Asad, D.

Abstract Introduction Rheumatoid arthritis (RA) is a systemic autoimmune rheumatic disease (SARD) primarily associated with articular involvement, but is often associated with lung involvement, sometimes preceding articular symptoms. Common pulmonary manifestations include interstitial lung disease (ILD), airway, and serosal involvement. RA-related pleural disease can mimic empyema due to the pleural fluid's green, pus-like appearance, exudative nature, low pH, markedly low glucose, and elevated lactate dehydrogenase (LDH) levels. Empyema sometimes yields negative cultures which can accentuate the diagnostic challenge in such cases. This report presents a patient with RA-related pleural lung disease who was referred to our hospital with trapped lung presumed to be secondary to empyema in the setting of pleural-based pulmonary abscess. Case Report A 66-year-old female with a 22-year history of RA presented with recurrent right-sided pleural effusions and progressive dyspnea over three years. Her initial presentation in 2022 involved a large right-sided pleural effusion, suspected to result from a ruptured pleural-based pulmonary abscess that led to empyema and subsequently a trapped lung. Pleural fluid analysis showed elevated LDH (1364 U/L), low glucose (45 mg/dL), high cholesterol (121 mg/dL), and low triglycerides (79 mg/dL). Due to refractory exudative effusion and a comprehensive negative infectious evaluation (bacterial, mycobacterial, and fungal cultures), RA-related pleural disease was suspected. The patient underwent video-assisted thoracoscopic surgery (VATS), which revealed pleural-based rheumatoid nodules and pleural thickening. (figure1) Lung and pleural biopsies confirmed RA-associated fibrinous pleuritis, RA-associated follicular bronchiolitis, and usual interstitial pneumonitis. Given the complexity of the infection, a thoracotomy with decortication and pleurectomy was planned and conducted in stages. Immunosuppressive regimen was switched from leflunomide to rituximab. Discussion This case underscores the diagnostic complexity in distinguishing RA-associated pleural effusion from empyema. Features such as pleural nodularity resembling a pulmonary abscess, unilateral exudative effusion, grossly purulent pleural fluid, low pH and glucose, and elevated LDH levels led to an initial misdiagnosis of empyema. Characteristic pleural fluid, along with persistent negative cultures and absence of sepsis pointed towards RA-related pleural disease. VATS and biopsy were instrumental in establishing the final diagnosis through characteristic histopathological findings of RA-associated pleural, parenchymal and airway involvement. Conclusion For RA patients with pleural effusion suggestive of empyema, especially in the context of negative cultures and no signs of sepsis, RA-related pleural disease should be a consideration. Early recognition and timely immunosuppressive therapy escalation can prevent complications such as trapped lungs and reduce the necessity for extensive surgical interventions. Figure1: