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Pleural Effusions for USMLE Step 3

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Pleural Effusions for the USMLE Step 3 Exam
Pleural effusion is a common clinical problem requiring an integrated approach that includes diagnosis, management, and understanding of potential complications.
Classification of Pleural Effusions
Transudative vs. Exudative Effusions
The first step in evaluating a pleural effusion is determining whether it is transudative or exudative using Light’s criteria. This classification guides further diagnostic and treatment decisions.
  • Transudative Effusion: Results from systemic factors affecting hydrostatic or oncotic pressures.
    • Common causes:
    • Heart failure: The most common cause, leading to elevated pulmonary capillary pressure.
    • Cirrhosis: Reduced oncotic pressure from hypoalbuminemia.
    • Nephrotic syndrome: Hypoalbuminemia due to massive protein loss in urine.
Transudate vs Exudate Pleural Effusion
  • Exudative Effusion: Results from local inflammation, malignancy, or infection, leading to increased capillary permeability or impaired lymphatic drainage.
    • Common causes:
    • Malignancy: Commonly metastatic, obstructing lymphatic flow.
    • Parapneumonic effusion: Occurs due to bacterial pneumonia.
    • Pulmonary embolism: Causes inflammation and infarction of lung tissue.
    • Tuberculosis: A chronic infection causing lymphocyte-predominant exudative effusion.
Light’s Criteria
Exudative effusions meet at least one of the following:
  • Pleural fluid protein/serum protein ratio > 0.5.
  • Pleural fluid LDH/serum LDH ratio > 0.6.
  • Pleural fluid LDH > two-thirds of the upper limit of normal for serum LDH.
Clinical Presentation
The clinical manifestations vary depending on the cause and size of the effusion.
  • Symptoms:
    • Dyspnea: Most common, especially in large effusions.
    • Pleuritic chest pain: Sharp pain worsened by inspiration, especially in inflammatory effusions (e.g., pneumonia, pulmonary embolism).
    • Cough: Non-productive in most cases.
  • Physical Exam Findings:
    • Dullness to percussion: Suggests fluid accumulation.
    • Decreased breath sounds: Over the area of the effusion.
    • Decreased tactile fremitus: Due to fluid impeding sound transmission.
    • Egophony: Enhanced resonance of voice sounds near the upper border of the effusion.
Diagnostic Approach
Imaging
  • Chest X-ray (CXR): Initial diagnostic tool.
    • Findings: Blunting of the costophrenic angles. A lateral decubitus view can differentiate free-flowing from loculated effusions.
  • Ultrasound: More sensitive than CXR, guides thoracentesis.
  • CT Scan: Provides detailed imaging, especially useful for identifying underlying causes such as malignancies or loculated effusions.
Thoracentesis
Thoracentesis is essential for both diagnosis and treatment. It involves sampling pleural fluid for analysis.
  • Pleural Fluid Analysis:
    • Protein and LDH: To classify as transudative or exudative.
    • Cell count and differential:
    • Neutrophils suggest bacterial infection (parapneumonic effusion).
    • Lymphocytes suggest tuberculosis or malignancy.
    • Glucose: Low in infections, malignancy, or rheumatoid pleuritis.
    • pH: Low (<7.2) in complicated parapneumonic effusion or malignancy.
    • Cytology: Detects malignant cells.
    • Microbiological cultures: Essential if infection is suspected.
Treatment
Management depends on the underlying cause, severity of symptoms, and whether the effusion is recurrent.
Therapeutic Thoracentesis
  • Indications:
    • Symptomatic relief for large effusions causing respiratory distress.
    • Diagnostic purposes when the cause is unknown.
Cause-Specific Management
  • Heart failure: Diuresis to manage fluid overload.
  • Empyema: Requires drainage via chest tube and antibiotics.
  • Malignant effusions: Repeated thoracentesis, pleurodesis, or indwelling pleural catheters.
  • Parapneumonic effusion: Antibiotics, and if necessary, chest tube drainage for empyema.
Complications
  • Pneumothorax: A risk of thoracentesis.
  • Re-expansion pulmonary edema: Occurs if large volumes of fluid are rapidly drained.
Key Points
  • Pleural effusions are classified as transudative or exudative using Light’s criteria, with exudates caused by local processes like infection, malignancy, or pulmonary embolism.
  • Common symptoms include dyspnea and pleuritic chest pain, with physical exam findings such as dullness to percussion and decreased breath sounds.
  • Diagnostic tools include imaging (CXR, ultrasound) and thoracentesis, with fluid analysis guiding further management.
  • Treatment includes therapeutic thoracentesis for symptomatic relief, along with managing the underlying cause (e.g., diuretics for heart failure, antibiotics for empyema).

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