Reliability and Validity of the Computerized Dynamic Posturography Sensory Organization Test in People with Multiple Sclerosis Jeffrey R. Hebert, PT, PhD; Mark M. Manago, PT, DPT Background: People with multiple sclerosis (MS) frequently have impaired postural control (balance). Psychometric properties of clinical tests of balance for individuals with MS, including the computerized dynamic posturography sensory organization test (CDP-SOT), are poorly understood. This study aimed to determine the reliability and discriminant validity of the CDP-SOT in people with MS. Methods: The CDP-SOT was performed on 30 participants with MS. A 2-week–interval, repeatedmeasures (sessions 1 and 2) design was implemented to investigate test-retest reliability of the CDP-SOT and the ability of the CDP-SOT to discriminate between participants with lower versus higher disability. Self-reported disability level was based on Patient-Determined Disease Steps (PDDS) scale scores: lower (PDDS scale score, 0–3; n = 17) and higher (PDDS scale score, 4–6; n = 13). Results: All six conditions of the CDP-SOT had good-to-excellent reliability (interclass correlation coefficients, 0.70–0.90) and excellent reliability for composite scores (0.90). Composite scores were significantly greater in the lower-disability group versus the higher-disability group at session 1 (70.89 vs. 48.60, P = .001) and session 2 (74.82 vs. 48.85, P = .002). Conclusions: The CDP-SOT is a reliable measure of balance and accurately differentiates disability status in people with MS. Collectively, the results support clinical application of the CDP-SOT as a reliable and valid measure of disease-related progression of impaired balance related to sensory integration and its utility in determining changes in balance in response to treatment. Int J MS Care. 2017;19:151–157.
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ultiple sclerosis (MS) is a chronic disease of the central nervous system that leads to progressive worsening of upright postural control. Owing to multifocal central nervous system involvement, visual1 and somatosensory2 afferent feedback are commonly adversely affected in individuals with MS. Moreover, the high prevalence of MS-related From the Department of Physical Medicine and Rehabilitation and Department of Neurology, University of Colorado School of Medicine, Aurora, CO, USA (JRH); and Department of Rehabilitation, University of Colorado Health, Physical and Aquatic Therapy– Stapleton, Denver, CO, USA (MMM). Correspondence: Jeffrey R. Hebert, PT, PhD, Department of Physical Medicine and Rehabilitation and Department of Neurology, University of Colorado– Anschutz Medical Campus, 12631 E. 17th Ave., Mail Stop F493, Aurora, CO 80045; e-mail: [email protected]. DOI: 10.7224/1537-2073.2016-027 © 2017 Consortium of Multiple Sclerosis Centers.
involvement of the primary sensory integration brain structures (eg, brainstem, cerebellum) results in impaired central integration of these sensory systems along with the vestibular system. This is important because humans require efficient and effective central sensory integration (CSI) of the visual, somatosensory, and vestibular sensory systems to maintain homeostatic balance control (balance as a function of CSI [balance f CSI])3 to maintain societal participation and prevent falls. Dysfunctional balance f CSI has been implicated in people with MS as leading to impaired postural control4,5 and falls.6 As such, it is vital that clinicians implement the most reliable and valid measures of balance f CSI to determine the functionality of this essential upright postural control domain to optimize appropriate exercise prescriptions for people with MS.
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Balance f CSI is a complex physiological process that many clinical measures of postural control are unable to quantify. The computerized dynamic posturography sensory organization test (CDP-SOT) has initial support as a valid measure of balance f CSI and falls in people with MS.7,8 It has been applied as a primary outcome in controlled trials of balance9 and vestibular rehabilitation10 training for individuals with MS, supporting the responsiveness of the CDP-SOT to targeted treatment of impaired balance f CSI in this patient population. The CDP-SOT has also been applied as a gold standard for the validation of novel outcome measures of postural control.11 The reliability of the CDP-SOT has been established in healthy young12 and older13 adults and in patients with stroke,14 transtibial amputation,15 and low back pain.16 However, investigations of the reliability of the CDPSOT in people with MS are lacking. In addition, the ability of the CDP-SOT to quantify differences in balance f CSI based on disability level is currently absent from the literature. This is a concern because the cornerstone of disability advancement is progressive worsening of gait and mobility. The reason for this cumulative disability is often multifactorial; however, it is plausible that impaired balance f CSI is a key physiological factor. Collectively, improved knowledge of the repeatability of the CDP-SOT and the utility of the CDP-SOT as a valid measure of balance f CSI will greatly improve the application of this instrumentation in the clinical setting. The purpose of this study was to determine the reliability and discriminant validity of the CDP-SOT in people with MS. We hypothesized that 1) the CDPSOT will have high test-retest reliability in participants with MS and 2) CDP-SOT scores will be statistically significantly lower in participants with MS with higher disability than in those with MS with lower disability.
Methods Participants This study enrolled 30 individuals with MS to perform the CDP-SOT at two visits 14 days apart. The participants were recruited through advertisements at the University of Colorado Hospital and the University of Colorado Denver Anschutz Medical Campus. Eligibility for people with MS included age 18 to 60 years, confirmed diagnosis of MS, ability to provide consent and follow simple directions, and ability to walk at least 25 feet with bilateral support (Patient-Determined Disease
Steps [PDDS] scale score ≤6). The exclusion criteria included wheelchair dependence, inability to ambulate, other neurologic conditions besides MS, participation in vestibular rehabilitation or balance training in the past 2 months, and an MS-related exacerbation or medication change in the past month.
Computerized Dynamic Posturography Balance f CSI was measured using the CDP-SOT on the SMART Balance Master system (version 9.0; Neurocom International Inc, Clackamas, OR). The CDP-SOT is designed to assess balance f CSI through a series of six conditions that progressively challenge components of sensory integration needed to maintain upright postural control. The SMART Balance Master system consists of a pressure-monitored force platform and dynamic visual surround. The force platform is able to detect participant sway based on the change in center of mass of the participant. Depending on the condition, the force platform or the visual surround has the ability to move in the anteroposterior (sagittal) plane to match the participant’s sway. The act of moving either the force platform or the visual surround to exactly match the participant’s sway is termed sway reference. The six conditions are 1) eyes open, no sway reference; 2) eyes closed, no sway reference; 3) eyes open, visual surround sway reference; 4) eyes open, support platform sway reference; 5) eyes closed, support platform sway reference; 6) eyes open, support platform and visual surround sway reference. Each condition consists of three 20-second trials. For each trial, participants were asked to stand quietly with their arms at their sides, head and neck looking straight ahead, and eyes open or eyes closed, depending on the condition. To prevent a fall to the ground during the test, participants wore a harness that was anchored to the frame of the SMART Balance Master in a way that did not restrict normal sway. Participants were also closely guarded by a physical therapist experienced in working with people with MS. A fall was defined as stepping off the force platform or depending on the harness for support. During all the conditions, equilibrium scores were generated. The equilibrium score was determined through a computer-generated algorithm that compares the participant’s sway in the sagittal plane with expected limits of stability based on normative values. An equilibrium score of 100 signifies no sway, scores closer to 0 indicate higher sway, and a score of 0 indicates a fall.
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The composite score was calculated using a weighted average of the equilibrium scores for each condition. The composite score ranges from 0 to 100, with higher scores indicating better balance f CSI.
Disability Disability due to MS was measured using the PDDS scale, a valid surrogate for the Kurtzke Expanded Disability Status Scale (EDSS).17 The PDDS scale is a patient-reported outcome that focuses primarily on walking ability and asks the participant to select one of nine items (score, 0 to 8) that best describes his or her disability. Lower disability was defined as a PDDS scale score of 0 to 3 and higher disability as a PDDS scale score of 4 to 6.18,19 A score of 0 signifies mild symptoms and essentially normal function, whereas a score of 3 indicates symptoms from MS that affect daily activities, but walking is usually without an assistive device. A score of 4 means walking with a unilateral assistive device most or all of the time, and 6 indicates the need for bilateral assistance for walking short distances and occasional use of a wheelchair.
Procedures A local scientific ethics committee, the Colorado Multiple Institutional Review Board, guided by the ethical principles for human subject research and in accordance with the United States Department of Health and Human Services policy and regulations (45 CFR 46), approved the study protocol, and all the participants provided signed informed consent before participation. The CDP-SOT was performed during two sessions 2 weeks apart. At the first session, the participants also filled out the PDDS scale.
Statistical Analysis Descriptive statistics were used to characterize the participants. Test-retest reliability between the sessions was assessed using the two-way random-effects, single-measurement interclass correlation coefficient (ICC[2,1]); ICC values of 0.75 to 1.0 were considered excellent; 0.40 to 0.74, fair to good; and less than 0.40, poor.20 Two-sided independent t tests were used to evaluate differences between the lower- and higherdisability groups for the composite CDP-SOT scores as well as equilibrium scores for each condition. Discriminant validity was confirmed by statistically significant group differences using two-sided t tests (α = .05). All the analyses were performed using IBM SPSS Statistics for Windows, version 23.0 (IBM Corp, Armonk, NY).
Results All the participants returned for the second visit, with a mean (SD) follow-up time of 15.4 (3.5) days. A description of the study sample, including disability level, is provided in Table 1. Table 2 reports the mean scores for the CDP-SOT, as well as the test-retest ICC(2,1) values for the composite, equilibrium, and strategy scores in each of the six conditions. The ICC(2,1) values (95% confidence intervals) for the six conditions ranged from 0.70 (0.46-0.84) to 0.90 (0.80-0.95), with 0.90 (0.80-0.95) for the composite score. The differences in the CDP-SOT scores between disability groups are presented in Table 3. The lowerdisability group had significantly higher mean composite CDP-SOT scores than the higher-disability group at session 1 (mean difference = 22.27, P = .001) and session 2 (mean difference = 25.98, P = .002). Test-retest reliability ICC(2,1) values (95% confidence intervals) for the composite score were 0.84 (0.62-0.94) for the lowerdisability group and 0.84 (0.56-0.98) for the higherdisability group. There was not a significant difference in age between the groups (P = .393). Last, the equilibrium scores for CDP-SOT conditions 2 through 6 were found to be significantly higher in the lower-disability group compared with the higher-disability group (P < .001 to P = .026), whereas no significant difference was found between the disability groups for condition 1 (P = .053) (Figure 1).
Discussion Reliability is a principal psychometric property of tests and outcome measures. Clinicians rely on evidence Table 1. Demographic and clinical characteristics of 30 participants with MS Variable
Participants
Age, mean (SD), y Female sex, No. (%) PDDS scale score, median (IQR) PDDS scale score, No. 0 1 2 3 4 5 6
43.2 (10.5) 27 (90) 3 (2) 1 4 3 9 9 2 2
Abbreviations: IQR, interquartile range; MS, multiple sclerosis; PDDS, Patient-Determined Disease Steps.
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Hebert and Manago Table 2. Across 2 weeks test-retest reliability of equilibrium, strategy, and composite scores for the six CPD-SOT conditions in people with MS Equilibrium score, mean (SD) Session
Condition 1
Condition 2
Condition 3
Condition 4
Condition 5
Condition 6
Composite score, mean (SD)
Day 1 90.93 (4.63) 79.01 (20.63) 78.49 (18.77) 66.67 (23.75) 40.50 (23.91) 43.16 (26.88) 61.2 (17.1) Day 2 90.09 (6.55) 76.09 (23.57) 75.01 (21.75) 70.96 (23.64) 46.86 (26.99) 48.48 (29.21) 63.6 (21.0) ICC(2,1) 0.70 (0.46-0.84) 0.82 (0.65-0.91) 0.81 (0.64-0.90) 0.87 (0.75-0.94) 0.77 (0.58-0.89) 0.90 (0.80-0.95) 0.90 (0.80-0.95) (95% CI) Abbreviations: CDP-SOT, computerized dynamic posturography sensory organization test; CI, confidence interval; ICC(2,1), random-effects interclass correlation coefficient; MS, multiple sclerosis. Note: For definitions of conditions 1 to 6, see the Computerized Dynamic Posturography subsection of the text.
Table 3. Comparison of age, mean CDP-SOT scores, and CDP-SOT test-retest reliability ICCs based on disability level MS disability levela Factor Age, mean (SD), y CDP-SOT composite 1, mean (SD) CDP-SOT composite 2, mean (SD) ICC(2,1) (95% CI)
Lower (n = 17)
Higher (n = 13)
Mean difference (95% CI)
P value
41.8 (10.6) 70.89 (9.14) 74.82 (9.05) 0.84 (0.62 to 0.94)
45.2 (10.6) 48.60 (17.14) 48.85 (23.34) 0.84 (0.56 to 0.98)
−3.39 (−11.4 to 4.6) 22.27 (11.20 to 33.33) 25.98 (11.39 to 40.56) –
.393b .001c .002c –
Abbreviations: CDP-SOT, Computerized Dynamic Posturography Sensory Organization Test; CI, confidence interval; ICC(2,1), randomeffects interclass correlation coefficient; MS, multiple sclerosis. a A Patient-Determined Disease Steps scale score of 1 to 3 is lower disability; 4 to 6, higher disability. b Equal variance independent-samples t test. c Unequal variance independent-samples t test.
of this property when making decisions about which tests provide the highest level of measurement stability. As such, the primary purpose of the study was to determine the test-retest reliability of the CDP-SOT in ambulatory individuals with MS. The CDP-SOT has previously been shown to be a reliable and valid measure of balance f CSI in several different community and patient population groups.12-16 To our knowledge, this is the first study to determine test-retest reliability and discriminant validity of the CDP-SOT in people with MS. A primary result of the present study is that the CDP-SOT is a statistically significantly reliable test of balance f CSI in people with MS. The test-retest reliability coefficients, ranging from 0.70 to 0.90 for conditions 1 to 6, and the composite score in the present study for individuals with MS are consistent with findings from a previous study involving individuals with transtibial amputation (range, 0.67–0.90).15 Furthermore, the reliability coefficients in the present study for people with MS have a narrower range compared with findings from a study of individuals with chronic low back pain (range, 0.26–0.89)16 and a greater coefficient than that reported in a sample of individuals with a stroke (composite score–only coefficient, 0.81)14 and for the
six-condition range found in adults 65 years and older (range, 0.15–0.70).13 Performance-based clinical tests of balance frequently require the determination of both rater and test-retest reliability psychometric properties. However, the computerized instrumentation of the CDP-SOT is a unique measure of balance f CSI. The CDP-SOT uses a standard computerized algorithmic approach to measuring balance f CSI that helps minimize rater-specific error and eliminates rater interpretation of patient test performance. Therefore, in the present study, the CDP-SOT underwent test-retest analyses only, and it was found that the reliability of the CDP-SOT composite score was excellent (0.90). This finding is similar to the test-retest reliability of the summary scores from other performance-based clinic tests of balance for people with MS, such as the Berg Balance Scale (range, 0.85–0.96)21-23 and the Dynamic Gait Index (0.85).23 It can be postulated that as disability progresses, people with MS routinely modify daily activities that are less challenging to CSI. However, these strategies are not always successful, and as a result, balance f CSI is further impaired, and this can result in increased loss of balance and risk of falls. To this point, we also aimed to determine the utility of the CDP-SOT to identify balance
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Fig. 1. Comparison of Equilibrium Scores on each of the six conditions of the CDP-SOT by disability group
100 90
P = .053a 92.94 88.9
Lower Disability P = .021a 87.71
86.04
P = .017a 76.78
80 Equilibrium Score
Higher Disability
P = .026a
67.64
70
68.62
P < .001b
60
53.44
P = .008a 54.90
52.80
50 40 30
27.79
24.41
20 10 0
1
2
3 4 CDP-SOT Condition
5
6
* Figure 1.Computerized Comparison of equilibrium each ofTest; the psix conditions of the CDP-SOT: Dynamic Posturographyscores Sensoryfor Organization = p-values (2-tailed); Equal variance ** computerized dynamic posturography sensory organization test (CDP-SOT) in the lowerindependent samples t-test; Unequal variance independent samples t-test
disability (Patient-Determined Disease Steps [PDDS] scale score of 1–3) and higherdisability (PDDS scale score of 4–6) groups
All the P values are two-tailed. aUnequal variance independent-samples t test. bEqual variance independent-samples t test. For definitions of conditions 1 through 6, see the Computerized Dynamic Posturography subsection of the text.
f CSI deficits based on disability level. The CDP-SOT differences for the comparisons between disability levels in the present study are greater than those in previous reports that applied the CDP-SOT as a discriminant test of fall risk. In older adults, CDP-SOT condition 2 was the only score that was significantly different between fallers and nonfallers (equilibrium score difference of 3.5),24 and in people with MS, an equilibrium score difference of 8.4 was reported for CDP-SOT condition 3 between fallers and nonfallers.8 Moreover, in the present study, both disability groups presented with progressively worse equilibrium scores from condition 1 to condition 6. This trend is consistent with previous work by Hebert and Corboy,3 where it was reported that the decline in CDP-SOT equilibrium scores progressed from the less CSI-challenging conditions (condition 1, 93.3 and condition 2, 89.1) to the most CSI-challenging conditions (condition 5, 60.0 and condition 6, 63.1). Findings from the present study extend this knowledge by demonstrating the differential worsening of equilibrium based on disability level. The CDP-SOT equilibrium scores for people with MS with higher disability were significantly lower than those for people with MS with lower disability, with the largest
differences found for conditions 5 and 6. These findings are in line with previous reports of progressive worsening of mobility,25,26 static balance dysfunction,27-29 and falls30-32 in people with MS with advanced disability, including a greater level of walking aid support. However, the present study is the first to report contrasting balance f CSI performance on individual conditions of the CDP-SOT based on disability. The mechanisms responsible for these findings cannot be elucidated in the present study. However, the brainstem33,34 and cerebellum35,36 are the primary central processors of CSI, and the presence of brainstem (P < .001) and cerebellar (P < .001) involvement are significantly associated with quicker advancement of disability in people with MS.37 Based on this knowledge, it can be theorized that greater MS-related involvement of these brain structures might explain the disability-dependent progressive worsening of balance f CSI performance observed in the present study. Future studies (eg, functional neuroimaging) are needed to determine the neural structures and functional network connectivity that are responsible for the variability in balance f CSI and whether these relationships further correlate with disability level.
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Findings from this study indicate that the CDPSOT is a valid measure to distinguish disability levels in people with MS and highlights the problem of impaired balance f CSI in individuals with MS with higher disability levels. With this knowledge, clinicians have early evidence of the expected balance f CSI control capacity among distinct disability levels and that the CDP-SOT allows for identifying limitations in more challenging balance f CSI tasks, ultimately aiding clinicians in the design and implementation of more targeted treatment strategies. Limitations of the study need to be recognized. Calculations of other psychometric properties, such as the minimal detectable change (MDC) of the CDP-SOT, were not possible owing to the sample size. This is primarily because smaller sample sizes can lead to large variances in measures, prohibiting valid MDC analyses. Larger studies are needed to extend the present findings of the psychometric properties of the CDP-SOT in people with MS including MDC. Future studies should also implement the clinician-administered Kurtzke EDSS to allow for characterization of disability on a larger scale and to include multiple functional system values assessed in the EDSS (eg, sensory, pyramidal, cerebellar) to expand investigation of the CDP-SOT based on disability status.
Conclusion This study indicates that the CDP-SOT is a reliable measure of balance f CSI and accurately differentiates disability status in people with MS who are ambulatory. The results support the clinical application of the CDPSOT as a reliable and valid measure of disease-related
PracticePoints • The computerized dynamic posturography sensory organization test (CDP-SOT) is a reliable and valid clinical test of balance as a function of central sensory integration (balance f CSI) in people with MS. • The CDP-SOT should be considered a measure of change in balance f CSI after treatment and quantification of balance f CSI based on disability. • Balance f CSI is significantly worse in people with MS with advanced disability and to a greater degree during more challenging balance f CSI– related conditions.
progression of balance f CSI–related instability in people with MS, which can be used to measure balance f CSI changes in response to treatment. Larger longitudinal studies investigating clinically meaningful changes in CDP-SOT scores due to the natural course of MS and in response to treatment need to be conducted. Investigations of the CDP-SOT as a valid measure of fall risk and of safe and effective free-living physical activity participation will also determine additional clinical utility of the CDP-SOT. Last, mechanistic studies are also needed that investigate the underlying reasons for differences in CDP-SOT scores based on disability in people with MS found in the present study. o Acknowledgments: The PDDS scale is provided for use by the North American Research Committee on Multiple Sclerosis (NARCOMS) Registry (http://www.narcoms.org/pdds). NARCOMS is supported in part by the Consortium of Multiple Sclerosis Centers (CMSC) and the CMSC Foundation. Financial Disclosures: The authors have no conflicts of interest to disclose.
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IJMSC Now in PubMed Central and PubMed The International Journal of MS Care (IJMSC) now participates in PubMed Central (PMC), a free electronic archive of full-text biomedical and life sciences journal literature at the US National Institutes of Health’s National Library of Medicine (NLM). Newly published articles can be accessed in PMC soon after publication, along with older articles going back to 2011. Citations and abstracts of these articles are retrievable in PubMed, the NLM’s journal abstract database (which includes the MEDLINE subset), through various types of searches. PMC, which launched in 2000, serves as a digital counterpart to the NLM’s print journal collection. It is a repository for journal literature deposited by participating publishers, as well as for author manuscripts that have been submitted in compliance with the NIH Public Access Policy and similar policies of other research funding agencies. Currently, more than 3 million articles from nearly 5000 journals are archived in PMC. The availability of IJMSC content in PMC and PubMed will make it more discoverable to researchers, health professionals, and the public. Each IJMSC search result in PubMed contains a link to the full-text article. This increased visibility and accessibility should lead to wider citation of IJMSC articles, helping to advance research and clinical practice in multiple sclerosis. Copyright to IJMSC material deposited in PMC remains with the Consortium of Multiple Sclerosis Centers, which is clearly indicated to PMC users. In addition to being available in PMC and PubMed, IJMSC is indexed in the Cumulative Index to Nursing and Allied Health Literature (CINAHL) and Rehabilitation & Sports Medicine Source (EBSCO Publishing), as well as Scopus. International Journal of MS Care 157
M
ultiple sclerosis (MS) is a chronic disease of the central nervous system that leads to progressive worsening of upright postural control. Owing to multifocal central nervous system involvement, visual1 and somatosensory2 afferent feedback are commonly adversely affected in individuals with MS. Moreover, the high prevalence of MS-related From the Department of Physical Medicine and Rehabilitation and Department of Neurology, University of Colorado School of Medicine, Aurora, CO, USA (JRH); and Department of Rehabilitation, University of Colorado Health, Physical and Aquatic Therapy– Stapleton, Denver, CO, USA (MMM). Correspondence: Jeffrey R. Hebert, PT, PhD, Department of Physical Medicine and Rehabilitation and Department of Neurology, University of Colorado– Anschutz Medical Campus, 12631 E. 17th Ave., Mail Stop F493, Aurora, CO 80045; e-mail: [email protected]. DOI: 10.7224/1537-2073.2016-027 © 2017 Consortium of Multiple Sclerosis Centers.
involvement of the primary sensory integration brain structures (eg, brainstem, cerebellum) results in impaired central integration of these sensory systems along with the vestibular system. This is important because humans require efficient and effective central sensory integration (CSI) of the visual, somatosensory, and vestibular sensory systems to maintain homeostatic balance control (balance as a function of CSI [balance f CSI])3 to maintain societal participation and prevent falls. Dysfunctional balance f CSI has been implicated in people with MS as leading to impaired postural control4,5 and falls.6 As such, it is vital that clinicians implement the most reliable and valid measures of balance f CSI to determine the functionality of this essential upright postural control domain to optimize appropriate exercise prescriptions for people with MS.
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Balance f CSI is a complex physiological process that many clinical measures of postural control are unable to quantify. The computerized dynamic posturography sensory organization test (CDP-SOT) has initial support as a valid measure of balance f CSI and falls in people with MS.7,8 It has been applied as a primary outcome in controlled trials of balance9 and vestibular rehabilitation10 training for individuals with MS, supporting the responsiveness of the CDP-SOT to targeted treatment of impaired balance f CSI in this patient population. The CDP-SOT has also been applied as a gold standard for the validation of novel outcome measures of postural control.11 The reliability of the CDP-SOT has been established in healthy young12 and older13 adults and in patients with stroke,14 transtibial amputation,15 and low back pain.16 However, investigations of the reliability of the CDPSOT in people with MS are lacking. In addition, the ability of the CDP-SOT to quantify differences in balance f CSI based on disability level is currently absent from the literature. This is a concern because the cornerstone of disability advancement is progressive worsening of gait and mobility. The reason for this cumulative disability is often multifactorial; however, it is plausible that impaired balance f CSI is a key physiological factor. Collectively, improved knowledge of the repeatability of the CDP-SOT and the utility of the CDP-SOT as a valid measure of balance f CSI will greatly improve the application of this instrumentation in the clinical setting. The purpose of this study was to determine the reliability and discriminant validity of the CDP-SOT in people with MS. We hypothesized that 1) the CDPSOT will have high test-retest reliability in participants with MS and 2) CDP-SOT scores will be statistically significantly lower in participants with MS with higher disability than in those with MS with lower disability.
Methods Participants This study enrolled 30 individuals with MS to perform the CDP-SOT at two visits 14 days apart. The participants were recruited through advertisements at the University of Colorado Hospital and the University of Colorado Denver Anschutz Medical Campus. Eligibility for people with MS included age 18 to 60 years, confirmed diagnosis of MS, ability to provide consent and follow simple directions, and ability to walk at least 25 feet with bilateral support (Patient-Determined Disease
Steps [PDDS] scale score ≤6). The exclusion criteria included wheelchair dependence, inability to ambulate, other neurologic conditions besides MS, participation in vestibular rehabilitation or balance training in the past 2 months, and an MS-related exacerbation or medication change in the past month.
Computerized Dynamic Posturography Balance f CSI was measured using the CDP-SOT on the SMART Balance Master system (version 9.0; Neurocom International Inc, Clackamas, OR). The CDP-SOT is designed to assess balance f CSI through a series of six conditions that progressively challenge components of sensory integration needed to maintain upright postural control. The SMART Balance Master system consists of a pressure-monitored force platform and dynamic visual surround. The force platform is able to detect participant sway based on the change in center of mass of the participant. Depending on the condition, the force platform or the visual surround has the ability to move in the anteroposterior (sagittal) plane to match the participant’s sway. The act of moving either the force platform or the visual surround to exactly match the participant’s sway is termed sway reference. The six conditions are 1) eyes open, no sway reference; 2) eyes closed, no sway reference; 3) eyes open, visual surround sway reference; 4) eyes open, support platform sway reference; 5) eyes closed, support platform sway reference; 6) eyes open, support platform and visual surround sway reference. Each condition consists of three 20-second trials. For each trial, participants were asked to stand quietly with their arms at their sides, head and neck looking straight ahead, and eyes open or eyes closed, depending on the condition. To prevent a fall to the ground during the test, participants wore a harness that was anchored to the frame of the SMART Balance Master in a way that did not restrict normal sway. Participants were also closely guarded by a physical therapist experienced in working with people with MS. A fall was defined as stepping off the force platform or depending on the harness for support. During all the conditions, equilibrium scores were generated. The equilibrium score was determined through a computer-generated algorithm that compares the participant’s sway in the sagittal plane with expected limits of stability based on normative values. An equilibrium score of 100 signifies no sway, scores closer to 0 indicate higher sway, and a score of 0 indicates a fall.
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The composite score was calculated using a weighted average of the equilibrium scores for each condition. The composite score ranges from 0 to 100, with higher scores indicating better balance f CSI.
Disability Disability due to MS was measured using the PDDS scale, a valid surrogate for the Kurtzke Expanded Disability Status Scale (EDSS).17 The PDDS scale is a patient-reported outcome that focuses primarily on walking ability and asks the participant to select one of nine items (score, 0 to 8) that best describes his or her disability. Lower disability was defined as a PDDS scale score of 0 to 3 and higher disability as a PDDS scale score of 4 to 6.18,19 A score of 0 signifies mild symptoms and essentially normal function, whereas a score of 3 indicates symptoms from MS that affect daily activities, but walking is usually without an assistive device. A score of 4 means walking with a unilateral assistive device most or all of the time, and 6 indicates the need for bilateral assistance for walking short distances and occasional use of a wheelchair.
Procedures A local scientific ethics committee, the Colorado Multiple Institutional Review Board, guided by the ethical principles for human subject research and in accordance with the United States Department of Health and Human Services policy and regulations (45 CFR 46), approved the study protocol, and all the participants provided signed informed consent before participation. The CDP-SOT was performed during two sessions 2 weeks apart. At the first session, the participants also filled out the PDDS scale.
Statistical Analysis Descriptive statistics were used to characterize the participants. Test-retest reliability between the sessions was assessed using the two-way random-effects, single-measurement interclass correlation coefficient (ICC[2,1]); ICC values of 0.75 to 1.0 were considered excellent; 0.40 to 0.74, fair to good; and less than 0.40, poor.20 Two-sided independent t tests were used to evaluate differences between the lower- and higherdisability groups for the composite CDP-SOT scores as well as equilibrium scores for each condition. Discriminant validity was confirmed by statistically significant group differences using two-sided t tests (α = .05). All the analyses were performed using IBM SPSS Statistics for Windows, version 23.0 (IBM Corp, Armonk, NY).
Results All the participants returned for the second visit, with a mean (SD) follow-up time of 15.4 (3.5) days. A description of the study sample, including disability level, is provided in Table 1. Table 2 reports the mean scores for the CDP-SOT, as well as the test-retest ICC(2,1) values for the composite, equilibrium, and strategy scores in each of the six conditions. The ICC(2,1) values (95% confidence intervals) for the six conditions ranged from 0.70 (0.46-0.84) to 0.90 (0.80-0.95), with 0.90 (0.80-0.95) for the composite score. The differences in the CDP-SOT scores between disability groups are presented in Table 3. The lowerdisability group had significantly higher mean composite CDP-SOT scores than the higher-disability group at session 1 (mean difference = 22.27, P = .001) and session 2 (mean difference = 25.98, P = .002). Test-retest reliability ICC(2,1) values (95% confidence intervals) for the composite score were 0.84 (0.62-0.94) for the lowerdisability group and 0.84 (0.56-0.98) for the higherdisability group. There was not a significant difference in age between the groups (P = .393). Last, the equilibrium scores for CDP-SOT conditions 2 through 6 were found to be significantly higher in the lower-disability group compared with the higher-disability group (P < .001 to P = .026), whereas no significant difference was found between the disability groups for condition 1 (P = .053) (Figure 1).
Discussion Reliability is a principal psychometric property of tests and outcome measures. Clinicians rely on evidence Table 1. Demographic and clinical characteristics of 30 participants with MS Variable
Participants
Age, mean (SD), y Female sex, No. (%) PDDS scale score, median (IQR) PDDS scale score, No. 0 1 2 3 4 5 6
43.2 (10.5) 27 (90) 3 (2) 1 4 3 9 9 2 2
Abbreviations: IQR, interquartile range; MS, multiple sclerosis; PDDS, Patient-Determined Disease Steps.
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Hebert and Manago Table 2. Across 2 weeks test-retest reliability of equilibrium, strategy, and composite scores for the six CPD-SOT conditions in people with MS Equilibrium score, mean (SD) Session
Condition 1
Condition 2
Condition 3
Condition 4
Condition 5
Condition 6
Composite score, mean (SD)
Day 1 90.93 (4.63) 79.01 (20.63) 78.49 (18.77) 66.67 (23.75) 40.50 (23.91) 43.16 (26.88) 61.2 (17.1) Day 2 90.09 (6.55) 76.09 (23.57) 75.01 (21.75) 70.96 (23.64) 46.86 (26.99) 48.48 (29.21) 63.6 (21.0) ICC(2,1) 0.70 (0.46-0.84) 0.82 (0.65-0.91) 0.81 (0.64-0.90) 0.87 (0.75-0.94) 0.77 (0.58-0.89) 0.90 (0.80-0.95) 0.90 (0.80-0.95) (95% CI) Abbreviations: CDP-SOT, computerized dynamic posturography sensory organization test; CI, confidence interval; ICC(2,1), random-effects interclass correlation coefficient; MS, multiple sclerosis. Note: For definitions of conditions 1 to 6, see the Computerized Dynamic Posturography subsection of the text.
Table 3. Comparison of age, mean CDP-SOT scores, and CDP-SOT test-retest reliability ICCs based on disability level MS disability levela Factor Age, mean (SD), y CDP-SOT composite 1, mean (SD) CDP-SOT composite 2, mean (SD) ICC(2,1) (95% CI)
Lower (n = 17)
Higher (n = 13)
Mean difference (95% CI)
P value
41.8 (10.6) 70.89 (9.14) 74.82 (9.05) 0.84 (0.62 to 0.94)
45.2 (10.6) 48.60 (17.14) 48.85 (23.34) 0.84 (0.56 to 0.98)
−3.39 (−11.4 to 4.6) 22.27 (11.20 to 33.33) 25.98 (11.39 to 40.56) –
.393b .001c .002c –
Abbreviations: CDP-SOT, Computerized Dynamic Posturography Sensory Organization Test; CI, confidence interval; ICC(2,1), randomeffects interclass correlation coefficient; MS, multiple sclerosis. a A Patient-Determined Disease Steps scale score of 1 to 3 is lower disability; 4 to 6, higher disability. b Equal variance independent-samples t test. c Unequal variance independent-samples t test.
of this property when making decisions about which tests provide the highest level of measurement stability. As such, the primary purpose of the study was to determine the test-retest reliability of the CDP-SOT in ambulatory individuals with MS. The CDP-SOT has previously been shown to be a reliable and valid measure of balance f CSI in several different community and patient population groups.12-16 To our knowledge, this is the first study to determine test-retest reliability and discriminant validity of the CDP-SOT in people with MS. A primary result of the present study is that the CDP-SOT is a statistically significantly reliable test of balance f CSI in people with MS. The test-retest reliability coefficients, ranging from 0.70 to 0.90 for conditions 1 to 6, and the composite score in the present study for individuals with MS are consistent with findings from a previous study involving individuals with transtibial amputation (range, 0.67–0.90).15 Furthermore, the reliability coefficients in the present study for people with MS have a narrower range compared with findings from a study of individuals with chronic low back pain (range, 0.26–0.89)16 and a greater coefficient than that reported in a sample of individuals with a stroke (composite score–only coefficient, 0.81)14 and for the
six-condition range found in adults 65 years and older (range, 0.15–0.70).13 Performance-based clinical tests of balance frequently require the determination of both rater and test-retest reliability psychometric properties. However, the computerized instrumentation of the CDP-SOT is a unique measure of balance f CSI. The CDP-SOT uses a standard computerized algorithmic approach to measuring balance f CSI that helps minimize rater-specific error and eliminates rater interpretation of patient test performance. Therefore, in the present study, the CDP-SOT underwent test-retest analyses only, and it was found that the reliability of the CDP-SOT composite score was excellent (0.90). This finding is similar to the test-retest reliability of the summary scores from other performance-based clinic tests of balance for people with MS, such as the Berg Balance Scale (range, 0.85–0.96)21-23 and the Dynamic Gait Index (0.85).23 It can be postulated that as disability progresses, people with MS routinely modify daily activities that are less challenging to CSI. However, these strategies are not always successful, and as a result, balance f CSI is further impaired, and this can result in increased loss of balance and risk of falls. To this point, we also aimed to determine the utility of the CDP-SOT to identify balance
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Fig. 1. Comparison of Equilibrium Scores on each of the six conditions of the CDP-SOT by disability group
100 90
P = .053a 92.94 88.9
Lower Disability P = .021a 87.71
86.04
P = .017a 76.78
80 Equilibrium Score
Higher Disability
P = .026a
67.64
70
68.62
P < .001b
60
53.44
P = .008a 54.90
52.80
50 40 30
27.79
24.41
20 10 0
1
2
3 4 CDP-SOT Condition
5
6
* Figure 1.Computerized Comparison of equilibrium each ofTest; the psix conditions of the CDP-SOT: Dynamic Posturographyscores Sensoryfor Organization = p-values (2-tailed); Equal variance ** computerized dynamic posturography sensory organization test (CDP-SOT) in the lowerindependent samples t-test; Unequal variance independent samples t-test
disability (Patient-Determined Disease Steps [PDDS] scale score of 1–3) and higherdisability (PDDS scale score of 4–6) groups
All the P values are two-tailed. aUnequal variance independent-samples t test. bEqual variance independent-samples t test. For definitions of conditions 1 through 6, see the Computerized Dynamic Posturography subsection of the text.
f CSI deficits based on disability level. The CDP-SOT differences for the comparisons between disability levels in the present study are greater than those in previous reports that applied the CDP-SOT as a discriminant test of fall risk. In older adults, CDP-SOT condition 2 was the only score that was significantly different between fallers and nonfallers (equilibrium score difference of 3.5),24 and in people with MS, an equilibrium score difference of 8.4 was reported for CDP-SOT condition 3 between fallers and nonfallers.8 Moreover, in the present study, both disability groups presented with progressively worse equilibrium scores from condition 1 to condition 6. This trend is consistent with previous work by Hebert and Corboy,3 where it was reported that the decline in CDP-SOT equilibrium scores progressed from the less CSI-challenging conditions (condition 1, 93.3 and condition 2, 89.1) to the most CSI-challenging conditions (condition 5, 60.0 and condition 6, 63.1). Findings from the present study extend this knowledge by demonstrating the differential worsening of equilibrium based on disability level. The CDP-SOT equilibrium scores for people with MS with higher disability were significantly lower than those for people with MS with lower disability, with the largest
differences found for conditions 5 and 6. These findings are in line with previous reports of progressive worsening of mobility,25,26 static balance dysfunction,27-29 and falls30-32 in people with MS with advanced disability, including a greater level of walking aid support. However, the present study is the first to report contrasting balance f CSI performance on individual conditions of the CDP-SOT based on disability. The mechanisms responsible for these findings cannot be elucidated in the present study. However, the brainstem33,34 and cerebellum35,36 are the primary central processors of CSI, and the presence of brainstem (P < .001) and cerebellar (P < .001) involvement are significantly associated with quicker advancement of disability in people with MS.37 Based on this knowledge, it can be theorized that greater MS-related involvement of these brain structures might explain the disability-dependent progressive worsening of balance f CSI performance observed in the present study. Future studies (eg, functional neuroimaging) are needed to determine the neural structures and functional network connectivity that are responsible for the variability in balance f CSI and whether these relationships further correlate with disability level.
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Findings from this study indicate that the CDPSOT is a valid measure to distinguish disability levels in people with MS and highlights the problem of impaired balance f CSI in individuals with MS with higher disability levels. With this knowledge, clinicians have early evidence of the expected balance f CSI control capacity among distinct disability levels and that the CDP-SOT allows for identifying limitations in more challenging balance f CSI tasks, ultimately aiding clinicians in the design and implementation of more targeted treatment strategies. Limitations of the study need to be recognized. Calculations of other psychometric properties, such as the minimal detectable change (MDC) of the CDP-SOT, were not possible owing to the sample size. This is primarily because smaller sample sizes can lead to large variances in measures, prohibiting valid MDC analyses. Larger studies are needed to extend the present findings of the psychometric properties of the CDP-SOT in people with MS including MDC. Future studies should also implement the clinician-administered Kurtzke EDSS to allow for characterization of disability on a larger scale and to include multiple functional system values assessed in the EDSS (eg, sensory, pyramidal, cerebellar) to expand investigation of the CDP-SOT based on disability status.
Conclusion This study indicates that the CDP-SOT is a reliable measure of balance f CSI and accurately differentiates disability status in people with MS who are ambulatory. The results support the clinical application of the CDPSOT as a reliable and valid measure of disease-related
PracticePoints • The computerized dynamic posturography sensory organization test (CDP-SOT) is a reliable and valid clinical test of balance as a function of central sensory integration (balance f CSI) in people with MS. • The CDP-SOT should be considered a measure of change in balance f CSI after treatment and quantification of balance f CSI based on disability. • Balance f CSI is significantly worse in people with MS with advanced disability and to a greater degree during more challenging balance f CSI– related conditions.
progression of balance f CSI–related instability in people with MS, which can be used to measure balance f CSI changes in response to treatment. Larger longitudinal studies investigating clinically meaningful changes in CDP-SOT scores due to the natural course of MS and in response to treatment need to be conducted. Investigations of the CDP-SOT as a valid measure of fall risk and of safe and effective free-living physical activity participation will also determine additional clinical utility of the CDP-SOT. Last, mechanistic studies are also needed that investigate the underlying reasons for differences in CDP-SOT scores based on disability in people with MS found in the present study. o Acknowledgments: The PDDS scale is provided for use by the North American Research Committee on Multiple Sclerosis (NARCOMS) Registry (http://www.narcoms.org/pdds). NARCOMS is supported in part by the Consortium of Multiple Sclerosis Centers (CMSC) and the CMSC Foundation. Financial Disclosures: The authors have no conflicts of interest to disclose.
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IJMSC Now in PubMed Central and PubMed The International Journal of MS Care (IJMSC) now participates in PubMed Central (PMC), a free electronic archive of full-text biomedical and life sciences journal literature at the US National Institutes of Health’s National Library of Medicine (NLM). Newly published articles can be accessed in PMC soon after publication, along with older articles going back to 2011. Citations and abstracts of these articles are retrievable in PubMed, the NLM’s journal abstract database (which includes the MEDLINE subset), through various types of searches. PMC, which launched in 2000, serves as a digital counterpart to the NLM’s print journal collection. It is a repository for journal literature deposited by participating publishers, as well as for author manuscripts that have been submitted in compliance with the NIH Public Access Policy and similar policies of other research funding agencies. Currently, more than 3 million articles from nearly 5000 journals are archived in PMC. The availability of IJMSC content in PMC and PubMed will make it more discoverable to researchers, health professionals, and the public. Each IJMSC search result in PubMed contains a link to the full-text article. This increased visibility and accessibility should lead to wider citation of IJMSC articles, helping to advance research and clinical practice in multiple sclerosis. Copyright to IJMSC material deposited in PMC remains with the Consortium of Multiple Sclerosis Centers, which is clearly indicated to PMC users. In addition to being available in PMC and PubMed, IJMSC is indexed in the Cumulative Index to Nursing and Allied Health Literature (CINAHL) and Rehabilitation & Sports Medicine Source (EBSCO Publishing), as well as Scopus. International Journal of MS Care 157
