Benign Asbestos Pleural Effusion

Benign asbestos pleural effusion is an exudative pleural effusion caused by asbestos exposure, with no malignancy found on assessment and follow up. It is the earliest pleural manifestation of asbestos exposure, and the most frequent in the first 20 years after exposure.

The latency is usually 10 to 20 years, much shorter than for mesothelioma (30 to 40 years), and the effusion is more likely at higher cumulative exposure. About a third to a half of people have no symptoms. The diagnosis can only be made by excluding other causes, and malignant mesothelioma should be reconsidered if the effusion persists or recurs.

Pathophysiology. Inhaled fibres migrate to the visceral and parietal pleura, causing mesothelial injury and a low grade inflammatory response with increased capillary permeability. Fluid accumulates as an exudate, and visceral pleural fibrosis follows in many.

Pleuritic chest pain, dyspnoea and fever in about a third, with the rest found incidentally on a radiograph. The effusion is usually small to moderate and unilateral, and may be bilateral or recur on the opposite side. Examination shows dullness and reduced breath sounds. Pleural plaques are often present on the pleura.

Weight loss, constant chest pain, a large effusion or a rapidly recurrent effusion needs prompt workup for mesothelioma.

• Documented exposure to asbestos, with an appropriate latency, and no other cause of effusion.
• Pleural fluid: exudate, often blood stained, with lymphocytes or eosinophils and no malignant cells on cytology (repeat cytology when the first is negative).
• Chest radiograph and CT with contrast: effusion, pleural plaques, and sometimes parenchymal bands. Absence of nodular or circumferential pleural thickening, mediastinal pleural involvement or a pleural mass.
• Thoracoscopy with pleural biopsy when the effusion persists beyond 3 months, recurs, or CT shows suspicious features, since cytology alone misses most mesotheliomas.
• Exclude tuberculosis (adenosine deaminase, culture), pulmonary embolism, heart failure, infection and other malignancy.
• Follow up for at least 3 years with no evidence of malignancy is needed to confirm the diagnosis.

Differential diagnosis.

• Malignant mesothelioma
• Lung cancer or metastatic pleural disease
• Tuberculous pleurisy
• Parapneumonic effusion
• Pulmonary embolism
• Rheumatoid or lupus pleurisy

• Observation: most effusions resolve spontaneously in 3 to 4 months without treatment, and some last up to a year.
• Therapeutic thoracentesis (up to 1.5 L at a time) for dyspnoea, with fluid analysed at each tap.
• Analgesia for pleuritic pain: paracetamol 1 g every 6 hours (maximum 4 g daily) and ibuprofen 400 mg every 8 hours with food.
• No proven role for corticosteroid, and it does not prevent fibrosis.
• Recurrent effusion: repeat imaging, thoracoscopy and biopsy to exclude mesothelioma, then pleurodesis if symptoms continue.
• Reduce further exposure and advise smoking cessation (smoking multiplies the lung cancer risk with asbestos). Arrange vaccination against influenza, pneumococcus and COVID-19.
• Record the exposure for occupational disease reporting and compensation where laws allow, and give the patient a copy of the diagnosis.

Complications and prognosis. Recurrence occurs in about 30%. Diffuse pleural thickening follows in 20 to 50% and can cause restrictive lung disease. Asbestos related lung cancer and mesothelioma remain risks for life.

Monitoring. Radiograph at 4 to 6 weeks and 3 months, CT at 3 and 6 months, then every 6 to 12 months for 3 years. Spirometry with DLCO at baseline and when symptoms change.

Referral and escalation. Refer to a respiratory physician or pleural service for thoracoscopy, and to occupational medicine.