of similar age, height, and weight. Characteristics of the subject groups are shown in table 1. Hand Tremor Measure and Categorization As expected, most subjects with ET had ET-type hand tremor on at least 1 side. Figure 2 shows examples of recorded hand tremor from a control subject (CN07) and an ET subject with obvious hand tremor during testing (ET07); both subjects were 67-year-old right-handed women. In the ET group, 19 subjects had bilateral ET-type hand tremor and 5 subjects had unilateral ET-type hand tremor (2 dominant, 3 nondominant). Of these 24 ET subjects, 11 also presented with head tremor. The remaining 6 ET subjects did not have ET-type hand tremor during measurement. Five of these subjects had head tremor and 1 subject had been formally diagnosed as having ET on the basis of hand tremor and reported the presence of visible hand tremor on a regular but not constant basis. Postural hand tremor values for the dominant and nondominant hands of ET subjects categorized as either having or not having ET-type hand tremor are reported in table 2. These values for the ET tremor group varied widely, as reflected by the 10th- and 90th-percentile values. It is important to note that—based on TDQ scores, the high percentage (73%) of community cases, and the low percentage (20%) using tremor-reducing medication—the ET subjects tested in the present study primarily had mild ET, with a few moderate cases. Therefore, even the highest postural hand tremor values in the tremor group are likely substantially smaller than what could be expected in more severe ET. Upper-Extremity Function Measures Examination of mean values and the distribution of all calculable z scores confirmed that our control group was very similar to other healthy comparison groups reported in the literature for the BBT,34, 35 the PPT,37, 38 and the TEMPA (no comparative norms for those under 60y).36 For the BBT task, there was a main group effect for data from both the dominant (F2,57=3.69, P=.031) and nondominant sides (F2,57=4.88, P=.011) when comparing control subjects to ET subjects with and without ET-type hand tremor (figs 3A, 3B). Post hoc analysis showed that control subjects performed better than ET subjects with ET-type hand tremor on both the dominant (P=.031) and nondominant sides (P=.021). In terms of performance on the BBT, this means that ET subjects who had ET-type tremor transferred, on average, 7 (dominant) and 8 (nondominant) fewer blocks over the 60-second test period compared with controls. In the PPT, there was a trend for ET subjects categorized as having ET-type tremor in the dominant hand to have reduced performance compared with the control group (fig 4A); however, the ANOVA showed no significant group effect (F2,57=3.02, P=.057). There was a significant group effect for data from the nondominant side (F2,57=3.51, P=.037) (fig 4B), with post hoc analysis showing that ET subjects with ET-type tremor in the nondominant hand had significantly reduced performance on the unilateral task of the PPT (P=.038). Whereas control subjects were averaging almost 14 pegs placed in 30 seconds with the nondominant hand, ET subjects categorized as having ET-type tremor on the nondominant side placed an average of 12 pegs in 30 seconds. The PPT also comprises 2 bimanual tasks consisting of placing the maximum number of pegs with both hands simultaneously and an assembly task with pegs, washers, and collars. To analyze these components of the PPT, it was necessary to divide the ET group into subjects with ET-type tremor in neither hand (n=6) and those with ET-type tremor in either or both hands (n=24). There was a significant group effect for the paired peg–placing task (F2,57=3.48, P=.038) and the assembly task (F2,57=4.57, P=.015) (see figs 4C, 4D), with post hoc analyses showing a significant reduction in performance in ET subjects with ET-type tremor in either and both hands for both the paired (P=.03) and assembly tasks (P=.01). Overall, the performance of subjects with ET was significantly impaired in the TEMPA when compared with controls, which is reflected by the increased time taken to complete the various tasks (fig 5). For the unilateral tasks of the TEMPA, there were significant group effects for data from both the dominant (F2,57=8.89, P<.001) and nondominant sides (F2,57=4.47, P=.016). Similar to the results from the BBT, post hoc analysis showed that ET subjects categorized as having ET-type tremor in the dominant (P=.001) or nondominant hands (P=.021) performed significantly worse than control subjects (see figs 5A, 5B). Interestingly, the performance of ET subjects categorized as having no ET-type tremor in the dominant hand was also significantly worse than controls (P=.043). To complete the 4 unilateral tasks, ET subjects with ET-type hand tremor took an average of 4.5 seconds longer than controls with the dominant hand and 4.0 seconds longer with the nondominant hand. ET subjects categorized as having no ET-type tremor in the dominant hand took 4.0 seconds longer than controls to complete the unilateral tasks. To analyze bilateral tasks and the TEMPA total time, ET subjects were grouped in the same manner used for the bilateral tasks of the PPT. There was a significant group effect for the bilateral tasks (F2,57=4.40, P=.017), and post hoc analysis showed that ET subjects categorized as having ET-type tremor in at least 1 hand performed the bilateral tasks significantly more slowly than control subjects (P=.014). On average, this ET subgroup took almost 8 seconds longer to complete the 4 bilateral tasks when compared with the control group (see fig 5C). In terms of overall performance—that is, total TEMPA time—ANOVA showed a significant group effect (F2,57=6.10, P=.004), with a significant difference between the total time of the control group and ET subjects with ET-type tremor in at least 1 hand (P=.003) (see fig 5D). Relation Between Tremor and Upper-Extremity Function Measures Correlation analysis showed no association between dominant-hand tremor severity and dominant-side BBT, PPT, and TEMPA scores for the control group and ET subjects with and without ET-type hand tremor. On the nondominant side, there was no association between hand tremor values and corresponding unilateral BBT, PPT, and TEMPA scores in control subjects and in ET subjects with no ET-type tremor. There was, however, a significant correlation between tremor values from ET subjects with ET-type tremor in the nondominant hand and TEMPA (r=.73, P<.001), BBT (r=−.73, P<.001), and PPT scores (r=−.61, P=.004). These results indicate that those subjects with ET-type tremor in the nondominant hand who had more severe tremor tended to take longer to complete the unilateral TEMPA task (positive correlation) and placed fewer pegs and transferred fewer blocks during the PPT and BBT (negative correlations). TDQ scores did not correlate with upper-extremity functional measures and measures of tremor severity in either the dominant or nondominant hands. Discussion Activity Limitations in ET Our recruitment process resulted in a sample of people with ET who predominantly had mild hand tremor. Nevertheless, we found significant differences in time-based measures of upper-extremity function between ET subjects and controls in tasks requiring varying levels of fine pinch grip, gross grasping, object transportation, and precision placement. Furthermore, postural hand tremor severity was proportional to functional performance on the nondominant side but not on the dominant side. These findings represent disability, albeit to a small degree, based on the observed differences between groups. For example, a difference of 7 or 8 blocks in the BBT is similar to the difference in the norms reported for healthy adults in their thirties compared with those in their fifties.34 Similarly, the difference of 2 pegs on the unilateral PPT task found between controls and ET subjects with ET-type hand tremor is similar to the differences reported between the dominant and nondominant hands in young adults or between young adults and older adults.37 These limitations are mild in contrast to those reported for similarly aged subjects who have other neurologic diagnoses. For example, on the BBT, chronic stroke subjects placed an average of 30 fewer blocks using the paretic upper extremity than our ET subjects using either side.41 On the PPT, subjects with multiple sclerosis placed an average of 5 to 6 fewer pegs on each of the single-peg subtests than our ET subjects.42 On the TEMPA, many chronic stroke subjects are not able to complete the tasks without modification, in which case the functional score is reported rather than the execution time.43 In subjects with multiple sclerosis for whom TEMPA execution times were reported, subtotals for unilateral tasks with each upper extremity and for bilateral tasks, as well as total time, all were approximately 4 times the values we report for ET subjects.44 These contrasts put in perspective the fact that the disability in people with mild ET is much less than in other populations. However, our findings suggest that people with mild ET are performing similarly to control subjects a decade or so older, or as if the dominant hand was becoming as limited as a typical nondominant hand. Nature of Measures Our findings show that it is possible to quantify upper-extremity disability in people with ET using measures not focused on tremor. To date, most of the reports of disability in people with ET have relied on tremor-focused measures.8, 13, 14, 15, 45 Although this approach has obvious face validity, especially for evaluating outcomes of treatment to reduce tremor, there are 2 evident drawbacks. First, the extent of disability cannot be compared with other disease groups, and there are no population norms for tremor-focused measures. The second and more serious drawback is that most methods of assessing functional disability in tremor cases are ordinal scale systems. Although well-designed ordinal scale systems are useful in many areas of rehabilitation, such systems are, by definition, incapable of doing more than ordering the degree of limitation. Moreover, they frequently have floor or ceiling effects such that subtle abnormalities are missed. In contrast, time-based measures generally avoid the floor or ceiling effect problem and intervals between levels (time or item count) are known to be equal. Furthermore, rater bias is minimized and the principal source of error is at the experimenter-stopwatch interface. Thus, avoiding floor or ceiling effects and having constant intervals between levels improves the validity of correlational analysis to examine associations among measures of disability and tremor. Association of Tremor Severity With Activity Limitations Our correlation analysis showed that there was a significant association between performance on timed tasks and tremor severity in the nondominant upper extremity. This association was in the expected direction: that is, greater tremor severity was associated with poorer performance on the functional tasks. More specifically, this association was between the log-transformed tremor amplitude and untransformed functional task scores, meaning that placing 1 peg fewer on the PPT or 1 block fewer on the BBT was related to a 10-fold increase in tremor amplitude. Thus, the relation between tremor severity and functional deficits appears to be exponential, at least for the nondominant hand. In contrast, we found no relation between tremor severity and functional deficits in the dominant upper extremity. We will first discuss the extent to which these findings are consistent with those of other studies and subsequently discuss possible reasons for these findings. In a study of 20 subjects with ET, Bain et al13 reported that an acceleration measure of hand tremor in the dominant hand did not correlate with measures of activities of daily living (ADLs), writing impairment, or spiral drawing. Interestingly, they found a significant correlation between an ordinal scale rating of observed tremor and both their acceleration measure and their ADL, writing, and drawing measures. They attributed these findings to the observation that the raters included both periodic (ie, tremor) and aperiodic irregularities in their ratings of severity, supporting the concept that tremor alone does not have a strong relation with disability in the dominant hand.13 In a separate study of 15 subjects with ET, Bain et al14 reported that an acceleration measure of tremor severity correlated significantly with an ordinal rating of spiral drawing, a joystick-based tracking task, and amount of water spilled when holding a cup of water. Data were recorded from both hands and the results were pooled. The latter report contains graphs of data that show a highly skewed distribution of tremor severity very similar to what we found before log-transforming our measure of tremor severity. Other graphs in the latter report show that all 3 of their functional measures had a substantial floor effect. The significant correlations they found thus included several cases of severe hand tremor associated with functional scores well above the floor effect of the hand measures; had they not included subjects with severe tremor, they would not likely have found significant correlations. It is a general principle of correlation analysis that a wider range of data values makes it more likely to show covariance (ie, find a significant correlation coefficient), but that does not mean that the nature of the relation remains similar when considering less extensive ranges of data values.46 In relation to hand tremor, this means that severe tremor may be associated with severe activity limitations, but the association may be weaker or nonexistent with less severe tremor. The importance of tremor severity range to the identification of a relation between tremor and disability is well illustrated by 2 reports by Louis et al.8, 15 They developed a 15-item test to assess functional performance in ET subjects in which tasks such as pouring liquid, copying sentences, and placing keys in locks are rated 0 (no difficulty) to 4 (unable to perform) by an observer.15 Among 50 subjects with ET, the total functional score correlated significantly with an accelerometry measure of tremor severity. However, when data from only the mild tremor cases were included, there was no significant correlation between functional score and tremor severity.15 Neither raw data nor separate analyses for dominant and nondominant hands were provided, but the means, standard deviations, and ranges of functional scores suggest that a potential reason for no correlation was a floor effect in the functional score. In a subsequent study of 89 subjects with ET, scores from the same functional performance scale were significantly associated with age, anxiety, and tremor severity rated by an observer but notably not with a tremor severity measure based on acceleration.8 Among their subjects with ET, 37 of the 89 were community patients in whom tremor is generally less severe than in clinic patients. This report is consistent with ours in finding measurable disability among community subjects with mild ET, and we attribute our ability to find a significant correlation between tremor severity and functional performance to the better measurement properties of our functional performance measures. The significant correlations we found between tremor severity and functional performance, however, were only for data from the nondominant hand. With the dominant hand, ET subjects showed greater functional deficits than controls but not in proportion to their tremor severity. We propose that this is related to subjects’ more frequent use of this hand. Some components of the BBT, PPT, and TEMPA resemble tasks that are frequently performed by people primarily with the dominant hand, but the extent of this practice may vary across subjects. Not only may practice contribute more to score variation than tremor severity, but practice may also lead to adaptations that reduce the impact of tremor on common functional tasks. The mean group difference between ET subjects and controls nonetheless suggests that features of the disorder of ET result in slowed performance. In addition to hand tremor, we suggest that 2 other features of ET likely contributed to our findings. The first feature is head tremor. Almost all functional hand tasks involve a component of hand-eye coordination, which necessarily depends on oculomotor and head control. Head movement is a normal part of gaze shifting during hand movements about a workspace comparable in size to that of the functional tests we used.47 Moreover, the proportion of gaze movement created by head movement is typically greater in older adults (>40y).48 Not only have eye movement abnormalities been shown in ET,27 but also this is a population in which head tremor is known to affect a substantial proportion of patients,1 as indeed it did in our sample. Although the head tremor is often subtle, we speculate that it likely complicates the nervous system’s task of gaze control for hand coordination, especially in the age range of most people with ET. The second feature is ataxia. In kinematic analyses of upper-extremity movement, ET subjects have shown movement abnormalities similar to subjects with ataxia from cerebellar dysfunction.24, 26 Tandem gait abnormalities have also been found in ET49, 50, 51 that are in some respects very similar to abnormalities associated with cerebellar dysfunction.51 Thus, the reduced performance we measured in functional hand tasks may have arisen, at least partially, from subtle ataxia. Conclusions On time-based measures of upper-extremity functional impairment, subjects with ET show measurable disability. The extent of disability in a group of mostly community patients with ET with mild tremor is comparable to an aging effect or to having a dominant hand perform like a nondominant hand. Although time-based measures appear better suited than ordinal scale ratings for assessing the relation between tremor severity and disability, our findings are consistent with other reports that tremor severity does not correlate well with disability, especially with regard to the dominant upper extremity. From a clinical perspective, our findings confirm that disability is present in this highly prevalent but underdiagnosed condition. From a research perspective, our findings underscore the fact that much work remains to be done to understand why people with ET have functional disability. Suppliers
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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, and 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 author(s) or upon any organization with which the author(s) is/are associated. PII: S0003-9993(06)00100-6 doi:10.1016/j.apmr.2006.01.017 © 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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