[Pleural effusion as initial presentation of rheumatoid arthritis. Cytological diagnosis].

A 24-year-old woman with an unremarkable history presented with a large right-sided pleural effusion. Analysis of the pleural fluid showed a sterile exudate with a low sugar level. Complementary analyses were unable to pinpoint the etiology. The effusion was drained and the patient was released with no specific diagnosis. Nine months later the effusion recurred and the initial laboratory analyses were the same. Pleural fluid cytology revealed the presence of an amorphous necrotic background and non-small cells with multiple nuclei, two signs that constitute part of the pathognomonic triad of rheumatoid pleural effusions, the third characteristic benign fusiform histocytes. The biochemical characteristics of the pleural fluid thus suggested rheumatoid pleural effusion, and cytology confirmed the diagnosis. Corticoid therapy effected spectacular recovery, but when the dose was reduced, rheumatoid symptoms presented in the joints. Rheumatoid arthritis should be considered as a possible explanation for unexplained pleural effusion. Cytology must be used for diagnosis.