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 (IQR 55–78). 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 61 (29%), infection 43 (20.5%), heart diseases/cardiac intervention 17 (8.1%), or trauma 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
Eosinophilic pleural effusion is a non-specific diagnostic entity and should not, by itself, be regarded as a relevant factor in clinical decision-making.