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Persons with spinal cord injury (SCI) may experience a range of symptoms typically labeled as “spasticity.” Previous efforts to develop assessment tools for measuring spasticity have failed to represent the experiences of persons who live with the condition. The purpose of this multi-center study was to develop an instrument to measure the impact of spasticity on affected persons’ quality of life.
Based on 24 semi-structured interviews were conducted, a developmental form of the PRISM was developed. It was administered to 180 persons at 5 sites. Subscales were developed based on factor analytic results. Evidence for the reliability and validity of the scores was evaluated.
Seven subscales were developed, including one that measures positive impacts of spasticity. Results of reliability and validity assessments indicate that the PRISM subscale scores can be effective measures of the impact of spasticity in the population of veterans with SCI.
Spinal cord injury (SCI) can suddenly change a person’s life physically, emotionally and socially. Persons with severe lesions frequently experience involuntary movements or spasms, altered motor control, weakness or paralysis, and altered sensation or pain. The motor control problems typically are labeled “spasticity.” These problems can substantially impact the quality of life of those affected. In surveys of patients’ perceptions of problems associated with their spinal cord injury (SCI), spasticity has been consistently identified in the top three to five life concerns.(1) Because the experience of spasticity or altered motor control is multidimensional in nature and broad in scope, there is a need for a comprehensive means of assessing its impact.(2) Previous efforts to develop instruments for measuring spasticity have focused on explicit mechanical properties but failed to attend to and, consequently, failed to represent the experiences of persons who live with spasticity.(3)
The purpose of this multi-center study was to develop, from the perspective of persons with SCI, an instrument to measure the impact of abnormal muscle control or involuntary muscle movement on persons’ quality of life.
A total of 212 persons participated in the study. Twenty-four participated in semi-structured interviews, eight participants in a focus group responded to and evaluated a first draft of the PRISM, and 180 completed a developmental form of the PRISM. Of the 180, 36 completed the instrument a second time so that we could evaluate test/retest reliability. Participants were recruited from the Veteran’s Administration Medical Centers (VAMC) in Cleveland, Dallas, Palo Alto, and Houston. In addition, participants were recruited from The Institute for Rehabilitation and Research (TIRR), Houston, Texas. The Institutional Review Boards at all sites approved the study protocol. Persons were included if they had sustained a SCI, were over the age of 18, spoke and read English, and stated that they, currently or in the past, had experienced spasticity.
Twenty-four participant interviews were conducted by one of the authors (Hart) who had extensive experience in research and education programs with and for persons who have SCI. Consistent with established qualitative methods (4, 5), the interviews were semi-structured and comprised of queries such as “I am interested in learning about your experience with having involuntary movements. Can you tell me about it?” Interviews were audio-taped, transcribed and then evaluated by two of the team experienced in qualitative research (Engebertson & Mahoney). The data were reviewed and summarized with particular attention to identifying recurrent themes and recording the language participants used to describe their experiences. A domain analysis of reported experiences ensured that the instrument was grounded in the phenomenon under investigation. Seven specific domains were identified that described participants’ experiences: physical characteristics, impact on activities (positive and negative), psychological sequelae, financial costs, impact on interpersonal relations, functional self-management, and attributions. Descriptive sub-categories within each domain were identified. Details of these results are reported elsewhere (3).
Based on the qualitative findings, the psychometrician on the study team (Cook) drafted an initial pool of items with particular attention to participants’ natural language statements. Items were written to reflect the themes and categories in all of the identified domains. In the development of an instrument, it is important to begin with more items than are likely to be included in the final measure. This allows developers to be “choosy” and select the items that prove to have the strongest psychometric properties. In the current study, we developed 65 candidate items. Because there is no agreed upon clinical definition of spasticity and persons with SCI may classify a range of experiences as spasticity, we were careful to specify the kind of experiences on which we wished participants to report. The introductory text for the questionnaire stated:
The following questions are about your experience of abnormal muscle control or involuntary muscle movement. Different people have different terms they use for abnormal muscle control and involuntary muscle movement. Some of these are: (1) spasticity, (2)muscle stiffness (tone), (3) spasms, (4) clonus (bouncing), (5) when muscles don’t cooperate together like they’re supposed to, and (6) when trying to move one part of my body causes another part to move also.
The stem for the items stated, “Over the PAST WEEK, my abnormal muscle control or involuntary muscle movement…” The items that followed queried respondents about both the positive and negative impacts of their abnormal muscle control or involuntary muscle movement (AMC/IMM). The initial items were reviewed by an expert team of researchers and clinicians with experience in SCI. Items were modified based on input, and a 5-point Lickert-type response scale was chosen in which ‘0’ = never true for me, ‘1’= rarely true for me, ‘2’ = sometimes true for me, ‘3’ = often true for me, and ‘4’ = very often true for me.
Using cognitive testing methods (6), we evaluated the initial item pool with a focus group of 8 participants with SCI and self-reported spasticity. Participants commented in particular on whether the instructions and item wording were easy to understand and whether the item content comprehensively captured their experiences of AMC/IMM. Items were revised based on input from the participants. We created a survey that included the 65 items plus demographic and clinical questions. In addition, one item asked respondents to compare the positive and negative effects of their involuntary muscle control. Response options were: “1” positive strongly outweighs negative, “2” positive slightly outweighs negative, “3” positive and negative are equal, “4” negative slightly outweighs positive, and “5” negative strongly outweighs positive.
A survey containing the PRISM developmental items was administered to a sample of 180 persons with SCI who reported experiencing AMC/IMM. In addition to completing the questionnaire at enrollment, a subsample of 36 persons, recruited from the Houston sites, took home a copy of the instrument along with a posted envelope in which to return the completed instrument. Participants were instructed to return the second copy of the instrument within one week. However, as we report below, most were returned after a longer time period.
A clinical subsample (N=33) recruited from the Houston sites (Houston VAMC=25, TIRR=8) underwent a clinical exam and were classified based on the ASIA impairment scale (AIS). All exams were conducted by a physical therapist with clinical and research experience in SCI. This subsample reported on global severity (i.e., “mild,” “moderate”, or “severe”) and frequency (“no spasms” to “spasms occurring more than ten times per hour”). They also reported the degree to which spasms interfered with their function (i.e., did not interfere, made function difficult, or prevented function). All study data were double-entered into an electronic database.
Mplus software (7) was used to examine the factor structure and construct validity of the item responses. Mplus was chosen because it accounts for the categorical nature of the data. An exploratory, first order factor analysis was conducted utilizing the polychoric correlation matrix. The optimal number of factors representing the associations among the variables was determined by several methods (8) including a parallel analysis (9, 10), a scree test (11), examination of eigenvalues, and an examination of the residual correlation matrix. The factors were estimated with an Unweighted Least Squares method, extracted using a principal axes (or “common factor”) solution, and then rotated with a Varimax orthogonal rotation followed by a Promax oblique rotation. The pattern matrix was used to interpret the factor solutions.
The reliability of the PRISM was assessed by calculating the inter-item consistency of subscale items (Cronbach’s Alpha). The reproducibility of scores was evaluated by calculating the test/retest correlation (intraclass correlation coefficients, ICCs (12).
We share the view that “content validity is built into a test from the outset through the choice of appropriate items.” (13) The content-related validity of the PRISM is supported by the domain analysis of patient interviews and review of the candidate items by an expert review panel. In addition to content validity, we evaluated the PRISM’s ability to discriminate “known groups.” That is, we formed a priori hypotheses regarding what groups of participants were more likely to experience the impact of AMC/IMM. Specifically, we developed the following hypotheses:
Because the clinical subsample size was small, for the statistical comparisons we collapsed interference and severity ratings into two categories each. Those who reported that their problematic spasms were “mild” were compared to those reporting that they were “moderate” or “severe.” Those who reported that they experienced no interference with function were compared to those who reported that their problematic spasms interfered or prevented function. Because group sizes were unequal and data were categorical, all statistical comparisons were made using the less powerful but more appropriate Mann-Whitney U statistical test of mean ranks.
The 180 participants responding to the developmental questionnaire were between 2 months and 56 years post-injury and had a mean age of 52 (SD=12 years). The racial/ethnic breakdown was 72.1% Caucasian, 21.2% African American, 4.5% Hispanic, 0.6 % Asian, and 1.7% “other.” Additional demographic and clinical variables are reported in Table 1. Forty-nine participants were recruited from the Houston VAMC, 64 from Dallas, 21 from Cleveland, 32 from Palo Alto, and 14 from Houston TIRR.
As Table 1 indicates, the demographic and clinical characteristics of the clinical subsample were similar to those of the rest of the study population, though, in the clinical subsample, there was a higher proportion of women. The average age was 51 years (SD=10). ASIA impairment scale scores were obtained for 32 of the 33 participants for whom clinical data were gathered, with 21 classified as ASIA-A, 1 as ASIA-B, 3 as ASIA-C, and 7 as ASIA-D.
The clinical subsample of 33 participants also reported on the severity, frequency, and interference of their “problematic spasms,” 28% described it as “mild”, 50% as “moderate”, and 22% as “severe”. Twenty-four percent of the subsample reported that their problematic spasms did not interfere with function, 58% that it made function difficult, and 18% that it prevented function.
Of the 65 PRISM items, only 55 items were included in the exploratory factor analysis. Ten items were judged not to pertain strictly to the impact of AMC/IMM (Appendix A). Some of the ten had wording that was descriptive of the experience of AMC/IMM rather than the intensity of its impact (e.g., “…my abnormal muscle control…was unpredictable”) and others queried respondents about AMC/IMM “triggers” (e.g., “…my abnormal muscle control…was triggered by my emotions”).
An exploratory first order factor analysis was conducted based on the responses of the 147 persons who answered all 55 remaining items. The purpose of this analysis was twofold. First, we wanted to associate items with distinct subscales. Also, because we began with a larger item pool than we expected to use, we wanted to identify items that could be deleted from the item pool. The multiple approaches used to determine the number of factors were consistent in suggesting a 12 factor solution. The factors were rotated using a Varimax orthogonal rotation followed by a Promax oblique rotation. The 12 extracted factors accounted for 65% of the variance in the data. We elected to develop seven subscales representing the first seven factors. In all but one case, the subscales consisted of all items that loaded at 0.400 or above on one of the seven factors. One item, “Caused me to worry” was factorially complex, loading almost equally on the first (0.491) and second factors (0.496). Because this item did not help distinguish among impact factors, it was deleted from consideration for the PRISM measure. Factor eight had four items associated with it, items concerning sleep, fatigue, and AMC/IMM as “a warning that something was going on” (e.g., urinary infection). Because these items did not define a clearly interpretable dimension, we elected not to include a subscale to assess this factor. Factors nine through twelve were defined by only one or two items. These factors and the items most highly associated with them were dropped from further consideration. Factor loadings for all items are presented in Appendix B. Items that were not retained in the final PRISM are shaded.
We labeled the factors based on input from the researchers who conducted and analyzed the participant interviews and from clinicians and researchers experienced in SCI. The seven factors were labeled Social Avoidance/Anxiety (SAA), Psychological Agitation (PA), Daily Activities (DA), Need for Assistance/Positioning (NAP), Positive Impact (PI), Need for Intervention (NI), and Social Embarrassment (SE) (See Appendix B).
As described earlier, items were scored from 0 to 4, with higher scores indicating greater impact. Subscale scores were obtained by averaging item scores and multiplying by the number of items in the subscale (SAA=11 items, PA=5 items, DA=6 items, NAP=5 items, PI=4 items, NI=5 items, and SE=5 items). For each subscale, if a participant responded to fewer than 4 items OR fewer than 80% of the subscale items, scores were recorded as “missing”. Table 2 reports the descriptive statistics for the subscale scores. For almost every subscale, observed scores extended over the full range of the subscale. Scores were somewhat skewed toward higher scores; that is, relative to the range of the scale, more persons scored in lower ranges (indicating less impact).
Table 3 reports the correlations between pairs of subscales. As expected, the PI subscale correlated positively with the other subscales. The fact that these correlations were moderate and not high suggests that the domains measured are distinct. The PI subscale was the least highly correlated with the other subscales (0.070 to 0.286) suggesting that whether persons experience positive impacts from AMC/IMM is relatively independent of whether they experience negative impacts.
In addition to presenting the descriptive statistics described above, Table 2 reports the internal consistency (Cronbach’s alpha) and reproducibility (ICC) for each subscale. Internal consistency was lowest for the NI subscale (0.74) and highest for the SAA subscale (0.96). ICC values were high for all seven subscales (range = 0.82 to 0.91). Unfortunately, study staff failed to enter the return date for half (N=17) the retest forms. Of those for whom the date was available, one participant turned it in the next day, and another waited 49 days. On average, there was an 11 day span between the first and second administrations (SD=13 days).
The clinical subsample (N=33) reported the global severity and frequency of problematic spasms and the degree to which problematic spasms interfered with function. The distributions of responses to these questions are reported in Table 4. We evaluated validity by developing and testing a priori hypotheses regarding the relationship between PRISM subscales scores and responses to the severity and interference questions. The resulting probabilities and mean ranks are reported in Table 5. All mean ranks were in the expected direction for both questions. All the comparisons based on severity responses were statistically significant (Mann-Whitney U, p<.05, 1-tailed). However, only two of the comparisons based on interference ratings were statistically significant (DA and NI).
All participants (N=180) reported on the relative strength of positive and negative effects of AMC/IMM. The distribution of responses is reported in Table 6. We compared scores on the PRISM Positive Impact (PI) subscale with respect to participants’ judgments regarding whether the positive effects of AMC/IMM outweighed the negative ones. The two groups compared were those reporting that the positive impacts either “slightly” or “strongly” outweighed the negative (N=38) to those reporting that the negative impacts either “slightly” or “strongly” outweighed the positive (N=82). Those reporting that the impact of each was “about equal” were excluded for this analysis. For those reporting that positive impact outweighed negative impact, the mean rank Positive Impact Subscale score was 76.3. For those with the opposite judgment, the mean rank was 51.3. This difference was statistically significant (Mann-Whitney U, p<.001, 1-tailed).
The PRISM is a new instrument that standardizes the collection of self-report information relevant to the clinical assessment of AMC/IMM. Priebe et al. (2) noted that spasticity is a multidimensional phenomenon in persons with SCI. The PRISM subscales assess the impact of altered motor control with respect to social avoidance and anxiety, psychological agitation, daily activities, need for assistance or positioning, need for interventions, and social embarrassment, as well as the positive impact of altered motor control.
There are a number of limitations to this developmental work. Our exploratory factor analysis of 55 variables was conducted with a smaller sample size than would have been optimal (N=147). Since our purpose was to identify constructs for inclusion in the PRISM, we considered the sample size minimally adequate for measurement development. For factor analytic-based measurement validation, however, a substantially larger sample size is preferred.
Ten items were dropped from the initial item pool because they were judged to be descriptive of the nature of AMC/IMM as opposed to indicators of its impact. Though exclusion of these items was consistent with our goal of developing an evaluative instrument, the loss of these items has content validity implications, since the items represent content that participants associated with their experience of AMC/IMM. In future research, the development of one or more checklists should be explored. For example, a checklist could be developed with which participants report on the nature of their AMC/IMM and the conditions and circumstances that trigger it. Checklists are qualitatively different from evaluative instruments (e.g., Lickert-type scales). With checklists, items are not summed because there is interest in the specific answers to each item of the checklist. A checklist could be used to answer the question, “what aspects of the environment trigger respondents’ AMC/IMM.” Though it was beyond the scope of the current study, it would be worthwhile in future research to develop such an instrument to augment the PRISM subscales and provide information that would be valuable both for clinical and research purposes.
A limitation of the PRISM’s scoring system is that, in it, item scores are averaged and multiplied. This approach fails to take into account the fact that the measurement level of the item scores is ordinal, not equal interval. Though the categorical nature of Lickert-type data is seldom considered in the scoring of health outcome scales, we recognize this as a limitation. An alternative would be to score the subscales by calculating the median of the item scores. The net effect of scoring the subscales in this way, however, would be that there would be only five possible scores (1–5). We judged this disadvantage to be more problematic than applying mathematical operations that are not optimal for ordinal-level data. A more elegant solution would be to calibrate the items of the subscales using an item response theory model (IRT) (14). One of the many advantages of IRT modeling is that, compared to summing or averaging categorical item scores, it produces scores that more closely approximate an equal interval scale. Larger sample sizes are required for IRT parameter estimation (e.g. >250). The next step in our development of the PRISM is to collect subscale responses from a large sample and calibrate these responses using an IRT model.
There are a number of clinical implications of the study results. Current measures focus on physical manifestations of spasticity with the implicit assumption that all spasticity is bad and more is worse. Since “you get what you measure,” studies based on previously developed measures are unlikely to consider the possibility that patients might find some aspects of spasticity beneficial. Because the PRISM offers the opportunity to explore the range of spasticity’s impact, it may encourage a more nuanced approach to the management of spasticity, one that focuses on appropriate control of abnormal motor control, rather than suppression of motor control.
The meaning of existing, physically-based measures will be informed by comparisons with the PRISM subscales. This too may help optimize treatment. For example, some measures may be found to be better correlated with self-reported impact of spasticity. If so, these should be favored under the assumption that the patient is the best judge of how they are doing.
The results of this study support the notion that interventions for AMC/IMM should focus on restoration of active control rather than abolition of all motor activity associated with AMC/IMM. Many interventions (e.g., Intrathecal baclofen) markedly suppress motor excitability at the spinal level with a consequent suppression of residual voluntary motor control. Yet, in the current study, almost one-fourth of study participants reported that the positive impacts of their altered motor control outweighed the negative. This finding provides a compelling reason for considering persons’ subjective impressions in selecting treatment interventions. Future research should evaluate whether persons for whom the positive impact outweighs the negative have different patterns or physical features of AMC/IMM than do persons for whom this is not the case. Another research question worth investigating is the relationship between persons’ evaluations of the relative positive and negative impacts of their altered motor control and the degree to which their treatment is considered “optimized.”
Though it is frequently done, it is inaccurate to describe any instrument as reliable or valid. It is the scores obtained with the instrument that will be reliable and valid for particular populations and specified purposes. For this reason the validation of an instrument is a continuing process as it is evaluated in different samples and used for a variety purposes. The work presented here is developmental in nature, but our results indicate that the PRSIM scores can be valid and reliable in the veteran population with SCI. Evidence to this effect included the findings that: (1) ranks of subscale scores were consistent with the rankings of self-reported levels of severity and interference, (2) the content of the measure is grounded in persons’ reported experiences, (3) the scores were both internally consistent and reproducible across time. The PRISM is the only instrument developed to assess, from the perspective of persons with SCI, the wide range of AMC/IMM’s impact. We were not able to test concurrent validity because no previous scales have attempted to describe the experience of persons with disabilities. The only self-report scale currently in the literature is the Penn spasm frequency scale (15) that focuses on only one narrow aspect of spasticity, and does not probe other aspects of the experience. We expect future research to add to the body of evidence regarding the PRISM’s value and limitations.
Funding Source: Supported by a grant from the Rehabilitation Research and Development Service, Veterans’ Health Administration, Department of Veterans Affairs (No. B2212B).
My abnormal muscle control or involuntary muscle movement:
|Made me anxious about going out in public||.998||.055||−.137||.012||.131||−.275||.143|
|Kept me from going out among strangers||.995||−.039||.009||.042||−.129||−.034||.013|
|Kept me from wanting to go out in public||.992||.015||−.101||.054||−.026||−.049||.003|
|Kept me from going out with friends||.937||−.038||−.005||.035||−.084||.013||.002|
|Made me anxious about going out with friends||.932||.131||−.095||−.030||.126||−.302||.093|
|Interfered with romantic relationship||.654||−.138||.238||−.053||.008||−.042||−.059|
|Interfered with sexual activity||.597||−.148||.318||−.143||.012||.130||−.052|
|Caused me to avoid physical contact with other people||.534||.103||.112||−.078||−.095||.083||.104|
|Made me feel depressed||.460||.325||−.092||−.083||−.061||.274||.086|
|Kept me from being as happy as I could be||.440||.380||−.018||−.033||.065||.195||−.137|
|Caused me to feel hopeless||.416||.041||.139||.031||−.106||.152||.171|
|Made me feel uncertain about the future||.359||.147||−.009||−.074||−.057||.322||.162|
|Bothered me a lot||.123||.798||−.009||.022||−.045||−.045||−.078|
|Made me feel out of control of my body.||−.018||.747||.118||−.038||.010||−.091||.107|
|Made me feel frustrated||.194||.739||−.071||.142||.079||.173||−.118|
|Made me feel powerless||−.014||.600||.192||.080||−.005||−.099||.159|
|Put me in a bad mood||.319||.411||−.110||.120||−.011||−.051||−.059|
|Caused me to worry||.491||.496||−.106||−.058||−.078||.067||−.024|
|Made grooming (hair, teeth) difficult for me or my attendant||.084||−.109||.859||.038||−.072||.006||.079|
|Made dressing difficult for me or my attendant||−.018||.160||.646||.133||.084||.073||.078|
|Made personal hygiene (e.g. toileting, cleaning) difficult for me or my attendant||.200||.242||.606||.103||−.056||−.177||−.177|
|Made eating or feeding difficult for me or my attendant||.232||−.041||.539||.126||−.126||−.051||.136|
|Made transfers hard for me or my attendant||−.294||.059||.506||.139||.085||.156||.316|
|Interfered with my ability to exercise.||−.135||.148||.491||−.051||.133||−.043||.076|
|Made me need someone to reposition me.||−.137||.086||.040||.792||.013||−.205||−.128|
|Caused me to depend on others||−.071||.024||.121||.523||−.240||.025||.174|
|Cause me to need safety devices (bed rails, foot loop)||.052||.014||.044||.515||−.021||.034||.084|
|Made it hard to keep my arms or legs inside my chair||.327||−.095||.150||.490||.009||−.059||.196|
|Drastically changed the position of my body||−.093||.088||.177||.475||.119||.084||.051|
|Helped me keep my muscles exercised||−.173||.175||−.093||−.088||.705||−.068||.251|
|Helped me stretch my muscles.||−.097||−.017||−.098||−.095||.691||−.070||.333|
|Helped me or my attendant change my positions||.166||−.098||.196||.049||.689||.066||−.120|
|Helped with transfers (e.g. from chair to bed)||.072||−.119||.109||.185||.631||.219||−.191|
|Made me need more treatment than I could afford.||−.085||−.045||.149||−.124||−.013||1.03||−.138|
|Caused me to increase the amount of prescription medication I took||−.087||.044||−.079||.031||.050||.637||.196|
|Made me want to find alternative, non-medical therapies||.007||.298||−.014||.023||.059||.577||−.058|
|Caused me to use over-the-counter medications||.167||−.070||−.172||−.032||.021||.446||.216|
|Made me want encouragement or emotional support from friends and family||.034||.027||−.183||.227||−.010||.407||−.020|
|Made breathing difficult||.177||.086||.207||.125||.120||.235||.146|
|Caused strangers to stare at me.||.260||.043||.036||.072||.076||−.087||.766|
|Caused strangers to notice me||.246||−.040||.123||.087||.142||−.116||.731|
|Caused me embarrassment||.305||.226||.160||−.172||.081||.046||.500|
|Caused others to avoid touching me||−.073||−.037||.106||.018||.035||.180||.467|
|Made me fearful that I would cause myself physical injury||.159||−.006||.142||−.006||−.136||.104||.431|
|Alerted me that something was going on in my body (e.g. UTI, bladder, too long in one pos)||−.032||.089||−.162||.222||.170||−.147||−.153|
|Interrupted my sleep||.041||.187||.070||.001||−.027||−.233||.019|
|Left me feeling very tired||.240||.103||.160||−.061||−.016||−.009||−.024|
|Caused me to eat less||.448||−.093||−.006||−.028||.117||−.011||.089|
|Interfered with my bladder control||.013||.197||.194||−.184||.035||.045||−.025|
|Interfered with my bowel control||.323||−.057||.195||−.061||.135||.014||−.158|
|Enhanced sexual activity||.044||−.161||−.029||.009||.159||.194||.100|
|Interfered with my ability to participate in activities||.390||−.082||.077||−.099||−.009||.254||.048|
|Kept me from working or doing household tasks as much as I wanted to||.433||−.057||−.025||.085||−.058||.298||−.030|
|Caused me to modify the kinds of clothing I wore||.166||−.115||−.193||.125||.020||−.010||.385|
|Caused me to seek relief by drinking alcohol or using marijuana||−.160||.190||−.083||.007||−.020||.023||.119|