Background: Primary Sjögren's Syndrome (pSS) is an autoimmune disease characterized by involvement of the exocrine glands, but multiple organ systems may also be affected. The main extraglandular involvement is the arthritis, which is characterized by a chronic non-erosive polyarthritis of large and small joints. The main differential diagnosis is rheumatoid arthritis (RA), which is sometimes difficult in clinical practice, due to similarities between the initial clinical manifestations of RA and polyarthritis of pSS, and also by the presence of rheumatoid factor in both diseases. The antibody directed to cyclic citrullinated peptide (anti-CCP) is a sensitive and specific marker for RA, and it was also detected in 6.9 to 22.1% of pSS patients, but with highly variable clinical significance. Furthermore, the anti-mutated citrullinated vimentin (anti-MCV), identified as a serum marker of severe RA, was recently found in 14% of pSS patients, but its clinical significance is unknown.Objectives: To evaluate the frequencies of antibodies directed to citrullinated peptides (anti-CCP, anti-MCV, anti-Sa e antifilagrin) and their possible associations with the organ involvements, disease activity score and also with the possible presence of synovitis, tenosynovitis, tendon tears and joint erosions detected by the high resolution ultrasonography examination.Methods: Fifty consecutive pSS patients (The American-European Consensus Group Criteria, 2002) of both gender, with 18 - 69 years, in regular follow-up at the Sjögren's Syndrome Clinic of the Rheumatology Division (HC-FMUSP), and 50 gender-, age-, ethnicity-matched healthy volunteers will be evaluated. Clinical assessment will be conducted through a standardized protocol. Disease activity will be measured by the EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI). Serum levels of anti-CCP, anti-MCV and anti-Sa will be determined by ELISA, and the antifilagrin antibody will be detected by indirect immunofluorescence. Antinuclear antibodies (ANA), anti-Ro (SS-A)/ La (SS-B), anti-alpha-fodrin and cryoglobulins will also be evaluated. The possible presence of synovitis, tenosynovitis, tendon tears and joint erosions in the hands and wrists will be assessed by the high resolution ultrasonography examination.
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