Strober B, Zhao Y, Tran MH, Gnanasakthy A, Nelson LM, McLeod LD, Mordin M, Gottlieb A, Elewski B, Lebwohl MG. Psychometric evaluation of the Psoriasis Symptom Diary using phase 3 trial data. Poster presented at the 2014 ISPOR 19th Annual International Meeting; May 2014. Montreal, Canada. [abstract] Value Health. 2014 Jun; 17(3):A288. doi: 10.1016/j.jval.2014.03.1676.

Objectives: To evaluate reliability, validity, and responsiveness of the Psoriasis Symptom Diary (PsD) using data from patients with moderate-to-severe chronic plaque-type psoriasis.

Methods: Analyses were completed using pooled data from the screening (1-4 weeks) and induction (12 weeks) periods of two randomized, double-blind, double-dummy, placebo-controlled, multicenter phase 3 trials (N = 820; CAIN457A2302 and CAIN457A2303) designed to assess the safety and efficacy of secukinumab. Patients aged 18+ years were randomized 1:1:1 in CAIN457A2302 to subcutaneous treatment groups (secukinumab 150 mg, secukinumab 300 mg, and placebo); and 1:1:1:1 in CAIN457A2303 including an etanercept 50 mg (twice per week) group. The 16-item PsD (24-hour recall period; 0 to 10 numerical rating scale) was electronically administered each evening. Intraclass correlations were calculated to estimate test-retest reliability. Construct validity hypotheses were evaluated based on correlations with the Psoriasis Area and Severity Index (PASI), Investigator’s Global Assessment (IGA), Patient Global Impression of Change (PGIC), the Dermatology Life Quality Index (DLQI), and the EuroQol 5-Dimension Health Status Questionnaire (EQ-5D). Mean differences between known groups and responsiveness effect sizes were computed. Phase 2 derived anchor-based PGIC thresholds and cumulative distribution function (CDF) plots were used to describe meaningful change.

Results: The PsD items yielded high intraclass coefficients (> 0.90). Correlations were in the anticipated direction and by week 12 were moderate to strong (0.41 to 0.73) in magnitude, demonstrating construct validity. Item-level means differed predictably and significantly across known groups based on the PASI and IGA. Responsiveness effect size estimates were moderate to large (0.6 to 1.4). CDF plots show that the percentage of responders was consistently higher in the treatment arms than placebo across the range of change scores.

Conclusions: Results support the reliability, validity, and responsiveness of the PsD and its use as a tool to enhance treatment decisions in patients with moderate-to-severe plaque psoriasis.

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