Most patients with primary Sjögren's syndrome test negative for anti-cyclic citrullinated peptide antibody and anti-keratin antibodies, in contrast to patients with rheumatoid arthritis, a new study shows.
However, primary Sjögren's syndrome should not be ruled out in patients testing positive for these antibodies, reported J. E. Gottenberg from Bicetre Hospital in Le Kremlin Bicetre, France and colleagues (Ann. Rheum. Dis. 2005;64:114-7).
The clinical manifestations of Sjögren's syndrome and rheumatoid arthritis may be very similar, and the prevalence of rheumatoid factor is the same in both conditions, noted the authors.
The study involved 134 patients who fulfilled the American-European Consensus Group criteria for primary Sjögren's syndrome, and who did not fulfill American College of Rheumatology criteria for rheumatoid arthritis.
Patients were tested for anti-cyclic citrullinated peptide (anti-CCP) antibodies using enzyme-linked immunosorbent assay, while anti-keratin antibodies (AKA) were assessed using indirect immunofluorescence. Tests were also done for rheumatoid factor and Sjögren's syndrome antibodies, and patients were clinically evaluated for the presence of synovitis and extraglandular involvement.
Radiographs of the hands and feet were taken to rule out the presence of erosions that would indicate a primary diagnosis of rheumatoid arthritis.
Ten of the patients (7.5%), tested positive for anti-CCP, and 7 (5.2%) tested positive for AKA. This compared to data from an unpublished study showing a 68.9% prevalence of anti-CCP in patients with rheumatoid arthritis by other investigators.
“To our knowledge, this is the first study to analyze the prevalence of anti-CCP and AKA in a cohort of patients with primary Sjögren's syndrome,” they reported.
“Our study confirms that anti-CCP and AKA may be detected in patients with no radiographic evidence of erosions after a long follow-up.”
The possibility that patients with anti-CCP antibodies could be prone to developing rheumatoid arthritis should not be ruled out, noted the authors.
“It is known that anti-CCP can be present years before the first signs of rheumatoid arthritis. In three anti-CCP-positive patients with polysynovitis, the use of DMARDs [disease-modifying anti-rheumatic drugs] might have prevented progression to rheumatoid arthritis,” they wrote.
They recommend that anti-CCP-positive patients receive cautious clinical and radiographic follow-up to confirm that their disease does not evolve into rheumatoid arthritis.
However, the fact that the anti-CCP-positive patients had a mean disease duration of 11 years without erosions suggests that “the production of anti-CCP antibodies … could be less intimately related to the pathogenesis of rheumatoid arthritis than was previously hypothesized.”