Prevalence of Anti-Synthetase Syndrome in Patients of Interstitial Lung Disease with Connective Tissue Diseases and Autoimmune Features: A Cross-Sectional Study

Objective: Anti-synthetase syndrome (ASS) is a rare autoimmune disease with heterogenous manifestations. Interstitial lung disease (ILD) is one among its common manifestations. The aim of this study was to evaluate the prevalence of ASS in cases of ILD associated with autoimmune features and describe the clinical, serological, and radiological profile in them. Methods: This cross-sectional study included a total of 100 patients: 50 cases each of connective tissue disease-related ILD (CTD-ILD) and interstitial pneumonia with autoimmune features (IPAF). Results: Four cases of CTD-ILD and 7 cases of IPAF had anti-ARS auto-antibodies. All eleven of them fulfilled Connor's criteria for ASS. The classic triad of arthritis, myositis, and ILD was present only in two cases. Anti-nuclear antibody (ANA) was positive in 63.6%. Anti-Jo1 (54.56%), Anti-PL12(27.3%), anti-PL7(18.2%), and anti-EJ(18.2%) were the anti ARS autoantibodies. Though generally considered to be mutually exclusive, anti-PL12 and anti-EJ antibodies were found together in two cases. Myalgia was associated with all four ARS antibodies. Anti-Jo1 antibody was associated with Raynaud's phenomenon, polyarthralgia, polyarthritis, and myopathy. Anti-PL7 antibody was associated with myopathy and mechanic's hands. Anti-PL12 and anti-EJ antibodies were associated with inflammatory poly-arthritis, polyarthralgia, and unexplained fever. Non-specific interstitial pneumonia (NSIP) was the most common radiologic pattern of ILD (81.8%). The remaining two had Usual interstitial pneumonia (UIP) pattern and were positive for anti-Jo1 antibody. Conclusion: ASS can present in many ways, often incomplete at the onset without the classic clinical triad. Anti-ARS autoantibodies can be found in established CTDs. Anti-cytoplasmic antibodies (not ANA) must be used to screen for ASS in suspected cases.