Minimal clinically important difference (MCID) for work productivity and activity impairment (WPAI) questionnaire in psoriasis patients

BACKGROUND: The clinical meaningfulness of improvements in the Work Productivity and Activity Impairment Questionnaire for Psoriasis (WPAI-PsO) reported by patients with psoriasis in response to treatment is unknown due to the lack of any publications that report minimal clinically importance differences (MCID) for WPAI-PsO outcomes.

OBJECTIVE: To determine the MCIDs for the work productivity loss and activity impairment domains of the Work Productivity and Activity Impairment Questionnaire for Psoriasis (WPAI-PsO) using results from three Phase 3 trials of ixekizumab.

METHODS: MCIDs for WPAI-PsO domains were derived using treatment agnostic data from patients participating in UNCOVER-1/-2/-3. The analysis included patients randomized to placebo and two ixekizumab treatment groups (ixekizumab either every 2 weeks or 4 weeks) from the trials. WPAI-PsO was administered at baseline and Week 12 for UNCOVER-1/-2/-3 and at Weeks 24, 36, 52 and 60 in UNCOVER-1/-2. MCIDs for the WPAI-PsO domains through Week 12 were derived using an anchor-based method supplemented with the distribution-based method. Anchors included 75%/90%/100% improvement in Psoriasis Area and Severity Index, Static Physicians Global Assessment (sPGA[0] and sPGA[0,1]) and Dermatology Life Quality Index MCID). MCIDs were triangulated using receiver operating characteristics (ROC) and distribution-based methods.

RESULTS: The analyses included 3126 patients (Placebo: 792, Ixekizumab: 2334). All anchors were shown to be valid. Significant differences in the domains of WPAI-PsO were observed between patients achieving clinically meaningful improvement in the validated anchors (all P-values < 0.001). ROC analyses suggested a 20% improvement in the work productivity loss or activity impairment components best represented the benefit of meeting a clinical meaningful improvement in the validated anchors. The distribution-based method supported the results of the anchor-based method.

CONCLUSION: The MCIDs for both the work productivity loss and the activity impairment domains of WPAI-PsO were estimated to be 20% in patients with PsO.