Back
ditki Logo
medical & biological sciences

Pleural Effusions for ABIM

Start your One-Week Free Trial
Already subscribed? Log in »
Pleural Effusions for the American Board of Internal Medicine Exam
Pleural effusion refers to the abnormal accumulation of fluid within the pleural space, between the visceral and parietal pleurae. It can result from a wide range of pathological processes affecting the lungs, heart, kidneys, or systemic inflammatory states. Diagnosing and managing pleural effusion is crucial, as it often reflects underlying serious diseases.
Classification of Pleural Effusions
Transudative vs. Exudative
The first step in evaluating a pleural effusion is to determine whether it is transudative or exudative using Light's criteria.
Transudate vs Exudate Pleural Effusion
  • Transudative Effusion: Results from imbalances in hydrostatic or oncotic pressures, often due to systemic conditions like heart failure or cirrhosis.
    • Common Causes:
    • Heart failure: Increased hydrostatic pressure in the pulmonary circulation.
    • Cirrhosis: Reduced oncotic pressure due to hypoalbuminemia.
    • Nephrotic syndrome: Significant loss of albumin in the urine, leading to decreased plasma oncotic pressure.
  • Exudative Effusion: Occurs due to increased permeability of pleural surfaces or impaired lymphatic drainage, often caused by local inflammatory processes or malignancy.
    • Common Causes:
    • Infections (parapneumonic effusion, tuberculosis): Increased pleural permeability due to inflammation.
    • Malignancy: Disruption of pleural lymphatic drainage, commonly seen in metastatic cancers.
    • Pulmonary embolism: Infarction or inflammation of the pleura.
Light’s Criteria
Exudative effusions meet at least one of the following criteria:
  • 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.
If none of these criteria are met, the effusion is considered transudative.
Clinical Presentation
The symptoms of pleural effusion often depend on the size of the effusion and the underlying cause.
  • Symptoms:
    • Dyspnea: Most common symptom, often worsening with larger effusions.
    • Pleuritic chest pain: Seen in inflammatory effusions (e.g., pneumonia, pulmonary embolism).
    • Cough: Non-productive and often due to irritation of the pleura.
  • Physical Exam Findings:
    • Dullness to percussion: Over areas of fluid accumulation.
    • Decreased or absent breath sounds: Due to fluid obstructing sound transmission.
    • Decreased tactile fremitus: Reduced vibration through the pleural fluid.
    • Egophony: Increased resonance of voice sounds, especially near the upper margin of the effusion.
Diagnostic Approach
Imaging
  • Chest X-ray (CXR): Initial imaging modality.
    • Findings: Blunting of the costophrenic angle, fluid layering on decubitus views. Large effusions may cause mediastinal shift.
    • Lateral decubitus X-ray: Useful in detecting small pleural effusions and determining if the fluid is free-flowing or loculated.
  • Ultrasound: More sensitive than CXR and allows for real-time guidance during thoracentesis.
  • CT Scan: Provides detailed imaging, particularly useful in detecting underlying malignancies or loculated effusions.
Thoracentesis
The key diagnostic procedure in pleural effusion is thoracentesis, where pleural fluid is sampled and analyzed.
  • Indications:
    • New effusions of unknown cause.
    • Large effusions causing respiratory compromise.
    • Concern for infection or malignancy.
  • Pleural Fluid Analysis:
    • Cell count and differential:
    • Neutrophil predominance suggests infection (e.g., parapneumonic effusion).
    • Lymphocyte predominance suggests tuberculosis or malignancy.
    • Protein and LDH levels: Differentiates between transudative and exudative effusions.
    • Glucose level: Low in infections, rheumatoid pleuritis, and malignancy.
    • pH: Low pH (<7.2) suggests infection or malignancy.
    • Cytology: For detecting malignant cells in exudative effusions.
    • Microbiologic cultures: Essential in suspected infections.
Special Tests
  • Amylase: Elevated in esophageal rupture or pancreatic disease.
  • Triglycerides: Elevated in chylothorax, typically >110 mg/dL.
  • Adenosine deaminase (ADA): Elevated in tuberculosis-related pleural effusion.
Common Causes and Their Features
Parapneumonic Effusion and Empyema
  • Parapneumonic Effusion: Effusion associated with bacterial pneumonia.
    • Uncomplicated parapneumonic effusions are sterile and respond to antibiotics.
    • Empyema: Refers to pus within the pleural space, often requiring drainage in addition to antibiotics.
Malignant Pleural Effusion
Malignancies are a common cause of exudative effusions, especially lung cancer, breast cancer, and lymphoma.
  • Key Features:
    • Recurrent, large effusions.
    • High pleural fluid protein and LDH.
    • Positive cytology for malignant cells.
Tuberculous Effusion
  • Predominantly lymphocytic.
  • High protein and elevated ADA.
  • Acid-fast bacilli may be present, but culture often needed for confirmation.
Heart Failure (Transudative Effusion)
  • Bilateral effusions are common, and treatment focuses on addressing the underlying heart failure.
  • Thoracentesis typically reveals low protein and low LDH levels.
Treatment
The management of pleural effusion is based on its underlying cause.
Therapeutic Thoracentesis
  • Indications:
    • Large effusions causing dyspnea.
    • Effusions refractory to medical management (e.g., heart failure despite diuresis).
  • Risks: Includes pneumothorax, re-expansion pulmonary edema, and infection.
Treatment by Cause
  • Heart failure: Diuretics to reduce fluid overload.
  • Parapneumonic effusion/empyema: Antibiotics with or without chest tube drainage.
  • Malignant effusion: Therapeutic thoracentesis may provide symptomatic relief. In recurrent cases, pleurodesis or indwelling pleural catheters can be considered.
  • Chylothorax: Conservative management includes a low-fat diet with medium-chain triglycerides or total parenteral nutrition. Surgery may be necessary in some cases.
Key Points
  • Pleural effusions are classified as transudative or exudative, with exudates diagnosed using Light's criteria.
  • Common causes of transudative effusions include heart failure and cirrhosis, while exudative effusions are often due to infections, malignancies, or pulmonary embolism.
  • The diagnostic cornerstone is thoracentesis, which provides crucial information about the cause of the effusion through pleural fluid analysis.
  • Management is tailored to the underlying etiology, with therapeutic thoracentesis indicated for symptomatic relief in large effusions.
  • Complicated effusions like empyema require both antibiotics and drainage. Malignant effusions often necessitate repeated thoracentesis or pleurodesis.

Related Tutorials