Unilateral Pleural Effusion

Unilateral Pleural Effusion

This week past we discussed a case of a man presenting with a 3 week history of worsening dyspnea. On chest x-ray he had a large right-sided pleural effusion.

There were several teaching points for the case:

1.       Differential diagnosis of shortness of breath: We discussed that although there is a long differential diagnosis for shortness of breath, operationally we are thinking about the top 3-4 most likely and serious causes in our heads when seeing a patient. For shortness of breath this could include:

a.       Heart failure

b.      Pneumonia

c.       COPD

d.      Acute coronary syndrome  

In this case, we know there is a large right-sided pleural effusion, so it shapes our differential diagnosis further.

Differential diagnosis of a pleural effusion includes:

Transudate	Exudate
Heart Failure	Infection (bacterial parapneumonic, mycobacterial, fungal, viral, parasitic)
Nephrotic syndrome	Malignancy
Liver cirrhosis	PE
Constrictive pericarditis	Collagen vascular disease (RA, SLE, GPA, EGPA)
	GI (pancreatitis, esophageal rupture)
	Hemothorax
	Chylothorax
	Other (post-CABG, post-radiation, uremia, drug-induced, sarcoidosis

As you can see, the differential diagnosis is broken down by transudate and exudate. But how do we tell? We do a diagnostic thoracentesis and analyze the fluid using Light’s criteria.

-          Guidelines suggest all effusions of >1cm in the decubitus view without a known diagnosis should be investigated with a thoracentesis.

-          Guidelines suggest diagnostic thoracentesis does not need to be performed for bilateral effusions in a clinic setting strongly suggestive of a transudate (i.e. heart failure)

-          Guidelines suggest that for the initial diagnostic thoracentesis the following be sent:

o   Cytology, protein, LDH, pH, Gram stain, culture and sensitivity

-          Don’t forget to measure the serum LDH and total protein in order to be able to calculate Light’s Criteria

Light’s Criteria
Pleural fluid total protein/serum total protein	>0.5
Pleural fluid LDH/serum LDH	>0.6
Pleural fluid LDH	>2/3 upper limit of normal
Note: any one of the above positive = exudative. Highly sensitive (98%) but specificity 83% (will misidentify some transudative effusions as exudative

Due to Light’s Criteria proneness to misidentify some transudative effusions as exudative (especially if there has been diuresis for heart failure which can concentrate the fluid), one can use Extended Light’s Criteria to help clarify.

Extended Light’s Criteria = total protein gradient

                                             = serum total protein minus pleural fluid total protein

The fluid is transudative if the total protein gradient is > 31 g/L.

In this case the pleural effusion was exudative on diagnostic thoracentesis.

When working up the unilateral pleural effusion further the following diagnostic algorithm can be used:
From the BTS guidelines on page 11 at: https://www.brit-thoracic.org.uk/document-library/clinical-information/pleural-disease/pleural-disease-guidelines-2010/pleural-disease-guideline/

Further reading

Hooper C et al; BTS pleural guidelines group. Investigations of a unilateral pleural effusion in adults: British Thoracic Society Plerual Disease Guideline 2010. Torax. 2010;65 Suppl 2.

McGrath EE, Anderson PB. Diagnosis of pleural effusion: a systematic approach. Am J Crit Care. 2011;20(2):119-27.

Craig, J., Gold, W. L., & Leis, J. A. (2013). A 44-year-old man with a parapneumonic effusion.Canadian Medical Association Journal, 185(3), 232-234.