Further validation of a questionnaire to assess flare in psoriatic arthritis: determination of cut-off and longitudinal change

Objective The previously developed FLARE questionnaire assesses the multidimensional aspects of a flare of psoriatic arthritis (PsA). We aimed to further validate this questionnaire. Methods Reanalysis of data from the ReFLAP study ( NCT03119805 ), a longitudinal observational study carried out in 14 countries. Demographic, clinical and patient reported data were collected at baseline and one follow up visit. A previously developed PsA-specific flare instrument (FLARE), range 0-10 was completed at both time points: mean interval 4.5 months. Using a patient-anchor question for perceived flare (yes/no), the optimal cut-off for defining a flare was obtained using ROC analysis. Based on this cut-off, patients were compared for flare yes/no using clinical and self-reported data, including composite measures of disease activity. The magnitude of score differences in people newly developing a disease flare were compared with independent samples t scores. Results Of 147 patients, 61 (41%) reported a flare at baseline; the optimal score cut-off from the FLARE questionnaire was 4 (sensitivity 0.86, specificity 0.76) and, using this cut-off patients in flare had significantly worse clinical and patient reported outcomes. Of those patients reporting a flare, the most frequently affirmed items from the questionnaire referred to pain, mobility, frustration and fatigue. Those with a new flare at the second visit had patient-reported and clinical change scores significantly worse than those not reporting a flare. Conclusion This study has provided further data on the FLARE questionnaire performance and validity. The instrument is ready for use in clinical trials and longitudinal observational studies.