Pleural Effusions
Case 1 Answers
A 60 year-old man with a history of multiple myocardial infarctions presents to his primary care provider complaining of increasing dyspnea on exertion. He can no longer push his lawn mower around his yard and has difficulty climbing stairs. He also notes orthopnea and difficulty getting his shoes on because his feet and ankles are swollen. His provider performs a chest x-ray and notes the presence of cardiomegaly and a moderate-sized right pleural effusion. After lateral decubitus films confirm that the effusion is free-flowing, the provider performs a diagnostic thoracentesis. The pleural fluid studies show: LDH 100 (serum value 250, upper limit of normal for serum 180), total protein 2.5 (serum value 7.5). There are 200 white cells and only trace RBCs. The white blood cell differential includes 70% macrophages, 15% lymphocytes and 5% polymorphonuclear leukocytes. The gram’s stain is negative.
How do you interpret the results of the pleural fluid studies? Is this effusion a transudate or an exudate?
Light’s criteria states that a pleural effusion is exudative if it means one of three criteria: LDH > 2/3 the upper limit of normal for serum, pleural fluid: serum protein ratio > 0.5 and pleural fluid: serum LDH ratio > 0.6. In this case, the LDH is less than 2/3 the upper limit of normal for serum, the protein ratio is 0.33 and the LDH ratio is 0.4. Therefore, this effusion should be classified as a transudate.
You should be aware that Light’s criteria will misclassify transudates as exudates in 15-30% of cases. One of the leading examples of this is when a patient is on chronic diuretic therapy. The fluid will appear as an exudate on lab testing when, in fact, it is due to a transudative process such as heart failure.
What is the leading item on the differential diagnosis for this patient’s pleural effusion? What other items would you consider on the differential for this type of effusion?
The leading items on the differential diagnosis for transudative effusions include heart failure, hepatic hydrothorax, nephrotic syndrome, hypoalbuminemia and atelectasis with a trapped lung. Less common causes of transudative effusions include peritoneal dialysis, urinothorax (urine in the pleural space due to urinary tract obstruction) and a duro-pleural fistula (a communication between the subarachnoid space and the pleural space allowing accumulation of CSF in the pleural space). Given the history described in the case of a man with prior myocardial infarctions and other symptoms suggestive of cardiomyopathy (orthopnea, lower extremity edema), you would consider heart failure to be the leading item on the differential diagnosis.
What additional diagnostic studies should you order?
Your initial steps should be to identify the etiology of the effusion. Therefore you would consider ordering a B-type natriuretic peptide and echocardiogram to rule out cardiomyopathy. If those studies are unrevealing, you would order a urine protein-to-creatinine ratio, chemistry panel and albumin level to investigate the possibility of nephrotic syndrome and a liver panel and INR to check for evidence of chronic liver disease.
How should this pleural effusion be managed?
In general with transudative processes, the main priority in managing the effusion is treating the underlying problem. You can do a large volume thoracentesis for relief of symptoms but unless the underlying problem is resolved, the effusion is likely to reaccumulate and cause recurrent symptoms. Therefore, if the patient has heart failure, you would get that person on an appropriate medication regimen for their heart failure. Similarly, you would need to pursue treatment for the cause of a nephrotic syndrome. With the less common causes such as urinothorax or duro-pleural fistula, the same principle applies. You need to remove the predisposing condition (eg. the urinary tract obstruction or the defect in the dural lining)
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