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

William Tillett, Chen-Yen Lin, Art Zbrozek, Aubrey Trevelin Sprabery, Julie Birt

Research output: Contribution to journalArticle

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.

Original languageEnglish
Pages (from-to)379-391
Number of pages13
JournalRheumatology and therapy
Volume6
Issue number3
Early online date1 Jun 2019
DOIs
Publication statusPublished - 1 Sep 2019

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