To describe the clinical characteristics and outcomes of systemic sclerosis ‐mixed connective tissue disease (SSc‐MCTD) and SSc‐overlap.
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.
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.
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.