Outcome of patients with undifferentiated chronic monoarthritis: retrospective study of 46 cases.

Objective: To determine the natural history of undifferentiated monoarthritis of more than 3 months' duration and to evaluate the usefulness of classic diagnostic tools for identifying factors associated with outcomes.

Method: Retrospective study of 46 patients with undifferentiated monoarthritis of more than 3 months' duration.

Results: Full resolution was the outcome in 50% of cases. Rheumatoid arthritis and spondyloarthropathy were the most common diagnoses in the remaining patients. HLA-B27 status was the only significant predictor of outcome: progression to spondyloarthropathy was significantly more common (P = 0.05) among HLA-B27-positive patients. Mean time to full recovery was significantly shorter than mean time to disease progression (12 vs. 45 months, P = 0.0015). Intraarticular glucocorticoid injections were effective in over 50% of patients. Arthritis relief during the month following the injection was associated with self-limited disease. The role for magnetic resonance imaging in managing patients with undifferentiated monoarthritis remains unclear.

Conclusion: In patients with undifferentiated monoarthritis, the likelihood of a full recovery is 50%. The only significant predictor of outcome was positive HLA-B27 status, which was associated with progression to spondyloarthropathy.