Abstract
OBJECTIVE: To systematically investigate the rheumatic disease spectrum associated with anti-PM/Scl antibodies and to clarify their clinical significance in idiopathic inflammatory myopathies (IIM). METHODS: Patients who were tested positive for anti-PM/Scl antibodies by immunoblotting at Peking University People' s Hospital from January 2016 to December 2024 were enrolled. Clinical and immunolo gical data were systematically collected and compared across the subgroups defined by anti-PM/Scl75, anti-PM/Scl100, or dual antibody positivity. RESULTS: A total of 422 anti-PM/Scl-positive patients were enrolled. Among them, 83.2% (351/422) were diagnosed with connective tissue disease (CTD), 7.8% (33/422) were not diagnosed with CTD, and 9.0% (38/422) had an undetermined clinical diagnosis. Among 422 patients, most commonly represented by IIM (19.7%), systemic sclerosis (SSc, 14.2%), overlap syndrome (11.8%), undifferentiated CTD (UCTD, 10.4%), rheumatoid arthritis (6.9%), Sjögren syndrome (6.4%), and systemic lupus erythematosus (6.2%), the remaining diseases accounting for 24.4%. Within the IIM subgroup, dermatomyositis predominated (74.7%), followed next by anti-synthetase syndrome (21.7%) and immune-mediated necrotizing myopathy (3.6%). Anti-PM/Scl75 antibodies were detected in 52.1% (220/422) of the total patients, anti-PM/Scl100 in 43.6% (184/422), and both in 4.3% (18/422). In the subsequent detailed analysis of the anti-PM/ Scl-positive subgroup, double-positive patients showed a significantly higher prevalence of SSc (38.9% vs. 14.1% vs. 12.0%, P=0.015) and interstitial lung disease (ILD, 70.6% vs. 28.8% vs. 35.4%, P=0.002) than those individuals with single antibody positivity alone. Raynaud phenomenon was observed more frequently in both the double-positive and anti-PM/Scl75-positive groups than in the anti-PM/Scl100-positive group (29.4% vs. 21.3% vs. 10.9%, P=0.007). The measured proportion of peri-pheral CD8(+) T cells was also higher in double-positive patients (35.9%±14.1% vs. 30.4%±11.2% vs. 26.5%±9.7%, P= 0.008), whereas absolute regulatory T-cell levels were lower in the anti-PM/Scl75-positive group compared directly with the anti-PM/Scl100-positive group [7.6% (5.4%, 10.9%) vs. 9.0% (7.9%, 12.0%) vs. 8.8% (5.2%, 9.7%), P=0.017]. Additionally, co-positivity for anti-PM/Scl and other myositis- specific or myositis-associated antibodies was strongly associated with an increased frequency of ILD (P < 0.05). CONCLUSION: Anti-PM/Scl antibodies define a broad disease spectrum encompassing IIM, SSc, overlap syndromes, and UCTD. Dual positivity for anti-PM/Scl75 and anti-PM/Scl100 identifies patients prone to systemic sclerosis and pulmonary involvement, suggesting additive pathogenic effects of the two antibody specificities.