Definition and prevalence of residual disease in inflammatory arthritis: a systematic literature review and meta-analysis.
OBJECTIVE: To assess how residual disease (i.e., clinically relevant signs/symptoms despite achieving treatment targets) is defined in rheumatoid arthritis (RA), psoriatic arthritis (PsA) or axial spondyloarthritis (axSpA), and estimate the prevalence/severity of residual disease in these diseases. METHODS: Systematic review of original research in RA/PsA/axSpA. Two key residual disease components were extracted: (1) the patient's disease state (often remission/low disease activity) and (2) which residual signs/symptoms were measured, e.g. swollen joints or fatigue (indicators of residual disease). Frequencies of the disease states and indicators were described (Objective 1). Prevalence (%) and severity (absolute score on instrument, e.g. fatigue NRS) of residual disease was analysed by indicator, using random effects meta-analysis (≥4 studies) or descriptively (<4 studies) (Objective 2). RESULTS: Regarding residual disease definitions (59 studies), disease states were almost exclusively disease activity-based (>99%), but with much variation in specific instruments/thresholds. Across diseases, physician-reported (66%) and patient-reported (73%) indicators were used more often than laboratory indicators to define residual disease (46%). Especially peripheral joint counts, pain, physical function and CRP were frequently used (42-56% of studies). The prevalence of residual disease (84 studies) was notable. For example, 5-25% of RA and PsA patients in remission still had swollen joints, and up to one-third reported relevant pain or fatigue. For axSpA, evidence was limited. CONCLUSION: Residual disease definitions in RA/PsA/axSpA are based on various disease activity instruments/thresholds and indicators (signs/symptoms). Residual disease affects up to half of patients. Future research should aim for a consensus-based definition of residual disease.