POS0003 DEVELOPMENT AND VALIDATION OF A DISEASE SPECIFIC PATIENT REPORTED OUTCOME FOR GIANT CELL ARTERITIS

Abstract

BackgroundGiant cell arteritis (GCA) is caused by inflammation of the blood vessels of the head and neck; patients can present with cranial, ocular or large vessel vasculitis involvement. Treatment is with glucocorticoids, steroid sparing agents and biologics to control inflammation and protect sight.ObjectivesThe aim of this study was to produce a validated disease specific PROM for patients with GCA, to capture the impact of GCA and its treatment on health-related quality of life.MethodsPatients with clinician- confirmed GCA from the UK, either diagnosed in the last three years or with a flare in the last year, were included in the survey. A longlist of 40 candidate questionnaire items, each with a 5-point Likert scale, had previously been developed, based on a qualitative study with patients from the UK and Australia [1]. In this cross-sectional survey, patients completed the 40-item draft GCA-PROM alongside EQ5D-5L, CAT-PRO5 and self-report of GCA disease activity. Rasch and factor analysis were used in an iterative manner to determine the underlying construct validity of the new PROM. Items were fitted to the Rasch model to determine its construct validity, reliability, unidimensionality and statistical sufficiency of the total score from the scale. Factor analysis was used to establishing factor structure. Item reduction decisions were be based on clinical importance, lack of fit to the Rasch model, and redundancy detected during principal component analysis. External validity was tested by comparing the scores of the newly validated GCA-PROM (i) in participants who self-identify as having ‘active disease’ versus patients ‘in remission’ (known groups validity) (ii) with scores derived from EQ5D-5L and CAT-PRO5 (convergent validity).ResultsThe survey included 428 patients; 327 (76%) cranial GCA, 114 (26.6%) large vessel vasculitis and 142 (33.2%) ocular involvement. 285 (67%) of participants were female with a mean age (SD) of 74.2 (7.2). 167 (39%) temporal artery biopsies and 177 (41.4%) temporal artery ultrasounds, and 51 (11.9%) Positron Emission Tomography and Computed Tomography (PET-CT)s were reported as positive. 108 (25%) received second-line immunosuppressants, and 34 (7.9%) anti-IL6 therapy. Active disease was reported in 197 (46%). Four factors (domains) were identified after deletion of 10 redundant items: Acute symptoms (8 items), Activities of daily living (7 items), Psychological (7 items) and Participation (8 items). The four domains were analysed as ‘super-items’ and shown to fit the Rasch model. The overall scale had an adequate fit to the Rasch model: X2 = 25.219, DF=24, p=0.394 including reliability PSI=0.828. The raw-to-linear transformation scale was calibrated to enable parametric analyses if desired. Each domain was shown to have known-groups validity (p<0.001 patients reporting active versus inactive disease) and correlation with EQ5D-5L and CAT-PRO5 (Rs) ranging between 0.4.42 and 0.778.ConclusionThe GCA-PROM is a new patient reported outcome measure for patients with GCA which demonstrates good internal and external validity.