Clinical features and disease outcomes of undifferentiated arthritis in Thailand

Background: Undifferentiated arthritis (UA) comprises arthritis not yet identifiable as a specific rheumatic disease. Few reports exist on the natural course of UA in Thai patients. Objective: To study the clinical features and natural course of UA in Thai patients. Method: A retrospective, analytical study was performed among Thai patients diagnosed with UA seen at Srinagarind Hospital, Khon Kaen, Thailand, between January 2002 and December 2007. Results: The medical records of 95 UA patients were reviewed. The mean age at onset was 40.7 ± 14.7 years (range, 15–78). The female:male ratio was 1.25 : 1.00. Common presentations included asymmetrical oligoarthritis followed by polyarthritis. The knee was the most commonly affected joint, followed by the wrist and ankle. Complete remission occurred within 6 months of onset in 4.2% of cases. A diagnosis was specified in 29 patients (30.5%) during the follow‐up period (which averaged 17.1 ± 24.0 months range, 6–84]), including reactive arthritis (in 9 patients), undifferentiated spondyloarthropathy (7), rheumatoid arthritis (6), psoriatic arthritis (4), ankylosing spondylitis (1), gout (1) and unclassified connective tissue disease (1). UA was the default diagnosis for 66 patients (69.5%) after 24 months of follow‐up. Hyperglobulinemia was correlated with persistent arthritis (i.e., > 6 months, P = 0.045). The only predictive factor for RA development was old‐age at onset (P = 0.038). Conclusion: The most common presentation of Thai UA was asymmetrical oligoarthritis and most patients had persistent arthritis correlated with hyperglobulinemia. Elderly‐onset, without any radiographic changes or rheumatoid factor, was predictive of RA development during follow‐up.