Attending Physician HCA Florida Orange Park Hospital
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Introduction: Pleural effusions are traditionally classified as transudative or exudative using Light’s criteria. However, chronic loop diuretic therapy can concentrate pleural fluid, falsely lowering pleural protein and LDH, leading to misclassification and delaying diagnosis of underlying conditions. We present a case of gouty pleuritis, demonstrating this diagnostic challenge, and discuss alternative approaches.
Description: A 67-year-old male with a history of chronic heart failure presented with progressive dyspnea, chest pain, and bilateral pleural effusions. Over the past year, he had multiple hospitalizations for similar symptoms, with thoracentesis repeatedly yielding pleural fluid classified as transudative by Light’s criteria. This led to escalating loop diuretic therapy for presumed CHF exacerbations. During the current admission, thoracentesis drained 1200 mL of pleural fluid. Analysis again indicated a transudative profile (protein 2.5 g/dL, LDH 91 IU/L; serum protein 5.8 g/dL, serum LDH 186 IU/L). Despite continued diuretic therapy, the patient’s symptoms persisted, and effusions recurred. The lack of therapeutic response prompted further analysis of the pleural fluid. Microscopy revealed monosodium urate crystals, establishing the diagnosis of gouty pleuritis. Despite lacking typical systemic gout symptoms, crystal identification confirmed the diagnosis. The patient was initiated on colchicine and corticosteroids while diuretics were tapered, resulting in clinical improvement. He was discharged on allopurinol for long-term management.
Discussion: Gouty pleuritis is a rare cause of exudative pleural effusion. Chronic loop diuretic therapy can distort pleural fluid biochemistry, falsely producing transudative profiles due to hemoconcentration. While Light’s criteria remain highly sensitive, its specificity is limited to 83%. This limitation highlights the need for additional tools like serum-pleural albumin gradient, fluid cholesterol, and pleural NT-proBNP. Persistent effusions with transudative profiles but unexplained symptoms warrant further workup including crystal analysis and potential pleural biopsy. Integrating clinical, biochemical, and procedural findings is essential to diagnose atypical and unresponsive effusions, enabling targeted therapy.
