Diffuse Pleural Thickening

Diffuse pleural thickening is fibrous thickening of the visceral pleura, usually with adherence to the parietal pleura. The most frequent occupational cause is asbestos exposure, often after a benign pleural effusion.

Definition. Radiographically it is thickening over a quarter or more of the chest wall, often with costophrenic angle obliteration. CT definitions use continuous thickening over several centimetres in extent, with thickness of 3 mm or more (thresholds vary).

Causes. Asbestos, previous empyema or haemothorax, tuberculous pleurisy, drug reactions, connective tissue disease, previous thoracic surgery or radiotherapy.

Epidemiology. It follows benign asbestos effusion in a substantial proportion of cases and appears 10 to 40 years after first exposure.

Course. Many patients stabilise, while some have progressive restriction and disabling dyspnoea.

Pathophysiology.

Fibre induced inflammation spreads from the parietal to the visceral pleura. Fibrin deposition, organisation and collagen laying result in fusion of the pleural layers.

Encasement restricts lung expansion and chest wall movement, reducing lung volumes. Underlying parenchymal fibrosis may coexist.

• Exertional dyspnoea, often disproportionate to parenchymal disease.
• Chest wall pain, often dull and persistent.
• Reduced chest expansion and dullness over affected areas.
• Often a history of prior effusion.

Red flags.

• Constant or worsening chest pain, weight loss, sweats.
• Rapid growth, nodularity, circumferential thickening, mediastinal involvement or thickness over 1 cm.
• Blood stained effusion.

• Exposure history and prior pleural events.
• Chest radiograph and CT with contrast for extent, thickness and exclusion of nodularity or mass.
• Lung function: restrictive pattern with reduced FVC and TLC; DLCO often preserved when corrected for volume.
• Pleural biopsy when features suggest malignancy or imaging is ambiguous.

Differential diagnosis. Mesothelioma, metastatic pleural disease, empyema sequelae, fibrothorax, tuberculous pleurisy, rheumatoid pleural disease, drug induced pleural thickening.

• Exposure cessation, smoking cessation, vaccination, pulmonary rehabilitation.
• Analgesia: paracetamol 1 g orally every 6 hours as needed, maximum 4 g in 24 hours (3 g if under 50 kg, chronic alcohol excess or liver disease), for the shortest period that controls pain. Monitor liver function with prolonged use. Reduce dose in hepatic impairment; extend dosing interval when eGFR is under 30. Specialist pain review for persistent pain.
• Decortication is occasionally considered in selected patients with severe disability, preserved underlying lung function and good performance status. Morbidity is high and benefit is uncertain.
• Long term oxygen when resting PaO2 is under 7.3 kPa, or 7.3 to 8 kPa with polycythaemia or cor pulmonale.

Monitoring. Spirometry and imaging at 6 to 12 months initially, earlier if symptoms or imaging change.

Referral and escalation. Respiratory physician; urgent thoracic referral when malignancy is suspected; occupational notification and compensation where required.