A 54-year-old man complains of cough, shortness of breath, and pleuritic left-sided chest pain. Examination and CXR are compatible with a large left-sided pleural effusion. At thoracentesis, the pleural fluid is straw colored and slightly turbid, with a WBC count of 53,000/mL, RBC count of 1200/mL, glucose of 42 mg/100 mL, total protein of 5 g/100 mL, LDH of 418 IU/L, and pH of 7.2. Simultaneous serum total protein is 8 g/100 mL (normal, 68 g/100 mL), and serum LDH level is 497 IU/L (normal, 52149 IU/L). Gram stain is positive for gram-negative rods.
Which of the following is the most likely cause of his pleural effusion?
- parapneumonic effusion
- congestive heart failure
- malignant effusion
- trauma
- nephrotic syndrome
Answer(s): A
Explanation:
Although the differential diagnosis of a pleural effusion is large, the diagnostic possibilities may be narrowed by classifying the fluid as transudative or exudative. Exudates are characterized by a pleural fluid- to-serum protein ratio greater than 0.5, pleural fluid LDH greater than 200 IU/L, or pleural fluid- toserum LDH ratio greater than 0.6. Other common findings in exudative effusions are a WBC count greater than 1000/mL, glucose less than 60 mg/100 mL, and grossly hemorrhagic fluid. Causes of transudative effusions include CHF, nephrotic syndrome, cirrhosis with ascites, and myxedema. Causes of exudative fluid include parapneumonic effusion, neoplasm, pulmonary infarction, tuberculosis, and fungal infection among others. Alow pleural fluid pH (<7.30) limits the differential diagnosis to empyema, carcinoma, collagen vascular disease, esophageal rupture, tuberculosis, or hemothorax. Uncomplicated parapneumonic effusions have WBC counts under 40,000/mL, normal glucose levels, and a pH under 7.30; a positive Gram stain or culture constitutes a complicated parapneumonic effusion. These tend to loculate and form adhesions if not immediately and thoroughly drained by chest tube placement.