Abstract
Objectives
Impaired postural control in individuals with multiple sclerosis (MS) is associated with falls. The objective was to evaluate the direction-specific limits of stability in people with MS.
Methods
Balance control of 18 individuals with relapsing-remitting MS and 18 healthy controls was assessed using instrumented (Limits of Stability (LOS) test) and clinical (Berg Balance Scale (BBS) and Activities-specific Balance Confidence (ABC) scale) tests.
Results
There were significant differences in reaction time, movement velocity, endpoint excursion, maximum excursion, and directional control measures of the LOS test between individuals with MS and healthy controls. The BBS and ABC clinical balance measures were significantly lower in individuals with MS compared to control subjects. The directional control impairment was seen in the right side and backward diagonals (backward-right and backward-left) directions. A significant difference between the fallers and non-fallers was found on all the components of the LOS test. There was a significant correlation between the BBS and ABC scores and different components of the LOS test.
Conclusions
Direction-specific impairment of limits of stability components was observed in individuals with MS. This information could be used in balance rehabilitation of people with MS.
1
Introduction
Balance impairment is frequently described as one of the early symptoms of multiple sclerosis (MS) and approximately 75% of individuals with MS experience impairment of balance during the course of the disease . Impairment in balance control could be seen in people with MS with significant clinical symptoms , with minimal symptoms , and even with no clinical symptoms . Balance impairment is a significant contributing factor for fall risk in people with MS and is also often associated with mobility limitations and reduced engagement in physical activity .
Quantifying the balance impairments is an essential part of monitoring the progression of the disease as well as assessing the therapeutic outcomes . Clinical balance assessments such as the Berg Balance Scale , Tinetti performance-oriented mobility assessment , and Timed Up and Go Test provide important information on balance deficits and fall risks in individuals with MS. However, studies have shown that the use of these assessment tools is limited by a ceiling effect and that these tests have limited value when trying to assess fall risks in active older adults . It is also widely accepted that instrumented tests of balance allow obtaining more accurate measurements of subjects’ postural stability . For example, assessment of postural stability using the limits of stability (LOS) is a valid and reliable outcome measure .
It was reported in the literature that individuals with MS have reduced LOS scores as compared to healthy controls . For example, individuals with MS showed deficiency in performance of the functional reach test, step test, and while responding to a brief backward tug . It was also described in the literature that individuals with MS compared to healthy controls have significant balance deficits and poor balance confidence levels . However, there is not enough information on the direction-specific balance impairment in individuals with MS. Hence, the aim of this study was to investigate the components of limits of stability in individuals with MS and compare their performance with that of healthy age and gender matched control subjects. We hypothesized that individuals with MS, as compared to healthy controls, will demonstrate impairment of limits of stability in the diagonal and backward directions.
2
Material and methods
2.1
Subjects
Eighteen individuals with relapsing-remitting MS and eighteen age and gender matched healthy control subjects participated in the study ( Table 1 ). The inclusion criteria for individuals with MS were Expanded Disability Status Scale (EDSS) score of ≤ 4 (fully ambulatory, self-sufficient, and able to stand and walk without any aid or orthosis at least 500 meters), no relapse within the last three months, and normal or corrected to normal vision. All participants were right hand and leg dominant as confirmed by the Edinburg Inventory. Based on self-reports about experiencing falls during the previous 12 months, individuals with MS were categorized as either fallers (two or more than two falls) or non-fallers. The study was approved by the university’s Institutional Review Board.
| Variables | MS ( n = 18) | Controls ( n = 18) | P -value |
|---|---|---|---|
| Age (years) | 52.7 ± 12.2 | 50.0 ± 13.3 | 0.531 |
| Height (cm) | 166.6 ± 9.6 | 163.4 ± 8.0 | 0.292 |
| Weight (kg) | 70.1 ± 13.0 | 72.3 ± 11.1 | 0.590 |
| BMI (kg/m 2 ) | 25.4 ± 5.5 | 27.0 ± 3.6 | 0.301 |
| ABC score | 70.28 ± 20.47 | 93.77 ± 6.25 | < 0.001 |
| BBS score | 48.61 ± 6.73 | 55.17 ± 1.25 | < 0.001 |
| Gender ratio (male: female) | 4:14 | 4:14 | – |
| MS duration (years) | 18.8 ± 9.4 | – | – |
| EDSS score | 2.69 ± 0.6 | – | – |
2.2
Instrumentation
Computerized dynamic posturography was used to perform the limits of stability test (EquiTest, NeuroCom, USA). The subjects were required to stand straight on the EquiTest platform keeping the cursor representing their body’s center of gravity (COG) over the initial position shown on the computer monitor . The subjects’ feet were aligned along the heel and medial malleolus landmarks printed on the top of the platform. The subjects were then instructed to shift their body weight (using their ankle joints as the primary axis of motion, without changing the feet position) in eight different directions (one direction at a time) as quickly as possible following the appearance of a target on the monitor. Each direction of the target was randomly selected by the researcher and displayed for eight seconds only once. The eight directions were: forward (FW), backward (BW), right (RT), left (LT), forward-right (FWRT), forward-left (FWLT), backward-right (BWRT), and backward-left (BWLT). For each direction the EquiTest software measured movement reaction time (ReT), movement velocity (MVL), endpoint excursion (EPE), maximum excursion (MXE), and movement directional control (DCL) . The ReT in seconds reflects the onset of intentional movement toward the target as soon as the specific target appears on the screen. The MVL is the average speed of the center of gravity (COG) movement in degrees per second quantified for 5% to 95% of the distance from the center of the monitor (initial position) to the target. The EPE is the distance of the first movement toward the designated target, expressed as a percentage of maximum LOS distance. The endpoint is considered to be the point at which the initial movement toward the target ceases. The EPE is the excursion of the COG movement at first attempt in a particular direction: it provides a measure of how far the patient is willing to move on his first attempt shifting toward the target and reflects the participant’s perception of his own safety limits . The MXE refers to a maximum distance achieved during the trial: as such, the MXE is larger than the EPE. Both the EPE and MXE were calculated and expressed as a percentage of the maximum LOS distance (theoretical limits of stability). The theoretical LOS refers to the body leaning in ankle joints with angles of 8 degrees right-side, 8 degrees left-side, 8 degrees anteriorly, and 4.5 degrees posteriorly . The measure of DCL is a comparison of the path of movement exhibited by the participant in the intended direction in which the values approaching 100% is a straight path i.e. toward the target, to the amount of extraneous movement away from the target, and is presented as a percentage (%). In addition, the composite score was calculated as an average score of the eight direction scores for each, ReT, MVL, EPE, MXE and DCL, and used to compare the groups of fallers and non-fallers.
Clinical balance measures included Berg Balance Scale (BBS) and Activities-specific Balance Confidence (ABC) scale.
The BBS is a valid and reliable tool to assess balance in individuals with MS. BBS contains 14 items where participants are rated on their ability to maintain positions or perform movements with increasing difficulty level and the ability to change positions . Each item score ranges from 0 (unable to perform task) to 4 (normal). The maximum attainable score is 56.
The ABC scale is a valid and reliable scale of balance confidence used in individuals with MS ; it is correlated with the outcomes of the instrumented tests of balance. It contains a 16-item self-report questionnaire rating balance confidence in performance of various ambulatory activities without losing balance .
2.3
Statistical analysis
A two way ANOVA was performed with the factors of group (MS and controls) and direction (8 directions) for each continuous variable (ReT, MVL, EPE, MXE, and DCL). Bonferonni correction was used for post-hoc comparisons. Mann–Whitney U test was used for the ordinal scale outcome measures EDSS, BBS and ABC scores and sub-group of fallers vs non-fallers. Spearman correlation coefficient ( ρ ) was used to evaluate the association between ABC scores, BBS scores, and the components of the LOS test. The statistical significance was set at P < 0.05. Fisher exact test was used for comparing the frequency of patient distribution with cerebellar insolvent between the groups.
2
Material and methods
2.1
Subjects
Eighteen individuals with relapsing-remitting MS and eighteen age and gender matched healthy control subjects participated in the study ( Table 1 ). The inclusion criteria for individuals with MS were Expanded Disability Status Scale (EDSS) score of ≤ 4 (fully ambulatory, self-sufficient, and able to stand and walk without any aid or orthosis at least 500 meters), no relapse within the last three months, and normal or corrected to normal vision. All participants were right hand and leg dominant as confirmed by the Edinburg Inventory. Based on self-reports about experiencing falls during the previous 12 months, individuals with MS were categorized as either fallers (two or more than two falls) or non-fallers. The study was approved by the university’s Institutional Review Board.
| Variables | MS ( n = 18) | Controls ( n = 18) | P -value |
|---|---|---|---|
| Age (years) | 52.7 ± 12.2 | 50.0 ± 13.3 | 0.531 |
| Height (cm) | 166.6 ± 9.6 | 163.4 ± 8.0 | 0.292 |
| Weight (kg) | 70.1 ± 13.0 | 72.3 ± 11.1 | 0.590 |
| BMI (kg/m 2 ) | 25.4 ± 5.5 | 27.0 ± 3.6 | 0.301 |
| ABC score | 70.28 ± 20.47 | 93.77 ± 6.25 | < 0.001 |
| BBS score | 48.61 ± 6.73 | 55.17 ± 1.25 | < 0.001 |
| Gender ratio (male: female) | 4:14 | 4:14 | – |
| MS duration (years) | 18.8 ± 9.4 | – | – |
| EDSS score | 2.69 ± 0.6 | – | – |
2.2
Instrumentation
Computerized dynamic posturography was used to perform the limits of stability test (EquiTest, NeuroCom, USA). The subjects were required to stand straight on the EquiTest platform keeping the cursor representing their body’s center of gravity (COG) over the initial position shown on the computer monitor . The subjects’ feet were aligned along the heel and medial malleolus landmarks printed on the top of the platform. The subjects were then instructed to shift their body weight (using their ankle joints as the primary axis of motion, without changing the feet position) in eight different directions (one direction at a time) as quickly as possible following the appearance of a target on the monitor. Each direction of the target was randomly selected by the researcher and displayed for eight seconds only once. The eight directions were: forward (FW), backward (BW), right (RT), left (LT), forward-right (FWRT), forward-left (FWLT), backward-right (BWRT), and backward-left (BWLT). For each direction the EquiTest software measured movement reaction time (ReT), movement velocity (MVL), endpoint excursion (EPE), maximum excursion (MXE), and movement directional control (DCL) . The ReT in seconds reflects the onset of intentional movement toward the target as soon as the specific target appears on the screen. The MVL is the average speed of the center of gravity (COG) movement in degrees per second quantified for 5% to 95% of the distance from the center of the monitor (initial position) to the target. The EPE is the distance of the first movement toward the designated target, expressed as a percentage of maximum LOS distance. The endpoint is considered to be the point at which the initial movement toward the target ceases. The EPE is the excursion of the COG movement at first attempt in a particular direction: it provides a measure of how far the patient is willing to move on his first attempt shifting toward the target and reflects the participant’s perception of his own safety limits . The MXE refers to a maximum distance achieved during the trial: as such, the MXE is larger than the EPE. Both the EPE and MXE were calculated and expressed as a percentage of the maximum LOS distance (theoretical limits of stability). The theoretical LOS refers to the body leaning in ankle joints with angles of 8 degrees right-side, 8 degrees left-side, 8 degrees anteriorly, and 4.5 degrees posteriorly . The measure of DCL is a comparison of the path of movement exhibited by the participant in the intended direction in which the values approaching 100% is a straight path i.e. toward the target, to the amount of extraneous movement away from the target, and is presented as a percentage (%). In addition, the composite score was calculated as an average score of the eight direction scores for each, ReT, MVL, EPE, MXE and DCL, and used to compare the groups of fallers and non-fallers.
Clinical balance measures included Berg Balance Scale (BBS) and Activities-specific Balance Confidence (ABC) scale.
The BBS is a valid and reliable tool to assess balance in individuals with MS. BBS contains 14 items where participants are rated on their ability to maintain positions or perform movements with increasing difficulty level and the ability to change positions . Each item score ranges from 0 (unable to perform task) to 4 (normal). The maximum attainable score is 56.
The ABC scale is a valid and reliable scale of balance confidence used in individuals with MS ; it is correlated with the outcomes of the instrumented tests of balance. It contains a 16-item self-report questionnaire rating balance confidence in performance of various ambulatory activities without losing balance .
2.3
Statistical analysis
A two way ANOVA was performed with the factors of group (MS and controls) and direction (8 directions) for each continuous variable (ReT, MVL, EPE, MXE, and DCL). Bonferonni correction was used for post-hoc comparisons. Mann–Whitney U test was used for the ordinal scale outcome measures EDSS, BBS and ABC scores and sub-group of fallers vs non-fallers. Spearman correlation coefficient ( ρ ) was used to evaluate the association between ABC scores, BBS scores, and the components of the LOS test. The statistical significance was set at P < 0.05. Fisher exact test was used for comparing the frequency of patient distribution with cerebellar insolvent between the groups.
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