A 52-year-old man with a 10-year history of rheumatoid arthritis presents with progressive dyspnea and pleuritic chest pain. Chest X-ray reveals a right-sided pleural effusion. Thoracentesis is performed and pleural fluid analysis shows: protein 4.2 g/dL (serum protein 6.8 g/dL), LDH 180 IU/L (serum LDH 250 IU/L), glucose 15 mg/dL, pH 7.0, cholesterol crystals present. What is the most appropriate next step in management?