Pleural effusions: role of commonly available investigations

Previous studies have reported high rates of undetermined causes of pleural effusions. We aimed to find out the proportion of pleural effusions in which the aetiology is uncertain despite commonly available investigations.

A prospective study was carried out at the University of Malaya Medical Centre from May 2001 to January 2002. All patients with pleural effusion admitted to the medical wards and non-medical wards during that period were included in the study.

Of 111 patients with pleural effusion, malignancy was the commonest cause of pleural effusion (34.2 percent), followed by tuberculosis (22.5 percent) and parapneumonic effusions (18.9 percent). There were only two patients (1.8 percent) with undetermined cause despite extensive investigations. Carcinoma of the lung was the commonest cause of malignant effusions and bronchoscopic biopsy gave the highest yield of histological diagnosis (66 percent), followed by pleural fluid cytology (59 percent) and pleural biopsy (50 percent). The combination of these three procedures increased the diagnostic yield to 96 percent. In tuberculous pleural effusion, pleural fluid staining for acid-fast bacilli was negative in all cases but mycobacterial culture was positive in 24 percent of cases while pleural biopsy gave a better yield of 68.8 percent. Examination of sputum and bronchoalveolar lavage specimens confirmed the diagnosis of tuberculosis in 40 percent of cases. A combination of these investigations yielded the diagnosis in 92 percent of patients with tuberculous effusion.

Malignancy is the commonest cause of pleural effusion, followed by tuberculosis and pneumonia, in patients treated in a teaching hospital in Malaysia. The number of undetermined causes could be minimised with a combination of readily-available and established investigations.