Chiari malformation Type 1 (CM-I) is a common and often debilitating neurological condition. According to some estimates, CM-I is identified in almost 1% of all brain and cervical spine MRI studies,55 although recent evidence suggests that in children the MRI prevalence may be closer to 4%.80 While some individuals with radiological evidence of CM-I are asymptomatic, the clinical manifestations of the disease are broad, complicating efforts to guide patient management and study treatment response.
Corresponding to the recent expansion in the utilization of MRI is the growth in research related to CM-I. The number of PubMed results for the term “Chiari Malformation” increased from 83 in the year 2000 to 162 in the year 2012. This expanding research drive is focused in large part on comparative effectiveness research,18,28 and more recently extends to efforts to improve the reporting of clinical outcomes.2,27 Nevertheless, despite this recent emphasis on the inclusion of outcome tools in published research, there remains only anecdotal evidence describing the approaches used in contemporary research to evaluate treatment results. Therefore, a critical evaluation of current outcome reporting systems is needed to effectively interpret the published literature and to promote the development of clinically meaningful and rigorously validated outcome measures. The objective of this systematic review is to comprehensively assess the outcome methods used in the contemporary CM-I literature to lay a foundation for future clinical research in this growing field.
Methods
Inclusion and Exclusion Criteria
For this review, we only included studies that 1) reported clinical outcomes in patients with CM-I after a therapeutic intervention; 2) were original research articles; 3) included at least 10 patients or, if a comparative study, at least 5 patients per group; and 4) were restricted to patients with CM-I. We excluded from the final analysis review articles, meta-analyses, editorials, abstracts not accompanied by a full-text article, and studies only examining treatment results related to a single sign or symptom, rather than general clinical outcomes.
Search Procedures and Data Abstraction
We systematically searched the biomedical literature in PubMed, Embase, the Cochrane Database of Systematics Reviews, the Cumulative Index to Nursing and Allied Health Literature, and ClinicalTrials.gov, in addition to performing a manual search of reference lists to identify relevant publications between January 2003 and August 2013. We searched the controlled vocabulary of each database and used plain language in creating a search strategy for the terms “Arnold Chiari Malformation” (including 27 additional variations for Chiari Type I malformation), “Treatment Outcome,” “Data Collection,” “Questionnaires,” and “Outcome and Process Assessment (Health Care).” The final search results were limited to human studies and English-language articles.
All titles and abstracts identified from the search procedure were independently evaluated by 2 reviewers (J.K.G. and E.M.). Instances of disagreement were resolved by discussion, and articles were subsequently chosen for detailed review. Decisions regarding the application of inclusion criteria were agreed upon by both reviewers and D.D.L. Data from full-length articles meeting inclusion criteria, including patient demographics and narrative summaries of outcome methods, were abstracted using a standardized form designed a priori. Outcome systems were then independently evaluated and classified by both reviewers according to predetermined criteria. Disagreements were resolved by discussion, or when needed, a third arbiter (D.D.L.). Descriptive summary statistics were calculated using SPSS (version 21, IBM).
Article Appraisal
The primary aim for this review was to identify the outcome methods used in the CM-I literature. However, to facilitate a uniform comparison among heterogeneous approaches, we also appraised articles for their adherence to a set of criteria that we defined a priori as key to reporting clinical outcomes in this population. We thus noted 1) inclusion of patient-response instruments (i.e., an outcome measure based on direct patient responses rather than clinician impression of available data); 2) inclusion of any quality of life or overall function assessment; 3) evaluation of new disease-related symptoms that developed after treatment; 4) appropriate multidimensional assessment of outcome for distinct signs or symptoms present preoperatively in individual patients; 5) documentation of rates of revision surgery for persistent disease; and 6) inclusion of detailed reports of headache symptom resolution, given that headaches are the most stereotypical but often poorly defined symptom associated with CM-I.
Results
Our initial literature search returned a total of 669 results, including 518 unique citations (Fig. 1). After abstract appraisal, 97 articles were selected for full-text review, and 4 additional results were added from review of article references. Our final analysis included 74 articles. Basic study characteristics, including sample size and patient ages, along with additional abstracted information regarding the outcome measures used, are shown in the Appendix.
A flow chart demonstrating the databases searched in the systematic review and the results retrieved. CINAHL = Cumulative Index to Nursing and Allied Health Literature.
Outcome Measures
There was a wide array of methods used to evaluate clinical outcome. However, we identified 3 broad approaches into which all systems could be categorized: 1) providing overall “gestalt” impression of improvement (e.g., patient “improved,” “remained unchanged,” or “worsened”); 2) providing a description of improvement for each individual or group of signs and symptoms (sign/symptom-specific reporting); and 3) utilizing one of several standardized outcome scoring systems, defined as any formalized, quantifiable metric for assessing outcome. We further divided standardized scores into those that primarily evaluated disease-specific improvement in signs, symptoms, and overall function—including measures adopted from the general spine literature96 and visual analog scales (VASs) for symptoms such as pain1,64—and those assessing general quality of life or disability (general function score). Applying this categorization, we found at least 18 different approaches to classifying clinical outcome, although this number is higher if minor modifications made by some groups to gestalt and sign/symptom-specific systems are considered.
Overall, we found that gestalt was the most common system used (used in 45 studies), and 35 articles (47%) relied on gestalt impression alone to evaluate clinical outcome (Fig. 2). Sign/symptom-specific reporting was present in 20 studies (27%), and was the lone outcome measure in 9 (12%). Twenty-two articles (30%) used standardized scoring systems.
A summary of the systems used to evaluate clinical outcomes in patients treated for CM-I. The Venn diagram demonstrates the approximate prevalence of each method as well as the overlap of various systems used in the same article. Figure is available in color online only.
Six articles used a total of 11 quality of life or general disability tools to evaluate clinical outcome (Table 1). No measure was used more than once. Four of these 11 tools demonstrated varying degrees of criterion validity in patients with CM-I, i.e., the instrument's assessments were correlated with well-accepted measures of outcome.13,32 One tool, the Headache Disability Index, failed to meet a threshold for accurate discrimination of meaningful improvement prespecified by the study's authors.27 Notably, the validity of all 4 tools was established in the same study, and only adult patients were included.27 The reliability of these tools was not specifically assessed in patients with CM-I.
General quality of life or disability scales used to evaluate clinical outcomes in patients with CM-I
| Outcome Tool* | Age Group | CM-I Validity | Reliability in CM-I |
|---|---|---|---|
| EuroQol-5D21 | Adults | Yes† | No |
| Headache Disability Index70 | Adults | No | No |
| Karnofsky Performance Scale94 | Adults & children | No | No |
| Neck Disability Index89 | Adults | Yes† | No |
| Noudel et al.'s adapted functional grading system63 | Adults & children | No‡ | No‡ |
| Rankin Scale87§ | Adults & children | No | No |
| Short Form-12 Health Survey71 | Adults | Yes† | No |
| Short Form-36 Health Survey71 | Adults, unclear if children as well | No | No |
| Sickness Impact Profile 59 | Adults & children | No | No |
| VAS for Disease Impact on Daily Life82 | Adults & children | No | No |
| Zung Self-Rating Depression Scale100 | Adults | Yes† | No |
All outcome tools used only once.
Demonstrated criterion validity, i.e., the instrument's assessments were correlated with well-accepted measures of outcome.
Scale originally published in French and could not be directly evaluated.
The citation provided refers to the modified Rankin Scale, although the article included in the review does not distinguish whether the original or modified Rankin Scale was used.
Disease-specific scoring systems were more common than general function scores, with a total of 6 scales used in 17 studies (Table 2). The most common measures used were modifications of the Klekamp and Samii score (n = 6 articles) and the Japanese Orthopaedic Association (JOA) score (n = 4). Visual analog scale scores for pain symptoms (n = 3) were grouped into a single category. Validations were attempted for 2 of the 6 scales, with 1 (the Chicago Chiari Outcome Scale [CCOS]) demonstrating criterion validity in retrospective chart review,2,93 and another (the VAS for either head or neck pain) failing to meet a prespecified threshold for meaningful discrimination of outcome.27 Among the 6 disease-specific tools, reliability statistics in patients with CM-I were only available for the CCOS.
Disease-specific scales used to evaluate clinical outcomes in patients treated for CM-I
| Outcome Tool | Age Group Studied | CM-I Validity | Reliability in CM-I | No. of Studies Used |
|---|---|---|---|---|
| Asgari score (modified)24,39* | Adults | No | No | 2 |
| CCOS2 | Adults & children | Yes (criterion validity) | Mean score deviation = 1.56 ± 0.74 points (interrater reliability) | 2 |
| JOA score96 | Adults & children | No | No | 4 |
| Klekamp & Samii score5,37† | Adults & children | No | No | 6 |
| Limonadi score45 | Adults & children | No | No | 1 |
| VAS-pain64‡ | Adults | No | No | 3 |
Two articles created slightly different modifications of the same original scale, although the basic structure was comparable for both instruments.
Two modifications were developed from a spine outcome system created by Klekamp and Samii,38 although both tools were substantially similar.
Visual analog scales for pain symptoms—including head, neck, and extremity pain—are grouped together.
Inclusion of Disease-Appropriate Information
Our ability to consistently assess the outcome methods used by each study was complicated by the heterogeneity of the approaches identified, including a majority of nonstandardized systems, and the absence of accepted guidelines for reporting treatment results in CM-I. To facilitate uniform evaluation of all studies, we appraised each article for the adequacy of its reporting in 6 domains particularly relevant to patients treated for CM-I. These results are summarized in Table 3.
Assessment of 6 key domains relevant to reporting clinical outcome in CM-I and the number of papers fulfilling each domain
| Study Domain | No. of Papers (%) |
|---|---|
| Source of outcome evaluation | |
| Clinician impression | 67 (90.5) |
| Patient-response instrument | 5 (6.8) |
| Clinician impression + patient-response instrument | 2 (2.7) |
| Quality of life assessed | 22 (29.7) |
| New symptoms reported | 28 (37.8) |
| Multidimensional assessment performed | 38 (51.4) |
| Revision surgery reported | 45 (60.8) |
| Method of reporting headache symptoms | |
| Not reported or included in general pain scale | 19 (25.7) |
| Described a single “headache” group | 14 (18.9) |
| Combined headache w/ neck or back pain | 6 (8.1) |
| Evaluated headaches by specific location/character | 14 (18.9) |
| Unclear | 21 (28.4) |
Overall, only 7 articles (9%) used direct patient-response instruments when reporting clinical outcome. The vast majority of studies relied on clinician impressions of disease, commonly based on review of the existing medical record. Although the method of data collection was often unspecified, VASs were always considered patient-response instruments. Specifically among studies using standardized scoring systems, 4 (67%) of 6 articles using general function scores incorporated patient-response instruments, whereas only 3 (18%) of 17 articles using disease-specific systems included such measures.
When evaluating the inclusion of quality of life assessments, we used a liberal definition that included any explicit consideration during outcome assessment of the influence of disease on quality of life or general function, whether based on clinician or patient impressions and whether a validated system was implemented. Even with this generous definition, less than 30% of articles included measures that considered the impact of disease on a patient's overall function or well-being.
A minority of articles (38%) explicitly considered new Chiari-related symptoms developing after surgery when evaluating outcome, more commonly focusing only on resolution of preoperative symptoms. Slightly more common, approximately half (51%) of the included studies explicitly provided a multidimensional appraisal of outcome for multiple distinct signs and symptoms present in individual patients preoperatively; the remaining articles typically provided only a 1-dimensional evaluation of whether patients globally “improved” or not. Most articles directly reported rates of revision surgery for persistent disease, although a sizable minority (39%) did not.
In assessing how each article evaluated patients' common but often difficult-to-characterize headache symptoms, we identified 4 general approaches that were used. Fourteen studies (19%) reported headache outcome based on specific location or character. More commonly, headaches were not reported or were grouped in a general pain category (26%). In addition, 19% of articles reported all headaches as a single symptom type, and 28% of articles did not provide sufficient information to allow confident determination of how outcomes were analyzed.
Discussion
To our knowledge, this is the first systematic and comprehensive assessment of the outcome methods used in the CM-I literature. Overall, we found a great deal of inconsistency among the approaches used, with at least 18 different combinations of outcome systems identified. Most studies used gestalt impression to define outcome, with less than one-third using a standard scoring system and far fewer relying on a tool specifically validated in patients with CM-I. These results highlight the significant need for commonly accepted standards to guide clinical outcome reporting in CM-I research.
Identifying one, or even a few, consistent approaches to reporting outcome is essential to interpreting results from individual investigations as well as to comparing results across studies. Simple gestalt impression, the most common method identified, provides little detail about disease evolution and, due to its inherent ambiguity, is likely to be applied inconsistently across and even within studies.22 Likewise, when not part of a composite score, sign/symptom-specific reporting does not permit a clear comparison of results across patients. These shortcomings and the diversity of systems currently used severely limit the ability to generalize results beyond a single sample. An initiative by the National Institute of Neurological Disorders and Stroke, the Common Data Elements Project,61 has addressed the inconsistent reporting of results for a number of neurological conditions,47,48,75 but only now are foundations and other groups with an interest in CM-I considering such efforts.
While reliable and consistent reporting is critical, another key consideration in outcomes assessment is instrument validity. Among the 17 standardized systems identified, 5 have been validated in CM-I patients.2,27,93 However, only 1, the CCOS, has been validated in adults and children.2,93 A 4-item scale assessing pain symptoms, nonpain symptoms, functionality, and complications, the CCOS is designed for retrospective chart review and thus is not suited for prospectively measuring patient-defined disease burden before and after treatment. In addition, some CCOS subscores, particularly functionality, have poor interrater reliability.93 Notably, all instrument validations focused on criterion validity, or the extent to which the system at hand correlates with well-accepted measures.13,32 By contrast, the recently developed Chiari Symptom Profile has shown strong content validity (i.e., covering all the areas intended) but has not yet been applied to outcomes research.60 Demonstrating validity in multiple domains is an important aspect of developing a meaningful outcome scale.
Because symptomatic outcomes for patients with CM-I are inherently subjective, one critical but often overlooked component of measuring outcomes is the utilization of patient-response instruments. In recent years, major initiatives including the Patient-Centered Outcome Research Institute25,76,90 and the Patient-Reported Outcomes Measurement Information System (http://www.nihpromis.org/) have promoted the incorporation of patient perspectives and values into treatment decisions. However, despite such efforts, only 7 articles (9%) in the contemporary CM-I literature incorporated any direct measure of patient opinion when reporting outcome. Consequently, there is little evidence regarding how patients' views of their own health change after CM-I surgery. Future research should strive to incorporate direct patient responses when assessing clinical outcome.
While patient-response measures lay a foundation for meaningful assessments, we identified several additional characteristics necessary in studies evaluating outcome in patients with CM-I. Many of the shortcomings we observed, such as not accounting for new symptoms postoperatively or not providing a multidimensional outcome assessment of distinct signs and symptoms present preoperatively, likely reflect the reliance on 1-dimensional gestalt assessments. Similarly, the limited assessment of headache symptoms reflects the need for validated tools that capture the complexity of the symptoms present in patients with CM-I.
To aid the development of novel outcome metrics, we created the checklist shown in Table 4. This Chiari-focused framework can be used along with general guides for evaluating health measurement instruments56 to appraise the quality of future scales. Until new metrics are developed, researchers interested in studying general quality of life could use tools such as the EuroQol-5D, which has shown criterion validity in adults.27 However, given the substantial limitations of current systems, we are unable to endorse 1 or more disease-specific tools. Rather, we recommend researchers use our proposed checklist to weigh the strengths and weaknesses of existing methods in the context of their studies' goals.
A checklist for evaluating clinical outcome methods in CM-I treatment studies
| Key elements of a CM-I clinical outcome metric | Yes | No |
|---|---|---|
| Do measures of symptomatic outcome incorporate direct patient reporting? | () | () |
| Does the outcome metric include a specific assessment of patient quality of life? | () | () |
| Does the outcome metric assess for new symptoms that developed after initial surgery? | () | () |
| Does the outcome metric provide a sufficient multidimensional assessment of outcome for distinct signs & symptoms present preoperatively in individual patients? | () | () |
| Does the outcome metric assess in sufficient detail the location & character of headache symptoms? | () | () |
| Does the study report the rate of revision surgery for persistent disease? | () | () |
| Is the outcome metric valid in CM-I patients?* | () | () |
| Is the outcome metric reliable in CM-I patients? | () | () |
For a more detailed description of different types of validity, such as criterion, construct, and content validity, see resources provided by the COSMIN initiative.57
Significantly, this study has several limitations. Most importantly, the classifications outlined, such as whether an article considered new symptoms developing after treatment or how an article evaluated multiple unique signs and symptoms in individual patients, inevitably involved subjective determination based on the limited information provided in each article. In addition, this review was restricted to the English-language literature, which may have excluded certain metrics.
Conclusions
In this review, we have identified significant weaknesses in the contemporary methods used to assess clinical outcomes in patients with CM-I and have provided a framework to improve future evaluations. The conclusive trends identified in this review, including the reliance on gestalt measures, highlight the critical need for multidisciplinary collaboration to develop patient-based, validated, and disease-specific tools for reporting clinical outcome in CM-I. Adopting such standardized scales will enable the most informative and generalizable conclusions to be drawn from each study and will serve as a critical step toward improving patient care.
Author Contributions
Conception and design: Greenberg, Milner, Lipsey, Piccirillo, Limbrick. Acquisition of data: Greenberg, Milner. Analysis and interpretation of data: Greenberg, Milner, Yarbrough, Piccirillo, Smyth, Park, Limbrick. Drafting the article: Greenberg, Lipsey. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Greenberg. Statistical analysis: Greenberg. Administrative/technical/material support: Limbrick. Study supervision: Limbrick.
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APPENDIX: Complete list of, and basic information about, each article meeting inclusion criteria
| Authors & Year | Sample Size | Participant Age Group | Outcome System | Standardized Score | Source of Outcome Data |
|---|---|---|---|---|---|
| Alfieri & Pinna, 2012 | 109 | Adult | DSS + SSR | VAS-pain | CI, PRI |
| Aliaga, et al., 2012 | 146 | Child + adult | DSS | CCOS | CI |
| Anderson et al., 2003 | 11 | Child + adult | Gestalt | NA | CI |
| Arora et al., 20045 | 17 | Child + adult | DSS | Klekamp & Samii score | CI |
| Arora et al., 20044 | 48 | Child + adult | DSS | Klekamp & Samii score | CI |
| Arruda et al., 2004 | 60 | Child + adult | Gestalt + SSR | NA | CI |
| Attenello et al., 2008 | 49 | Child | Gestalt + SSR | NA | CI |
| Attenello et al., 2009 | 67 | Child | Gestalt | NA | CI |
| Bao et al., 2013 | 147 | Child + adult | Gestalt | NA | CI |
| Batzdorf et al., 2013 | 177 | Child + adult | SSR | NA | CI |
| Behari et al., 2007 | 39 | Child + adult | DSS | Klekamp & Samii score | CI |
| Caldarelli et al., 2007 | 30 | Child | Gestalt | NA | CI |
| Chauvet et al., 2009 | 11 | Adult | SSR | NA | CI |
| Cui et al., 2011 | 20 | Unclear | Gestalt | NA | CI |
| Di, 2009 | 26 | Child | Gestalt + SSR | NA | CI |
| Dones et al., 2003 | 27 | Child + adult | SSR | NA | CI |
| El-Ghandour, 2012 | 46 | Adult | Gestalt | NA | CI |
| Erdogan et al., 2010 | 27 | Unclear | Gestalt | NA | CI |
| Foreman et al., 2012 | 48 | Child | Gestalt | NA | CI |
| Furtado et al., 2011 | 20 | Child | DSS + SSR | Asgari score | CI |
| Galarza et al., 2007 | 60 | Child | Gestalt | NA | CI |
| Godil et al., 2013 | 50 | Adult | DSS, GFS | VAS-head/neck, Neck Disability Index, Head-ache Disability Index, EuroQol-5D, SF-12, Zung Self-Rating Depression Scale | PRI |
| Heiss et al., 2010 | 16 | Child + adult | SSR | NA | CI |
| Hekman et al., 2012 | 167 | Child + adult | DSS | CCOS | CI |
| Hoffman & Souweidane, 2008 | 40 | Child + adult | Gestalt | NA | CI |
| Hyun et al., 2013 | 30 | Child + adult | DSS | JOA score | CI |
| Kalb et al., 2012 | 104 | Child + adult | Gestalt + SSR | NA | CI |
| Kim et al., 2004 | 11 | Child | Gestalt | NA | CI |
| Klekamp, 201236 | 107 | Unclear | DSS | Klekamp & Samii score | CI |
| Klekamp, 201237 | 359 | Unclear | Gestalt + DSS | Klekamp & Samii score | CI |
| Koç et al., 2007 | 18 | Adult | DSS | Asgari score | CI |
| Kumar et al., 2008 | 87 | Child + adult | DSS | Klekamp & Samii score | CI |
| Kunert et al., 2009 | 38 | Child + adult | Gestalt, GFS | Rankin Scale, Karnofsky Performance Scale | CI |
| Lam et al., 2013 | 22 | Adult | SSR | NA | PRI |
| Lee et al., 2012 | 25 | Adult | Gestalt, SSR | NA | CI |
| Levo et al., 2010 | 46 | Child + adult | Gestalt | NA | CI |
| Limonadi & Selden, 2004 | 24 | Child + adult | DSS | Limonadi score | CI |
| Litvack et al., 2013 | 110 | Child | SSR | NA | CI |
| Massimi et al., 2008 | 30 | Child | Gestalt + SSR | NA | CI |
| Massimi et al., 2011 | 15 | Child + adult | Gestalt | NA | CI |
| McGirt et al., 2006 | 130 | Child + adult | Gestalt | NA | CI |
| McGirt et al., 200851 | 44 | Child | Gestalt | NA | CI |
| McGirt et al., 200852 | 256 | Child | Gestalt | NA | CI |
| McGirt et al., 200853 | 256 | Child | Gestalt | NA | CI |
| Mottolese et al., 2011 | 82 | Child | Gestalt | NA | CI |
| Mueller & Oro', 2005 | 112 | Child + adult | GFS | Sickness Impact Profile | PRI |
| Navarro et al., 2004 | 96 | Child | Gestalt | NA | CI |
| Noudel et al., 2011 | 11 | Child + adult | GFS | Noudel's adapted functional grading system | CI |
| Ono et al., 2007 | 27 | Adult | DSS | JOA score | CI |
| Ono et al., 2010 | 20 | Adult | DSS | JOA score + VAS-pain | CI |
| Panigrahi et al., 2004 | 21 | Child + adult | Gestalt | NA | CI |
| Perrini et al., 2007 | 24 | Adult | SSR | NA | CI |
| Prat & Galeano, 2009 | 13 | Child + adult | Gestalt | NA | CI |
| Pritz, 2003 | 14 | Adult | Gestalt + SSR | NA | CI |
| Ramnarayan et al., 2008 | 51 | Child + adult | Gestalt + SSR | NA | CI |
| Romero & Pereira, 2010 | 16 | Adult | Gestalt | NA | CI |
| Sakushima et al., 2013 | 232 | Child + adult | SSR | NA | CI |
| Shamji et al., 2010 | 24 | Child | Gestalt | NA | CI |
| Sivaramakrishnan et al., 2004 | 12 | Adult | Gestalt | NA | CI |
| Spena et al., 2010 | 36 | Adult | Gestalt | NA | CI |
| Takayasu et al., 2004 | 16 | Child + adult | Gestalt | NA | CI |
| Tisell et al., 2009 | 23 | Child + adult | GFS + SSR | VAS-quality of life | PRI |
| Tubbs et al., 2004 | 22 | Child + adult | Gestalt | NA | CI |
| Tubbs et al., 2003 | 130 | Child + adult | Gestalt | NA | CI |
| Tubbs et al., 2011 | 500 | Child | Gestalt | NA | CI |
| Valentini et al., 2011 | 99 | Child | Gestalt | NA | CI |
| Ventureyra et al., 2003 | 24 | Unclear | Gestalt | NA | CI |
| Wetjen et al., 2008 | 29 | Child + adult | SSR | NA | CI |
| Williams et al., 2013 | 34 | Unclear | GFS | SF-36 | PRI |
| Yeh et al., 2006 | 130 | Child | Gestalt | NA | CI |
| Yilmaz et al., 2011 | 82 | Adult | DSS | JOA score | CI |
| Zamel et al., 2009 | 80 | Child + adult | Gestalt | NA | CI |
| Zhang et al., 2011 | 132 | Child + adult | Gestalt | NA | CI |
| Zhang et al., 2008 | 316 | Child + adult | Gestalt | NA | CI |
CI = clinician impression; DSS = disease-specific scale; GFS = general function scale; NA = not applicable; PRI = patient-response instrument; SF-12 = Short Form-12 Health Survey; SF-36 = Short Form-36 Health Survey; SSR = sign/symptom-specific reporting.
