Clinical characteristics and survival in systemic sclerosis-mixed connective tissue disease and systemic sclerosis-overlap syndrome.

OBJECTIVES: To describe the clinical characteristics and outcomes of systemic sclerosis -mixed connective tissue disease (SSc-MCTD) and SSc-overlap. METHODS: We included patients from the Australian Scleroderma Cohort Study who met ACR/EULAR criteria for SSc. Three mutually exclusive groups were created: SSc-MCTD, SSc-overlap and SSc-only. Univariate comparison of clinical features was performed by ANOVA or chi-square. Survival analysis was performed using Kaplan-Meier (KM) curves and Cox regression. RESULTS: Of 1728 patients, 97 (5.6%) had SSc-MCTD and 126 (7.3%) SSc-overlap. Those with MCTD-SSc were more commonly Asian (18.3% vs 10.1% in SSc-overlap and 3.6% in SSc-only, p<0.0001) and younger at disease onset (38.4 years versus 46.5 or 46.8 years, p<0.0001). Those with SSc-MCTD or SSc-overlap were more likely to have limited SSc. All three groups had similar frequency of interstitial lung disease (ILD), although pulmonary arterial hypertension (PAH) was less common in SSc-overlap. Synovitis and myositis were more common in SSc-overlap and SSc-MCTD than in SSc-only. KM curves showed better survival in SSc-MCTD than SSc-overlap or SSc-only (p=0.011), but this was not significant after adjustment for sex and age at disease onset. SSc-specific antibodies were survival prognostic markers, with ANA-centromere or anti-RNP conferring better survival than anti-Scl-70 or anti-RNA polymerase 3 (p=0.005). SSc-MCTD and SSc-overlap had lower mortality following diagnosis of ILD and PAH than patients with SSc-only. CONCLUSION: This study provides insights into the clinical characteristics of patients with SSc-MCTD, SSc-overlap and SSc-only and shows that anti-RNP antibodies are associated with better survival than anti-Scl-70 and anti-RNA polymerase III antibodies.