Pleural Thickening

Fibrous thickening of the visceral pleura, often fused with the parietal pleura, which restricts lung expansion. Diffuse pleural thickening is a continuous sheet of thickening that extends over more than a quarter of the chest wall, usually with blunting of the costophrenic angle. Focal thickening is a localised patch.

• Causes: asbestos exposure (benign asbestos pleural effusion leaves diffuse thickening in about 10 to 50% of cases, with a latency of 10 to 40 years), resolved empyema, haemothorax or tuberculous pleurisy, rheumatoid disease and other connective tissue diseases, drugs (nitrofurantoin, amiodarone, methysergide, bromocriptine, cabergoline), uraemia, radiotherapy, previous surgery or trauma, and mesothelioma, which must always be excluded.
• Mechanism: organisation of fibrin after pleural inflammation or injury, with collagen deposition and fusion of pleural layers. A rind that traps the lung (trapped lung) prevents re-expansion.
• Burden: dyspnoea and restriction are proportional to extent; the vital capacity may fall by 20 to 50% in bilateral diffuse disease.

Progressive exertional breathlessness, chest tightness, and dull pleuritic or constant chest wall pain; often asymptomatic when mild.

• Signs: reduced chest expansion, dull percussion note, quiet breath sounds over the thickened area, finger clubbing is not a feature of benign thickening and points to other disease.
• Occupational history of asbestos (shipyard, insulation, building, brake lining, mining) or past tuberculosis, empyema, chest trauma or relevant drugs.
• Features that raise the concern of malignancy: constant severe pain, weight loss, circumferential thickening, nodularity, involvement of the mediastinal pleura, thickness of more than 1 cm, and a growing mass.
• Differential diagnosis: malignant mesothelioma, pleural metastases, lymphoma, fibrous tumour of the pleura, pleural effusion with loculation, chronic empyema, rounded atelectasis, subpleural fat, interstitial lung disease, chest wall disease.
• Complications: restrictive ventilatory defect, respiratory failure with hypercapnia in extensive bilateral disease, chronic pain, recurrent infection, trapped lung, and malignant transformation in asbestos-exposed patients.

Chest X-ray: smooth or irregular pleural shadow, loss of costophrenic angle, reduced lung volume, calcification in old disease.

• CT chest with contrast: measures thickness, extent, nodularity, mediastinal involvement, calcification, associated parenchymal bands and asbestosis; features of malignancy are circumferential thickening, nodularity and mediastinal pleura involvement.
• PET-CT when malignancy is possible; benign thickening is only mildly avid, but infection and talc pleurodesis cause false positives.
• Spirometry and lung volumes: restrictive defect (FEV1/FVC 0.70 or more, with reduced total lung capacity and forced vital capacity), reduced transfer factor; resting and exertional oximetry.
• Biopsy (image-guided or thoracoscopic) for suspected malignancy, with histology and immunohistochemistry (calretinin, WT1, BAP1 loss).
• Tuberculosis testing (sputum or pleural fluid Xpert MTB/RIF), autoimmune serology (rheumatoid factor, antinuclear antibody), and a drug history review.

Remove the cause: stop implicated drugs (nitrofurantoin, amiodarone, cabergoline, bromocriptine, methysergide) in consultation with the prescriber, and treat active rheumatoid disease or uraemia.

• Supportive care: pulmonary rehabilitation (8 weeks, twice weekly), smoking cessation, annual influenza vaccine, one dose of a 20-valent pneumococcal conjugate vaccine.
• Analgesia for chest wall pain:
  • Paracetamol 1 g four times daily (500 mg four times daily if under 50 kg).
  • Ibuprofen 400 mg three times daily with food (avoid in renal impairment, peptic ulcer or anticoagulation).
  • Gabapentin 300 mg at night, increased by 300 mg every 3 days to 900 mg three times daily if neuropathic features, with dose reduction in renal impairment; or amitriptyline 10 to 25 mg at night.
  • Paravertebral or intercostal block, or morphine 5 mg orally every 4 hours as needed, for severe pain.
• Long-term oxygen for at least 15 hours daily when PaO2 is 7.3 kPa or less at rest.
• Corticosteroid after tuberculous or inflammatory effusion: prednisolone 0.5 mg/kg daily (usual adult dose 30 to 40 mg) for 4 to 6 weeks, then tapered over 4 weeks; evidence of benefit is limited.
• Decortication (open or thoracoscopic pleurectomy with release of the visceral peel):
  • Indications: symptomatic restriction with a trapped lung, a mature peel, a forced vital capacity of 60% predicted or less or progressive loss, and good underlying lung expansion on imaging.
  • Timing: usually 3 to 6 months after the inflammatory event, and after at least 2 months of effective antituberculosis treatment where relevant.
  • Results: breathlessness and lung function improve in about 60 to 80%; complications include air leak (up to 20%), bleeding and infection, with operative mortality of about 1 to 3%.
  • Avoid in extensive asbestos related diffuse thickening with diffuse lung disease, in whom benefit is small.
• Malignant disease: oncology referral for mesothelioma staging and systemic therapy; chemotherapy regimens are specialist-led.
• Special groups: children (usually after empyema or tuberculosis; physiotherapy and decortication for persistent trapped lung); pregnancy (avoid ibuprofen and gabapentin where possible, use paracetamol; defer decortication until after delivery unless life-threatening); elderly and frail (conservative care and oxygen); renal impairment (adjust gabapentin, avoid NSAIDs); occupational disease (document exposure, notify and help with compensation claims).
• Red flags: constant severe or worsening pain, weight loss, haemoptysis, new nodular thickening, rapid fall in lung function, new effusion, fever with a new collection.
• Follow-up: clinical review and spirometry yearly for stable benign disease; repeat CT at 6 to 12 months if the thickening changes or the diagnosis is uncertain; urgent review for any red flag; lifelong follow-up of asbestos-exposed patients for lung cancer and mesothelioma.