Clinical courses and predictors of outcomes in patients with monoarthritis: a retrospective study of 171 cases

Objectives To evaluate the clinical courses and outcomes of patients with monoarthritis and to investigate the predictive factors of clinical outcomes. Methods A retrospective analysis was performed of 171 patients with chronic monoarthritis at a single tertiary hospital between January 2001 and January 2011. Baseline characteristics, radiographic findings and the clinical course were reviewed. Results The most commonly involved joints were the knees (24.0%), followed by the wrists (22.8%) and ankles (18.7%). A final diagnosis was established in 74 (43.3%) patients. Thirty‐one (18.1%) patients were diagnosed with rheumatoid arthritis ( RA ), 23 (13.5%) with peripheral spondyloarthritis (SpA), and 19 (11.1%) with Behçet's disease ( BD ). Among 108 patients who were initially undiagnosed, 85 (78.7%) patients remained with undiagnosed monoarthritis, with relatively shorter symptom durations and requiring less treatment. The initially involved joint was a predictive factor for the final diagnosis: the wrist joint for RA (odds ratio [ OR ] 11.58, P  < 0.001), the ankle joint for SpA ( OR 6.19, P  < 0.001), and the knee joint for BD ( OR 3.43, P  = 0.014). Bony erosion at baseline was associated with progression to oligo‐ or polyarthritis ( OR 2.88, P  = 0.030) and with radiographic progression. Conclusions In patients presenting with monoarthritis, a final diagnosis was established in less than half of the patients, and a majority of undiagnosed patients showed benign clinical courses. The initially involved joint and the presence of erosion at baseline were predictors of the final diagnosis and of clinical outcomes.