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Lymphocytic exudative pleural effusion — ABIM Board MCQ

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HardPulmonary/Critical CareLymphocytic exudative pleural effusionABIM Board

A 64-year-old man with heart failure with preserved ejection fraction treated with furosemide presents with progressive dyspnea and a 10-lb unintentional weight loss. He has no fever, productive cough, orthopnea, or peripheral edema. Chest CT shows a unilateral right pleural effusion and mediastinal lymphadenopathy. Thoracentesis yields clear fluid containing 78% lymphocytes. Pleural fluid protein is 4.2 g/dL, serum protein is 6.5 g/dL, pleural fluid LDH is 260 U/L, and serum LDH is 320 U/L. Serum albumin is 3.8 g/dL and pleural fluid albumin is 2.7 g/dL. Pleural fluid glucose is 82 mg/dL and pH is 7.39. Which of the following is the most accurate interpretation?

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Correct answer: B — This is an exudative effusion requiring evaluation for malignancy or granulomatous disease.

The correct answer is B. The effusion satisfies two Light criteria: the pleural-to-serum protein ratio is 0.65 and the LDH ratio is 0.81, establishing an exudate. Although diuretics can cause cardiac effusions to be misclassified, the unilateral effusion, absence of congestion, albumin gradient of only 1.1 g/dL, weight loss, lymphocyte predominance, and mediastinal lymphadenopathy require evaluation for malignancy—particularly lymphoma or lung cancer—and granulomatous disease such as tuberculosis. Heart-failure effusions are usually transudative and commonly bilateral. Chylothorax cannot be diagnosed from protein or lymphocytes; pleural triglycerides or chylomicrons are required. Empyema is generally neutrophil predominant and is supported by pus, positive microbiology, low glucose, or pleural pH below 7.2, none of which is present.

Reference: Shen-Wagner J, Gamble C, MacGilvray P. Pleural Effusion: Diagnostic Approach in Adults. American Family Physician. 2023;108(5):464-475. https://pubmed.ncbi.nlm.nih.gov/24938565/