Clinical and serological features according to anti-DFS70 antibody status in undifferentiated connective tissue disease: a retrospective cross-sectional study.

This study aimed to compare demographic, clinical, laboratory, and autoantibody profiles between anti-dense fine speckled 70 (DFS70)-positive and -negative patients with undifferentiated connective tissue disease (UCTD). We retrospectively analyzed 284 UCTD patients followed at a tertiary rheumatology centre between January 2017 and December 2024. Patients fulfilling established classification criteria for a defined connective tissue disease were excluded. Patients were stratified according to anti-DFS70 status. Group comparisons were performed, and the Benjamini-Hochberg procedure was applied to control the false discovery rate. A multivariable logistic regression model was additionally used to evaluate the potential confounding effect of hydroxychloroquine use. Of 284 patients, 75 (26.4%) were anti-DFS70 positive and 209 (73.6%) were negative. After false discovery rate correction, arthritis/arthralgia was more frequent in the anti-DFS70-negative group than in the positive group (81.8% vs. 61.3%, adjusted p = 0.034), as was homogeneous ANA pattern (33.5% vs. 12.0%, adjusted p = 0.034). In multivariable analysis, homogeneous ANA pattern remained associated with anti-DFS70 negativity after adjustment for hydroxychloroquine use (OR 2.71, 95% CI 1.16-6.30, p = 0.021), whereas arthritis/arthralgia did not remain statistically significant (OR 1.92, 95% CI 0.95-3.90, p = 0.071). Anti-DFS70 negativity in UCTD was associated with homogeneous ANA pattern. Clinical associations, particularly arthritis/arthralgia, should be interpreted cautiously because of potential confounding by treatment exposure. Further prospective studies are warranted to clarify the clinical significance of anti-DFS70 status in UCTD.