Use of anti-citrullinated peptide and anti-RA33 antibodies in distinguishing erosive arthritis in patients with systemic lupus erythematosus and rheumatoid arthritis.

OBJECTIVES Systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) can both present with an erosive arthritis with the small joints of the hands affected. Therefore a serological marker would be useful to distinguish between these two diseases at onset. In this study anti-RA33 antibodies, which are found in patients with SLE and RA, and anti-citrullinated peptide antibodies (anti-CCP), which have recently been described as highly specific for RA, were assessed. METHODS Two hundred and thirty one patients receiving long term follow up for SLE were evaluated for arthritis and classified as erosive and non-erosive disease. Sixty six patients were tested for anti-RA33 and anti-CCP antibodies. All the patients were tested for rheumatoid factor (RF) and HLA-DR4 status. RESULTS Ten patients had erosive disease, six of whom were RF positive (60%), and six anti-RA33 positive (60%), whereas only two were anti-CCP positive (20%). Two hundred and twenty one patients had non-erosive disease, 40 of whom were RF positive (18%), 14 were anti-RA33 positive (6%), whereas only one patient was found to be anti-CCP positive (0.5%). CONCLUSION The presence of anti-CCP antibodies may be useful in distinguishing RA from erosive SLE. Anti-RA33 antibodies and RF are unhelpful.