Measurement properties of the Patient Global Assessment numerical rating scale in moderate-to-severe psoriasis.

Abstract

Patient Global Assessment (PtGA) has been recommended as one of the core domains in psoriasis clinical trials. Among multiple versions of PtGA, the single-question 11-point PtGA numeric rating scale (NRS) remains to be validated in patients with plaque psoriasis. To evaluate the psychometric charateristics of a 11-point PtGA NRS for disease severity in patients with moderate-to-severe plaque psoriasis. Data were analyzed from 759 patients with moderate-to-severe psoriasis in the Shanghai Psoriasis Effectiveness Evaluation CoHort (SPEECH), a prospective, multicenter, and observational registry assessing the comparative effectiveness and safety of biologics (adalimumab, ustekinumab, secukinumab or ixekizumab), conventional systemic therapies (acitretin or methotrexate), or phototherapy. The test-retest reliability of the PtGA NRS showed good agreement (intraclass correlation coefficient range 0.79-0.83). No floor or ceiling effects of PtGA NRS were observed. The PtGA NRS was significantly correlated with Psoriasis Area and Severity Index (PASI), static Physician Global Assessment (sPGA), body surface area, Dermatology Quality of Life Index (DLQI), and Hospital Anxiety and Depression Scale. Relatively large correlations of PtGA NRS with PASI and DLQI Symptoms and feelings domain (all correlations ≥ 0.4 except at baseline) supported convergent validity. The presence of psoriatic arthritis or joint symptoms had no significant association with the PtGA NRS. In multivariate regression analyses, the PtGA NRS at baseline was predicted by age, lesion extent, lesion intensity, patients' symptoms and feelings, and impact on work or school. The PtGA NRS displayed known-groups validity with the PASI, sPGA and DLQI score bands. The PtGA NRS was responsive to change in PASI and DLQI after treatment. Anchor- and distribution-based approaches supported -3 as the minimal important difference for PtGA NRS. An absolute PtGA NRS ≤ 2 during follow-ups was concordant with the state of minimal disease activity based on PASI 90 or PASI 90 plus DLQI 0/1. Sensitivity analysis using subgroup comparison and multiple imputation model yielded consistent conclusions. The PtGA NRS showed good reliability, validity, and responsiveness in patients with psoriasis, and was feasible in clinical trials and daily practice.