Aetiology, management and outcomes of eosinophilic pleural effusion: data from the International Multicentre Pleural Research Collaborative.

Background: Eosinophilic pleural effusion (EPE) is a relatively uncommon condition. The objective of this study was to evaluate the clinical, laboratory and radiological features of EPE in a multicentre cohort of patients. Methods: This retrospective study included patients with EPE, defined as pleural fluid in which eosinophils constitute ≥10% of the total nucleated cell count, treated between 2009 and 2021 at eight respiratory centres. Predefined data were collected in the International Multicentre Pleural Research Collaborative (IMPACT) registry. Results: The study included 210 patients (144 (68.6%) males), with a median age of 67 years (interquartile range (IQR) 55-78 years). Radiological evaluation showed unilateral effusion in 194 (94.2%) patients. Most EPEs (199; 95.7%) were exudates. The median pleural fluid eosinophil percentage was 23% (IQR 14.8-43.3%). The most common aetiologies were malignancy (n=61, 29%), infection (n=43, 20.5%), heart diseases/cardiac intervention (n=17, 8.1%) or trauma (n=16, 7.6%). In 42 (20%) patients, the cause of EPE remained undetermined. In univariate and multivariable analyses incorporating available clinical and laboratory data, EPE was not a significant predictor of either malignancy or benign disease. Conclusion: EPE is a nonspecific diagnostic entity and should not, by itself, be regarded as a relevant factor in clinical decision-making.