Comparison of polymorphonuclear- and lymphocyte-rich tuberculous pleural effusions

Most patients with tuberculous pleural effusions (TPE) have more than 50% lymphocytes in the pleural fluid. Data on patients in whom polymorphonuclear leukocytes (PMNLs) are the predominant cell type are scarce.

To compare the clinical, biochemical, microbiological and radiological characteristics between patients with predominantly PMNL and those with lymphocytic TPE.

Retrospective analysis of 214 consecutive patients with TPE.

The pleural fluid was PMNL-rich in 24 (11%) cases at the time of first thoracocentesis. Compared with those whose pleural fluid was predominantly lymphocytic, these patients showed a higher yield of mycobacteria in culture of sputum (50% vs. 25%, P = 0.03) and pleural fluid (50% vs. 10%, P < 0.01) on solid media, as well as higher pleural adenosine deaminase (ADA) levels (80 vs. 62 U/l, P = 0.02) at the expense of both ADA1 and ADA2 isoenzymes. A shift towards pleural lymphocytic predominance was observed in more than half of the PMNL-predominant patients subjected to repeat thoracocentesis.

The finding of a predominantly PMNL exudate should not rule out TPE, particularly when pleural ADA activity is elevated. The collection of sputum and pleural fluid samples for mycobacterial culture should be encouraged in the case of suspected PMNL-rich TPE, as they are frequently positive in this early stage.