Hi, Based on the history you have shared, the history makes it likely to be included in autoimmune or Rheumatological disorders that s why particularly lupus or RA was worked up but even in the absence other rheumatological disorders or systemic vasculitis may not be ruled out. I suggest taking extended anti nuclear antigens profile to broaden the index of suspicion and to rule out other possibilities. Though at this moment, the immediate test should be getting a chest CT or HRCT as well as chemical analysis and cultures of the pleural fluid which you are experiencing. It needs to be established that whether any infective cause is suspected as many infections can cause lungs and joint abnormalities concomitantly. Also uric acid levels and ferritin levels to rule out crystal arthropathies, may be needed. A Rheumatologist and infective diseases specialist opinion must be sought. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Saddiq Ulabidin, General & Family Physician