Exudative Pleural Effusions: Pathogenesis and Lab Findings
Authors: Sravya Kakumanu
Reviewers: Ben Campbell *Tara Lohmann * MD at time of publication
Chylothorax
Damage to thoracic duct
Leakage of lymphatic fluid into pleural space
Pulmonary embolism
Clot obstructs blood flow to lung
Infarcted lung tissue
Lung infection (e.g. pneumonia, tuberculosis)
Lung infection signals inflammatory response
Systemic Lupus Rheumatoid Erythematosus (SLE) arthritis (RA)
Autoimmune antibodies localize to pleura
Pleural tumors (primary or secondary from metastatic cancer)
Inflammatory cells migrate to affected site and release cytokines
↑ Permeability of pleural capillaries ↑ Fluid leakage across capillaries
Exudative Pleural Effusion
Cancer invades lymphatic drainage of pleural space (PS)
↓ Drainage of pleural fluid (PF) from pleural space
If infectious etiology
Tumor invasion = inflammatory response
See Pleural Effusions: X-ray Findings and Physical Exam Findings of Lung Diseases slides
↑ Permeable pleural capillaries allow ↑ protein and cell leakage into pleural space
If pleural tumour: Release of cancer cells into pleural space
Cancer cells on PF cytology 60-75% sensitive for malignancy
If rheumatoid arthritis:
Release of auto-antibodies into pleural space
Auto-antibodies initiate inflammatory response in pleural space
↑ Inflammatory cells have ↑ glucose metabolism in pleural space
Sterile PF with mildly elevated white blood cells, normal pH, normal glucose ↑ Inflammation at infection site damages endothelium of pleura
Pleural Infection Stage I: Simple Parapneumonic Effusion
↑ Inflammatory cells and bacterial cells in pleural space have ↑ glucose metabolism in pleural space
Bacterial invasion from infected parenchymaà pleural space
< 40mg/dL glucose in PF ↑ Activation of coagulation cascade and ↓ fibrinolytic activity ↑ Deposition of fibrin clots/membranes within pleural space creates loculated effusion (compartmentalized effusion due to septations in pleural space) ↑ Production of lactate dehydrogenase (LDH) (LDH maintains NAD+ supply during ↑ glucose metabolism) ↑ CO2 production pH of PF < 7.20 ↑ CO2 production pH of PF < 7.20 < 3.3mmol/L glucose in PF Pleural Infection Stage II: Complicated Parapneumonic Effusion Loculated effusion OR bacteria present OR ↓ pH + ↓ glucose ↑ Fibroblast proliferation creates thickened pleura ↑ Pus in pleural space Pleural Infection Stage III/Empyema: Loculated effusion and pus in pleural space PF/serum protein ratio ≥ 0.5 PF/serum LDH ratio ≥ 0.6 Light’s Criteria: Any criteria can be met to be an exudative pleural effusion PF LDH ≥ 2/3 upper limit of normal Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published August 9, 2022 on www.thecalgaryguide.com