What is the difference between reactive pleural effusion in pyelonephritis (Pelonephritis, inflammation of the kidney) and parapneumonic pleural effusion (associated with pneumonia)?

From the Guidelines

Reactive pleural effusion in pyelonephritis and parapneumonic pleural effusion are distinct entities with different underlying causes and management approaches, with the former typically resolving with antibiotic treatment of the underlying pyelonephritis and the latter often requiring drainage procedures along with antibiotics, as recommended by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America 1. The management of these conditions depends on various factors, including the size of the effusion, the presence of respiratory compromise, and the results of pleural fluid analysis.

• Small, uncomplicated parapneumonic effusions can be treated with antibiotic therapy alone, as stated in the guidelines 1.
• Moderate to large parapneumonic effusions, or those associated with respiratory distress or documented purulent effusions, should be drained, with the choice of drainage procedure depending on local expertise 1.
• The use of chest thoracostomy tube drainage with fibrinolytic agents or video-assisted thoracoscopic surgery (VATS) has been shown to be effective in the treatment of parapneumonic effusions, with decreased morbidity rates compared to chest tube drainage alone 1.
• The antibiotic treatment of parapneumonic effusion or empyema is similar to that for community-acquired pneumonia (CAP) without effusion, with the goal of covering the most common pathogens, including Streptococcus pneumoniae and Staphylococcus aureus 1.
• The distinction between reactive pleural effusion in pyelonephritis and parapneumonic pleural effusion is made through clinical context, imaging findings, and pleural fluid analysis, with the latter typically being exudative with potentially positive cultures in complicated cases 1.
• The British Thoracic Society guidelines for the management of pleural infection also provide recommendations for the diagnosis and treatment of parapneumonic effusions, including the use of chest tube drainage and the measurement of pleural fluid pH and lactate dehydrogenase (LDH) levels 1.

From the Research

Comparison of Reactive Pleural Effusion in Pyelonephritis and Parapneumonic Pleural Effusion

• Pyelonephritis is a rare cause of pleural effusion, with only a few reported cases in the literature 2, 3.
• The exact pathogenesis of transudative pleural effusion in pyelonephritis is unknown, but it may resolve spontaneously when the infection is adequately controlled 2.
• Parapneumonic pleural effusion, on the other hand, is a common complication of pneumonia, and its treatment depends on the underlying etiology of the effusion 4, 5.
• The diagnosis of pleural effusion involves determining its etiology, which can be done through thoracocentesis, laboratory testing, and cytological analysis 4, 5.
• The treatment of pleural effusion depends on its etiology, with transudative effusions usually being managed by treating the underlying medical disorder, and exudative effusions requiring specific treatment based on their cause 4, 5.

Key Differences

• Pyelonephritis-associated pleural effusion is typically transudative, while parapneumonic pleural effusion can be either transudative or exudative 2, 4.
• The treatment of pyelonephritis-associated pleural effusion involves antibiotics targeted toward the causative organism, while parapneumonic pleural effusion may require additional treatments such as pleurodesis or thoracoscopy 6, 5.
• The prognosis of pyelonephritis-associated pleural effusion is generally good, with resolution of the effusion after treatment of the underlying infection, while parapneumonic pleural effusion can have a more variable prognosis depending on the underlying cause 2, 5.

Diagnostic Approach

• Thoracocentesis should be performed for new and unexplained pleural effusions to determine the etiology of the effusion 4.
• Laboratory testing, including chemical and microbiological studies, as well as cytological analysis, can help distinguish between transudative and exudative pleural effusions 4, 5.
• Imaging studies, such as chest radiographs, can also be useful in evaluating the extent of the pleural effusion and guiding treatment 2, 5.