IntroductionWe present findings from the International Collaborative Effusion database, an ERS clinical research collaboration. Non-specific pleuritis (NSP) is a broad term that describes chronic pleural inflammation. Various aetiologies lead to NSP, which poses a diagnostic challenge for clinicians. A significant proportion of patients with this finding eventually develop a malignant diagnosis.Methods12 sites across 9 countries contributed anonymised data on 187 patients. 175 records were suitable for analysis.ResultsThe commonest aetiology for NSP was recorded as Idiopathic (80/175, 44%). This was followed by pleural infection (15%), benign asbestos disease (12%), malignancy (6%) and cardiac failure (6%). The malignant diagnoses were predominantly mesothelioma (6/175, 3.4%) and lung adenocarcinoma (4/175, 2.3%). The median time to malignant diagnosis was 12.2 months (range 0.8–32). There was a signal towards greater asbestos exposure in the malignant NSP group compared to the benign group (0.63versus0.27, p=0.07). Recurrence of effusion requiring further therapeutic intervention, nor initial biopsy approach were associated with a false negative biopsy. A computed tomography finding of a mass lesion was the only imaging feature to demonstrate a significant association (0.18versus0.01, p=0.02), though sonographic pleural thickening also suggested an association (0.27versus0.09, p= 0.09).DiscussionThis is the first multi-centre study of NSP and its associated outcomes. Whilst some of our findings are reflected by the established body of literature, other findings have highlighted important areas for future research, not previously studied in NSP.