MULTIPLE SCLEROSIS (MS) is the most common progressive

Transcription

1 215 Clinical Tests of Standing Balance: Performance of Persons With Multiple Sclerosis Dragana Frzovic, BPhty(Hons), Meg E. Morris, PhD, Lindsay Vowels, PhD ABSTRACT. Frzovic D, Morris ME, Vowels L. Clinical tests of standing balance: performance of persons with multiple sclerosis. Arch Phys Med Rehabil 2000;81: Objective: To investigate differences in performance between people with multiple sclerosis (MS) and control subjects on clinical tests of balance, and to assess performance consistency on balance tests in people with MS from morning to afternoon. Study Design: Two factor repeated measures design with a two group sample of convenience. Setting: Kingston Centre and the Camberwell Centre of the MS Society of Victoria, Australia. Subjects: Fourteen people with MS and 14 control subjects matched for age, height, and sex. Main Outcome Measures: Subjects were measured on their ability to maintain standing balance in steady stance, (feet apart, feet together, stride stance, tandem stance, and single leg stance), during self-generated perturbations (functional reach, arm raise, and step tests) and in response to an external perturbation. Participants with MS were also asked to rate their fatigue level in the morning and afternoon. Results: There were no differences between MS and control groups on the ability to maintain standing balance with feet apart, feet together, or in stride stance. Participants with MS performed more poorly than control subjects in tandem stance and single leg stance and in the functional reach test, arm raise test, step test, and in response to an external perturbation. There was little change in balance from morning to afternoon in participants with MS (ICCs (2,1).70 to.94), despite an increase in self-rated fatigue (t(14) 3.14, p.008). Conclusion: The ability to maintain balance in standing is a marked problem in people with MS despite the consistency of their performance from morning to afternoon. Key Words: Balance; Postural control; Physical therapy; Multiple sclerosis; Rehabilitation by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation From the School of Physiotherapy, Faculty of Health Sciences, LaTrobe University, Bundoora, Victoria (Ms. Frzovic, Dr. Morris); Westmead Hospital, New South Wales (Ms. Frzovic); and the Multiple Sclerosis Society of Victoria, Toorak (Dr. Vowels), Australia. Submitted for publication January 14, Accepted in revised form June 10, Supported by a scholarship from the National Multiple Sclerosis Society of Australia. Presented in part at the Fifth International Congress of the Australian Physiotherapy Association, May 15, 1998, Hobart, Australia. 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. Reprint requests to Professor Meg E. Morris, School of Physiotherapy, La Trobe University, Bundoora, 3083, Australia by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation /00/ $3.00/0 MULTIPLE SCLEROSIS (MS) is the most common progressive neurologic disease in young adults. 1 It leads to widespread degeneration of myelin sheaths surrounding the axons of sensory and motor neurons within the central nervous system (CNS). 2 Because of the variable distribution of demyelination throughout the CNS, people with MS may experience disorders of balance, coordination, strength, sensation, and vision. 3 Balance disorders are particularly problematic because they are associated with difficulty in moving from one position to another, sustaining an upright posture, and performing functional activities such as walking and turning, all of which predisposes people with MS to loss of equilibrium and falls. Adequate balance relies on integration of inputs from the visual, somatosensory, and vestibular systems, 4 which are frequently impaired in people with MS. 5 The visual system may be disturbed by plaques in the optic nerve leading to blindness, blurred vision, or diplopia. 2 Involvement of the vestibular tracts can be associated with vertigo and nystagmus. 5 Lesions in the long ascending sensory tracts can cause disordered proprioception and impaired vibration sense. 5 In addition, abnormal somatosensory evoked potential latencies have been observed, 6 which indicates that sensory integration may be distorted. Muscle weakness and spasticity further compromise the ability to balance by affecting the sequencing and force of muscle contraction. 3 As with other patient populations with balance disorders, people with MS have an increased prevalence of falls Common sequelae of falls include fractures, 14 abrasions and lacerations, compromised mobility, loss of confidence in performing tasks, and fear of falling. 15 Although considerable clinical resources are dedicated to the restitution of balance and falls prevention in people with MS 16 few studies of postural control have been done in this population. To enable clinicians to assess the severity of balance disorders and to evaluate the effectiveness of intervention, data on the performance of people with MS on clinical tests of balance are required. To be applicable in the clinical setting, balance tests must be reliable and valid, use readily available equipment, require little experience to master, and be easy to administer. 17 No single global clinical test reflects the complexity and multidimensional nature of balance. 18 Instead, balance assessments should incorporate protocols that test a person s ability to maintain steady standing under different stance conditions, to remain stable during and after self-generated perturbations, and to maintain stability in response to an external perturbation. 19 Steady stance tests using progressively smaller bases of support have been used extensively in balance studies on elderly people and those with neurologic disorders. 20 Typically, postural stability is assessed by timing the duration of steady stance with feet apart, feet together, in stride stance, in tandem stance, and in single-limb stance positions. 17,21 Comprehensive balance assessment, however, also must incorporate perturbations (challenges) to the postural control system. 22 Two types of perturbations are useful to assess: those arising from selfgenerated movements and those delivered by an external source. The most frequent demand made on the balance system is to control upright stance during perturbations that are

2 216 BALANCE TESTING IN MULTIPLE SCLEROSIS, Frzovic produced by self-initiated movement of the person s body. 21 Postural adjustments occur in anticipation of the destabilizing forces associated with these self-initiated body movements. 23 Given that CNS lesions in MS may cause disruptions to feed forward anticipatory processes, 24 one can predict that people with MS would perform more poorly on tests involving self-induced perturbations than would unimpaired subjects. Tests of self-generated perturbations include the Functional Reach test, 10,17,25,26 the Arm Raise test 17,21 and the Step test. 17,20 Loss of balance may also be caused by an inadequate response to an external perturbation to the center of mass. 27 Multiple sclerosis may compromise postural control mechanisms that depend on the integrity of central processing components and neural pathways. 23 Thus, people with MS are likely to perform more poorly than controls on external perturbation tests. When testing the balance of people with MS, the effects of fatigue should also be taken into consideration. Although fatigue, defined as a sense of physical tiredness and lack of energy, 28 has been estimated to affect 77% of people with MS, 29,30 little information exists to describe its physical and psychological manifestations. 30 Previous research has revealed that fatigue in MS generally worsens as the day progresses, 29,31 and one may predict that performance on balance tests would be better in the morning than in the afternoon. The purpose of the present study was to evaluate differences in performance between people with MS and control subjects on a set of clinical tests of balance. Because fatigue is a factor that may affect the physical performance of people with MS, a further aim was to evaluate the repeatability of clinical tests of balance over a 5-hour interval. We hypothesized that: (1) marked differences in performance between people with MS and control subjects would be found for all clinical tests of balance, and (2) people with MS would show marked inconsistency of performance from morning to afternoon on each of the balance tests. METHOD Subjects Twenty-eight subjects were included in the investigation. Fourteen people with MS (diagnosed by a neurologist, geriatrician, or rehabilitation specialist) were recruited from the MS Society of Victoria and the Kingston Centre Movement Disorders Clinic. Fourteen control subjects matched for age, gender, and height were recruited from a variety of sources of convenience. To be included in the study subjects were required to be able to walk a 14-meter distance three times without walking aids or assistance from another person and to provide informed consent according to the declaration of Helsinki. 32 Subjects were excluded if they had neurologic conditions other than MS, as judged by a neurologist or rehabilitation specialist. They were also excluded if they had coexisting orthopedic or cardiovascular disorders, visual impairment (blindness, hemianopia, diplopia, blurred vision, severe nystagmus) or tremor affecting locomotion or balance. The mean age of subjects with MS was years (standard deviation [SD] 11.78; range, 26 to 65) compared to years (SD 10.78; range, 23 to 60) for control subjects. Individual subject values for age, height, body weight, and duration of MS are in tables 1 and 2. Table 1: Characteristics of Subjects With Multiple Sclerosis Subject Gender Age (yrs) Height (cm) Weight (kg) Duration of MS (yrs) Medication 1 F Protaphane 2 F Betaferon Aropax Pro-banthine 3 F Madopar Permax 4 M Betaferon 5 M Betaferon 6 M Betaferon Methotrexate Prozac 7 M Tegretol 8 M Betaferon Zoloft 9 M F Betaferon Insulin 11 F Betaferon 12 M F F Procedure The research project was approved by the La Trobe University Human Ethics Committee, the National Multiple Sclerosis Society of Australia Research Advisory Board, and the Kingston Centre Research and Ethics Committee. Subjects underwent the set of clinical tests of balance at either the Kingston Centre Geriatric Research Unit or the MS Society of Victoria located in Camberwell. The test set, conducted by the second author, was repeated twice within a single day. The first testing session was conducted at 10:00 in the morning and the second test occurred at 3:00 in the afternoon. The order of tests was randomized for each subject to control for series effects. During the 5-hour interval between tests, lunch and refreshments were provided and subjects were requested to perform only light activities. Subjects were advised to wear comfortable clothing and footwear with low heels on the day of testing. It has been reported that fatigue levels in people with MS are worsened by heat 28 ; therefore testing of subjects with MS was not conducted if the outside temperature was above 32 Celsius. Before beginning the tests the examiner explained to the subjects the purpose and general procedure of the study and answered any questions. Subjects sex and age were recorded, as was lower limb dominance (ascertained by asking, With which leg would you kick a ball? ). Subjects with MS were Subject Table 2: Characteristics of Control Subjects Gender Age (yrs) Height (cm) Weight (kg) 1 M F M F M F M F M F M M F F

3 BALANCE TESTING IN MULTIPLE SCLEROSIS, Frzovic 217 interviewed about the duration of MS (in years), and their current medication was recorded. The data were checked with medical record reports. Height and weight measures were then documented for all subjects. Height was measured to the nearest 0.5cm by instructing subjects to stand with their heels against a wall to which a tape measure was adhered. Body weight, to a tenth of a kilogram, was obtained from digital scales. Subjects wore their own footwear for all balance tests. If their footwear was deemed unsuitable by the researcher, a pair of flat sandshoes (sandals) in the correct size was provided from the laboratory collection. The starting time of the balance testing was noted by the researcher. The tests of steady standing were timed in seconds with an accuracy of two decimal places using a digital stopwatch. The alignment of the feet for feet apart, step, and tandem stance was marked on the floor with footprint cutouts of removable contact paper (fig 1). Green contact paper was used for the right foot and red for the left foot. A tape measure and two strips of removable adhesive tape were used for the functional reach test. The arm raise and step tests were timed by the stopwatch and utilized a portable wooden step of 15cm height, 29cm width and 60cm length. The external perturbation test was rated on a 5-point ordinal scale described previously in detail by Pastor and associates 33 and categorized as follows: 0, stays upright without taking a step; 1, stays upright by taking one step; 2, stays upright by taking more than one step; 3, takes several steps followed by the need to be caught; 4, falls backwards without attempting to step. A standard 4-point walking frame was placed in front of all subjects during testing and a chair was positioned nearby. Steady stance. Performance in a variety of stance positions without hand support was quantified by means of a stopwatch, according to a modified protocol originally described by Goldie 21 and Smithson. 17 Subjects stood on footprint templates (fig 1) that corresponded to the stance position being tested. The stance positions included were: (1) feet apart, with feet placed 10cm apart; (2) feet together; (3) stride stance, with feet placed 10cm apart and with the toes of the rear foot in line with the heel of the front foot; (4) tandem stance, with one foot directly in front of the other with the heel of the front foot in contact with the toes of the rear foot; and (5) single leg stance, with the subject standing on one leg. Stride and tandem stances were each tested twice once with the right foot in front and once with the left foot in the front position. Single leg stance was also measured twice once with subjects standing on the right leg, and once with subjects standing on the left leg. The researcher carefully positioned subjects feet on the contact footprints for each stance condition. Subjects were instructed to look straight ahead and keep their arms down by their side during the testing time of a maximum of 30 seconds. The researcher said go at the start of timing and stop at the completion of the test. The tests were also concluded if subjects lost their balance, altered their foot position, or maintained the Fig 1. Foot alignment for feet apart, stride stance, and tandem stance. stance for the maximum testing period of 30 seconds. The time on the stopwatch when the researcher said stop was recorded on the data sheet. A 4-point frame was placed in front of subjects for safety reasons. The researcher stood posterolaterally to subjects and an assistant stood on the other side for supervision. Self-generated perturbations. Subjects underwent three tests of self-generated perturbation: (1) functional reach, (2) arm raise, and (3) step test. The functional reach test measured maximum forward excursion in static double support standing. 34 Subjects stood next to, but not touching, a wall to their right with their feet on footprints 10cm apart. Subjects were instructed to raise their right arm to 90 with their hand outstretched. The distal position of the third digit was recorded on the wall with a strip of removable adhesive tape (position 1). Subjects were instructed to reach as far forward as you can without moving your feet. The new distal position of the third digit was recorded with a second piece of tape (position 2). The maximum distance reached (ie, the difference between positions 1 and 2) was measured by the researcher with a tape measure. An assistant stood close behind the subject for supervision. For the arm raise test, which followed the protocol described by Goldie, 21 subjects stood on contact footprints with their feet 10cm apart next to the wall, but not touching it, with their arms by their side. An assistant stood close behind the subjects. The instruction given to the subject was to lift your arm up to shoulder height and back down to your side as many times as you can in fifteen seconds. The researcher demonstrated the desired range of movement by passively moving the subjects arm to 90 of shoulder flexion and down again twice. Timing of 15 seconds began when the researcher said go and ended when the word stop was called out by the researchers. The number of completed arm raises to shoulder height and back down to their side was counted by the researcher who stood anterolaterally to subjects. Performance for both upper limbs was measured. In the Step test, as detailed by Hill, 20 subjects stood unsupported with feet parallel. The 15-cm step was positioned 5cm in front of subjects. The researcher stood to one side of the subjects and an assistant stood on the other side. The instruction to place your foot fully onto the step and then off the step as many times as you can when I say go was accompanied by a demonstration of the task by the researcher. The verbal go instruction signified the start of the test and stop indicated the end of the measurement period of 15 seconds. The number of completed steps in 15 seconds was recorded. A completed step was defined as stepping the whole foot onto and then off the step. The test ceased if subjects lost their balance or altered their supporting foot position. Testing ceased twice in this study because two people with MS lost their balance and needed to be steadied by the assistant. Performance was recorded for both feet. External perturbation. Subjects stood with their feet 10cm apart on the contact footprints. The 4-point frame was positioned in front of subjects and the examiner stood behind. Two assistants also stood behind subjects on either side of the examiner. The examiner gave the instruction, I m going to give you a brief tap but I won t let you fall. In accordance with the procedure for the shoulder tug test outlined by Pastor, 33 no further information about the direction, force, or timing of the perturbation was provided. The examiner delivered a brief tug backward to the shoulders and graded the response according to the scale described by Pastor. 33

4 218 BALANCE TESTING IN MULTIPLE SCLEROSIS, Frzovic Fatigue. At the end of the morning and afternoon testing sessions the people with MS were asked to verbally rate their fatigue levels on a rating scale from 0 to 10; 0 represented no fatigue and 10 the worst fatigue ever experienced. Fatigue was only documented for people with MS because it is a common symptom, 28,31 whereas there is no evidence to suggest that such fatigue occurs in unimpaired individuals. Statistical Analysis The distributions for each of the variables were first examined for normality using Q-Q plots. 35 Because ceiling effects were present, the steady stance tests with feet apart, feet together, stride stance, tandem stance, and single limb stance were found to be markedly negatively skewed. Most subjects could maintain balance for close to the maximum testing time of 30 seconds. The data for these variables were therefore summarized using medians and interquartile ranges and analyzed using nonparametric statistics, such as the Wilcoxin signed-rank test 36 for within-subject comparisons and the Mann Whitney-U test 37 for between-groups comparisons. The data for the arm raise, functional reach, and step tests showed only minor departures from normality. Given that the MS and control groups were matched for sample size, the results were analyzed using parametric statistics. A mixed design 2 (time) by 2 (group) repeated measures analysis of variance (ANOVA) with time as the within-subjects factor was used to assess whether there was an interaction between the scores obtained by people with MS and control subjects and the time of day (morning or afternoon) and whether there were main effects for group and time. 35 One-way ANOVAs were then used to assess whether the changes in performance in people with MS from the morning to the afternoon were significant. The results for the external perturbation tests were analyzed using the Wilcoxin s Signed Ranks test and the Mann Whitney U tests, given that external perturbation responses were scored using an ordinal scale. Retest reliability from the morning to the afternoon was assessed using Spearman s rho 37 for the ordinal data and intraclass correlation coefficients (ICCs) 38 for the metric data. RESULTS Testing Times and Fatigue Ratings The mean morning test time was 10:29 a.m. (SD minutes; range, 9:30 to 11:10 a.m.) for people with MS and 10:20 a.m. (SD minutes; range, 9:20-10:50 a.m.) for control subjects. The mean afternoon test time was 3:20 p.m. (SD minutes; range, 2:30-4:10 p.m.) for people with MS and 3:19 p.m. (SD minutes; range, 2:15-3:50 p.m.) for control subjects. No statistically significant differences existed between groups for the test times in either the morning or afternoon. The mean perceived fatigue score for people with MS in the morning was 2.50 (range, 0-6) compared to 3.75 (range, 0-8) for the afternoon. This difference was statistically significant (t(14) 3.14, p.008). Differences in Balance Between People With Multiple Sclerosis and Control Subjects Steady stance. The majority of people with MS could maintain positions of feet apart and feet together for periods close to 30 seconds on each occasion (table 3). All control subjects were able to maintain steady standing with their feet apart and together for the maximum testing time of 30 seconds in the morning and afternoon (table 4). As a result, the differences between groups for these tests were not statistically significant. Table 3: Scores for Steady Stance Tests and the External Perturbation Test for Subjects With Multiple Sclerosis Condition Morning Afternoon Median IQR Median IQR Feet apart Feet together Right stride stance Left stride stance Right tandem stance Left tandem stance Right single limb stance Left single limb stance External perturbation Abbreviation: IQR, interquartile range. In contrast, not all the people with MS could maintain stride stance and tandem stance for the maximum testing time even though all of the control subjects could achieve this goal (tables 3 and 4). Mann-Whitney U tests confirmed that the difference between groups was statistically significant for right stride stance in the morning (U 56, p.007) and left stride stance in the morning (U 63, p.016) but was not statistically significant for the afternoon scores for right and left stride stance. In addition, Mann Whitney U tests revealed marked differences between the two groups for right tandem stance in the morning (U 14, p.0001) and afternoon (U 28, p.0002) and for left tandem stance in the morning (U 14, p.0001) and afternoon (U 35, p.0005). For single limb stance the median values for morning and afternoon scores for the control group subjects were very close to the maximum testing time of 30 seconds (table 4). In contrast, only some of the people in the MS group could maintain single leg stance for times close to 30 seconds (table 3). Statistically significant differences been groups were found for right single leg stance in the morning (U 14.5, p.0001) and afternoon (U 19, p.0001) and for left single limb stance in the morning (U 8.5, p.0001) and afternoon (U 16, p.0001). Self-generated perturbations. Tables 5 and 6 show moderate differences between the two groups for the functional reach test. Repeated measures ANOVAs did not identify an interaction between groups on the functional reach test as a function of the time of day. There was, however, a significant main effect for groups on this test (F(1, 26) 7.26, p.012). Similar differences between groups were evident for the arm raise test. Two-factor repeated measures ANOVAs confirmed significant main effects for group for the right-side arm raise test (F(1, 26) 17.81, p.005) and the left-side arm raise test (F(1, Table 4: Scores for Steady Stance Tests and the External Perturbation Test for Control Subjects Condition Morning Afternoon Median IQR Median IQR Feet apart Feet together Right stride stance Left stride stance Right tandem stance Left tandem stance Right single limb stance Left single limb stance External perturbation Abbreviation: IQR, interquartile range.

5 BALANCE TESTING IN MULTIPLE SCLEROSIS, Frzovic 219 Table 5: Scores for Self-Generated Perturbations for Subjects With Multiple Sclerosis Condition Morning Afternoon Functional reach (cm) (8.20) (8.00) Right arm raise (reps/15sec) (4.17) (4.09) Left arm raise (reps/15sec) (3.67) (4.09) Right step test (reps/15sec) 7.42 (4.03) 8.00 (4.40) Left step test (reps/15sec) 6.79 (4.10) 7.64 (4.65) Data reported as mean (standard deviation). 26) 16.46, p.005). The main effects for time of day were not statistically significant. The step test results also showed significant group main effects on repeated measures ANOVAs for the right side (F(1, 26) 39.43, p.0001) and left side (F(1, 26) 42.66, p.0001). The step test did not reveal a significant interaction effect for time for the right side or the left side. External perturbation. As seen in Tables 5 and 6 the external perturbation scores clearly discriminated between the two groups for morning and afternoon testing sessions. Twelve of the 14 control subjects scored 1 (stays upright without taking a step) for the external perturbation test over the two testing times. In contrast, the majority of people with MS had a score of 4 (takes one or more steps backward followed by the need to be caught) on both occasions. The Mann Whitney U tests identified statistically significant differences between the two groups for scores in the morning (U 22, p.0002) or afternoon (U 28, p.0002). Performance Consistency Over a 5-Hour Interval in People With MS Because inspection of the means, standard deviations, and raw scores for the feet-apart test indicated the presence of marked ceiling effects, we did not use correlational analyses for the feet apart data. Ceiling effects were not such a problem in the other tests, so we used correlational statistics to examine the relationship between morning and afternoon scores. The correlation coefficients showed a strong positive linear relationship between the scores from the morning to the afternoon for tests with feet together (rho.81), in right stride stance (rho.70), in left stride stance (rho.76) and in left single limb stance (rho.70). The correlation coefficients for right tandem stance (rho.86), left tandem stance (rho.93) and right single leg stance (rho.94) also showed highly consistent performance from the morning to the afternoon. Moderately strong repeatability existed for the arm raise scores from morning to afternoon with ICCs of.72 for the right side and.77 for the left side. High repeatability was evident for the functional reach test (ICC 0.89), the right-side step test (ICC.93) and the left-side step test (ICC.91). Paired t tests did not identify any significant changes in performance from morning to afternoon for any of the balance tests. Table 6: Scores for Self-Generated Perturbations for Control Subjects Condition Morning Afternoon Functional reach (cm) (5.88) (6.66) Right arm raise (reps/15sec) (8.57) (8.31) Left arm raise (reps/15sec) (8.38) (8.30) Right step test (reps/15sec) (3.46) (4.05) Left step test (reps/15sec) (3.35) (4.46) Data reported as mean (standard deviation). DISCUSSION The results of the present investigation showed that moderately disabled people with MS performed poorly on a range of clinical tests of balance in standing. Whereas age-matched control subjects could maintain steadiness in a range of stance positions, prevent overbalancing while moving their limbs, and recover from an unexpected push or pull using a stepping strategy, persons with MS showed poorly controlled responses that failed to prevent them from losing stability. Contrary to our predictions, however, people with MS were highly consistent in their responses and performed similarly in morning and afternoon testing sessions. Balance Impairment in MS Despite the high prevalence of falls in the MS population, 7-13 the present study is the first to detail impairments in balance and postural control in people with this demyelinating disease. Impairments were most apparent for clinical tests that required subjects to respond to internally generated and externally generated perturbations to their center of mass, rather than tests requiring them to maintain steady stance without perturbations. The steady stance tests with feet apart, feet together and in step stance lacked sensitivity because of the presence of ceiling effects. In particular, ceiling effects were evident for each of the steady stance conditions for control subjects and also for the feet apart condition in people with MS. The presence of ceiling effects is consistent with previous studies of steady stance in other patient populations. 17,21,39 Such findings indicate that 30-second tests may be useful in detecting postural instability in patients with severe levels of disability and that increasing the maximum trial duration from 30 seconds to 60 seconds or 90 seconds would probably improve discriminative validity when used for subjects with mild to moderate degrees of disability. Alternatively, clinicians could select the tandem stance and single leg steady stance positions to test balance we found that these more challenging stance conditions discriminated quite well between patients with mild to moderately severe MS and unimpaired individuals. Previous investigations have also shown that tandem stance and single leg stance tests discriminate well between unimpaired people and those with neurologic diseases. 17 The self-induced internal perturbations used to test balance in the present investigation were the functional reach test, arm raise test, and step test. Unlike the majority of steady stance tests, the results for the functional reach test showed marked differences between people with MS and control subjects. This finding was in agreement with prior research demonstrating that the functional reach test clearly differentiates between control subjects and frail elderly people 17,25 as well as people with Parkinson s disease. 17 The functional reach test not only provides a measure that discriminates between subjects with movement disorders and healthy elderly people, it reflects ability to perform everyday tasks of living that incorporate reaching out to grasp an object beyond arm s distance. The two other balance tests that incorporated self-induced perturbations to the center of mass, the arm raise test and the step test, also showed differences between able-bodied subjects and those with MS. As with the studies conducted on subjects with Parkinson s disease by Smithson 17 and on stroke subjects by Hill, 20 the arm raise and step test scores for control subjects were higher than those scored by persons with MS, and subjects in both groups showed very little change over time. The problem with the step test and arm raise test, however, is that scores can be confounded by the presence of movement disorders such as bradykinesia, incoordination, chorea, and weakness. Although

6 220 BALANCE TESTING IN MULTIPLE SCLEROSIS, Frzovic low scores on the step test and arm raise tests may reflect attempts to compensate for balance disturbance (ie, subjects deliberately reduce the number of movements to avoid losing their balance) it is equally possible that an inability to quickly lift the arm or step up and down could result from movement disorders. Because people with MS have a high incidence of concurrent movement disorders such as bradykinesia, incoordination and spasticity, this possibility cannot be discounted. Considering the possibility of movement disorders, the arm raise and step tests are probably not as useful as the functional reach in charting response to self-induced perturbations in people with MS. The external perturbation used to test balance in the present investigation was the Pastor 33 shoulder tug test. The control subjects effortlessly recovered steady stance following the unexpected pull backwards by the researcher, with most using a stepping strategy to prevent falling. In contrast, the majority of subjects with MS fell backwards, failed to elicit protective balance responses and had to be caught by the tester. It has been proposed that postural adjustments to unexpected external perturbations are preprogrammed by the CNS. 24,40 Because sclerotic plaques are often located in the cortical regions, people with MS may not always appropriately select and modulate responses to external perturbations to their center of mass, which may in turn, increase their risk of falling when walking around crowded environments such as shopping centers and train stations. Repeatability of Performance in People With Multiple Sclerosis One of the unexpected findings of the present study was that people with MS had highly consistent performance on balance tests from morning to afternoon sessions. Because MS is characterized by variability in motor performance arguably related to exacerbations and remissions in the disease, 3 we had hypothesized that postural stability and balance responses would vary greatly within subjects over the course of a day and wide variations between subjects would occur. This was not the case. Although patients reported feeling more fatigued in the afternoon than in the morning, their physical performance showed little change. The high repeatability of performance on the clinical tests of balance appears to be consistent with the findings of studies on other patient populations. For example, the correlation coefficients obtained for repeat performances in steady stance conditions are similar to those reported by Smithson 17 for subjects with Parkinson s disease. Moreover, the results for the functional reach test are in agreement with the high test-retest reliability reported in previous studies of functional reach in elderly subjects 25 and those with Parkinson s disease. 17 The retest reliability results for the external perturbation test were also similar to those found by Smithson 17 in a study of subjects with Parkinson s disease who were measured twice over a 7-day period. Performance consistency over a 5-hour interval suggests that repeat assessments may be useful to detect significant changes in the ability of people with MS to balance as a result of physical therapy or other types of intervention. Marked changes that occur in a single treatment session are unlikely to be due to measurement error or historical variables, and are more likely to be due to the treatment itself. Fatigue, Balance, and Multiple Sclerosis The results of the present investigation provide limited insight into the impact of fatigue on the performance of tests of balance from morning to afternoon. Although people with MS reported a marked increase in their feeling of fatigue from the morning to the afternoon, no significant changes in performance on balance tests were observed over this period. These results are in agreement with the findings of Schwartz and colleagues, 31 who observed that fatigue did not affect physical performance. Notwithstanding, one of the problems in interpreting self-reports of fatigue in people with MS is that the measurement scales used to quantify fatigue do not have established reliability and validity. Patients subjective reports of fatigue may have been influenced by related factors such as concentration, memory, and comprehension. Further research is required to clarify the exact nature of fatigue in MS and its effect on balance. Clinical Implications and Limitations The present study has shown that a small battery of clinical balance tests can be used to measure differences between people with MS and controls and appears to be suited to the measurement of physical therapy treatments for balance disorders. The test set can be administered in approximately ten minutes and minimal training is required for the clinician to learn the procedure. The tests that best discriminated between groups and were most reliable were tandem stance, single limb stance, functional reach, the arm raise test, the step test, and the external perturbation test. The arm raise and step test results, however, may have been confounded by movement disorders which can occur in addition to postural instability; therefore, these tests are not the best choice. The primary limitation of the investigation was that its control subjects came from a sample of convenience and all subjects in the experimental group were members of the MS Society of Victoria. Because not everyone with MS registers with the Society, caution must be taken when attempting to generalize the findings to the population of people with MS as a whole. Also, the study did not compare balance performance between subcategories of people with MS, such as those with spasticity, ataxia or sensory loss. These factors may have increased the within-group variability in the MS sample. Recent literature claims that studies of balance should allow for the potentially confounding influence of fear of falling. 34,41,42 The design of the present investigation did not account for the impact of fear of falling on performance of balance tests, and the test set did not include functional activities, such as walking or standing up from sitting, during which many falls occur. CONCLUSION Balance is markedly compromised in people with MS even though performance on clinical tests of balance is very consistent from the morning to the afternoon. The most suitable clinical tests for assessing balance in standing in people with MS are the tandem stance test, single limb stance test, functional reach test, and the external perturbation test. When treating patients, clinicians can be reasonably confident that the changes measured over the course of a day using these four tests are due to the effects of intervention rather than patient variability or measurement error. Acknowledgments: The authors thank Professor Robert Iansek, Ms. Robyn Tapp, and staff at the Geriatric Research Unit at Kingston Centre for their continued support and assistance with this project. We also thank the clinicians from the MS Society, Camberwell, for their valuable assistance and the people with and without MS who so generously volunteered to participate in this investigation. 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