Abstract
The most common primary end-point of the trial on treatment of traumatic spinal cord injury (SCI) is the degree of impairment. The American Spinal Injury Association (ASIA) Standards have been widely used to assess motor function and pin-prick and light-touch sensory function. In addition, pain assessment is another clinically relevant aspect of the impairment in individuals with SCI. Given this, we sought to systematically review the studies that focused on the psychometric properties of ASIA Standards and all previously used outcome measures of pain in the SCI population in the acute care setting. For the primary literature search strategy, the MEDLINE, CINAHL, EMBASE, and Cochrane databases were sought out. Subsequently, a secondary search strategy was carried out using the articles listed in the references of meta-analysis, systematic, and non-systematic review articles. Two reviewers (JCF and VN) independently selected the articles that fulfill the inclusion and exclusion, assessed the level of evidence of each article, and appraised the psychometric properties of each instrument. Divergences during those steps were solved by consensus between both reviewers. Of 400 abstracts captured in our primary search strategy on the ASIA Standards, 16 full articles fulfilled the inclusion and exclusion criteria. An additional 40 references were obtained from two prior systematic reviews on ASIA Standards. While 45 of 56 of the studies on ASIA Standards provided level 4 evidence, there were 11 level 2b evidence studies. Convergent construct validity (n = 34), reliability (n = 12), and responsiveness (n = 10) were the most commonly studied psychometric properties of the ASIA Standards, but two prior studies examined their content validity. Of the 267 abstracts yielded in our primary search on pain assessment, 24 articles with level 4 evidence fulfilled the inclusion and exclusion criteria. There was no study that examined pain assessment in the acute care setting. While 18 of 24 articles studied an instrument for assessment of pain intensity, the remaining six studies were focused on classifications of pain in the SCI population. In conclusion, the ASIA Standards represent an appropriate instrument to categorize and evaluate spinal cord injured adults over time with respect to their motor and sensory function. Nevertheless, further investigation of the psychometric properties of the ASIA Standards is recommended due to a lack of studies focused on some key elements of responsiveness, including minimal clinically important difference. The visual analog scale (VAS) is the most commonly studied instrument of assessment of pain intensity in the SCI population. However, further investigation is required with regard to its reliability and responsiveness in the SCI population. Our results also suggest that there is no instrument with appropriate psychometric properties for this particular population.
Introduction
T
The most commonly accepted primary end-point of the trial on treatment of SCI is an assessment of the degree of impairment. As defined by the International Classification of Functioning, Disability, and Health from the World Health Organization (WHO), impairment is related to the level of “motor and sensory function” (WHO, 2001). The instruments of choice for assessment of impairment of SCI in the clinical arena and research areas should preferably be proper for descriptive and evaluative purposes, as delineated by the framework of Kirschner and Guyatt (1985). The American Spinal Injury Association (ASIA) Standards have been widely used to assess motor function and pin-prick and light-touch sensory function in the SCI population in both clinical and research arenas. However, the ASIA Standards do not include assessment of pain, which is a common clinically relevant complication after traumatic SCI. Of note, there remained a paucity of outcome measures that comprehensively assesses autonomic function of individuals with SCI (Krassioukov et al., 2007). Recently, an international SCI research committee has developed an instrument for descriptive assessment of the impact of SCI on various organs and viscera that would allow the clinicians and researchers to appraise the degree of autonomic dysfunctions after SCI (Alexander et al., 2009). Nonetheless, psychometric properties of these novel autonomic standards have not been tested yet.
Given this background, we carried out a systematic review of the studies that were focused on the psychometric properties of ASIA score and all previously used outcome measures of pain in the SCI population in the acute care setting.
Methods
This systematic review included the ASIA Standards and several outcome measures of pain after traumatic SCI that were published in the literature. Based on the examination of their psychometric properties (i.e., item generation, item reduction, reliability, validity, and responsiveness), this review was focused on the following key questions: 1. Do the ASIA Standards have appropriate psychometric properties as outcome measure of motor and sensory function for acutely spinal cord injured patients? 2. What is the most reliable, validated, and responsive outcome measure of pain for patients with acute traumatic SCI?
Inclusion and exclusion criteria
This review included only original articles that assessed at least one psychometric property of either the ASIA Standards or an outcome measure of pain in patients with traumatic SCI. Case reports, editorial articles, and meeting abstracts were excluded.
Literature search strategy
In the primary literature search strategy, the MEDLINE, CINAHL, EMBASE, and Cochrane databases were sought out. Subsequently, a secondary search strategy was carried out using the articles listed in the references of meta-analysis, systematic, and non-systematic review articles that were captured in the primary search strategy.
Given that the first version of the ASIA Standards was published in 1982, the literature searches for this instrument addressed publications from 1982 to April 2009. The search strategy included the following specific terms: “ASIA Standards,” “American Spinal Injury Association Standards,” “ASIA score,” and “American Spinal Injury Association score.”
In a broad literature investigation, the searches for the instruments of pain assessments referred to publications since the beginning of the database records (1966) to April 2009. This search strategy included “pain” as the specific key word.
In both searches, the above specific key words were paired with the following medical subject headings: “spinal cord injury,” “SCI,” “tetraplegia,” “quadriplegia,” and “paraplegia.” The literature search was limited to articles written in English.
Data abstraction and synthesis
In the culling process, two reviewers (JCF and VN) independently selected the articles that fulfilled the inclusion and exclusion for each topic. Disagreements were resolved by a consensus between both reviewers.
The relevant data from each selected article were extracted by a research assistant. Subsequently, both reviewers assessed all clinical studies with respect to the extracted data and, hereafter, determined the level of evidence according to the criteria of Sackett and colleagues (2000). Then, every instrument of assessment of impairment was examined with regard to its psychometric properties using the quality criteria from Terwee and colleagues (2007). Divergences during those steps were resolved by consensus between both reviewers.
Definitions of psychometric properties
In this systematic review, the psychometric properties were classified according to Terwee and co-workers (2007), as delineated in Table 1. Content validity refers to the extent to which items in the instrument comprehensively represent the concepts of interest (Guyatt et al., 1993). Internal consistency refers to the extent to which items in a instrument (sub)scale are homogenously correlated and, hence, measure the same concept (Terwee et al., 2007). Criterion validity refers to the degree to which the instrument measures in comparison with the criterion or “gold standard” (Furlan et al., 2008). Of note, criterion validity was not assessed in this review, due to the lack of gold standard for assessing impairment in patients with SCI. Construct validity is frequently divided into convergent or divergent. While convergent construct validity indicates the degree of similarity between two constructs that theoretically should be related to each other, divergent construct validity reveals how dissimilar two constructs are that in theory should not be related to each other (Furlan et al., 2008). Reproducibility refers to the degree to which repeated measurements in steady patients provide similar results (Terwee et al., 2007). Reproducibility is generally divided into agreement and reliability. While agreement reflects the absolute measurement error, reliability refers to the degree to which patients can be distinguished from each other regardless of measurement error (Terwee et al., 2007). Responsiveness concerns the ability of a measurement instrument to accurately detect change when it has occurred (de Bruin et al., 1992). Floor or ceiling effects occur when more than 15% of examined patients reached the lowest or highest possible score, respectively (McHorney and Tarlov, 1995). Finally, interpretability concerns the degree to which one can assign qualitative meaning to quantitative scores (Lohr et al., 1996).
According to the criteria of Terwee and associates (2007).
Doubtful design or method: lacking a clear description of the design or methods of the study, sample size smaller than 50 subjects (should be at least 50 in every (subgroup) analysis), or important methodological weakness in the design or execution of the study.
MIC, minimal important change; SDC, smallest detectable change; LOA, limits of agreement; ICC, intraclass correlation; SD, standard deviation; +, positive rating; ?, indeterminate rating; −, negative rating; 0, no information available.
Establishment of recommendations
The authors answered the focused questions formerly compiled using the information summarized in the tables included here. Then, a panel of scientific experts in the field of acute SCI (including basic scientists, clinician-scientists, surgeons, rehabilitation specialists, nurses, and clinical epidemiologists) examined the summary tables and answers to the focused question, and eventually provided its evidence-based recommendations using a modified Delphi method (Reid, 1993).
Results
ASIA Standards
Of the 400 abstracts captured in our primary search strategy, 16 full articles fulfilled the inclusion and exclusion criteria and were reviewed by the two reviewers. An additional 40 references were obtained from a prior systematic review (Furlan et al., 2008).
While the majority of the studies on ASIA Standards provided level 4 evidence (45 of 56), there were 11 level 2b evidence studies (Table 2). Convergent construct validity (n = 34), reliability (n = 12), and responsiveness (n = 10) were the most commonly studied psychometric properties of the ASIA Standards, but two prior studies examined their content validity. Their item generation and reduction, as well as differences among the five versions of the ASIA Standards, are examined in detail elsewhere (Furlan et al., 2008).
AIS, ASIA impairment scale; ASIA, American Spinal Injury Association; CT, computed tomography; FIM, functional independence measure; LOE, level of evidence; MBI, modified Barthel index; MRI, magnetic resonance imaging; MVA, motor vehicle accident; NASCIS, National Acute Spinal Cord Injury Study; NR, not reported; pt(s), patient(s); QIF, quadriplegia index of function; SCI, spinal cord injury; SCIM, spinal cord independence measure; SSEP, somatosensory evoked potentials; TBI, traumatic brain injury; WISCI, walking index for spinal cord injury.
Using the criteria of Terwee and colleagues (2007), the ASIA Standards were assessed with regard to their quality based on the literature (Table 3). Generally speaking, convergent and divergent construct validity was shown in several prior studies that examined the ASIA Standards in the SCI population, but criterion validity was not previously studied due to the lack of a gold standard for assessment of impairment. In general, the ASIA Standards were found to be reliable instruments for descriptive and evaluative purposes in the SCI population. However, two previous studies suggested that the ASIA Standards are not reliable for assessment of SCI children who are less than 4 years old (Mulcahey and Gaughan, 2005; Mulcahey et al., 2007a). Although the ASIA Standards appear to be responsive to changes in the patients' motor and sensory function, there are four major issues with regard to their responsiveness as follows: (1) a neurological examination using the ASIA Standards earlier than 72 h may not be appropriate; (2) the use of ASIA upper and lower extremity motor sub-scores appears to be more appropriate than the use of a single ASIA motor score; (3) the minimal clinically important difference of the ASIA Standards is unknown; and (4) the functionally meaningful ASIA score threshold to document the benefit of a novel therapeutic intervention varies according to the level and severity of SCI. Finally, the psychometric properties of the ASIA Standards were relatively well tested in the acute care, rehabilitation, and community settings.
According to the criteria of Terwee and associates.
(+) positive rating; (−) negative rating; (?) indeterminate rating due to lack of information or poor study design/method; NA, not applicable; NR, not reported
Instruments of pain assessment
Of the 267 abstracts yielded in our primary search, 24 articles that fulfilled the inclusion and exclusion criteria were reviewed by the two reviewers. All 24 studies were level 4 evidence (Table 4). All those studies were carried out in the community or rehabilitation setting, but there was no study that examined pain assessment in the acute care setting. While 18 of 24 articles studied an instrument for assessment of pain intensity (Table 5), the remaining six studies focused on classifications of pain in the SCI population (Table 6). The visual analog scale (VAS) is the most commonly studied instrument of assessment of pain intensity in the SCI population. Although the construct validity of the VAS has been shown in several prior studies, further investigation is required with regard to its reliability and responsiveness in the SCI population. In addition to the paucity of studies on the classification instruments for pain in the SCI population, our results suggest that there is no instrument with appropriate psychometric properties for this particular population.
DPS, dysestheic pain syndrome; LOE, level of evidence; MPQ, McGill Pain Questionnaire; MRSCICS, Midwest Regional Spinal Cord Injury Care System; MVA, motor vehicle accident; NR, not reported; pt(s), patient(s); SCI, spinal cord injury; TBI, traumatic brain injury; VAS, visual analog scale.
According to the criteria of Terwee and associates (2007).
(+) positive rating; (−) negative rating; (?) indeterminate rating due to lack of information or poor study design/method; NA, not applicable; NR, not reported; VAS, visual analog scale; WUSPI, Wheelchair User Shoulder Pain Index.
According to the criteria of Terwee and associates (2007).
(+) positive rating; (−) negative rating; (?) indeterminate rating due to lack of information or poor study design/method; IASP, International Association for the Study of Pain; NA, not applicable; NR, not reported.
Discussion
Our systematic review indicates that the ASIA Standards represent an appropriate instrument to categorize and evaluate spinal cord injured adults over time with respect to their motor and sensory function. Nevertheless, further investigation of the psychometric properties of the ASIA Standards is recommended due to a lack of studies focused on some key elements of responsiveness. In addition, the visual analog scale (VAS) appears to be the most commonly studied instrument of assessment of pain intensity in the SCI population. Again, further investigation is required with regard to its reliability and responsiveness in the SCI population. Our results also suggest that there is no instrument with appropriate psychometric properties for this particular population.
ASIA Standards
The ASIA Standards are commonly used to classify and evaluate neurological deficit after SCI in both clinical and research arenas. In this systematic review, we identified 56 clinical studies that examine the psychometric properties of the ASIA standards in the assessment of motor and sensory function of patients with SCI. While convergent construct validity, reliability, and responsiveness were the most commonly studied psychometric properties of the ASIA Standards, criterion validity of the ASIA Standards was not assessed because there is no gold standard.
Generally speaking, the results of our systematic review suggest that the ASIA Standards is a reliable, valid, and responsive instrument for descriptive and evaluative purposes in the adult SCI population in the acute care, rehabilitation, and community settings. However, there are important issues with regard to reliability and responsiveness of the ASIA Standards that limit their use in particular circumstances. First, two previous prospective studies suggest the unsuitability of ASIA Standards for assessment of SCI in children who are under the age of 4 years (Mulcahey and Gaughan, 2005; Mulcahey et al., 2007a). Second, there are concerns with regard to the reliability of the ASIA Standards for assessments earlier than 72 h after acute SCI, due to previously reported variability when patients are examined within the first 24 h. Given this finding, it has been recommended that a 72 h assessment using ASI Standards should follow any earlier neurological evaluation of patients with acute SCI. Third, the use of ASIA upper and lower extremity motor sub-scores is recommended rather than a single ASIA motor score to reduce the floor to ceiling effects (Marino and Graves, 2004). An important precept of a multi-part scale is an overall unidimensionality. When no hierarchy of components is considered in an outcome measure, the concept of unidimensionality may become weak because some components can deteriorate while others improve and there is no consideration of which are more important. This is particularly important when looking at changes in severity of impairment. Finally, to our knowledge, the minimal clinically important difference of the ASIA Standards remains unknown.
Pain assessment
Our systematic review also examined the psychometric properties of pain assessments in the SCI population based on 24 studies that were captured in our search. None of these examined pain assessment in an acute care setting, but all studies were carried out in spinal cord injured individuals in the community or rehabilitation setting. While 75% of the studies were focused on assessment of pain intensity, the remaining 25% examined classification of pain in the SCI population. The VAS is the most commonly used instrument of assessment of pain intensity in the SCI population. However, there was no classification of pain with confirmed reliability, validity, and responsiveness for use among spinal cord injured individuals.
Clinical assessment of pain associated with SCI is difficult because spinal cord injured individuals commonly develop complex and multiple pain syndromes with varied characteristics and occurring simultaneously in different parts of the body. Prior taxonomies of pain after SCI usually classify pain according to the type of pain (neuropathic or nociceptive) as well as level and severity of SCI (Bryce et al., 2007; Siddall et al., 1997). Those premises should be taken into consideration in the classification of pain following SCI. However, it is difficult to accurately link particular pain features to specific mechanisms because individuals with SCI can develop several types of pain that often persist, can worsen over time, and usually interfere with patient's cognitive, emotional, and physical function (Siddall et al., 1997). Unlike the classification of pain, the instruments of assessment of pain intensity are commonly used in the research and clinical fields. Although there are different instruments of assessment of pain intensity in the literature, the VAS from 0 to 10 (or 0 to 100) is the most commonly used. Our results also suggest that while the construct validity of the VAS has been shown in several prior studies, further investigation is required with regard to its reliability and responsiveness in the SCI population.
Recommendations
In the Delphi process, a panel of scientific experts in the field of acute SCI (including basic scientists, clinician-scientists, surgeons, rehabilitation specialists, nurses, and clinical epidemiologists) consensually endorsed the recommendation for use of ASIA Standards for assessment of motor and sensory function (based on pin-prick and light-touch sensation) and VAS for assessment of pain intensity in patients with acute SCI. However, the expert panel also recognized the need for further investigations to confirm the performance of both instruments in the acute care setting.
Footnotes
Acknowledgment
The authors thank Ms. Swati Mehta for her assistance in the operations of the systematic review.
Author Disclosure Statement
The work was funded by a grant from the Rick Hansen Foundation through the Spinal Cord Injury Solutions Network.
