Eosinophilia in pleural effusions: A speculative negative predictor for malignancy

Background: Eosinophilic pleural effusion (EPE) is an eosinophil count more than 10% on cytology of pleural samples. Recently, it was reported that malignancy had been the most prevalent cause inducing EPE. Therefore, we conducted an analysis on the prevalence and etiology of EPE and investigated the relationship between EPE and malignancy. Materials and Methods: Data for pleural cell differential count from patients receiving thoracentesis during the period from January 2008 to December 2013 were compared with clinical data and established diagnosis of patients obtained via electronic chart review. Results: A total of 6,801 requests of pleural cytology from 3,942 patients with pleural effusion who had received thoracentesis were available at Far Eastern Memorial Hospital from 2008 to 2013, and of these subjects, 115 (2.9%) were found to have EPE. The most frequent cause of EPE was malignancy (33.0%, n=38), followed by parapneumonic effusions (27.8%, n=32), tuberculosis pleuritis (13.9%, n=16), transudate effusions (12.2%, n=14) and the presence of blood or air in pleural space (10.4%, n=12). Additionally, an inverse relationship of eosinophilia in pleural fluid was identified in patients with malignancy and EPE. The cut-offeosinophil count in pleural fluid was 15% for the most accurate discrimination between malignancy and benign disorders in patients with EPE. At the cut-offlevel, the sensitivity and specificity were 65.8% and 67.5%, respectively. Conclusions: Pleural fluid eosinophilia was a speculative negative predictor for malignancy, despite the fact that cancers, including lung cancers and metastatic cancers to lung, were the most leading cause of pleural fluid eosinophilia. An inverse correlation was observed between the pleural eosinophil percentage and the likelihood of malignancy in patients with EPE.