A 43-year-old woman with congestive heart failure, rheumatoid arthritis, and chronic hepatitis C with early liver cirrhosis complains of difficulty breathing. Her temperature is 37.8 C (100 F), blood pressure is 126/72 mm Hg, pulse is 97/min, and respirations are 28/min. Pulse oximetry is 94% on room air. Physical examination shows dullness to percussion at the right lung base. Chest x-ray shows moderate-size right pleural effusion and cannot rule out underlying infiltrates. Thoracentesis shows pleural fluid with glucose of 28 mg/dL and lactate dehydrogenase of 252 U/L. Which of the following explains the low pleural fluid glucose concentration?

Question

A 43-year-old woman with congestive heart failure, rheumatoid arthritis, and chronic hepatitis C with early liver cirrhosis complains of difficulty breathing.  Her temperature is 37.8 C (100 F), blood pressure is 126/72 mm Hg, pulse is 97/min, and respirations are 28/min.  Pulse oximetry is 94% on room air.  Physical examination shows dullness to percussion at the right lung base.  Chest x-ray shows moderate-size right pleural effusion and cannot rule out underlying infiltrates.  Thoracentesis shows pleural fluid with glucose of 28 mg/dL and lactate dehydrogenase of 252 U/L.  Which of the following explains the low pleural fluid glucose concentration?

Quizplus · Accepted Answer

Explanation: This patient's presentation is concerning for likely pneumonia with parapneumonic effusion. Pleural effusions are divided into transudates and exudates. Transudates are due to an imbalance between hydrostatic and oncotic pressures that increases fluid movement across the capillaries into the visceral pleura and pleural space. Transudative fluid requires no further intervention except for treatment directed at the underlying disease. Exudative effusions are due to pleural and lung inflammation resulting in increased capillary and pleural membrane permeability. Exudative effusions require more extensive diagnostic investigation. The Light criteria define an exudate as having at least one of the following: Pleural fluid protein/serum protein ratio >0.5 Pleural fluid lactate dehydrogenase (LDH)/serum LDH ratio >0.6 Pleural fluid LDH >2/3 of the upper limit of normal for serum LDH This patient's pleural fluid LDH of 252 U/L is >2/3 of the upper limit of normal for serum LDH (2/3*90 = 60 U/L). The low pleural glucose also indicates an exudative pleural effusion. Pleural fluid glucose <60 mg/dL is usually due to rheumatoid pleurisy, complicated parapneumonic effusion or empyema, malignant effusion, tuberculous pleurisy, lupus pleuritis, or esophageal rupture. (Pleural glucose <30 mg/dL in particular suggests an empyema or rheumatic effusion.) Glucose concentration in empyema is decreased due to the high metabolic activity of leukocytes (and/or bacteria) in the fluid. (Choice A) Elevated pleural amylase concentrations are found in pleural effusions due to esophageal rupture or pancreatitis. However, high pleural amylase is not responsible for the low glucose found in these effusions. (Choice C) Increased capillary hydrostatic pressure is the mechanism responsible for transudative pleural effusions. However, this patient has an exudative effusion due to the low pleural glucose and high pleural LDH. (Choice D) Increased permeability of the right hemidiaphragm leads to right-sided pleural effusions in cirrhosis, also known as a hepatic hydrothorax. Effusions due to cirrhosis are typically transudates. (Choice E) Inflammatory conditions cause pleural effusions by increasing the pleural membrane and capillary permeability. This mechanism establishes the effusion but does not directly decrease pleural glucose concentration. Educational objective: Empyemas are exudative effusions with a low glucose concentration due to the high metabolic activity of leukocytes and bacteria within the pleural fluid. References: Useful tests on the pleural fluid in the management of patients with pleural effusions. (http://www.ncbi.nlm.nih.gov/pubmed/10407695) Diagnosis of pleural effusion: a systematic approach. (http://www.ncbi.nlm.nih.gov/pubmed/21362716)

A 43-Year-Old Woman with Congestive Heart Failure, Rheumatoid Arthritis, and Chronic