Objectives: To compare systemic sclerosis (SSc) patients with and without anti-PM-Scl antibody.
Methods: We reviewed the medical records of 76 anti-PM-Scl antibody positive SSc patients and 2349 anti-PMScl negative SSc patients first evaluated during 1980-2004. Patients were included if they had a clinical diagnosis of SSc either alone or in overlap with another connective tissue disease. Anti-PM-Scl antibody was screened for by indirect immunofluorescence and tested by Ouchterlony double immunodiffusion.
Results: Anti-PM-Scl antibody positive patients had a significantly higher frequency of a positive ANA with nucleolar staining (87% vs. 32%, p<0.0001) and were younger at both symptom onset (p=0.004) and first physician diagnosis of SSc (p<0.001). They were classified more often as having overlap with another connective tissue disease, particularly polymyositis-dermatomyositis, and more frequently had limited cutaneous involvement (72% vs. 52%, p=0.001). Maximal skin thickening was less in anti-PM-Scl antibody patients (mean modified Rodnan total skin score 6.0±6.3 vs. 15.9±14.2, p<0.001). Anti-PM-Scl antibody positive patients less frequently had peripheral vascular (91% vs. 98%, p=0.0002) and gastrointestinal (52% vs. 79%, p=0.0001) disease. Lung involvement overall had a similar distribution between both groups. However, radiographic evidence of pulmonary fibrosis was more frequent in anti-PM-Scl antibody positive patients (50% vs. 37%, p=0.05) and pulmonary arterial hypertension was less often detected (5% vs. 15%, p<0.04). Skeletal muscle involvement (51% vs. 14%, p<0.0001) and subcutaneous calcinosis (p<0.003) were both significantly more often observed in anti-PM-Scl antibody positive patients. Joint, heart, and kidney involvement were similar in both groups. Overall survival was significantly better for anti-PM-Scl antibody positive patients (10 year cumulative survival rate 91% vs. 65%, p=0.0002). After adjustment for age, sex and limited vs. diffuse cutaneous involvement, patients with anti-PM-Scl antibody were significantly less likely to die (HR=0.32, 95% CI, [0.14, 0.72] p=0.006).
Conclusions: SSc patients with anti-PM-Scl antibody are younger and significantly more often have limited cutaneous involvement, skeletal muscle disease, pulmonary fibrosis and calcinosis compared to anti-PM-Scl antibody negative SSc patients. Ten-year cumulative survival is significantly better in anti-PM-Scl antibody positive SSc patients.