Rheumatoid arthritis (RA) is a complex pathology to identify at an early stage. A large number of patients with recent onset polyarthritis (ROP) do not usually fulfil the ACR criteria for diagnosis of the disease and are classified as having undifferentiated polyarthritis. The aim of this study is to verify with certainty the diagnosis of patients whose illness has not been classified after four years of follow-up, and correlate their actual status with the levels of anti-cyclic citrullinated peptide (anti-CCP) antibodies and rheumatoid factor (RF) found.
After one year of follow-up, 56 patients from a total of 322, included from January 2002 in the ROP Unit, did not meet ACR criteria for any rheumatic disease. The anti-CCP antibodies and RF levels were determined in the initial clinical assessment.
After four years of follow-up, 12 new diagnoses were made in the 56 patients with undifferentiated polyarthritis: 3 seronegative RA, 8 seropositive RA and 1 psoriatic arthritis. The anti-CCP antibodies levels were positive for 5 of these 12 patients (median anti-CCP 228.6 U/mL), and all were RF positive. Six of the 7 anti-CCP antibodies negative patients were diagnosed of RA (3 seropositive and 3 seronegative for RF) and 1 was diagnosed of psoriatic arthritis (anti-CCP antibodies negative and RF positive). Forty-four patients still displayed undifferentiated polyarthritis and were RF negative.
A positive result for RF and anti-CCP antibodies in patients who do not meet the ACR diagnostic criteria could be a useful indicator of the presence of future RA.