Clinical Characteristics of Young-Onset Versus Elderly-Onset Rheumatoid Arthritis: A Systematic Review and Meta-Analysis.

Rheumatoid arthritis (RA) is a chronic inflammatory disease with a prevalence of 1%, mainly affecting women aged 25-45. It is classified by the age of onset into young-onset rheumatoid arthritis (YORA, 16-65 years) and elderly-onset rheumatoid arthritis (EORA, over 65 years), with EORA often presenting suddenly with systemic symptoms and large joint involvement due to age-related immune changes. This systematic review and meta-analysis compare the clinical and epidemiological characteristics of EORA and YORA. Observational studies were selected from PubMed, Scopus, Embase, Web of Science, and the Cochrane Central Database up to November 2023, focusing on a comparative analysis of both disease types with similar clinical progression and treatment duration limited to one month. Statistical analysis was performed in RStudio (Version 4.1.3, Posit Software, Boston, MA) using the "meta" package, applying a random effects model, inverse variance method, and Hartung-Knapp adjustment. Results for continuous variables were combined and grouped using the Cochrane formula, with medians and interquartile ranges transformed for uniformity. Four studies met the criteria. A trend was observed toward higher disease activity at diagnosis in the EORA group (mean difference (MD: 0.19, 95% CI -1.90 to 2.27), indicated by Disease Activity Score-28 (DAS28) and Simplified Disease Activity Index (SDAI) indices (MD 6.17, 95% CI -20.60 to 32.94). The EORA group also had higher Health Assessment Questionnaire (HAQ) scores (MD 0.21, 95% CI -0.03 to 0.46) and a greater number of painful (MD 1.31, 95% CI -0.86 to 3.47) and swollen joints (MD 2.35, 95% CI 0.77 to 3.92). Extra-articular manifestations, including rheumatoid nodules, lung involvement, and secondary Sjögren's syndrome, were more common in EORA patients (p < 0.004). In conclusion, the findings suggest that patients with EORA present with more intense disease activity at onset, a higher prevalence of extra-articular manifestations, greater levels of disability, and more pronounced radiographic changes. Despite these initial differences, EORA patients ultimately achieve long-term remission rates similar to those with YORA.