From Dyspnea to Diagnosis: Neutrophilic Pleural Effusion With Elevated Adenosine Deaminase As the First Clue to New-Onset Rheumatoid Arthritis

Rheumatoid arthritis (RA) rarely announces itself with a pleural effusion, yet when it does, the biochemical and pleural fluid profile often leads to a suspicion of infectious etiology at first. We describe a 44‑year‑old woman whose initial manifestation of seropositive RA was a large, unilateral, neutrophil‑rich, adenosine‑deaminase (ADA)-positive pleural effusion. The case draws attention to a diagnostic pitfall: elevated pleural fluid ADA-although classically associated with tuberculous pleuritis-can also occur in rheumatoid pleuritis, highlighting that ADA levels must be interpreted in the full clinical context and should not, by themselves, prompt initiation of anti-tuberculous therapy. By combining serial fluid analysis with targeted serology, we avoided unnecessary antimycobacterial therapy, initiated immunosuppression early, and achieved complete radiographic resolution. The report emphasizes the need to identify extra-articular conditions (especially pleural involvement) as potential early indicators of RA development.