Patient global assessment in psoriatic arthritis – what does it mean? An analysis of 223 patients from the Psoriatic arthritis impact of disease (PsAID) study

Abstract

Objective

Patient global assessment is a key outcome measure in psoriatic arthritis. To explore the meaning of patient global assessment in psoriatic arthritis by examining associations to domains of health assessed by the Psoriatic arthritis impact of disease score.

Methods

Post-hoc analysis of a multicentre cross-sectional study of patients with psoriatic arthritis. Data collection included patient global assessment, specific joint and skin global patient assessments, Psoriatic arthritis impact of disease questions covering physical (including joints and skin), psychological and social impact, and other comparator outcomes. Univariate analyses (Pearson correlation) and multivariate linear regression were performed to explain patient global assessment and the specific joint and skin global patient assessments.

Results

Among 223 patients (mean age: 51.0 [standard deviation, ±13.3] years; mean disease duration: 9.9 [±10.1] years; mean swollen joint count: 4.1 [±5.1]; 84.3% with current psoriasis [mainly of less than 5% body surface area]), 50.2% were females. Mean patient global assessment was 4.8 (±2.7), mean joint and skin patient assessments were respectively 5.6 (±2.5) and 4.1 (±3.0). Intraclass correlation between patient global assessment and joint or skin patient assessment was respectively 0.71 (95% confidence interval, 0.64–0.77) and 0.52 (95% confidence interval, 0.42–0.60). In multivariate analyses, patient global assessment was explained (R² of model: 0.754) by coping (β = 0.287); pain (β = 0.240); work and/or leisure activities (β = 0.141); and anxiety (β = 0.109).

Conclusions

Patient global assessment in psoriatic arthritis was explained mainly by physical, but also psychological aspects of the disease.

Introduction

Psoriatic arthritis (PsA) is a heterogeneous disease, which includes varying levels of peripheral joint involvement and skin manifestations. Evaluating its outcomes should reflect all these different aspects [1], [2], [3], [4], [5]. Outcome measures in rheumatology (OMERACT) and the Group of research and assessment of psoriasis and psoriatic arthritis (GRAPPA) have proposed six core domains to be measured in clinical trials and observational studies of PsA: peripheral joint activity, skin activity, pain, patient global assessment (PGA), physical function and health-related quality of life [1]. Furthermore, over the recent years, patient reported outcomes (PROs) have been increasingly recognized as important efficacy endpoints [6], [7]. PGA is one of the most widely used PROs in PsA [8], [9], however, we lack information on the concepts encompassed in PGA, from the patient's perspective. PGA may include physical aspects, e.g. of musculoskeletal disease, or skin or nail disease, or a composite of all these domains; but also psychological or social aspects [10].

Recently, the European league against rheumatism (EULAR) developed the Psoriatic arthritis impact of the disease (PsAID) questionnaire, a score reflecting the impact of PsA based on the patients’ perspective [11]. The PsAID questionnaire assesses 12 domains of health, ranging from pain or physical activity to anxiety or embarrassment. The PsAID composite score was found to correlate strongly with PGA [11]. However, the specific relationships between PsAID questions reflecting different domains of health and PGA were not assessed [11].

GRAPPA has also suggested using other PGA questions, specific to joints and skin: the joint and skin patient assessments [8]. In an initial study, PGA appeared to be related to both of these patient assessments [8]. Variations in wording of patient assessment are relevant, as has been shown in rheumatoid arthritis [12]. Thus, the new wordings proposed by GRAPPA [8] should be further assessed.

The objectives of the present study were to explore the notion of PGA in PsA from the patients’ perspective by describing its construct validity against the PsAID questions and other outcome measures in PsA. Furthermore, we explored the construct validity of the 2 specific (joint, skin) patient assessments proposed by GRAPPA [8].