Evolution of idiopathic pleural effusion: a prospective, long-term follow-up study

The management of idiopathic pleural effusion remains controversial. Because the long-term evolution of this entity is not well known, two different approaches, aggressive and conservative, have been proposed. We conducted a 10-year study of the evolution of idiopathic pleural effusion.

Between 1984 and 1994, we prospectively studied 40 consecutive patients (30 men and 10 women; mean [+/- SD] age, 53.8 +/- 19.4 years) with exudative pleural effusion undiagnosed after exhaustive evaluation. The pleural fluid adenosine deaminase level was below 43 IU/L in all; periodic chest radiographs and clinical evaluation were carried out in all patients for a mean of 62 months (range, 36 to 108 months). Further diagnostic procedures were performed whenever the effusion recurred or when indicated by the clinical picture.

Effusions resolved in a mean time of 5.6 months (range, 7 days to 48 months). Five patients (12.5%) had one or more relapses of their pleural effusion, and in a further 5 (12.5%), the effusion persisted unchanged for more than 1 month. In 32 cases (80%), no potential cause of the effusion was detected. The diagnoses in the remaining eight cases were asbestos pleural effusion in three, pulmonary adenocarcinoma in one, mesothelioma in one, congestive heart failure in one, liver cirrhosis in one, and rheumatoid arthritis in one. Tuberculosis was not detected in any of the cases, although 19 patients initially had positive tuberculin tests.

Most idiopathic pleural effusions follow a benign course. Our results support conservative treatment of patients with idiopathic pleural effusion. Antituberculous treatment does not appear to he warranted, regardless of tuberculin test results, if the pleural fluid adenosine deaminase level is not elevated.