Asbestosis

Asbestosis is a type of pneumoconiosis caused by the inhalation of asbestos fibers and occurs primarily as a result of occupational exposure. After a long latency period, this condition manifests with nonspecific symptoms, e.g., coughing and dyspnea, which are caused by fibrotic changes in the lungs. The diagnosis is established based on a history of occupational exposure (such as working with textiles, cement, ship-building, insulation) and characteristic changes on chest x-ray (reticular opacities and pleural plaques). Currently, there is no curative treatment for asbestosis. Management consists of measures that provide symptomatic relief like oxygen therapy, prompt antimicrobial treatment of respiratory infections, cessation of exposure, and immunization against influenza and pneumococcal pneumonia. Long-term exposure to asbestos can lead to complications like fibrosis, respiratory failure, and malignancy (especially bronchogenic carcinoma, and mesothelioma). Pleural effusion may be the first sign of a malignant mesothelioma. A combination of chemotherapy, surgery, and/or radiation therapy is used to manage malignant mesothelioma. The prognosis of patients with malignant mesothelioma is poor, with the mean survival time being ∼ 1 year.

• Type of pneumoconiosis caused by inhalation of asbestos fibers
• Risk factors
  • Occupations involving the manufacture or demolition of ships, plumbing, roofing, insulation, heat-resistant clothing, and brake lining
  • Smoking

References: ^[1][2]

• Inhalation of airborne asbestos fibers into alveoli ; → inflammation and fibrosis of pleural parenchyma → risk of carcinogenic effects

A high cumulative dose of asbestos is associated with a higher incidence of asbestosis. In smokers, the disease progresses more rapidly because mucociliary clearance is impaired.

References: ^[1]

• Long latent period
• Exertional dyspnea
• Dry cough → productive cough
• Digital clubbing
• Bilateral fine, basal end-inspiratory rales

References: ^[1][3]

• Imaging
  • Chest x-ray
    • Diffuse bilateral infiltrates predominantly in the lower lobes
    • Interstitial fibrosis
    • Supradiaphragmatic and pleural reticulonodular opacities/plaques
      • Initially, mostly linear infiltrates are seen.
      • Eventually, calcified (ivory white) or noncalcified plaques appear.
    • Rounded atelectasis
    • In some cases, pleural effusion
    • Radiographs are classified by the extent of radiographic abnormalities according to the WHO International Labor Office classification. ^[4]
  • HR-CT
    • Parenchymal fibrosis (especially basilar, peribronchiolar, and septal)
    • Pleural plaques and pleural reticulonodular opacities
    • Supradiaphragmatic opacities/plaques
    • Subpleural linear opacities
• Pulmonary function test: restrictive ventilatory defects (decreased pulmonary compliance)
  • Early: decreased DL_CO
  • Later: reduced vital capacity and total lung capacity
  • Normal to increased ratio of FEV₁ to FVC
• Bronchoalveolar lavage : microscopic asbestos bodies
  • Occasionally found in alveolar sputum sample, stain positive with Prussian blue
  • Appear as ferruginous bodies: dumbbell-shaped and golden-brown fusiform rods, surrounded by an iron protein coat
• Biopsy
  • Microscopic asbestos bodies
  • Fibrosis

Although asbestos is commonly found in roofing materials, it predominantly affects the lower lobes of the lungs.

References:^[1][3][5]

• Idiopathic pulmonary fibrosis
• Interstitial pneumonitis
• Chronic empyema
• Combined pulmonary fibrosis and emphysema
• Other pneumoconioses (see “Overview of pneumoconioses”)

The differential diagnoses listed here are not exhaustive.

• No curative treatment exists; management includes the following measures.
  • Cessation of exposure
  • Oxygen therapy
  • Immunization against influenza and pneumococcal pneumonia
  • Antimicrobial treatment of respiratory infections
• Palliative care in the case of advanced disease

References: ^[3]

Mesothelioma ^[6]

• Definition: malignant tumor that develops from mesothelial cells
• Epidemiology
  • Sex: ♂ > ♀ (3:1)
  • Age range: ∼ 40–70 years
• Etiology
  • Secondary to asbestos exposure
  • Alcohol, smoking, and diet do not increase the incidence of mesothelioma.
• Localization
  • Pleural mesothelioma (most common)
  • Peritoneal mesothelioma (rarely)
  • Pericardial mesothelioma (very rarely)
• Clinical findings
  • Dyspnea and nonpleuritic chest pain (most common)
  • Fever, sweats, weight loss, fatigue
  • Features of pleural effusion: dull percussion; absent or reduced breath sounds on affected side
• Diagnosis ^[7]
  • Pleurocentesis; : bloody (exudative) pleural effusion
  • Imaging (chest x-ray and CT)
    • Multiple nodular pleural lesions (pleural thickening)
    • Ipsilateral hemothorax
    • Reduced size of ipsilateral lung fields
    • Obliteration of the diaphragm
  • Laparoscopy, thoracoscopy, and pleuroscopy with stained biopsy: ; reveal mesothelioma cells and psammoma bodies
    • Risk of implantation metastasis. ^[8]
    • It is important to differentiate mesothelioma from adenocarcinoma.
      • Immunohistochemistry: Mesothelioma often stains positive for; mesothelin, serum mesothelin-related protein (SMRP), calretinin, cytokeratin 5/6 (negative in most adenocarcinomas), and vimentin. ^[9]
      • Electron microscopy shows tumor cells with long and slender microvilli (in contrast to the short and stubby microvilli found in adenocarcinomas), tonofilaments, and desmosomes.
• Treatment ^[10]
  • Radiation, with or without chemotherapy (cisplatin and pemetrexed)
  • Surgery (pleurectomy or pneumonectomy) may be indicated in cases with severely impaired pulmonary function
• Prognosis: poor, with a mean survival time of ∼ 1 year

Other

• Malignancy
  • Bronchogenic carcinoma (most common malignant complication of asbestosis; smoking has a synergistic effect with asbestos that further increases the risk of lung cancer)
  • Laryngeal cancer
  • Also of the esophagus, biliary system, kidneys, and ovaries
• Pulmonary hypertension
• Cor pulmonale
• Right-sided heart failure
• Progressive respiratory failure
• Caplan syndrome

The most common malignancy associated with asbestosis is bronchogenic carcinoma, not mesothelioma.

We list the most important complications. The selection is not exhaustive.