A 3-year-old girl is brought to the emergency department due to difficulty breathing. The patient first developed a fever and cough 5 days ago, and they have progressively worsened. Her appetite is poor, she has lost weight, and her urine output has decreased. The patient's family moved from Thailand 2 years ago, but she has not traveled anywhere since. Immunizations are up to date. Temperature is 39.4 C (102.9 F), blood pressure is 86/60 mm Hg, pulse is 150/min, and respirations are 36/min. Pulse oximetry is 90% on room air. Examination shows a tired-appearing girl with subcostal retractions and diminished breath sounds over the right chest. Complete blood count shows a leukocyte count of 17,000/mm3 (65% neutrophils, 15% band forms, 15% lymphocytes), hemoglobin of 11.5 g/dL, and a platelet count of 470,000/mm3. Chest x-ray reveals a right lower lung opacity and pleural effusion. A pigtail catheter is placed, and fluid analysis is as follows:
| Triglycerides | 5 mg/dL (normal: <50) |
| pH | 7.1 |
| Glucose | 30 mg/dL |
| Protein | 4.0 g/dL |
| Lactate dehydrogenase | 1,100 U/L |
| Leukocytes | 60,000/mm3 |
| Neutrophils | 90% |
| Lymphocytes | 9% |
| Monocytes | 1% |
Which of the following is the most likely diagnosis in this patient?
Parameter | Uncomplicated | Complicated | Empyema |
Etiology | Inflammatory fluid from pneumonia → pleural space | Bacterial invasion into pleural fluid | Bacterial colonization → purulent fluid |
Pleural fluid | pH = 7.20, ↓/normal glucose, LDH ratio >0.6 | pH <7.20, ↓ glucose, LDH ratio >0.6 | pH <7.20, ↓ glucose, LDH ratio >0.6 |
Pleural fluid | Negative | Positive or negative | Positive |
LDH = lactate dehydrogenase. | |||
This patient with fever, shortness of breath, and evidence of pneumonia (ie, right lower lung opacity) and pleural effusion on chest x-ray has a parapneumonic effusion. Parapneumonic effusions are exudative effusions that can develop as a complication of pneumonia due to inflammation and infection from an adjacent lung infection, resulting in accumulation of fluid in the pleural space.
As the inflammation and infection spread through the pleural space, parapneumonic effusions can present as a spectrum of disease:
Patients initially develop an uncomplicated (ie, simple) parapneumonic effusion as the inflammatory fluid enters the pleural space. Because the fluid is sterile, the pH is >7.2, glucose is normal to slightly decreased, and lactate dehydrogenase (LDH) is normal (Choice F).
Patients can progress to a complicated parapneumonic effusion when bacteria or other microorganisms begin to invade the pleural space. Therefore, in these patients, signs of infection are seen on fluid analysis (eg, pH <7.2, low glucose); however, Gram stain and culture are usually negative.
A complicated parapneumonic effusion becomes an empyema when the fluid is grossly purulent. In these patients, fluid analysis shows frank signs of bacterial infection with a pH <7.2 (due to acid production by bacteria), low glucose (<40-60 mg/dL due to bacterial/neutrophil utilization), neutrophil-predominant leukocyte counts >50,000/mm3, and significantly elevated LDH (>1,000 IU/L). Gram stain and culture are positive.
Management of empyema includes broad-spectrum intravenous antibiotics and chest tube drainage.
(Choice A) A chylothorax occurs when there is disruption of the thoracic duct, leading to accumulation of chyle (often secondary to trauma or malignancy) in the pleural space. Fluid analysis of chylothorax typically shows elevated triglyceride levels and a lymphocyte, not a neutrophil, predominance.
(Choice C) Heart failure causes a transudative effusion; this patient has an exudative effusion (eg, pleural fluid LDH > 2/3 upper limit of normal serum LDH). In addition, with effusion due to heart failure, pleural fluid analysis typically shows low protein levels (<3.0 g/dL).
(Choice D) Malignant effusion is an exudative fluid containing malignant cells in the pleural space. Fluid analysis can have an elevated LDH and low glucose; however, there is typically a low leukocyte count (<5,000/mm3). In addition, this patient's 5-day history of fever and cough is more consistent with pneumonia complicated by effusion.
(Choice E) Mycobacterium tuberculosis effusions typically present with chronic, not acute, symptoms. Although pleural fluid may show low glucose and pH, leukocyte counts are low with a lymphocytic predominance.
Educational objective:
An empyema occurs after bacterial pneumonia leads to bacterial colonization of the pleural fluid. Pleural fluid shows a pH <7.2, a low glucose level, neutrophil-predominant leukocyte counts >50,000/mm3, and a significantly elevated lactate dehydrogenase level.