Introduction and Objectives Eosinophilic pleural effusions (EPE) are a relatively uncommon finding in the investigation of undifferentiated pleural effusions. Traditionally defined as a cell count ≥10% eosinophils, it was initially felt to be a marker of benign disease, however, subsequent studies found malignancy to be the commonest aetiology,¹ with other causes, including infection, blood/air and drug reactions less frequent. Our aim is to use prospective data to examine the relative incidence and aetiology of EPE, and its prognostic significance.

Methods We recruited 803 consecutive patients presenting to a pleural service, between 03/2008 and 03/2015, with undiagnosed pleural effusions. Pleural biochemistry, cytology, thoracic USS, chest radiograph and CT scans were performed. Biopsies and thoracoscopy were performed as clinically indicated. Patients were followed-up for minimum duration of 12 months with final diagnosis decided by independent review by 2 respiratory consultants. Survival data was calculated from study entry to death and censored on 07/2017.

Results Of the 803 patients, 398/803 (49.6%) had a malignant pleural effusion(MPE). 57 (7.1%) had eosinophil count (EC) ≥10%. With this threshold, MPE was the commonest cause, at 24/57 (42%), followed by infection 9 (16%) and inflammatory pleuritis (IP) 5 (9%). With higher thresholds of EC, the relative frequency of malignancy decreased. At ≥30% EC, malignancy accounted for 4/20 cases, infection 4/20, drug/toxin 3/20, unknown 3/20, benign asbestos pleural effusion 2/20, pulmonary embolism 2/20, IP 1/20 and heart failure 1/20. Mortality rates were lower in EPE relative to non-EPE, with 6 months and 1 year mortality rates for EPE 19%–33% respectively, with non-EPE 36%–50%. The higher the EC, the lower mortality, with hazard ratios compared to non-EPE at 0.6, 0.5, 0.3, 0.2, 0.2 for ≥10%,≥20%,≥30%,≥40% and ≥50% EC respectively (p<0.01).

Conclusion Higher eosinophil counts are associated with decreased mortality and lower rates of malignant vs benign effusions. The threshold ≥10% is not helpful in differentiating MPE from benign disease. We suggest a higher threshold of ≥30% would hold greater clinical significance and therefore be a more useful definition for clinicians.

Reference

1. Rubins JB, Rubins HB. Aetiology and prognostic significance of eosinophilic pleural effusions: A prospective study. Chest 1996;110(5):1271–4.

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Abstract S25 Figure 1

Kaplan-meier survival curves for Eosinophilic vs Non-Eosinophilic effusions.