Abstract
Objective To determine the minimal important change (MIC) and meaningful change value (MCV) of the Disease Activity Index for Psoriatic Arthritis (DAPSA) and the effect size (ES) of DAPSA.
Methods This was a retrospective cohort study, recruiting 106 patients who agreed to participate in the research from the Department of Dermatology, Xiangya Hospital, between November 1, 2019, and April 1, 2023. An anchor-based method using linear regression analyses was used to determine the MICs and MCVs of the DAPSA. The anchor question assessed whether the patient’s well-being had changed since their previous visit, employing a 5-point Likert scale that ranged from “much improved” to “much deteriorated.”
Results The overall MIC value was 8.4 (95% CI 0.01-16.75). The MIC improvement was 9.5 (95% CI 0.89-18.14) and MIC deterioration was 1.1 (95% CI −9.81 to 12.05). The overall MCV was 10.5 (95% CI 4.34-16.72). MCV improvement was 11.4 (95% CI 5.95-16.95) and MCV deterioration was 1.1 (95% CI −9.81 to 12.05). The ES was 0.6.
Conclusion A change in DAPSA of 8.4 is indicative of an MIC, offering physicians an additional means to contextualize the patient’s perception of disease activity during treatment, and a change in DAPSA of 10.5 is likely to be regarded as MCV. These values can enhance the utility of DAPSA in psoriatic arthritis clinical trials.
- disease activity index for psoriatic arthritis
- meaningful change value
- minimal important change
- psoriatic arthritis
Psoriatic arthritis (PsA) is an inflammatory disorder characterized by widespread musculoskeletal inflammation and extraarticular manifestations, including peripheral arthritis, axial spine disease, attachment point inflammation, finger and toe inflammation, skin lesions, and nail disease, which significantly affect patient quality of life.1-3 The disease course of PsA is prolonged and easy to relapse. It has a high rate of deformity and disability in the middle and late stages, causing a huge burden to society. Therefore, it is very important to evaluate PsA disease activity effectively and control disease activity.1,2,4
The Disease Activity Index for Psoriatic Arthritis (DAPSA) is the most commonly used measure of PsA disease activity.5,6 The information required for the calculation includes tender joint count (TJC), swollen joint count (SJC), patient global assessment visual analog scale (VAS-PtGA), patient pain assessment visual analog scale (VAS-ptPain), and C-reactive protein (CRP) levels. It has critical values of remission status and of low, medium, and high disease activity. Compared with other PsA-specific assessment measures, it is more convenient and has been more widely used in the clinic setting.7 Concurrently, the treatment objectives for PsA are continually evolving and increasingly oriented toward a patient-centered approach.8 Therefore, a patient perspective assessment tool is needed to assess disease activity of PsA. In order for DAPSA scores to be representative of patient-centered disease activity, it is critical to explore the association between changes in DAPSA scores and patients’ assessments of changes in their own disease activity.
The minimal important change (MIC) is a concept that represents the change in the minimum score value of the disease activity as perceived by the patient, which can reflect an individual patient’s assessment of the change in their own condition.9 The meaningful change value (MCV) is the truly meaningful change in disease activity that patients perceive as reflecting their response to treatment. The MIC and MCV of DAPSA remain unknown, hindering the assessment of the effect of changes in DAPSA at the individual level as well as the assessment of efficacy from a patient perspective.
The purpose of this study was to determine the MIC and MCV values of the DAPSA score, as well as calculate their improvement and deterioration values, and the effect size (ES), so that the change in DAPSA score could represent the assessment of patients’ own disease activity change.
METHODS
Patients and setting. This was a retrospective cohort study, recruiting 116 patients who agreed to participate in the research from the Department of Dermatology, Xiangya Hospital, between November 1, 2019, and April 1, 2023. Prior to their involvement in the study, all patients provided informed consent. Ethical approval for this study was granted by the ethics committees of Xiangya Hospital of Central South University, under the approval number 202302083-2.
Eligibility criteria for study participation required patients to meet the Classification for Psoriatic Arthritis (CASPAR) criteria. The diagnosis of PsA was made by a combination of an experienced dermatologist and an experienced rheumatologist.10 Patients with poor Chinese comprehension or those experiencing concurrent severe medical conditions that hindered their ability to complete the questionnaire were excluded from the study.
Data collection. Baseline demographic and clinical characteristics of patients were initially documented on a case report form and subsequently anonymized and transcribed into an electronic database. During each patient visit, the individual components of DAPSA were collected to evaluate disease activity. DAPSA comprised SJC of 66 joints, TJC of 68 joints, PtGA (measured on a VAS ranging from 0-10 cm), ptPain (also measured on a VAS ranging from 0-10 cm), and CRP (measured in mg/dL).11 The minimum time interval between DAPSA measurements was 1 month. However, because of the coronavirus disease 2019 (COVID-19) pandemic, the maximum interval could be extended to 8 months. Patients with missing DAPSA scores and noncompliant time intervals were excluded. After filtering, data remained for 106 of the original 116 patients. To gauge changes in their condition between visits, patients were presented with an anchor question consisting of a 5-point Likert scale during the second visit. They were asked, “How was your overall well-being in the past week compared to your previous visit?” Response options for this question included (1) much improved, (2) slightly improved, (3) no change, (4) slightly deteriorated, and (5) greatly deteriorated.
Statistical analyses. Continuous data were presented as mean values accompanied by their corresponding SDs, whereas categorical data were expressed as counts and percentages. To determine the MIC and the MCV, linear regression was employed, adhering to the assumptions of linearity. Specifically, the overall MIC (MICoverall), improved MIC (MICimp), and deteriorated MIC (MICdet) were calculated to represent the transitions from the “no change” group to the “slightly improved/deteriorated” groups, the “no change” to “slightly improved” group, and the “no change” to “slightly deteriorated” group, respectively. In addition, we defined the overall MCV (MCVoverall), improved MCV (MCVimp), and deteriorated MCV (MCVdet) as the step from the “no change” group to the “much improved/deteriorated” groups, the “no change” group to the “much improved” group, and the “no change” group to the “much deteriorated” group, respectively. We constructed linear regression models using SPSS software, and the mean value of the predicted outcome, along with its corresponding 95% CI, represented the MIC or MCV. We included sex as a covariable in the linear regression to minimize sex bias. Further, we used the same method to calculate the MIC and MCV in the male and female groups, respectively. To facilitate a meaningful interpretation of the MICs and MCVs, we calculated the ES of the DAPSA using the formula ES = (mean [post] − mean [previous])/SD [previous]. All statistical analyses were performed using SPSS for Windows V26.0. A significance level of P < 0.05 was considered statistically significant.
RESULTS
Patient characteristics. Our cohort consisted of 106 patients with PsA whose clinical features are shown in Table 1. Of these patients, 70.7% were male, the mean age was 44 (SD 13.9) years, and 19.8% had axial involvement. The mean duration of disease was 3.5 (SD 5.5) years, and the mean DAPSA score was 21.9 (SD 19.5) at the first follow-up and 11.1 (SD 14.2) at the second follow-up. During follow-up, 2.8% of patients were not treated systematically with disease-modifying antirheumatic drugs (DMARDs), 69.8% were treated with a biologic DMARD, and 27.4% were treated with a conventional synthetic DMARD. Other patient characteristics, joint symptoms, and extraarticular manifestations are shown in Table 1.
Characteristics of a routine practice cohort of patients with PsA (N = 106).
Determination of MIC and MCV in DAPSA. The MICoverall value was 8.4 (95% CI 0.01-16.75). The MICimp was 9.5 (95% CI 0.89-18.14) and MICdet was 1.1 (95% CI −9.81 to 12.05). The MCVoverall was 10.5 (95% CI 4.34-16.72), MCVimp was 11.4 (95% CI 5.95-16.95), and MCVdet was 1.1 (95% CI −9.81 to 12.05). The ES was 0.6 (Table 2). When results were stratified for sex, women had a lower MIC than men, but the difference for sex was not significant and sex showed no statistical significance in linear regression (data not shown).
MIC and MCV for the DAPSA, including values for improvement and deterioration.
DISCUSSION
The DAPSA is among the most specific outcome measures used to assess disease activity in patients with PsA.11 Well-established cut-off values for specific disease activity states are available.12 However, it is crucial to determine the MIC and MCV from the patient’s perspective to enhance the practical application of DAPSA in both routine clinical practice and clinical trials.13 The results of our analysis of our routine practice cohort revealed an MICoverall of 8.4 and MCVoverall of 10.5. The ES of 0.6 indicates a medium ES. Notably, the MICimp and MCVimp exceed the MICdet and MCVdet. This may indicate that patients have high expectations for the treatment outcome of PsA; that is, the deterioration of the disease is more perceptible at the individual level than the improvement of the disease. To the best of our knowledge, the current study provides the first initial patient-centered estimates of MIC and MCV for DAPSA, marking a significant contribution to our understanding of its clinical relevance.
A previous study calculated the MIC and MCV for the Psoriatic Arthritis Disease Activity Score (PASDAS) in patients with PsA.13 However, it is worth noting that the PASDAS, owing to its comparatively intricate formula, may present challenges in its application within busy clinical settings when juxtaposed with the simpler DAPSA score.14,15 Moreover, we employed an anchor-based method to ascertain the MIC and MCV from the patient’s viewpoint. The anchor-based approach offers the advantage of establishing a direct link between the score changes and the patients’ perceptions, as indicated by the anchor. Previous research has demonstrated various applications of the anchor-based method, including linear regression, receiver-operating characteristic analysis, and mean change analysis. Compared to the latter 2 methods, the linear regression analysis method offers the advantage of encompassing all change groups, ranging from “no change” to “much improved/deteriorated,” and it demonstrates robustness in the face of data distribution deviations.13,16,17 To gain deeper insights into the trends we observed, further research with larger sample sizes is warranted. Interestingly, our study yielded an ES of 0.6, surpassing the ESs reported in previous research,13 signifying a more favorable outcome. It should be mentioned that there was a narrow range between the MIC and MCV values of DAPSA scores in our results. This relationship could perhaps be interpreted by the inference that only a small objective change is required for the patient to subjectively feel an improvement from “slightly improved/deteriorated” to “much improved/deteriorated.”
We acknowledge certain limitations in our study. First, the follow-up visits were not scheduled at specific time intervals because of the disruptions caused by the COVID-19 pandemic. Hence, recall bias could not be completely avoided because of the longer intervals for some patients. Second, our study relied on a single anchor question. It is plausible that this anchor question may not have been sufficiently comprehensive to identify more substantial and clinically significant changes. In future studies, we recommend considering the use of multiple anchors to evaluate the robustness and replicability of our current findings.
We suggest that future research should critically assess the terms “minimal” and “meaningful,” as their interpretation can be context dependent. It is important to recognize that a single anchor may not consistently pinpoint what is genuinely minimal or meaningful in a given clinical scenario. Although MIC and MCV are widely recognized terms in the literature, their significance remains subjective and context specific. Moreover, the field employs a variety of terms and methods to estimate MIC and MCV, and it remains unclear which approach holds the most promise in terms of accuracy. Thus, ongoing investigation is warranted to better define and standardize these critical concepts.
In conclusion, our findings indicate that the DAPSA is responsive to improvement on the 5-point Likert scale. An alteration in the DAPSA total score of 8.4 is indicative of an MIC, offering physicians an additional means to contextualize the patient’s perception of disease activity during treatment, and a change of 10.5 is likely to be regarded as MCV. These values can enhance the utility of DAPSA in PsA clinical trials.
Footnotes
This work was supported by National Natural Science Foundation of China (81974479, 81773329, 82073447, 82003362, 82003354).
Y. Liu and M. Tan contributed equally as co-first authors.
M. Zhang and Y. Kuang contributed equally to this work as co-senior authors.
The authors declare no conflicts of interest relevant to this article.
- Accepted for publication February 29, 2024.
- Copyright © 2024 by the Journal of Rheumatology
REFERENCES
DATA AVAILABILITY
The data underlying this article cannot be shared publicly because of the privacy of individuals who participated in the study. The data will be shared on reasonable request to the corresponding author.
