A Threshold of Meaning for Work Disability Improvement in Psoriatic Arthritis Measured by the Work Productivity and Activity Impairment Questionnaire

Abstract

Introduction: The Work Productivity and Activity Impairment Specific Health Problem Questionnaire (WPAI:SHP) is used to assess the impact of an intervention on work productivity in patients with psoriatic arthritis (PsA). Unfortunately, studies reporting changes or improvements in domains of WPAI:SHP by patients with PsA have a limited threshold of meaning due to the absence of published minimal clinically important differences (MCIDs). Our objective was to determine the MCIDs for improvement in WPAI:SHP in patients with active PsA.

Methods: MCIDs for WPAI:SHP domains (presenteeism, work productivity loss, and activity impairment) were derived for patients with active PsA who were biologic naïve or TNF inhibitor (TNFi) experienced using 24-week results from two phase 3 trials (SPIRIT-P1 and SPIRIT-P2). MCIDs were derived using the anchor-based method supplemented by the distribution-based method. Anchors included achievement of the American College of Rheumatology 20 responder index (ACR20), the minimal disease activity (MDA), and the Health Assessment Questionnaire and Disability Index (HAQ-DI) MCID (improvement ≥ 0.35). Anchor validity was assessed by biserial correlation and analysis of covariance modeling against the domains. MCIDs were triangulated using the receiver operating characteristic (ROC) method supplemented by the distribution-based method.

Results: The analyses included 417 biologic-naïve and 363 TNFi-experienced patients. ACR20, MDA, and HAQ-DI were valid anchors. Significant differences in WPAI:SHP domain scores were observed between patients achieving ACR20, MDA, or HAQ-DI compared to patients not achieving these clinical thresholds (all P < 0.001). ROC analyses suggested that a ≥ 20% improvement in presenteeism, a 15% improvement in work productivity loss, and a 20% improvement in activity impairment represented clinically meaningful improvements in both populations. The distribution-based method supported the results.

Conclusion: MCIDs for the presenteeism, work productivity loss, and activity impairment domains were estimated to be 20%, 15%, and 20%, respectively, in biologic-naïve or TNFi-experienced PsA populations. These results will help improve the meaningfulness of WPAI:SHP improvements reported by PsA patients.

Trial registration: SPIRIT-P1: NCT01695239, SPIRIT-P2: NCT02349295.

Funding: Eli Lilly and Company.

Keywords: Biologic naïve; Psoriatic arthritis; TNFi experienced; WPAI; Work productivity.

Fig. 1

Anchor evaluation by biserial correlation analyses of ACR20, ACR50, ACR70, MDA, and HAQ-DI MCID (improvement ≥ 0.35) for the presenteeism (a), work productivity loss (b), and activity impairment (c) domains of WPAI:SHP in patients with PsA who were biologic naïve or TNFi experienced (inadequate responders to TNFi or TNFi-intolerant patients). The dotted line corresponds to a correlation coefficient threshold of 0.371. HAQ-DI Health Assessment Questionnaire and Disability Index, MCID minimal clinically important difference, MDA minimal disease activity, TNFi tumor necrosis factor inhibitor, WPAI:SHP Work Productivity and Activity Impairment:Specific Health Problem Questionnaire

Fig. 2

Anchor evaluation by logistic modeling of ACR20, ACR50, ACR70, MDA, and HAQ-DI MCID for the presenteeism (a), work productivity loss (b), and activity impairment (c) domains of WPAI:SHP in patients with PsA who were biologic naïve or TNFi experienced (inadequate responders to TNFi or TNFi-intolerant patients). HAQ-DI Health Assessment Questionnaire and Disability Index, MDA minimal disease activity, MCID minimal clinically important difference, TNFi tumor necrosis factor inhibitor, WPAI:SHP Work Productivity and Activity Impairment: Specific Health Problem Questionnaire

Fig. 3

Anchor evaluation by analysis of covariance (ANCOVA) modeling for the presenteeism (a), work productivity loss (b), and activity impairment (c) domains of WPAI:SHP in biologic-naïve and TNFi-experienced patients (inadequate responders to TNFi or TNFi-intolerant patients). Domain change from baseline at week 24 was stratified by anchor achievement status, adjusting for baseline WPAI:SHP domain score. All comparisons between those who met and those who did not meet the anchors within a population group had P < 0.001. HAQ-DI Health Assessment Questionnaire and Disability Index, MCID minimal clinically important difference, MDA minimal disease activity, TNFi tumor necrosis factor inhibitor, WPAI:SHP Work Productivity and Activity Impairment: Specific Health Problem Questionnaire

Fig. 4

Responder definitions of the WPAI:SHP presenteeism domain as determined by the receiver operating characteristic (ROC) method using WPAI:SHP domain changes from baseline at week 24 for ACR20 (a), MDA (b), and HAQ-DI MCID (c) in biologic-naïve patients and ACR20 (d), MDA (e), and HAQ-DI MCID (f) in TNFi-experienced patients (inadequate responders to TNFi or TNFi-intolerant patients). MCIDs were derived from the region reflecting a balance between specificity and sensitivity, with the lower limit defined by half the standard deviation of the distribution-based method. HAQ-DI Health Assessment Questionnaire and Disability Index, MCID minimal clinically important difference, MDA minimal disease activity, TNFi tumor necrosis factor inhibitor, WPAI:SHP Work Productivity and Activity Impairment: Specific Health Problem Questionnaire

Fig. 5

Responder definitions of the WPAI:SHP work productivity loss domain as determined by the receiver operating characteristic (ROC) method using WPAI:SHP domain changes from baseline at week 24 for ACR20 (a), MDA (b), and HAQ-DI MCID (c) in biologic-naïve patients and ACR20 (d), MDA (e), and HAQ-DI MCID (f) in TNFi-experienced patients (inadequate responders to TNFi or TNFi-intolerant patients). MCIDs were derived from the region reflecting a balance between specificity and sensitivity, with the lower limit defined by half the standard deviation of the distribution-based method. HAQ-DI Health Assessment Questionnaire and Disability Index, MCID minimal clinically important difference, MDA minimal disease activity, TNFi tumor necrosis factor inhibitor, WPAI:SHP Work Productivity and Activity Impairment: Specific Health Problem Questionnaire

Fig. 6

Responder definitions of the WPAI:SHP activity impairment domain as determined by the receiver operating characteristic (ROC) method using WPAI:SHP domain changes from baseline at week 24 for ACR20 (a), MDA (b), and HAQ-DI MCID (c) in biologic-naïve patients and ACR20 (d), MDA (e), and HAQ-DI MCID (f) in TNFi-experienced patients (inadequate responders to TNFi or TNFi-intolerant patients). MCIDs were derived from the region reflecting a balance between specificity and sensitivity, with the lower limit defined by half the standard deviation of the distribution-based method. HAQ-DI Health Assessment Questionnaire and Disability Index, MCID minimal clinically important difference, MDA minimal disease activity, TNFi tumor necrosis factor inhibitor, WPAI:SHP Work Productivity and Activity Impairment: Specific Health Problem Questionnaire