Spirometric Abnormalities in Adult Mixed Connective Tissue Disease and Their Association with Disease Duration, Activity, And Severity: An Analytical Case–Control Study

Background: Mixed Connective Tissue Disease (MCTD) is a systemic autoimmune rheumatic disorder characterized by overlapping features of systemic lupus erythematosus, systemic sclerosis, and inflammatory myopathy, along with anti-U1 ribonucleoprotein antibodies. Pulmonary involvement, particularly interstitial lung disease and pulmonary vascular complications, is a major determinant of morbidity and survival. However, limited data exist correlating spirometric abnormalities with disease duration, activity, and severity in adult MCTD patients. Objective : To evaluate spirometric abnormalities in adult patients with MCTD and analyze their association with disease duration, disease activity, and disease severity. Methods: This hospital-based analytical case–control study included 120 participants: 60 adult MCTD patients and 60 age- and sex-matched healthy controls. Spirometry was performed according to ATS/ERS guidelines. Parameters assessed included forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), FEV₁/FVC ratio, and peak expiratory flow rate (PEFR). Spirometric patterns were classified as normal, restrictive, obstructive, or mixed. Associations between spirometric parameters and disease duration, activity, and severity were evaluated using appropriate statistical tests, with p < 0.05 considered significant. Results: Baseline demographic characteristics were comparable between groups. MCTD patients demonstrated significantly higher prevalence of dyspnea (56.7% vs 10.0%, p < 0.001), fatigue (56.7% vs 8.3%, p < 0.001), and cough (25.0% vs 5.0%, p = 0.002). Spirometric assessment revealed significantly reduced FVC, FEV₁, and PEFR in MCTD patients compared to controls (p < 0.001), with relative preservation of FEV₁/FVC ratio, indicating a predominantly restrictive ventilatory defect. Increasing disease duration correlated with declining FVC and FEV₁ (p < 0.05). Higher disease activity and severity were significantly associated with lower spirometric indices (p < 0.05). Conclusion: Adult MCTD patients exhibit significant restrictive spirometric impairment associated with disease chronicity and inflammatory burden. Routine spirometric surveillance may facilitate early detection of pulmonary involvement and improve clinical management