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Abstract

Objective

To describe the classification, demographic and clinical features, and survival in anti–U3 RNP autoantibody–positive patients with systemic sclerosis (SSc).

Methods

Medical records of 108 anti–U3 RNP–positive and 2,471 anti–U3 RNP–negative SSc patients first evaluated during 1985–2003 were reviewed. Anti–U3 RNP antibody was detected by protein and RNA immunoprecipitation. Disease classification, demographic and clinical features, organ system involvement, and survival were compared between the 2 patient groups, by Student's t-test, chi-square analysis, and Mantel-Haenszel test.

Results

The anti–U3 RNP–positive group had a higher proportion of African American patients (27% versus 5%; P < 0.001) and male patients (29% versus 19%; P = 0.021), and was younger at the time of first physician diagnosis (mean age 42.8 years versus 47.4 years; P = 0.001). The 2 groups had similar proportions of patients with diffuse cutaneous involvement (47% and 45% in those with and those without anti–U3 RNP, respectively). However, among patients with diffuse cutaneous involvement, the mean maximum modified Rodnan skin score was significantly lower in the anti–U3 RNP group (22.3 versus 27.9; P < 0.001). Skeletal muscle involvement was more frequent in anti–U3 RNP–positive patients (25% versus 14%; P = 0.002), as was “intrinsic” pulmonary arterial hypertension (PAH) (31% versus 13%; P < 0.001). The frequency of gastrointestinal involvement, cardiac involvement, pulmonary fibrosis, and “renal crisis” did not differ significantly between the 2 groups. Survival was worse in the anti–U3 RNP–positive group (hazard ratio 1.38 [95% confidence interval 1.05–1.82]). PAH was the most common known cause of death in patients with anti–U3 RNP (30%, versus 10% in the anti–U3 RNP–negative group; P < 0.001).

Conclusion

The present findings demonstrate that the frequencies of African American race and male sex are greater among SSc patients with anti–U3 RNP antibody than those without, and the former group is younger at SSc diagnosis. Anti–U3 RNP–positive patients have more frequent skeletal muscle involvement and PAH, the latter being the most common cause of death.