One year outcome of undifferentiated polyarthritis

To identify variables that can predict a progressive outcome after one year of follow up in patients presenting with undifferentiated polyarthritis (UPA) at an early arthritis clinic.

New patients with arthritis in two or more joints of less than three years' duration were categorised at entry as UPA or as rheumatoid arthritis (RA) based on the clinical diagnosis of the rheumatologist. Outcome variables after one year were radiographic damage (Sharp/van der Heijde score) and functional status (Health Assessment Questionnaire: HAQ score). A progressive disease at one year was defined as radiographic progression > or =4, or one year radiographic damage > or =10, or HAQ score > or =1. The baseline variables of patients with UPA with a progressive or mild outcome were compared.

280 patients (70% women; median age 56 years (range 18-90), median duration of symptoms 3.5 months) were included. 203 (72%) patients were clinically diagnosed as having RA and 77 (27%) as having UPA. The group of patients with progressive UPA (n=32 (42%)) had a significantly higher mean age, prevalence of arthritis of the hands, and disease activity (DAS28) at the first visit compared with the patients of the mild UPA group (n=45 (58%)). The RA group had significantly more frequent serum IgM-RF positivity, higher mean disease activity (DAS28) and mean C reactive protein concentration, more frequent symmetric arthritis, and arthritis in more than three joint groups than the progressive UPA group. Six (19%) of the progressive UPA group versus eight (4%) of the RA group did not receive disease modifying antirheumatic drugs during the first year.

After one year of follow up, 32 (42%) of the patients with UPA had a progressive disease. A progressive outcome was associated with older age, higher disease activity, and arthritis of the hands at baseline. To avoid undertreatment of patients with UPA, treatment should be based on severity rather than on diagnosis.