Patients with anti-PM/Scl-positive and idiopathic inflammatory myopathy resemble anti-synthetase syndrome

Background Anti-PM/Scl autoantibody has been associated with an overlap between polymyositis (PM) and systemic sclerosis (SSc). However, due to limited studies, the relevance of this autoantibody in patients with idiopathic inflammatory myopathies (IIMs) without SSc was analyzed. Methods This single-center retrospective cohort study was conducted between 2004 and 2024. A total of 93 adult patients with IIMs (66 with dermatomyositis and 27 with PM - EULAR/ACR 2017) without SSc were included: 16 anti-PM/Scl(+) and 77 anti-PM/Scl(-). Patients with other types of IIMs, cancer-associated myositis, or overlap myositis, including SSc, as well as those with other myositis-specific and/or myositis-associated autoantibodies were excluded. Results The median age, sex distribution, and median follow-up duration were comparable between the anti-PM/Scl(+) and anti-PM/Scl(-) groups. There were no differences in clinical and laboratory characteristics, except for a higher frequency of lung involvement, joint involvement, "mechanics' hand," "hiker's feet," and Raynaud's phenomenon, in contrast to a lower frequency of facial rash and "V"-neck sign in patients with anti-PM/Scl(+) than in those with anti-PM/Scl(-) (all P < 0.05). Furthermore, patients with anti-PM/Scl(+) exhibited a higher frequency of disease relapse (68.8% vs. 33.8%), disease activity (50.0% vs. 24.7%), and immunosuppressant use (methotrexate or azathioprine) at the last medical evaluation (all P < 0.05). Severe infection and death rates were comparable between the groups. Conclusions Anti-PM/Scl positivity was observed in 17.2% of the sample analyzed in the present study. Patients with this autoantibody present clinical manifestations resembling anti-synthetase syndrome, with increased disease relapse and activity rates.