Dynamics of interstitial lung disease following immunosuppressive treatment differ between antisynthetase syndrome and systemic sclerosis

Background: Interstitial lung disease (ILD) is the main clinical feature of antisynthetase syndrome (ASS). In the absence of randomized controlled trials to guide therapy, treatment strategies are often extrapolated from other diseases, mainly systemic sclerosis (SSc). Objectives: Our aim was to evaluate the dynamics of ILD severity following immunosuppressive treatment (IST) in ASS compared to SSc. Design: A multicenter retrospective observational study. Methods: ASS (n = 22) and SSc (n = 32) subjects with ILD were included in the registries of three medical centers. All patients received ISTs. We analyzed changes in forced vital capacity (FVC) and diffusion capacity for carbon monoxide corrected for hemoglobin (DLCOc) after treatment initiation using linear mixed-effects models. Changes in high-resolution chest CT scans were analyzed by a radiologist blinded to clinical data. Results: The median (interquartile range) age was 66 (59–71), 72% were females, and 81% of IST included mycophenolate mofetil (MMF). Baseline demographics, comorbidities, and pulmonary functions were similar between the groups. Among the ASS group, the mixed-effects models showed significant improvements in FVC% (F = 11.3, p < 0.01) and DLCOc% (F = 7.1, p = 0.015) after treatment initiation over time, while in the SSc group, there were no significant changes in FVC% (F = 0.4, p = 0.551) and DLCOc% (F = 0.8, p = 0.384). Changes in FVC% and DLCOc% were higher in the ASS group compared with SSc (p = 0.017 and p < 0.01, respectively), which persisted after adjustment to steroid use and in a sub-analysis of patients with serial pre- and post-IST pulmonary functions. Both groups had improved total CT scores after IST, without changes in other radiologic scores. Conclusion: Immunosuppressive treatment, mostly with MMF, was associated with significant improvement of FVC% and DLCOc% in ASS, compared to their stabilization only in SSc. This should encourage future randomized controlled studies of MMF in ASS patients.