Pleural effusion

Question 1

Pleural effusion causes
Exudative
Transudative

Answer 1

=>Exudative:
Parapneumonic/Empyema
Malignancy
Pulmonary infarct
Rheumatoid
Autoimmune diseases
Pancreatitis
Drug induced- Methotrexate/Amiodarone

=>Transudate:
Cardiac failure
Liver cirrhosis
Nephrotic syndrome
Hypoalbuminemia
Peritoneal dialysis
Hypothyroidism

Question 2

Biochemical distinction

Answer 2

–> Light’s Criteria:
Exudate if ≥1 present:
1). Pleural fluid protein / serum protein ratio > 0.5
2). Pleural fluid LDH / serum LDH ratio > 0.6
3). Pleural fluid LDH > ⅔ of upper limit of lab’s normal serum LDH

4). The fluid LDH is over 200 IU/L

Question 3

Pseudoexudates
Limitations of Light’s criteria

Answer 3

=>Some effusions that are truly transudative can be misclassified as exudative by Light’s criteria eg- heart failure pts on diuretics.
->Serum-Effusion albumin gradient greater than 1.2 g/dL can help correctly classify it as a transudate.

Question 4

1. Appearance (1.5 marks)

Answer 4

• Clear, straw-coloured → More likely transudate (can still be exudate).
• Blood-stained → Malignancy, pulmonary infarction, Trauma
• Yellow/green → Rheumatoid disease.
• Pus → Empyema.
• Turbid → Inflammatory exudate.

Question 5

pH

Answer 5

• pH < 7.30 → Exudate more likely; DDx: malignant effusion, complicated parapneumonic effusion/empyema, rheumatoid, SLE, TB.
• pH < 7.20 → Strong predictor of empyema and best marker of complicated parapneumonic effusion.
• Normal pleural pH ≈ 7.60.
• Low pH may also occur in oesophageal rupture.

Question 6

Other Biochemistry

Answer 6

• Amylase ↑ → Pancreatitis-related effusion, oesophageal rupture.
• Cholesterol ↑ → Chylothorax.

Question 7

Glucose (1.5 marks)

Answer 7

• Low (<3.3 mmol/L)
  or
• pleural/serum glucose ratio <0.5 → Supports exudate.
• DDx: malignant effusion, complicated parapneumonic effusion/empyema, rheumatoid pleural disease (very low glucose common in rheumatoid), TB, pneumonia.

Question 8

Microscopy (1.5 marks)

Answer 8

• Cell count: rarely diagnostic; >50,000/ml → usually complicated parapneumonic effusion/empyema.
• Lymphocytosis (85–95%) → Rheumatoid, TB, malignancy.
• Neutrophilia → Parapneumonic effusion, pulmonary embolism.
• Eosinophilia (>10%) → Blood/air in pleural space, drugs (dantrolene, bromocriptine, nitrofurantoin), asbestos exposure, autoimmune (e.g. Churg–Strauss).

Question 9

Cytology (0.5 marks)
* Malignant cells
* Culture/Sensitivity

Answer 9

->Cytology
* Malignant cells: sensitivity ~60% overall; varies by malignancy type.

->Culture/Sensitivity
* Positive culture → Empyema.

Question 10

Limitations of Light’s criteria

Answer 10

=>Lack of specificity-
-Very sensitive for classifying exudates, but low specificity
“pseudoexudate” commonly occurs in cases of heart failure or liver cirrhosis.

=>Do not point to a specific cause- eg Exudate-Inflammation/ Infection/ Malignancy

=>Misclassification requires further testing eg- albumin gradient

=>Further investigations req. for diagnosing malignancy vs infection vs inflammation eg- Cytology, thoracoscopy for malignancy,

Question 11

Table limitations and how to overcome

Answer 11

Question 12

Causes of Empyema

Answer 12

• Bacterial pneumonia
• Lung abcess
• TB
• Oesophageal rupture
• Trauma
• Chest surgery