Three patient-reported outcomes may be considered as valid measures of physical function in psoriatic arthritis (PsA), according to research results published in Arthritis Research and Therapy.

Using data from the Remission/Flare in PsA study (ClinicalTrials.gov Identifier: NCT03119805), researchers sought to assess and compare the properties of patient-reported outcome measures — the Health Assessment Questionnaire-Disability Index (HAQ-DI), the Medical Outcome Survey 12-Item Short Form Instrument, specifically the physical functioning summary score (PCS12), and the PsA Impact of Disease-12 Functional Capacity (PsAID-FC) — for the assessment of physical function in patients with PsA.

In total, 466 patients were recruited and 394 were eligible for follow-up after a median of 4.1 months (interquartile range, 3.0-5.7 months). At baseline, missing data for each measure — HAQ-DI, PCS12, and PsAID-FC — were 1.3%, 7.5%, and 0.2%, respectively; at follow-up, these data were 0.8%, 4.1%, and 2.0%, respectively.

For all other analyses with baseline data, 414 patients (52% men) were included with complete data for all patient-reported outcome measures at baseline. For analysis of follow-up data, 350 patients with complete data from all 3 outcomes at both time points were included. At baseline, 40% and 58% of patients fulfilled low disease activity criteria by Minimal Disease Activity and Disease Activity Index for PsA, respectively. In terms of treatment, 63% of patients were receiving conventional disease-modifying antirheumatic drugs and 61% were receiving biologic disease-modifying antirheumatic drugs.

Patient-reported outcomes for physical function strongly correlated with each other (rho, >0.7). Investigators identified the highest correlation (rho, >0.9) between PsAID-FC and PsAID-12. The physical function patient-reported outcomes moderately to strongly correlated with patient global assessments for arthritis (rho, 0.61-0.78) and pain (rho, 0.61-0.77); moderately with tender joint count (rho, 0.39-0.51) and Disease Activity Index for PsA (rho, 0.55-0.72); weakly with swollen joint count (rho, 0.19-0.32); and very weakly with the patient global assessment for skin (rho, 0.24-0.36).

Change scores for physical function patient-reported outcome measures strongly correlated with each other, moderately with multiple disease activity indices, including joint count, pain, and patient global assessment for arthritis, and weakly with patient global assessment for skin.

Among 350 patients who were followed up and had a complete dataset for all 3 patient-reported outcome measures at both time points, 27%, 54%, and 18% reported that their conditions had either improved, not changed, or got worse, respectively. Compared with the change scores for the group that reported no change, change scores for all 3 patient-reported outcome measures in the group that reported “worse” outcomes were statistically significantly different, excluding changes scores in the “improved” group. All 3 physical functioning patient-reported outcome measures were more sensitive for worsening outcomes (standardized response mean, 0.37, -0.45, and 0.38, respectively) than for improving outcomes.

Study limitations included the lack of generalizability to patients with milder or early disease and the need to translate patient-reported outcome measures between languages.

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“HAQ-DI, PCS12, and PsAID-FC are valid measures of function for PsA,” the researchers concluded. “PsAID-FC, a single question, performed similarly to other [patient-reported outcome measures] and may be an additional option to measure PsA-specific physical function.”

Disclosure: This clinical trial was supported by Pfizer. Please see the original reference for a full list of authors’ disclosures.

Reference

Leung YY, Orbai A-M, de Wit M, et al; the ReFlap Study Group. Comparing the patient reported physical function outcome measures in a real-life international cohort of patients with psoriatic arthritis [published online January 21, 2020]. Arthritis Care Res. doi:10.1002/acr.24139