Reduced Forced Expiratory Flow at 50% in Connective Tissue Diseases: Clinical, Functional, and Radiological Correlations

Introduction Reduced Forced Expiratory Flow at 50% of forced vital capacity (FEF50) in systemic autoimmune rheumatic diseases (SARDs), including rheumatoid arthritis (RA), systemic sclerosis (SSc), and mixed connective tissue disease (MCTD), remains poorly characterized. This study assessed the prevalence of reduced FEF50 and its associated clinical, functional, and radiological features. Methods In this retrospective, single-center study conducted from 2013 to 2023, we included patients with RA, SSc, or MCTD who underwent pulmonary function testing and high resolution chest tomography (HRCT) within one year. Reduced FEF50 was defined as a FEF50 < Lower Limit of Normal (LLN). Obstructive ventilatory disorder (OVD) was defined as an FEV₁/FVC ratio below the LLN. Results Among 267 patients (128 RA, 110 SSc, and 29 MCTD; 79% women; mean age 60 years), reduced FEF50 was identified in 22.4%, 17.0%, and 19.4% of patients, respectively. Most patients with reduced FEF50 did not exhibit OVD (89% in RA and 77% in SSc). In RA, reduced FEF50 was associated with lower disease activity, whereas in SSc it was associated with limited cutaneous disease, anti-centromere antibodies, and a higher prevalence of digital ulcers. In both RA and SSc, HRCT findings were mainly characterized by mucoid impaction and mosaic attenuation. Conclusion Reduced FEF50 is relatively frequent in SARDs, including patients without overt obstructive or interstitial lung disease. Its association with specific clinical, biological and radiological features suggests that reduced FEF50 may reflect distinct airway abnormalities that warrant further investigation.