Volume 90, Issue 6 , Pages 975-981, June 2009
Driving Behaviors Among Community-Dwelling Persons With Multiple Sclerosis
Article Outline
Abstract
Schultheis MT, Weisser V, Manning K, Blasco A, Ang J. Driving behaviors among community-dwelling persons with multiple sclerosis.
Objective
The current study examined driver behaviors and patterns among drivers with multiple sclerosis (MS) as a function of disease severity and in comparison to drivers without MS.
Design
Between-group comparisons of participants with and without MS and cohorts of MS groups at varying levels of severity.
Setting
All data were collected in an outpatient research setting.
Participants
Community-dwelling persons (n=66) with clinically definite MS who were active drivers and healthy controls (n=30) were included.
Interventions
Not applicable.
Main Outcome Measures
Driving characteristics' measures included (1) driving frequency defined in days and miles driven per week, (2) self-reports of voluntarily limited driving behaviors, (3) changes in driving since MS diagnosis, and (4) self-rating as a driver. Driving performance was also assessed by using pass/borderline performance on a clinical behind-the-wheel evaluation.
Results
Mann-Whitney U tests showed a significant difference in driving frequency (P=.021) with MS participants reporting they drove fewer days per week than healthy control group. This was also seen between cohorts of MS drivers (P=.014), with high Expanded Disability Status Scale (EDSS) participants driving less frequently than the low EDSS group. Descriptive observations suggested that participants with moderate EDSS scores drove less and engaged in more self-limiting behaviors. Chi-square tests showed that participants with high EDSS scores were more likely to report changing their driving behavior after diagnosis (P=.01) and were more likely to not pass the behind-the-wheel evaluation (P<.001).
Conclusions
The current findings suggest that as disease severity progresses, differences in frequency of driving (days per week) and the use of self-limiting driving behaviors may vary. Furthermore, the findings also raise questions regarding the overall sensitivity of the most commonly used clinical driving assessment method (the behind-the-wheel evaluation) to accurately capture driving capacity in the milder stages of the disease process. The results indicate the need to consider issues related to driving as MS severity progresses, and, given the progressive nature of MS and the concerns of the validity of the most common clinical driving assessment measures (the behind-the-wheel evaluation), repeated assessment of driving ability may be the most effective approach for identifying driving difficulties among persons with MS.
Key Words: Automobile driving, Multiple sclerosis, Rehabilitation
List of Abbreviations: ANOVA, analysis of variance, DBQ, Driver Behavior Questionnaire, DMV, Department of Motor Vehicles, EDSS, Expanded Disability Status Scale, HC, healthy control, MS, multiple sclerosis
MULTIPLE SCLEROSIS IS A chronic inflammatory and neurodegenerative disorder of the central nervous system that is associated with physical, cognitive, and psychologic impairments that can negatively affect various aspects of independent functioning.1 One essential aspect of functional independence is the ability to drive a motor vehicle.
Research on MS and driving ability has suggested that the presence of cognitive and physical impairments can impact driving-related skills. For example, studies have shown that the presence of cognitive impairment alone can negatively affect performance on computerized measures of driving skills2 and results in a higher frequency of documented accidents among drivers with MS when compared with healthy controls and MS drivers without cognitive impairment.3 Other work has examined the contribution of lower-limb spasticity to performance in a driving simulator and reported that spasticity was associated with specific driving components, including maintaining speed and following another vehicle.4 This study and a handful of others have also expanded on defining the contribution of cognitive functioning on driving performance among drivers with MS. Specifically, areas of attention, information processing speed, executive functioning, and visuospatial skills are relevant to driving performance in this clinical population.4, 5, 6 In sum, in addition to the overall importance of driving for maintaining an independent lifestyle, the findings from these studies underscore that determining driving capacity is an important consideration for persons with MS.
By contrast, research examining factors related to driving status and driving behaviors is sparse. It can be argued that without an understanding of typical driving behaviors, which can include driving cessation and/or driving modifications, accurate prediction and measurement of driving are limited. Although not comprehensive, preliminary findings indicate some differences in driving patterns among this clinical population. For example, a study using self-reported driving measures found that drivers with MS reported a decrease in frequency of days per week driving.7 Another study examining awareness deficits and driving found that 23% of their sample had discontinued driving and that persons who continued to drive were physically and cognitively healthier, showed greater awareness of their deficits, and reported fewer barriers to driving than nondrivers with MS.8 Yet, little remains known about potential self-regulatory strategies, such as avoiding difficult driving conditions and general driving habits of this population.
Numerous studies have examined changes in driving behaviors or patterns among patients after an acute event, such as traumatic brain injury9 or stroke.10 By contrast, the course of MS is typically progressive rather than acutely acquired, and, therefore, findings from these studies cannot be generalized to the MS population. As such, it would be important to understand changes in driving behavior in relation to MS, and in particular, severity of MS. Finally, little is known about the use of current clinical driving assessment methods in MS. Anecdotal information from rehabilitation professionals suggests that many persons with MS are not evaluated for driving competency. In addition, the validity of the most common clinical measure of driving performance, the behind-the-wheel evaluation, has not been thoroughly assessed for persons with MS. Answers to these questions would assist in the identification of the risks for drivers with MS.
The current study was conducted to learn more about the driving behaviors of persons with MS. By using self-reported measures and a clinical driving assessment, the study examined driving exposure and driving habits, self-regulatory behaviors, and changes in driving as a function of MS diagnosis. These factors were examined and compared with non-MS drivers and at different stages of MS severity.
Methods
Participants
Participants with relapse-remitting and secondary progressive MS were recruited from a neurology clinic in an urban, tertiary-care teaching hospital and through advertisements posted in conjunction with local chapters of the National Multiple Sclerosis Society. The current study did not use a convenience sample but rather recruited over 110 potential participants from the community who, prior to enrollment, underwent a comprehensive telephone screening. A total of 66 individuals with a diagnosis of clinically definite MS verified though medical records submitted by a treating physician were included in the study. An additional 30 education- and sex-matched HCs were also included.
All participants were adults aged 18 years or older and were at least 1 month after their last clinical exacerbation. Participants with a history of other neurologic disease, psychiatric illness, or substance abuse were ineligible based on self-report and medical records from the treating neurologist. In addition, participants were excluded from the study if they were currently taking medications that have been shown to adversely affect cognition such as steroids, benzodiazepines, neuroleptics, opioids, or narcotic analgesics. MS participants were allowed to continue to take Avonex, Beta-Seron, and Copaxone because that reflected standard care for people with MS. Table 1 shows participant demographic variables and disease characteristics.
Table 1. Demographics: MS Versus Healthy Controls
| Characteristics | MS (n=66) | HCs (n=30) |
|---|---|---|
| Age | 43.2±8.07 | 37.3±10.33⁎ |
| Sex (% men/women) | 21.2/78.8 | 36.7/63.3 |
| Education (y) | 15.3±2.07 | 15.8±2.08 |
| Ethnicity (%) | ||
 White | 84.8 | 70.0 |
| Black | 9.1 | 13.3 |
| Asian/Asian American | 1.5 | 10.0 |
| Hispanic | 4.5 | 6.7 |
| Driving experience (y) | 24.8±7.56 | 17.8±9.29⁎ |
| EDSS mean (range) | 3.42 (1.5–6.5) | NA |
| Years since diagnosis | 8.88±6.43 | NA |
| Type of MS (%) | 8.1 (1.68) | 8.7 (0.9) |
| Relapsing remitting | 86.4 | NA |
| Secondary progressive | 7.6 | NA |
| Progressive relapsing | 3.0 | NA |
| Unknown | 3.0 | NA |
⁎P<.05, HC<MS group. |
At the time of testing, all participants held a valid driver's license in the states of New Jersey or Pennsylvania and were classified as “active” drivers, which was operationally defined as a minimum of 1 driving occasion during a 1-month period in the past year. New drivers (<1 year driving experience) were not included in the study. Only participants who had not received driving rehabilitation or retraining were included, and all were required to meet the minimum visual requirements as established by the DMV in their respective states. Participants with a history of reckless driving and/or loss of driving privileges were not included in the study.
The current study further divided the MS sample into varying levels of MS severity. The level of MS severity was determined based on the EDSS,11 the most common clinical measure to assess disease severity and progression in MS patients. The EDSS has good test-retest reliability (r=.93), but data on the interrater reliability are more varied, and estimates range from .32 to .98 depending on how the investigators operationalized reliability.12 In general, the reliability of the EDSS tends to decrease when participants in the moderate range compared with the extremes are assessed, which has been a common criticism of the scale. However, the validity of the scale is less disputed. The EDSS has shown high convergent validity with the Scripps Neurological Rating Scale (r=.78), the Ambulation Index, and the physical function domain of a quality of life scale (r=−.79).12 All participants' EDSS evaluations were conducted by a physician with experience administering and scoring the exam. The EDSS assesses predominantly physical and, to a lesser extent, visual and cerebral function. Total EDSS scores range from 0 (normal neurologic examination) to 10 (death from MS).
Measures
Driving behaviorsSelf-reported driving behaviors were assessed by using the DBQ. The DBQ is a questionnaire designed to obtain driving information not available from the DMV and assesses self-reported information regarding driving frequency, patterns, and habits in a standardized manner. It was developed by the principle investigator in conjunction with 2 certified driving specialists, each with a minimum of 10 years of professional experience as a rehabilitation driver evaluator, and has been used in a previous study13 documenting driving behaviors in individuals with traumatic brain injury.
Specifically, for this study, participants were asked to complete the DBQ during the testing sessions. The DBQ included questions regarding frequency (days and miles per week) self-rating of driving ability on a scale from 1 to 10 in which 1 indicated poor ability and 10 indicated excellent ability. Other questions inquired about driving characteristics (reasons for driving, driving alone or with someone) and voluntarily self-limited driving behaviors (when weather is bad, rush hour traffic, night, and highway). Participants were asked to rank their reasons for driving from the following choices: work, leisure, school, medical appointments, errands, and travel trips. For MS participants, changes in driving since diagnosis were also examined including overall change (same, less, a lot less, more, a lot more). In addition, participants were asked if they took part in any unsafe driving behaviors (speeding, drinking and driving, driving while tired, and during severe exacerbation) both prior to and after their diagnosis. For data-analysis purposes, changes in driving since diagnosis were dichotomized, with participants coded as either same (responding same) or different (any of the 4 responses indicating a change). Similarly, unsafe driving behavior was coded as a “yes” if participants selected any of the 4 responses.
Driving performanceAll participants were also administered a behind-the-wheel driving evaluation. The behind-the-wheel evaluation was selected because it is the preferred clinical tool and current criterion index for fitness to drive.14 The behind-the-wheel evaluation was administered by a certified driver rehabilitation specialist who was blind to the participant's diagnosis and required each participant to drive a dual-controlled automobile through a predetermined route spanning several driving environments (ie, residential, multilane, commercial) lasting approximately 30 minutes. Performance on the behind-the-wheel evaluation was quantified by using a 33-item checklist that evaluated performance on various domains of driving during the on-route drive. The evaluator rated each item on the behind-the-wheel checklist on a numeric scale that reflected adequate (score of 1), marginal (score of 2), or failing (score of 3) performance on each task, with lower scores reflecting better performance. A total performance score for the behind-the-wheel evaluation was calculated by summing the scores on 33 items, whereby the lowest (best) and highest (worst) possible score a participant could earn was 33 and 99 points, respectively. Among our sample, we observed a high number of individuals performing at ceiling on the behind-the-wheel evaluation. Subsequently, we elected to dichotomize the behind-the-wheel score for data-analysis purposes. Specifically, behind-the-wheel scores of 33 were classified as “pass,” whereas behind-the-wheel scores of 34 and above were classified as “borderline.” This methodology is consistent with previous studies6, 15, 16 that have integrated the use of a clinical behind-the-wheel evaluation.
Procedures
The current study was part of a larger and comprehensive study that was designed to examine the effects of MS-related cognitive and physical impairments among drivers with MS. For the current study, participants were screened for eligibility requirements by using a comprehensive telephone interview. Having met criterion, participants were given written informed consent approved by the institutional review board. All participants were interviewed to assess demographic and social history and were administered the DBQ. An EDSS was also completed at the time of testing and all participants underwent a behind-the-wheel evaluation.
Statistical Analyses
Three levels of analysis were planned to address the overall objectives of this study. First, general comparisons between driving behaviors of MS drivers and non-MS drivers were examined. Second, given the variability in MS presentation, a descriptive analysis of driving behaviors at varying levels of MS severity is presented to highlight changes in driving within this clinical population. Finally, to statistically evaluate the differences between MS drivers as a function of disease severity, inferential statistics were used to compare driving behaviors between groups of MS participants. The selection of EDSS cutoff values for the different MS groups were based on clinical observations and expertise. Specifically, for the inferential statistics, MS participants were divided into low EDSS (≤4) and high EDSS (≥4.5) groups to maximize statistical power. The midpoint of 4 was designated in collaboration with treating neurologists who consistently use the EDSS as a measure of severity in patients with MS. For the descriptive statistics, we elected to divide the sample into 3 groups to better highlight the differences as MS severity progresses. These 3 levels were also designated in collaboration with treating neurologists.
When dependent variables were continuous and test assumptions were met, group differences were examined by using ANOVA. Although a significant difference in age was noted, age was not included as a covariate because the assumption that the covariate and dependent variable be correlated was not satisfied. If the homogeneity of variance or normality assumptions for ANOVA was violated, Mann-Whitney nonparametric tests were used. When the dependent variables were categoric, chi-square tests for independence were used. The dependent variables were driving frequency (days and miles per week), self-rating of driving behavior (1–10), overall self-limited driving behavior (yes/no), and self-limited driving behavior in specific situations (yes/no when the weather is bad, rush hour/heavy traffic, nighttime, and highway use). For MS participants, change in driving since diagnosis (same/not same), participation in unsafe driving (yes/no), and behind-the-wheel performance (pass/borderline) were also included. All analyses used 2-tailed tests with P equal to .05.
Results
Multiple Sclerosis Versus Healthy Control Drivers
Frequencies of the following driving behaviors for the MS and HC groups are summarized in table 2: driving frequency (days and miles per week), self-rating of driving ability, and self-limitations. Distributions of the driving frequency in days per week for both MS and HC were negatively skewed, whereas distributions for frequency in miles per week for both groups were positively skewed. Mann-Whitney U tests showed that the 2 groups significantly differed on driving frequency (U=733.5, P=.021), with MS participants reporting they drove fewer days per week than the HC group; however, the miles driven per week category was not significant (U=771.5, P=.10). It should be noted that self-rating data for 9 of the HC and 1 MS participant were not available. An ANOVA comparing self-rating of driving ability (F1,84=2.36, P=.13) was not significant. Self-limitation data for 5 of the HC group and 1 participant in the MS group was not available, and chi-square tests examining all the self-limiting driving behaviors between HC and MS did not reveal significant group differences (all P>.05).
Table 2. Driving Characteristics: MS Versus HC
| Driving Characteristics | MS (n=65) | HC (n=25) |
|---|---|---|
| Frequency | ||
| Days/wk | 7.00(2.00) | 7.00(.25)⁎ |
| Miles/wk | 75.00(150.00) | 100.00(212.50) |
| Self-rating of driving ability (1–10)† | 8.10±1.68 | 8.70±0.90 |
| Do you limit your driving? (% yes) | 44.6 | 36.0 |
| Don't drive in bad weather? | 36.9 | 33.3 |
| Don't drive in heavy traffic? | 27.7 | 16.7 |
| Don't drive at night? | 16.9 | 4.2 |
| Don't drive on the highway? | 4.6 | 0.0 |
⁎P<.05. |
†Data are presented as mean ± SD. |
Multiple Sclerosis Drivers at Varying Levels of Severity: Descriptive Observations
Previous studies have indicated that there is a reduced driving frequency among persons with MS.7 To more accurately examine this, driving frequency measured both in days and miles driven per week was examined across 3 MS groups: MS participants with low EDSS (1.5–3.0; n=39), moderate EDSS (3.5–5.0; n=11), and high EDSS scores (5.5–6.5; n=16). As summarized in figure 1, driving frequency (days per week) was greatest among those MS participants in the low EDSS group (mean ± SD, 6.28±1.23), followed by the moderate EDSS group (mean ± SD, 5.86±1.38), with the high EDSS (and more severely impaired) group driving the least (mean ± SD, 5.19±1.56). A somewhat similar pattern was seen when examining driving frequency as measured by miles driven per week. The low EDSS and moderate EDSS groups reported driving the greatest miles per week (low: mean ± SD, 140±184.2; moderate: mean ± SD, 151.59±152.25), and the high EDSS group reported the least driving (mean ± SD, 102.63±106.62). The variability in the moderate EDSS group may indicate that these participants are driving greater distances in fewer days per week. Alternatively, the variability may have been influenced by the small sample size and low absolute differences between the groups.
Fig 1.
Driving frequency across 3 levels of MS severity.
Response to questions about general driving habits also revealed some differences between the 3 groups. For example, in response to a query about the primary reasons for driving, the low EDSS group reported work (41%) as the most common reason followed by errands (32%) and leisure (11%). By contrast, the moderate EDSS and high EDSS groups reported errands as their primary reason for driving (moderate EDSS=50%; high EDSS=40%) followed by work (moderate EDSS=25%; high EDSS=27%) and leisure (moderate EDSS=13%; high EDSS=13%). Interestingly, driving for medical appointments was not identified as a primary reason in the low and moderate EDSS group but was reported in 7% of the high EDSS group.
Figure 2 summarizes responses to questions about self-limiting behaviors. Specifically, the proportion of participants who responded “yes” to voluntary self-limited driving behaviors both in general and for specific driving conditions is presented. One remarkable observation was the fact that it was the moderate and not the high EDSS group that reported implementing the most self-limiting behaviors. It was also noted that despite these self-reported driving restrictions, participants in all 3 groups rated themselves with above average driving ability, with the low EDSS group reporting a self-rating mean ± SD of 8.53±1.5 on a scale of 1 through 10, the moderate group self-rating a mean ± SD of 7.27±2.1, and the high EDSS group self-rated their ability at 7.75±1.57.
Fig 2.
A summary of self-limiting driving behaviors in MS drivers at varying severity.
We also examined self-reported changes in driving behaviors after MS diagnosis. Specifically, figure 3 summarizes the percentage of MS drivers in each group who responded “yes” to participating in unsafe driving behaviors (eg, driving fast, drinking and driving) before and after their MS diagnosis. It was remarkable that all 3 groups reported a decrease in engaging in “unsafe” behaviors after their diagnosis. Inquiries about changes in overall driving behaviors indicated that participants in the high EDSS groups reported the most changes (62.5%), followed by the moderate EDSS group (36.4%), with the low EDSS group (26.4%) reporting the least changes.
Fig 3.
The percentage of self-reported unsafe driving behaviors before and after MS diagnosis across varying levels of MS severity.
Finally, following these observed differences between the 3 groups, the potential effect of cognition required consideration. Subsequently, the analysis comparing the 3 groups on a measure of global intelligence (Wechsler Abbreviated Scale of Intelligence) did not reveal significant differences (low EDSS: mean ± SD, 105.7±11; moderate EDSS: mean ± SD, 107±14.9; high EDSS: mean ± SD, 106.8±9.3). Similarly, no group differences were noted in performance on cognitive measures related to driving performance, including Trail Making Test part B (seconds) (low EDSS: mean ± SD, 71.2±25; moderate EDSS: mean ± SD, 72.1±28; high EDSS: mean ± SD, 73.6±24), Wechsler Adult Intelligence Scale Digit Span (scaled score) (low EDSS: mean ± SD, 10.5±2.7; moderate EDSS: mean ± SD, 9.9±3.5; high EDSS: mean ± SD, 10±2.6), Stroop (Interference T score) (low EDSS: mean ± SD, 53.2±5.8; moderate EDSS: mean ± SD, 52.7±5.6; high EDSS: mean ± SD, 50±6.2), and the Motor-Free Visual Perceptual–Revised (raw score) (low EDSS: mean ± SD, 37.9±2.5, moderate EDSS: mean ± SD, 37.2±3, high EDSS: mean ± SD, 37.6,SD=2.8).
Low Disease Severity Versus High Disease Severity in Multiple Sclerosis: Inferential Statistics
Given the observation of patterns across the 3 groups, inferential statistics were used to statistically analyze differences in driving characteristics across varying levels of MS severity. However, the current distribution minimized statistical power, and, subsequently, the group was divided into 2 subgroups: low EDSS (≤4, n=42) and high EDSS (≥4.5, n=24). Before statistical analysis, the following demographics (age, sex, years of education, years of driving experience) were examined for group differences (table 3).
Table 3. Demographics of the MS Sample: Low Versus High EDSS
| Characteristics | MS Low EDSS | MS High EDSS |
|---|---|---|
| (n=42) | (n=24) | |
| Age | 41.64±8.59 | 46.04±6.31⁎ |
| Sex (% men/women) | 19.0/81.0 | 25.0/75.0 |
| Education (y) | 15.42±2.05 | 15.04±2.14 |
| EDSS mean (range) | 2.20 (1.5–3.5) | 5.54 (4.0–6.5)⁎ |
| Years since symptom onset | 12.67±9.61 | 15.64±8.19 |
| Driving experience (y) | 23.09±8.17 | 27.71±5.31⁎ |
⁎P<.05, MS low<MS high group. |
The driving variables used for the driving behavior and performance analyses (frequency, self-rating, self-limited behaviors, changes since diagnosis, behind-the-wheel performance) for the MS sample according to group are summarized in table 4. ANOVA tests revealed that the 2 groups significantly differed on driving frequency when examining days per week (F1,64=6.34, P=.014), with high EDSS participants driving fewer days than the low EDSS group. However, miles driven per week did not significantly differ between the 2 groups. For miles driven per week, the distribution was positively skewed, and a Mann-Whitney significance test was used to compare the groups. This test was nonsignificant (U=451.5, P=.58). Chi-square tests showed that participants with high EDSS scores were more likely to report changing their driving behavior after diagnosis (χ21=6.67, P=.01). Driving performance, as measured by the behind-the-wheel evaluation, significantly differed between the low and high EDSS groups (χ21=25.67, P<.001), with the high EDSS group more likely to perform in the borderline range in the behind-the-wheel evaluation. Specifically, in the high EDSS group, a total of 12 individuals scored in the “borderline” category (indicating a score>33). Overall, the median behind-the-wheel score for the borderline group was 42, with scores ranging from 35 to 56 points. Qualitative evaluation of the behind-the-wheel performance showed the greatest variability in observed performance of turning/tracking behaviors, lane use/passing skills, and subjective evaluation of managing the cognitive demands (scan, identify, predict, decide, execute) of driving during the behind-the-wheel evaluation.
Table 4. Driving Characteristics of the MS Sample: Low Versus High EDSS
| Characteristics | MS Low EDSS | MS High EDSS |
|---|---|---|
| (n=41) | (n=24) | |
| Frequency | ||
| Days/wk | 6.26±1.25 | 5.40±1.50⁎ |
| Miles/wk† | 75.00±162.50 | 67.50±151.25 |
| Self-rating (1–10) | 8.37±1.71 | 7.71±1.57 |
| Self-limiting (% yes/no) | 41.5/58.5 | 50.0/50.0 |
| Bad weather | 31.7/68.3 | 45.8/54.2 |
| Heavy traffic | 31.7/68.3 | 20.8/79.2 |
| Nighttime | 14.6/85.4 | 20.8/79.2 |
| Highway | 2.4/97.6 | 8.3/91.7 |
| Change in driving (% yes/no) | 22.5/77.5 | 54.2/45.8⁎ |
| BTW performance (% pass/borderline) | 100.0/0.0 | 50.0/50.0⁎ |
⁎P<.05. |
†Data are presented as medians and interquartile ranges. |
Finally, an ANOVA examining self-rating of driving performance (F1,63=2.36, P=.13) and chi-square tests examining self-limiting driving behaviors (bad weather, heavy traffic, nighttime, highway) failed to find significant group differences (all P>.05).
Discussion
The findings from this study better define driving behaviors among persons with MS and provide insight into the variability of driving behaviors in relation to the severity of MS-related impairments. The latter point underscores the importance of integrating disease severity in studies of measurement or prediction of driving in MS. This is particularly helpful given that findings regarding the relationship between driving measures and EDSS score have been inconsistent, with some reporting no relationship5 and others reporting that disease severity can predict driving status.8
Specifically, the current study found that as level of MS-related impairment increased (as measured by the EDSS), participants reported a reduction in driving frequency (as measured by days per week) and increase in modification to driving behaviors, which included self-limiting driving behaviors (ie, not driving in bad weather). This difference in frequency was not found when “miles driven per week” was examined, although a trend was observed when those participants with greater severity reported driving less miles. What is noteworthy is that initial comparisons of the MS sample and a matched healthy control sample did not reveal these differences. These results suggest that a comparison of drivers with MS to traditional control groups may not provide adequate information, and more specific comparisons between other MS cohorts may be necessary to understand driving behaviors and capacity in this clinical population. In the current sample, reduced frequency of days per week driving was consistently seen, with MS drivers reporting less days driving than HCS and those with high EDSS scores reporting less days driving than those with low EDSS scores. Although critics of the EDSS have noted that it is highly focused on physical impairment (notably ambulation), this finding remains consistent with studies of other clinical populations that have indicated that ambulatory limitations are related to driving ability.17 In addition, both descriptive and inferential statistics of MS groups at varying levels of MS severity indicated some changes in driving behaviors. Based on self-report, the current sample indicated that the most commonly avoided driving situation was bad weather followed by heavy traffic and nighttime driving. This finding is consistent with previous reports that focused on adjustment of driving behaviors as a result of fatigue18 and that have looked at the relationship between self-awareness and invoking compensatory driving behaviors.8 In particular, it is also remarkable that despite participants reporting changes in their driving behaviors, overall self-rating of driving capacity did not vary across the groups. Although this finding is consistent with reports from the transportation literature that indicate tendency of overestimation of driving ability in most drivers,19 the clinical implications are that just asking a person to rate his/her driving may not be sufficient.
Unlike previous studies, the current findings also provide insight into the usefulness of the most commonly relied on clinical determinant of driving capacity and current criterion standard, the behind-the-wheel driving evaluation.14 Specifically, in the present study, 50% of participants in the high EDSS group performed in the borderline (less than perfect) range on the behind-the-wheel evaluation, whereas 100% of the low EDSS participants fell into the passing (perfect) category. Based on this, we concluded that the behind-the-wheel evaluation is only sensitive for participants in the moderate to severe range of impairment and may not be capturing more subtle difficulties in the less impaired group. This is a criticism that has been raised by other researchers.20 Given the variability in the clinical presentation of MS, in particular considering the role of cognitive impairments2 that may not be picked up by the EDSS, the use of the behind-the-wheel evaluation to determine driving capacity in this population remains questionable. Although the overall validity of the behind-the-wheel evaluation has been a long-standing question in driving research,13, 20 what raises trepidation is the fact that behind-the-wheel evaluations are commonly conducted in the early stages of diagnosis or treatment. In the case of MS, given the subtle decline in functioning that occurs throughout the years for most patients, the question of when to administer the behind-the-wheel evaluation becomes pertinent. One can also consider questions about the need for potential repeated assessment of driving ability as changes in MS severity occur.
The current study used a modest sample and as such was only able to examine differences in driving behaviors at 2 levels of severity. The study also had various exclusionary criteria (ie, no driver with history of reckless driving or loss of driving privilege) that may have contributed to the high-functioning sample, which may not be fully representative of the spectrum of MS impairment. Additional studies using larger samples, which would allow inferential analysis along the spectrum of MS severity, would provide further insight into when changes occur in driving behaviors and increase the overall generalizability of the findings. The current study also greatly relied on subjective measures of driving behaviors, and additional objective measures (ie, using driving reports from the DMV)13 or measures from collateral sources may provide additional information. Finally, although this study examined behaviors by using a cross-sectional design with only 3 cohorts, a longitudinal study that further examines the different levels of MS severity would further elucidate details of driving changes and behaviors.
Conclusions
The current study did not attempt to predict driving performance but rather investigated potential differences in driving behaviors among drivers with MS. In general, it has been established that a large percentage of persons continue to drive (ie, 77%) after their diagnosis of MS.8 However, questions about how and when they drive require consideration to more fully understand how MS-related impairments affect driving ability. The current findings suggest that as disease severity progresses, differences in frequency of driving (days per week) and the use of self-limiting driving behaviors may vary. Furthermore, the findings also raise questions regarding the overall sensitivity of the most commonly used clinical driving assessment method (the behind-the-wheel evaluation) to accurately capture driving capacity in the mild to moderate (EDSS<4.5) stages of the disease process. Although further research will be needed, these findings have several clinical implications. First, the results directly indicate the need to consider issues related to driving as MS severity progresses. In particular, this should not be limited to general queries of driving ability but include specific questions about driving behaviors (ie, frequency, modifications). Second, given the progressive nature of MS and the concerns of the validity of the most common clinical driving assessment measures (the behind-the-wheel evaluation), repeated assessment of driving ability may be the most effective approach for identifying driving difficulties among persons with MS.
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Supported by the National Multiple Sclerosis Society (grant no. RG 3353A1/1).
No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated.
PII: S0003-9993(09)00161-0
doi:10.1016/j.apmr.2008.12.017
© 2009 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.
Volume 90, Issue 6 , Pages 975-981, June 2009
