Movement Disorder Society-sponsored revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS): Scale presentation and clinimetric testing results†
Potential conflict of interest: All authors have confirmed they have no conflict of interest related to this effort.
Abstract
We present a clinimetric assessment of the Movement Disorder Society (MDS)-sponsored revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS). The MDS-UDPRS Task Force revised and expanded the UPDRS using recommendations from a published critique. The MDS-UPDRS has four parts, namely, I: Non-motor Experiences of Daily Living; II: Motor Experiences of Daily Living; III: Motor Examination; IV: Motor Complications. Twenty questions are completed by the patient/caregiver. Item-specific instructions and an appendix of complementary additional scales are provided. Movement disorder specialists and study coordinators administered the UPDRS (55 items) and MDS-UPDRS (65 items) to 877 English speaking (78% non-Latino Caucasian) patients with Parkinson's disease from 39 sites. We compared the two scales using correlative techniques and factor analysis. The MDS-UPDRS showed high internal consistency (Cronbach's alpha = 0.79–0.93 across parts) and correlated with the original UPDRS (ρ = 0.96). MDS-UPDRS across-part correlations ranged from 0.22 to 0.66. Reliable factor structures for each part were obtained (comparative fit index > 0.90 for each part), which support the use of sum scores for each part in preference to a total score of all parts. The combined clinimetric results of this study support the validity of the MDS-UPDRS for rating PD. © 2008 Movement Disorder Society
The Unified Parkinson's Disease Rating Scale (UPDRS) was originally developed in the 1980s1 and has become the most widely used clinical rating scale for Parkinson's disease (PD).2 In 2001, the Movement Disorder Society (MDS) sponsored a critique of the UPDRS, and this document lauded the strengths of the scale but identified a number of ambiguities, weaknesses, and areas in need of inclusion to reflect current scientific developments.3 The summary conclusions recommended the development of a new version of the UPDRS that would retain the strengths of the original scale, but resolve identified problems and especially incorporate a number of clinically pertinent PD-related problems poorly captured in the original version. Based on this critique, the MDS commissioned a revision of the scale, resulting in a new version, termed the MDS-sponsored UPDRS revision (MDS-UPDRS).4 This scale successfully passed initial clinimetric testing4 and was therefore submitted to a large-scale comparison with the original UPDRS. This report presents the MDS-UPDRS for the first time in published form and the clinimetric testing results of this large-scale program among native English speaking PD patients.
MDS-UPDRS (Table 1): The primary areas of revision were discussed in a prior publication.4 First, whereas the original four component (Parts I–IV) design was retained, the focus of each part has been changed, and the data acquisition methodology has been both clarified and modified. Part I concerns “nonmotor experiences of daily living,” Part II concerns “motor experiences of daily living,” Part III is retained as the “motor examination,” and Part IV concerns “motor complications.” Several questions from Part I and all questions from Part II have been designed to be amenable to a patient/caregiver questionnaire format and therefore can be completed without the investigator's input. For the remaining Part I questions that deal with complex behaviors and all questions in Part IV that deal with motor fluctuations and dyskinesias, the investigator is required to conduct the interview. Part III retains the objective assessments of parkinsonism, but all tasks now have specific instructions. Rater involvement time for administering the MDS-UPDRS is estimated to require less than 10 min for the interview items of Part I, 15 min for Part III, and 5 min for Part IV, resulting in an equivalent rater time investment to the original scale and meeting the 30-min goal. The remaining questionnaire items are answered by the patient or caregiver and, other than supervision, do not involve rater time. Whereas the detailed assessments still prioritize the motor aspects of PD, the screening questions on nonmotor elements are designed to capture both the presence and severity of clinically pertinent problems in this domain.
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Each question is anchored with five responses that are linked to commonly accepted clinical terms: 0 = normal, 1 = slight, 2 = mild, 3 = moderate, and 4 = severe. After each clinical descriptor, a short text follows, which describes the criteria for each response. Whereas each response is tailored to the question, the progression of disability or impairment is based on a consistent infrastructure. “Slight” (1) refers to symptoms/signs with sufficiently low frequency or intensity to cause no impact on function; “mild” (2) refers to symptoms/signs of frequency or intensity sufficient to cause a modest impact on function; “moderate” (3) refers to symptoms/signs sufficiently frequent or intense to impact considerably, but not prevent, function; “severe” (4) refers to symptoms/signs that prevent function.
The full MDS-UPDRS contains questions/evaluations (Table 1), divided across Part I (13), Part II (13), Part III (33 scores based on 18 items, several with right, left or other body distribution scores), and Part IV (6). The MDS-UPDRS rates 65 items in comparison to 55 on the original UPDRS, 48 that had 0 to 4 options and 7 with yes/no responses.
Nine new items in the MDS-UPDRS were not captured in any form on the original scale: anxious mood, dopamine dysregulation syndrome, urinary problems, constipation, fatigue, doing hobbies, getting in and out of bed, toe tapping, and freezing (objective rating). Lightheadedness was assessed in the original UPDRS as present or absent, but in the MDS-UPDRS, the symptom is assessed with the 0 to 4 rating system. Nighttime sleep problems and daytime sleepiness are assessed in the MDS-UPDRS and the yes/no sleep disturbances option is replaced from the original UPDRS. The question on Complexity of Motor Fluctuations in the MDS-UPDRS merges the three yes/no questions related to predicable, unpredictable, and sudden OFF period from the UPDRS. In regards to tremor, the original Action/Postural Tremor question has been divided into two questions focusing on each component of tremor separately. For rest tremor, whereas the UPDRS combined amplitude and constancy of tremor into its descriptors, on the MDS-UPDRS the severity ratings for each body part concern only the amplitude and a separate question rates the constancy.
Direct item-to-item mapping from the original UPDRS to the MDS-UPDRS was not envisioned to be possible, because the two scales were not conceptually identical. Nonetheless, because the new version was directly based on the original scale, a number of parallels and guidelines were utilized in the construction of the MDS-UPDRS. For some questions, the insertion of slight/mild/moderate/severe was sufficient to realign the rating options. In some cases, however, because the original scale often used “mild/moderate/severe/marked” the former rating of 1 (mild) now could be separated into two choices (slight 1 or mild 2) in the MDS-UPDRS. In such cases, the former moderate scores (2) advanced to 3 in the MDS-UPDRS and the former severe (3) and marked (4) were collapsed into one option (severe 4) in the MDS-UPDRS. In other cases, adjustments in the mid-ranges (2 and 3) were felt to be necessary in order to maintain a consistent conceptual framework of slight/mild/moderate/severe in the MDS-UPDRS. This decision to shift from mild/moderate/severe/marked to slight/mild/moderate/severe as the scale's clinical construct was anchored in two concepts: first, that many clinical trials focus on early PD where change among scores of normal, slight, and mild problems are important to document; and, second, that at the high range of impairment or disability (formerly severe and marked), functional differences may not be clinically relevant. Another conceptual anchor of the MDS-UPDRS, especially apparent in Parts I, II, and IV was the progressing disability from none (0) to a perception of the problem without interference (slight 1), to interference with isolated activity (mild 2), to interference with normal activity (moderate 3), to preclusion of normal activity (severe 4). This process was not utilized consistently in the original UPDRS, although parallels could be constructed between the two versions in many cases. Yes/no questions from the original Part IV were reformatted and refined to fit the 0 to 4 rating format of the rest of the scale in the MDS-UPDRS, so that a partial parallelism between the two versions could be mapped. New items that assessed features not assessed in the original UPDRS could not have any mapping possibility from the original scale. With these caveats, general mapping patterns between the two scales were outlined to allow a guide to raters making the transition between the UPDRS and the MDS-UPDRS, but were not constructed with the aim of allowing automatic substitution (Table 1). As part of the clinimetric plan, however, a review of score ranges for each part of the MDS-UPDRS was planned to be tested against the original version (see below).
ON and OFF definitions are provided to ensure uniformity among raters and the score sheet documents the ON/OFF status associated with the Part III assessment. For Parts I and II, the official scale will not separate ON from OFF, but, for special studies, the same questions can be asked separately for ON or OFF periods. Throughout the MDS-UPDRS, specific instructions are provided to enhance a uniform application. Finally, questions have been written to be culturally sensitive and applicable to patients of different ethnic and social backgrounds.
As an ongoing process, at the end of the MDS-UPDRS, clinicians and researchers are directed to an Appendix of Additional Scales. This portion of the MDS-UPDRS is not considered a static document, but, instead, it will be updated as deemed appropriate by the MDS Task Force of Rating Scales for PD (see Supp. Info. Appendix 1 for listing of scales). This appendix is designed to direct clinicians and research investigators to scales that cover in greater detail the components of the MDS-UPDRS that are only assessed with single items. The Task Force has previously published assessments of scales for depression and psychosis, and others are planned.5, 6 These assessments use a standard set of criteria to establish Recommended and Suggested scales in an effort to encourage reporting in a consistent manner and to facilitate comparisons among different reports. For items that have not had official Task Force reports, the subcommittee of the MDS-UPDRS dedicated to the Appendix has reviewed scales using the same criteria (Cristina Sampaio, chairperson).
CLINIMETRIC TESTING PROGRAM
Methods
Based on successful preliminary testing,4 the MDS-UPDRS validation program was designed to test the scale's intrinsic attributes, including internal consistency, factor structure, differential item functioning, and its comparability with the original UPDRS.
We recruited movement disorder specialists and experienced study coordinators to examine PD patients with both scales. Special attention was focused on recruitment of diverse race/ethnicity representations. Native English speakers (both raters and patients) participated. To complete separate clinimetric analyses within each racial/ethnic group, a minimal sample size of 650 per racial/ethnic group was desirable assuming that at least 10 observations per item were required.7 After obtaining individual IRB approval, each participating site recruited patients to undergo both the UPDRS and MDS-UPDRS in a single setting. Participation was based on a commitment to rate between 10 and 20 subjects who covered the range of mild to severe PD, based on clinical judgment. Scores were sent to a central database electronically and verified for completeness. Queries were resolved between the statistical center and individual raters, and once completed, a given case was entered into the full data set and double-checked for accuracy.
Statistical Analyses
To describe patient demographics, we computed means, standard deviations, and ranges. To assess relationships between the new and original version, we computed Pearson's correlations between the MDS-UPDRS and the UPDRS for total score and for each part. Correlations were computed to assess the relationships among the parts of the MDS-UPDRS. As a measure of internal consistency (reliability), Cronbach's alpha was calculated for each part. Further, floor and ceiling effects were examined by calculating the percentage of lowest and highest possible scores for each part. Mplus v. 4.218 was used for the factor analysis using polychoric correlations because of the ordinal nature of the data.
The factor analysis was run in two parts. An exploratory factor analysis (EFA), informed by eigenvalues and Scree plots, was used to determine the number of factors that best represents the data. A factor loading cutoff of 0.40 was used to determine those items to retain in a factor. As a second step, a confirmatory factor analysis (CFA) was used in the assessment of dimensionality, with a comparative fit index (CFI) ≥ 0.90 defined as an acceptable fit. If the CFI was less than 0.90, each factor was examined to identify poorly behaved items, i.e., those with high loadings on more than one factor.9 Based on the review of the items and the model fit statistics, additional EFAs and CFAs were run. The process was repeated until the most parsimonious model was found with a CFI ≥ 0.90. We assessed the entire scale as a single factor structure, each part as a separate set of factors, and all combinations of parts.
Results
Patient Sample
A total of 877 native English-speaking PD patients were examined with the UPDRS and MDS-UPDRS (560 men and 317 women). There were 682 non-Latino Caucasians and 195 (22%) of other race/ethnicity, specifically 49 African Americans, 87 Latinos, 1 native Hawaiian, 43 Asians, and 15 with other race/ethnicities. All Hoehn and Yahr stages were represented, with the majority of patients being stages II (stage I = 63, stage II = 467, stage III = 174, stage IV = 109, stage V = 53, missing 11). The mean age of the cohort was 68.2 years (SD: 10.8; range: 31–98), and the mean PD duration was 8.3 years (SD: 6.7; range: 0–40 years). Fifty-seven patients were not treated with antiparkinsonian medications. A total of 685 patients were treated with levodopa in combination with another symptomatic treatment for PD, 115 patients were on symptomatic therapy without levodopa, 5 patients were on levodopa alone, and 15 had missing treatment information. Motor fluctuations were observed in 483 patients and 304 patients had dyskinesia. A total of 723 were examined in the ON state and 99 in the OFF state, while ON/OFF information was not recorded for 55 patients.
Rater Sample
There were 69 raters from 39 English-speaking treatment centers (USA, 32; Canada, 2; UK, 5) who evaluated patients with the original and MDS-UPDRS instruments (see listing at end of manuscript). All raters were physicians or nurse coordinators regularly working with PD patients, regularly using the UPDRS for clinical care or research purposes, and all were recruited through the MDS. Raters were instructed to perform the UPDRS in their standard manner and to use the MDS-UPDRS following the instructions embedded in the new scale for each item. The choice of patients was left to the raters, but emphasis was placed by the Task Force team on recruitment of a maximal number of patients who were of a race/ethnicity other than non-Latino Caucasian with a full breadth of Hoehn and Yahr stages. The mean number of cases submitted by each rater was 11.4 (SD: 8.2; range: 1–29).
Clinimetric Profile of MDS-UPDRS
Internal consistency was computed for each of the MDS-UPDRS parts [Part I (13 items), alpha = 0.79; Part II (13 items), alpha = 0.90; Part III (33 items), alpha = 0.93; Part IV (6 items), alpha = 0.79]. Mean scores (SD) for each part were: Part I: 11.5 (7.0); Part II: 16.0 (10.0); Part III: 36.8 (18.4); Part IV: 4.0 (4.2). The distributions of the total scores in the MDS-UPDRS and original UPDRS were similar: UPDRS mean: 61.0 (SD: 30.3), covering 55 items; MDS-UPDRS mean: 68.4 (SD: 32.8), covering 65 items. The MDS-UPDRS showed strong concurrent validity based on high correlations between the two scales (total score r = 0.96), as well as between the individual parts of the two scales: [Part I, r = 0.76; Part II, r = 0.92; Part III, r = 0.96; Part IV (sum of items 32–39 covering dyskinesias and motor fluctuations on the UDPRS vs. total Part IV from the MDS-UPDRS), r = 0.89]. As a measure of internal validity, correlations among the MDS-UPDRS parts were examined. These analyses confirmed that each part assesses a different aspect of PD, with most parts, except Parts I and II, having relatively low correlations (Parts I and II, r = 0.67; Parts I and III, r = 0.43; Parts I and IV, r = 0.39; Parts II and IV, r = 0.44; Parts III and IV, r = 0.22). As anticipated, Parts II and III that covered patient perceptions of motor function and the objective examination were more highly correlated (r = 0.66). Our analysis for possible floor and ceiling effects demonstrated a low percentage of lowest and highest scores for Parts I to III: Part I, lowest 0.1%/highest 0.8%; Part II, lowest 0.1%/highest 0.7%; Part III, lowest 0.1%/highest 0.2%. In the case of Part IV, covering the presence and severity of motor complications, there was an expected floor effect, but no ceiling effect: lowest 36.7%/highest 0.1%. (see Supp. Info. Appendix 2 for histograms of each part).
Factor Structure
Exploratory testing of the combined four parts of the MDS-UPDRS did not identify a single factor structure that could be confirmed (CFI = 0.74). A factor structure combining Parts II and III was explored, but could not be confirmed. Several items had salient loadings on more than one factor and some items did not load on any factor. A factor structure was also explored for the combination of Parts II to IV. A factor structure with 12 factors was identified by the EFA; however, the CFI was <0.90, too low to provide confirmation. As seen earlier, several items had salient loadings on more than one factor, and some items did not load on any factor. These combined results preclude using a total MDS-UPDRS score or scores based on combinations of parts.
We then analyzed the MDS-UPDRS parts individually (see Supp. Info. Appendix 3 for Scree plots). This analysis and the confirmatory analysis identified a factor structure that was statistically consistent (CFI for each part was >0.90) and clinically meaningful (Table 2) for all parts. For Part I (CFI = 0.94), two factors were identified, one covering depression, anxiety, and apathy and the other covering the other nonmotor functions (shared variance = 42.5%). For Part II (CFI = 0.95), three factors were identified, one covering several fine motor functions, one covering tremor and eating tasks, and one focusing on several large motor functions (shared variance = 69.4%). For Part III (CFI = 0.91), seven factors were identified: midline function, rest tremor, rigidity, bradykinesia right upper extremity, bradykinesia left upper extremity, postural and kinetic tremors, and lower limb bradykinesia (shared variance 77.1%). For Part IV (CFI = 1.0), two factors were identified, one focusing on fluctuations including off-state dystonia and the other on dyskinesias (shared variance = 79.2%). Intercorrelations among factors for each part ranged from 0.04 to 0.71, indicating both unique and shared information provided by the different factors.
| Factor | Item | Item factor loading |
|---|---|---|
| Part I: Nonmotor aspects of experiences of daily living (CFI = 0.94, RMSEA = 0.06) | ||
| Factor 1 | Percent variance = 32.7 | |
| Daytime sleepiness | 0.57 | |
| Sleep problems | 0.40 | |
| Cognitive impairment | 0.48 | |
| Pain and other sensations | 0.48 | |
| Hallucinations and psychosis | 0.40 | |
| Urinary problems | 0.59 | |
| Constipation problems | 0.49 | |
| Features of DDS | 0.49 | |
| Light headedness on standing | 0.45 | |
| Fatigue | 0.54 | |
| Factor 2 | Percent variance = 9.8 | |
| Depressed mood | 0.83 | |
| Anxious mood | 0.66 | |
| Apathy | 0.53 | |
| Part II: Motor aspects of experiences of daily living (CFI = 0.95, RMSEA = 0.09) | ||
| Factor 1 | Percent variance = 53.0 | |
| Speech | 0.79 | |
| Saliva and drooling | 0.45 | |
| Chewing and swallowing | 0.60 | |
| Handwriting | 0.45 | |
| Doing hobbies and other activities | 0.45 | |
| Factor 2 | Percent variance = 8.7 | |
| Eating tasks | 0.68 | |
| Tremor | 0.43 | |
| Factor 3 | Percent variance = 7.7 | |
| Dressing | 0.64 | |
| Hygiene | 0.64 | |
| Turning in bed | 0.65 | |
| Getting out of bed | 0.73 | |
| Walking and balance | 0.82 | |
| Freezing | 0.76 | |
| Part III: Motor examination (CFI 0.91, RMSEA = 0.10) | ||
| Factor 1 | Percent variance = 36.8 | |
| Speech | 0.59 | |
| Facial expression | 0.53 | |
| Arising from chair | 0.77 | |
| Gait | 0.87 | |
| Freezing of gait | 0.83 | |
| Postural stability | 0.81 | |
| Posture | 0.70 | |
| Global spontaneity of movement | 0.64 | |
| Factor 2 | Percent variance = 15.1 | |
| Rest tremor amplitude, RUE | 0.72 | |
| Rest tremor amplitude, LUE | 0.71 | |
| Rest tremor amplitude, RLE | 0.73 | |
| Rest tremor amplitude, LLE | 0.71 | |
| Rest tremor amplitude, lip/jaw | 0.59 | |
| Constancy of rest tremor | 0.88 | |
| Factor 3 | Percent variance = 6.4 | |
| Rigidity, neck | 0.67 | |
| Rigidity, RUE | 0.73 | |
| Rigidity, LUE | 0.74 | |
| Rigidity, RLE | 0.80 | |
| Rigidity, LLE | 0.81 | |
| Factor 4 | Percent variance = 6.1 | |
| Finger tapping, right hand | 0.67 | |
| Hand movements, right hand | 0.66 | |
| Pronation/supination, right | 0.68 | |
| Factor 5 | Percent variance = 4.8 | |
| Finger tapping, left hand | 0.69 | |
| Hand movements, left hand | 0.72 | |
| Pronation/supination movements, left | 0.65 | |
| Factor 6 | Percent variance = 4.6 | |
| Postural tremor, right hand | 0.66 | |
| Postural tremor, left hand | 0.72 | |
| Kinetic tremor, right hand | 0.81 | |
| Kinetic tremor, left hand | 0.80 | |
| Factor 7 | Percent variance = 3.3 | |
| Toe tapping, right foot | 0.65 | |
| Toe tapping, left foot | 0.63 | |
| Leg agility, right leg | 0.64 | |
| Leg agility, left leg | 0.62 | |
| Part IV: Motor complications (CFI = 1.0, RMSEA = 0.05) | ||
| Factor 1 | Percent variance = 63.6 | |
| Time spent in the OFF state | 0.87 | |
| Functional impact of fluctuations | 0.84 | |
| Complexity of motor fluctuations | 0.83 | |
| Painful OFF state dystonia | 0.49 | |
| Factor 2 | Percent variance = 15.6 | |
| Time spent with dyskinesias | 0.72 | |
| Functional impact of dyskinesias | 0.94 | |
- CFI, comparative fit index; RMSEA, root mean square error of approximation.
DISCUSSION
The MDS-UPDRS was designed to be more comprehensive than the original UPDRS, with new items devoted to several nonmotor elements of PD.3, 4 The choice of the new items was based on input from the Task Force committee members, patient groups, and MDS members. Based on the published critique of the UPDRS,3 the five-point range for each item was retained, and clinical anchors of normal (0), slight (1), mild (2), moderate (3), and severe (4) were added to provide a consistency across items. Importantly, the MDS-UPDRS places greater emphasis on distinguishing relatively mild impairments and disabilities, drawing distinctions between slight and mild, whereas former distinctions between severe and marked are now collapsed into the severe rating (4). This decision was anchored in the realities that clinical trials are focusing increasingly on early disease, and functional differences between severe and marked impairments from the original scale may not be clinically relevant. As a result of this decision, for several items in the MDS-UPDRS, moderate impairment and disability is now rated as 3 instead of 2.
An important addition to the MDS-UPDRS is a set of detailed instructions. Because the MDS-UDPRS is envisioned to be the primary international rating scale for PD clinical care and research, an emphasis was placed on clear and detailed descriptions of methods for data acquisition. These are officially part of the scale, so that international colleagues can perform ratings in a systematic manner within and across centers. The instructions are intended to standardize the method of application of the scale so that the MDS-UPDRS data are collected uniformly. The scale has not yet been translated into non-English editions, and this effort will start in 2008 through the MDS. A clinimetric program for each language edition is planned and the Task Force will offer statistical assistance.
The MDS-UPDRS involves participation by patients and caregivers for the assessment of several nonmotor and motor experiences of daily living. These questions were written at seventh grade level and extensively tested in patient focus groups. The question on fatigue was included based on patient responses that this symptom has a high impact on health-related quality of life and was not otherwise captured in the scale. Because cognitive impairments frequently occur in PD,the questionnaire was designed to be completed by the patient alone, with the input of caregivers, or by the caregiver alone, depending on patient/caregiver preference.
Given the number of items to be assessed in the MDS-UPDRS, the patient sample required for adequate statistical analysis was large. We were, however, successful in recruiting colleagues internationally from English-speaking centers to help in this important effort. These colleagues were able to identify and examine PD patients across the spectrum of disabilities. Investigators were asked to select a gamut of severities among PD patients and to be attentive to obtaining diversity in gender and race/ethnicity. The distribution of this data set in terms of disease severity, drug treatment, gender, and ethnic balance should not be considered to be representative of the investigators' overall practice population, because the composition reflects an effort to have a clinically reasonable number of cases in different categories to test the clinimetric properties of the scale. Nonetheless, the majority of patients were Hoehn and Yahr stages II and III, a pattern seen in cross-sectional analyses in early, mid, and late disease.10 Based on the wide range of severities sampled and the distribution of high and low scores within each part, we are confident that the MDS-UPDRS is not limited by floor or ceiling effects.
We placed special emphasis on the recruitment of subjects of diverse race/ethnicity. Although we did not achieve our goal of 650 per racial/ethnic group, we did succeed in involving a much higher percentage of subjects of race/ethnicity other than non-Latino Caucasian (N = 195, 22% of our total sample) than the usual 0% to 10% reported in clinical trials (personal communication, M. Schneider and C. Swearingen). Other than non-Latino Caucasians, we did not have enough participants in any one racial or ethnic group to conduct statistical analyses within any specific subgroup. Efforts to enhance diversity in clinical trials of PD is a focus of US government funding,11 and this program demonstrates that PD investigators are able to exceed current performance in clinical trials. To continue to enhance this data set, the statistical center for the program (e-mail: [email protected]) will continue to accept additional ratings of the UPDRS vs. MDS-UPDRS for those patients other than non-Latino Caucasians.
The clinimetric analysis supports the reliability and validity of the MDS-UPDRS. It performs extremely well in comparison with the original version with high internal consistency for the entire scale as well as high internal consistency on each part. In addition, even though restructured, each part of the MDS-UPDRS correlates highly with the corresponding part of the original scale. The scaling modifications and item additions to the MDS-UPDRS provide new information while still capturing the features of PD from the original scale. On the other hand, because the item responses (0, 1, 2, 3, 4) have been substantially modified in terms of wording and concept, we cannot provide an algorithm with point-to-point or summary conversion numbers.
The technique of factor analysis is a particularly strong clinical/statistical method for scale evaluation, because it tests whether items cluster and allows clinicians to determine if these clusters fall into components that represent clinically relevant domains. Furthermore, it allows statistical assessment of whether the clusters correlate and thereby capture information about the overall entity being studied, in this case, PD. The MDS-UPDRS has excellent factor validity, and the factor analysis confirms that the items cluster in clinically pertinent domains. Because data are collected using three different methods, some based exclusively on patient or caregiver responses (questionnaire), some based solely on the investigator's assessments (motor examination), and some with a combination (complex behaviors and motor complications), we did not anticipate that the total score (combined Parts I–IV) would likely be a recommended outcome. Although the high correlation between the total scores on the original UPDRS and MDS-UPDRS demonstrates that the two scales are measuring the same overall entity of PD, the MDS-UPDRS factor analysis confirmed that neither the combined parts nor combinations based on different acquisition methods have a stable factor structure. However, when each part is considered separately, the factor structures are both clinimetrically sound and clinically pertinent. In this light, we recommend that each of the parts (I–IV) should be reported separately and not collapsed into a single “Total MDS-UPDRS” summary score.
Comparing the factor structure of Part III of the MDS-UPDRS to published factor analyses of the original UPDRS,12 the MDS-UPDRS identifies lower limb bradykinesia as a new factor, likely because of the addition of toe tapping as a separate rating. Attention was directed to separating postural from kinetic tremor, and extensive discussion within the group focused on the placement of “reemergent rest tremor.” Because reemergent tremor interferes with the holding of objects against gravity, this tremor was relegated to postural tremor.13 Despite these deliberations, the factor structure identified postural and kinetic tremors as a single factor and the rest tremor was distinct from this factor.
The final step in the clinimetric analysis will involve an assessment of differential item function (DIF). Although this type of analysis was never performed on the original UPDRS, our large sample size and available statistical programs will allow this level of scrutiny for all items. DIF is defined as group differences in item response, conditional on the state or trait assessed. As an example, if in two groups defined by gender, one rarely endorsed a high score for an item, while the other often endorsed a high score, but the two had similar scores on the overall part, this difference suggests that gender has an influence on the item interpretations or responses. DIF may be due to group differences in neurological burden, comprehension, adaptation, or bias. There are two types of DIF: uniform and nonuniform. Uniform DIF is present when item thresholds differ between the groups, but the slopes are parallel on the item characteristic curves. Nonuniform DIF is present when the two curves do not follow a linear progression across the rating options. The presence of either form of DIF would suggest that the item in question does not perform the same in different groups of the patient sample. We plan to examine three patient characteristics for the DIF analysis in our study sample: gender, race/ethnicity, and age. If DIF is identified, future modifications will be considered and tested in subsequent phases of our clinimetric program (see below). In this light, although we present the MDS-UPDRS for immediate application in clinical settings, we emphasize that the scale will continue to be evaluated and that further refinements may develop in the future based on additional and ongoing clinimetric analyses.
The Appendix of Additional Scales is officially part of the MDS-UPDRS and directs clinicians and researchers to scales that focus in more detail on areas of disability that are considered as single-item questions on the MDS-UPDRS. The MDS Task Force on Rating Scales in PD has initiated a number of critiques of available scales dealing with different areas of dysfunction, and rankings of Recommended and Suggested have been developed using predefined criteria.5, 6 The results of these reports have been supplemented by assessments by the MDS-UPDRS subcommittee dedicated to the Appendix and, as new clinimetric reports on scales are published and new scales are introduced, the Appendix will be updated. Because the nonmotor aspects of PD are an increasing focus of clinical decision-making and research, we recommend a uniform selection of scales so that different reports can be compared with similar measures.
The next steps in the MDS-UPDRS program include the non-English translations, testing the MDS-UDPRS for responsivity to change over time, and analysis of questions with DIF. The planned clinimetric program leaves several additional projects available for investigator-initiated research. Correlations between the MDS-UPDRS and other scales such as quality of life measures or global disease burden scales that are not specific for PD are encouraged by the authors, but are not part of this core program. Future clinical trials in PD will tend to be of longer duration (often 5 years or longer) as new therapies are tested to delay progression post-levodopa administration. The long duration makes it unlikely that the participant in a trial will have the same rater at every visit. Thus, it is important that temporal stability, sensitivity to change, and interrater reliability be established in the MDS-UPDRS. To facilitate interrater reliability, a Teaching Tape, modeled after the one developed for the motor section of the original UPDRS, is being developed.14
The MDS-UPDRS is available on the MDS web site (www.movementdisorders.org). Likewise, the Appendix of Additional Scales is also available electronically and will be updated through the MDS web site.
Acknowledgements
The MDS received unrestricted grants for the development of the UPDRS revision program from Boehringer-Ingelheim (USA), GlaxoSmithKline, and Pfizer, Inc. The UK Parkinson's Disease Society also provided support for assessment of subjects in the United Kingdom. Funding was also provided by the NINDS U01NS043127. We and the MDS acknowledge the work of the following colleagues whose data formed the core of the clinimetric comparison between the UPDRS and MDS-UPDRS: Pinky Agarwal, Saima Athar, Yvette Bordelan, Helen M. Bronte-Stewart, Richard Camicioli, Kelvin Chou, Wendy Cole, Arif Dalvi, Holly Delgado, Alan Diamond, Jeremy P. Dick, John Duda, Rodger J. Elble, Carol Evans, Virgilio G. Evidente, Hubert H. Fernandez, Susan Fox, Joseph H. Friedman, Robin D. Fross, David Gallagher, Christopher G. Goetz, Deborah Hall, Neal Hermanowicz, Vanessa Hinson, Stacy Horn, Howard Hurtig, Un Jung Kang, Galit Kleiner-Fisman, Olga Klepitskaya, Katie Kompoliti, Eugene C. Lai, Maureen L. Leehey, Iracema Leroi, Kelly E. Lyons, Terry McClain, Steven W. Metzer, Janis Miyasaki, John C. Morgan, Martha Nance, Joanne Nemeth, Rajesh Pahwa, Sotirios A. Parashos, Jay S. Schneider, Anette Schrag, Kapil Sethi, Lisa M. Shulman, Andrew Siderowf, Monty Silverdale, Tanya Simuni, Mark Stacy, Matthew B. Stern, Robert Malcolm Stewart, Kelly Sullivan, David M. Swope, Pettaruse M. Wadia, Richard W. Walker, Ruth Walker, William J. Weiner, Jill Wiener, Jayne Wilkinson, Joanna M. Wojcieszek, Summer Wolfrath, G. Frederick Wooten, Allen Wu, Theresa A. Zesiewicz, Richard M. Zweig.
Author Roles: All authors participated in MDS-UPDRS design, clinimetric analysis, interpretation of results, and manuscript writing. Dr. Goetz worked with the MDS to procure funding. Statistical analysis was conducted by Barbara Tilley, Stephanie Shaftman, and Glenn Stebbins with input from all other authors.
Appendix
