Ankylosing spondylitis (AS) has been considered a seronegative rheumatic disease based on absent or low levels of antibodies against citrullinated proteins. The present study was undertaken to evaluate whether a citrullinated and matrix metalloproteinase-degraded fragment of vimentin (VICM) could be a prognostic biomarker in AS.
VICM was measured in serum samples from healthy controls (n=35), control patients with rheumatoid arthritis (RA) (n=47), and patients with AS (n=201). The optimal cutoff for diagnostic sensitivity and specificity was determined by receiver operating characteristic curve analysis. Baseline and 2-year spine radiographs were available from 118 AS patients, and were scored using the modified Stoke AS Spine Score (mSASSS). We assessed correlations with patient demographic characteristics (age, disease duration), disease activity (Bath AS Disease Activity Index [BASDAI], C-reactive protein level), and disease severity (mSASSS) using Spearman's rho. The independent association of VICM with 2-year radiographic progression, defined as a change of >0 in the mSASSS or the development of a new syndesmophyte, was analyzed by multivariate regression.
Levels of degraded VICM were significantly higher in both RA patients and AS patients than in healthy controls (both P<0.001). AS patients with the highest levels of VICM had the largest burden of disease (P<0.01), i.e., highest mSASSS score and BASDAI. VICM levels were significantly and independently associated with radiographic progression after 2 years (β=0.69, P=0.0005). Patients with both a high VICM level and a high baseline mSASSS had the highest risk of radiographic progression (odds ratio 13 for mSASSS change, 32 for new syndesmophytes), with progression occurring in 67% of these patients.
The present findings show that serum VICM may be of prognostic value in AS. The data also suggest that citrullination may be relevant in AS pathogenesis.