INTRODUCTIONOnline communities contain a wealth of information containing unsolicited patient experiences that may go beyond what is captured by guided surveys or patient-reported outcome (PRO) instruments used in clinical settings. This study described patient experiences reported online to better understand the day-to-day disease burden of ankylosing spondylitis (AS).METHODSUnguided, English-language patient narratives reported between January 2010 and May 2016 were collected from 52 online sources (e.g., general/health social networking sites, patient-physician Q&A sites, AS forums). Using natural language processing combined with manual curation, patient-reported experiences within narratives were evaluated and categorized into social, physical, emotional, cognitive, and role activity (SPEC-R) concepts to assess functional impairment. The same SPEC-R categorization was applied to 5 AS-specific PRO instruments to evaluate their coverage of concepts extracted from patient narratives.RESULTSA total of 34,780 narratives from 3449 patients with AS were included. Physical aspects of AS (e.g., pain and mobility) were most commonly reported by patients (86.7%), followed by emotional (32.5%), cognitive (23.6%), role activity (8.7%) and social (5.1%). Some frequently discussed subconcepts were effectively captured by ≥ 2 PRO instruments, such as pain (65.3%), asthenia (19.9%), musculoskeletal impairment (19.9%), depression (9.9%), and anger/frustration (5.4%); others [e.g., anxiety (19.1%), mental impairment (3.2%), impulsivity (2.9%)] were not addressed by any of the PRO instruments.CONCLUSIONThese findings highlight the importance of analyzing patient experiences beyond clinical trial settings and physician reports; continuous assessment of existing PRO instruments in collaboration with patients may increase their utility in real-world settings.FUNDINGNovartis Pharmaceuticals Corporation.