Pleural Effusions
Case 5 Answers
A 70 year-old man with COPD and a known adenocarcinoma of the left lung presents with increasing dyspnea and is found to have a large left pleural effusion. Lateral decubitus x-rays reveal that the fluid is free-flowing and a thoracentesis is performed.
What studies should you order on the pleural fluid?
In addition to ordering an LDH, protein, cell count and differential and gram’s stain on the fluid, you should also order pleural fluid cytology. The presence of a known adenocarcinoma of the lung makes it possible that this effusion could be related to his malignancy.
The pleural fluid analysis reveals an LDH of 750 (serum value 130, upper limit of normal for serum 180) and a total protein of 5.0 (serum value 7.0). The grams’ stain is negative. The WBC differential includes 10% polymorphonuclear cells, 30% lymphocytes and 40% monocytes.
How would you interpret the results of these studies?
The LDH is well above the upper-limit of normal for serum and the pleural fluid: serum ratio for LDH is > 0.6 while the pleural fluid: serum ratio for protein is > 0.5. This effusion should, therefore, be classified as an exudative process.
Pleural fluid cytology is performed and comes back negative? If you are still suspicious of malignancy, how should you proceed from here?
Before proceeding with more invasive diagnostic steps such as pleural biopsies you should perform a second thoracentesis and resend the fluid for cytology. The sensitivity of the initial cytology varies between 50 and 70% but there is evidence that repeat thoracentesis will increase the diagnostic yield when the first thoracentesis is negative. There is little utility, however, to proceeding with a third thoracentesis if the second cytology specimen is negative.
How much fluid should you send to the lab for cytology?
The old saw with pleural fluid cytology has always been “more is better.” It turns out this is not the case. Multiple “optimal” collection volumes have been suggested in the literature but never proven to be effective. “More fluid” is actually a real pain for the laboratory as the fluid has to be spun down and examined in 50 cc aliquots and one can imagine how time consuming this would be if you sent down 2 liters of fluid. While the smallest reported volume with a positive cytologic analysis in the literature was 2-3 cc of fluid, it is probably appropriate to send around 50 to 100 cc of fluid as research has shown that fluid volumes in this range have comparable sensitivity and negative predictive value for the diagnosis of malignancy when compared to higher volumes (400-1500 cc).
The patient is subsequently found to have pleural involvement of his lung cancer. How does this change his lung cancer management?
The presence of a malignant pleural effusion means the patient how has T4 disease. If he has no distant metastases, he would be classified as Stage IIIb whereas if he has distant metastases he would have a Stage IV tumor. Designating him as a IIIb or IV cancer has a large impact on his management. Whereas he might have been a candidate for lung resection and curative surgery with a lower stage tumor, the presence of Stage IIIb or IV disease limits his options greatly. Survival at 5 years is non-existent and patients are limited largely to palliative chemotherapy with no chance of cure.
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