Parapneumonic effusion

# Overview
A parapneumonic effusion is a type of pleural effusion that arises as a result of a pneumonia.  There are three types of parapneumonic effusions: uncomplicated effusions, complicated effusions, and empyema.  Uncomplicated effusions generally respond well to appropriate antibiotic treatment.  Complicated parapneumonic effusions respond more variably: many resolve with antibiotics but may benefit from early pleural fluid drainage.  Treatment of empyemas includes antibiotics, complete pleural fluid drainage, and reexpansion of the lung.
- A parapneumonic effusion is any pleural effusion that is associated with a bacterial pneumonia, lung abscess or bronchiectasis.  40% of all patients with bacterial pneumonia develop a pleural effusion, and the development of a pleural effusion increases morbidity and mortality as compared with an isolated pneumonia. .  In general parapneumonic effusions have 3 stages:
Exudative: Due to capillary leak, causing a sterile effusion that has a poly predominance, with normal glucose and pH.  It is seen within the 1st 72, and will usually resolve with antibiotics alone.
Fibrinopurulent: Occurs during days 3-7.  The pleural fluid becomes infected with bacteria, and the lactate dehydrogenase (LDH) rises, as the glucose and pH fall.  As the fibroblasts get busy, loculations develop which limits the extension of the empyema.
Organization: Further fibroblast activity produces a pleural peel leading to restrictive lung disease.  Without definitive treatment, the empyema can drain externally (empyema necessitatis) or into the lung to produce a broncho-pleural fistula.
- Exudative: Due to capillary leak, causing a sterile effusion that has a poly predominance, with normal glucose and pH.  It is seen within the 1st 72, and will usually resolve with antibiotics alone.
- Fibrinopurulent: Occurs during days 3-7.  The pleural fluid becomes infected with bacteria, and the lactate dehydrogenase (LDH) rises, as the glucose and pH fall.  As the fibroblasts get busy, loculations develop which limits the extension of the empyema.
- Organization: Further fibroblast activity produces a pleural peel leading to restrictive lung disease.  Without definitive treatment, the empyema can drain externally (empyema necessitatis) or into the lung to produce a broncho-pleural fistula.
- Approximately 20% of all parapneumonic effusions evolve into empyema.  Hippocrates described empyema thoracis around 400 BC and predicted drainage of the pleural cavity as the treatment of choice.  The term empyema refers to either the presence of gross pus in the pleural space, or a positive gram stain on pleural fluid analysis.  60% of empyemas evolve from a parapneumonic effusion, 20% after thoracic surgery and 20% from thoracic trauma, esophageal perforation, thoracentesis or subdiaphragmatic infection.  The majority of patients who develop empyema have underlying disease, most frequently alcoholism (especially in patients with anaerobic infections), malignancy and diabetes.

# Historical Perspective
-  was first discovered by , a , in  during/following .
- In ,  mutations were first identified in the pathogenesis of .
- In , the first  was developed by  to treat/diagnose .

# Classification
-  may be classified according to  into  subtypes/groups:
- Other variants of  include , , and .

# Pathophysiology
- The pathogenesis of  is characterized by , , and .
- The  gene/Mutation in  has been associated with the development of , involving the  pathway.
- On gross pathology, , , and  are characteristic findings of .
- On microscopic histopathological analysis, , , and  are characteristic findings of .

# Causes
-  may be caused by either , , or .
-  is caused by a mutation in the , , or  gene.
- There are no established causes for .

# Differentiating  from other Diseases
-  must be differentiated from other diseases that cause , , and , such as:

# Epidemiology and Demographics
- The prevalence of  is approximately  per 100,000 individuals worldwide.
- In , the incidence of  was estimated to be  cases per 100,000 individuals in .

## Age
- Patients of all age groups may develop .
-  is more commonly observed among patients aged  years old.
-  is more commonly observed among .

## Gender
-  affects men and women equally.
-  are more commonly affected with  than .
- The  to  ratio is approximately  to 1.

## Race
- There is no racial predilection for .
-  usually affects individuals of the  race.
-  individuals are less likely to develop .

# Risk Factors
- Common risk factors in the development of  are , , , and .

# Natural History, Complications and Prognosis
- The majority of patients with  remain asymptomatic for .
- Early clinical features include , , and .
- If left untreated,  of patients with  may progress to develop , , and .
- Common complications of  include , , and .
- Prognosis is generally , and the  of patients with  is approximately .

# Diagnosis

## Diagnostic Criteria
- The diagnosis of  is made when at least  of the following  diagnostic criteria are met:

## Symptoms
-  is usually asymptomatic.
- Symptoms of  may include the following:

## Physical Examination
- Patients with  usually appear .
- Physical examination may be remarkable for:

## Laboratory Findings
- There are no specific laboratory findings associated with .
- A    is diagnostic of .
- An  concentration of   is diagnostic of .
- Other laboratory findings consistent with the diagnosis of  include , , and .

## Imaging Findings
- There are no  findings associated with .
-  is the imaging modality of choice for .
- On ,  is characterized by , , and .
-  may demonstrate , , and .

## Other Diagnostic Studies
-  may also be diagnosed using .
- Findings on  include , , and .

# Treatment

## Medical Therapy
- There is no treatment for ; the mainstay of therapy is supportive care.
- The mainstay of therapy for  is  and .
-  acts by .
- Response to  can be monitored with  every .

## Surgery
- Surgery is the mainstay of therapy for .
-  in conjunction with  is the most common approach to the treatment of .
-  can only be performed for patients with  .

## Prevention
- There are no primary preventive measures available for .
- Effective measures for the primary prevention of  include , , and .
- Once diagnosed and successfully treated, patients with  are followed-up every . Follow-up testing includes , , and .