Outcomes in patients with incipient undifferentiated arthritis.

OBJECTIVE: To determine outcomes in patients with onset within the last year of peripheral inflammatory arthritis that does not meet classification criteria for any specific disease. METHODS: Symptoms and laboratory tests were evaluated at baseline and 14 to 60 months later in 43 patients, 32 women and 11 men, with a mean age of 50 years. RESULTS: At baseline, a presumptive clinical diagnosis was made in 16 of the 43 patients. Diagnoses at last follow-up were undifferentiated inflammatory arthritis in seven cases, mild rheumatoid arthritis in 18, psoriatic arthritis in two, Sjogren's syndrome in two, lupus in one, and paraneoplastic syndrome in one. The remaining 12 patients were free of inflammatory joint symptoms; three had symptoms of osteoarthritis and nine were asymptomatic. Factors present at baseline and predictive of progression to definite rheumatoid arthritis were a positive test for rheumatoid factor, presence of an HLA DRB1*04 allele, and a presumptive clinical diagnosis of rheumatoid arthritis. CONCLUSION: 55% of our patients developed a specific inflammatory joint disease, and 42% developed rheumatoid arthritis, which was consistently mild. Resolution of all inflammatory joint symptoms occurred in 28% of cases. A number of clinical laboratory, and genetic findings of use for predicting the outcome of undifferentiated arthritis were identified.