Incidence and Risk Factors of Pleural Effusion in Patients with Autoimmune Diseases: A Retrospective Cohort Study

Background: Pleural effusion is a common manifestation of autoimmune and connective tissue disorders, but large-scale data on its incidence, risk factors, and outcomes are limited. This study aimed to assess the clinical characteristics, hospital course, and outcomes of patients with pleural effusion associated with autoimmune diseases compared to those without autoimmune conditions. Methods: We conducted a single-center retrospective cohort study of adult patients admitted with pleural effusion. Patients were divided into two groups: those with autoimmune diseases (study group, n = 1,346) and those without autoimmune conditions (control group, n = 1,278). Data were extracted from electronic health records, and subgroup analyses were performed for rheumatoid arthritis and systemic lupus erythematosus. Statistical comparisons were made using t-tests and chi-square tests. Results: Patients with autoimmune diseases were slightly younger (61.4 vs. 64.1 years, p = 0.002) and had a higher prevalence of exudative effusions (50.9% vs. 44.2%, p = 0.01). Mean length of stay (LOS) was significantly longer in the autoimmune group (10.2 vs. 8.8 days, p < 0.001), with SLE patients experiencing the longest hospitalization (12.3 days). Thoracentesis was more frequent among autoimmune patients (39.2% vs. 31.5%, p < 0.001), whereas chest tube placement was more common in controls (22.9% vs. 15.8%, p < 0.001). Mechanical ventilation was required more often in autoimmune patients (14.0% vs. 5.5%, p < 0.001). Corticosteroid and antibiotic use were also higher in the autoimmune cohort. Conclusion: Autoimmune pleural effusions are usually exudative, require respiratory support, prolong hospitalization, and warrant prospective studies to improve risk assessment and management.