Pseudochylothorax

Pseudochylothorax (chyliform effusion or cholesterol effusion) is a long standing pleural effusion that looks milky or turbid but has high cholesterol content and low triglyceride, unlike true chylothorax. It forms in a pleural space that is thickened and fibrotic, with poor drainage of fluid.

The effusion has usually been present for 5 years or more. Causes are tuberculous pleurisy (the commonest worldwide), rheumatoid pleurisy, empyema, previous artificial pneumothorax or plombage, haemothorax, and chronic pleural disease with trapped lung. Other causes include paragonimiasis, echinococcosis, and rare reports in malignancy, lupus and yellow nail syndrome.

Pathophysiology. A thick fibrous pleural peel prevents absorption, and cell breakdown (red cells, leucocytes and cell membranes) releases cholesterol into the fluid, where it precipitates as crystals or stays in lipoprotein complexes. Fluid is mainly cholesterol, not chylomicrons.

Often mild symptoms or none, with a chronic, usually unilateral effusion with dull percussion and reduced breath sounds. Others have dyspnoea, cough, chest discomfort or pleural thickening, and signs of the cause (previous tuberculosis, rheumatoid arthritis, nodules). Chyle related malnutrition and lymphopenia are absent.

Fever, pain and purulent fluid need urgent assessment, since empyema can complicate chronic effusions.

• Pleural fluid appearance: milky, turbid, or greenish yellow ("gold paint" appearance with a shimmer) that does not clear on centrifugation or on adding ether.
• Pleural fluid biochemistry: cholesterol above 5.18 mmol/L (200 mg/dL) with a pleural fluid to serum cholesterol ratio above 1.0, and triglyceride usually below 1.24 mmol/L (110 mg/dL). Fluid is an exudate by usual criteria.
• Microscopy under polarised light: cholesterol crystals (rhomboid, notched plates) are found in about 25 to 50%. Chylomicrons are absent on lipoprotein electrophoresis, which separates it from chylothorax (triglyceride above 1.24 mmol/L with chylomicrons).
• Pleural fluid cell count, culture for bacteria, tuberculosis (smear, culture, nucleic acid test), adenosine deaminase, cytology, and rheumatoid factor and anti-cyclic citrullinated peptide.
• Imaging: chest radiograph and CT showing pleural thickening or calcification and a trapped lung, with an effusion that persists unchanged.
• Pleural biopsy if the cause is unclear.
• Look for the cause: tuberculosis history, rheumatoid disease, occupational and asbestos exposure.

Differential diagnosis.

• True chylothorax (thoracic duct injury, lymphoma, lymphangioleiomyomatosis)
• Empyema
• Malignant effusion
• Tuberculous effusion without pseudochylous change
• Rheumatoid effusion
• Hepatic hydrothorax or cardiac effusion

• Treat the underlying cause: antituberculosis treatment for active tuberculosis (rifampicin 10 mg/kg, maximum 600 mg, isoniazid 5 mg/kg, maximum 300 mg, pyrazinamide 25 mg/kg and ethambutol 15 mg/kg daily for 2 months, then rifampicin and isoniazid for 4 months, with pyridoxine 10 to 25 mg daily), and rheumatoid disease control with the rheumatologist.
• Asymptomatic: observation with periodic imaging.
• Symptomatic: therapeutic thoracentesis (up to 1.5 L at a time) for dyspnoea, though fluid re-accumulates, and a tunnelled pleural catheter for recurrent symptomatic effusion in those unfit for surgery.
• Decortication by video assisted or open surgery to release the trapped lung and remove the peel, for patients with significant symptoms, impaired lung function and expandable lung on imaging, who can tolerate surgery. This is the definitive treatment.
• Treat infection (empyema) with antibiotics and drainage.
• No role for dietary fat modification, octreotide or a thoracic duct procedure, since lymph is not involved.

Complications and prognosis. The effusion is benign and stable, but may cause restrictive lung disease, infection or chronic pleural thickening. Prognosis depends on the cause.

Monitoring. Symptom review and chest imaging every 6 to 12 months, and spirometry yearly in those with thickening.

Referral and escalation. Refer to a respiratory physician for diagnosis and a thoracic surgeon for decortication in symptomatic patients.