Morning Report – July 26 – Pleural Effusions and Tuberculosis

In morning report on July 26 we discussed an approach to pleural effusions in the context of a patient with pleural tuberculosis. See a summary of the main learning points below.

If a pleural effusion is noted on imaging, a thoracentesis should be performed if:

  • There is clinical suspicion for an exudative effusion
  • The cause of the pleural effusion is unclear
  • For suspected parapneumonic effusion that is >1cm on imaging in the left lateral decubitus position

Indications for a chest tube in the context of a pleural effusion include:

  • Drainage of frank pus on thoracentesis
  • Positive pleural fluid gram stain or culture
  • Pleural fluid pH <7.2 or glucose <3.4
  • Pleural effusion >50% of hemithorax or loculations on imaging

Calculation of Light’s Criteria provides a systematic, validated approach to evaluating pleural fluid studies.  It can save the clinician significant time and avoid unnecessary additional work-up. Remember however, that Light’s criteria is more sensitive than specific for exudative effusions. An exudate is less likely when all Light’s criteria are absent (LR- 0.04). An exudate cannot be ruled out if at least one of three of the following Light’s criteria are present:

  • Pleural fluid protein / serum protein >0.5
  • Pleural fluid LDH / serum LDH >0.6
  • Pleural fluid LDH > 2/3 serum LDH upper limit of normal

The diagnosis of an exudative pleural effusion is most likely if:

  • Pleural fluid cholesterol level > 55mg/dL (LR+ 7.1-250)
  • Pleural fluid LDH > 200 (LR+ 18)
  • Pleural fluid cholesterol / serum cholesterol > 0.3 (LR+ 14)

The differential diagnosis of a pleural effusion can be divided by exudative and transudative etiologies:

MalignancyHeart failure
PancreatitisHepatic hydrothorax
Eosinophilic granulomatosis with polyangiitis Hypoalbuminemia
Granulomatosis with polyangiitis Nephrotic syndrome
LupusPeritoneal dialysis
Lung abscessUrinothorax

A tuberculosis pleural effusion may have the following characteristics:

Cell count1000 and 6000 cells/mm. Lymphocyte predominant.
Protein>30 g/L
LDHCommonly elevated (>500)
pHLess than 7.4
Glucose 3.3 -5.6 (can be very low <2.8)

If suspicious for a tuberculosis pleural effusion, pleural fluid for AFB and mycobacterial culture can be sent; however, the sensitivity of these tests are low. If strongly suspicious, a pleural biopsy should be arranged. 

Treatment for active tuberculosis can be remembered by the 4-2-2-4 rule. 4 drugs for 2 months, then 2 drugs for 4 months. The typical regimen used is rifampin and isoniazid for 6 months total and pyrazinamide and ethambutol for the first 2 moths of treatment. Patients should be counselled on the side effects of TB drug therapy including rash, elevated liver enzymes, neuropathy (with pyrazinamide), and eye toxicity (with ethambutol). Steroids should be added to the treatment regimen in cases of TB meningitis or pericardial disease. A longer duration of therapy may be considered if persistent cavitary lesions, culture positivity at 2 months of treatment, or in cases involving the central nervous system or bone. 

Treatment for latent tuberculosis is typically isoniazid for 9 months.

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