Asbestosis

Asbestosis

Asbestosis is a slow, progressive diffuse interstitial fibrosis as a consequence of dose-related inhalation exposure to fibers of asbestos in miners, millers, workers of asbestos textiles, and insulators.

Clinically, the lung involvement is characterized by bilateral diffuse interstitial fibrosis, more pronounced in the lower lobes, and pleural thickening, leading to shortness of breath and dry cough.

Asbestos exposure can lead to the spectrum of pulmonary pathology, including pulmonary fibrosis; asbestos-related pleural plaque disease (ARPD), both focal and diffuse; and malignancies (lung cancer or mesothelioma).

Epidemiology & Demographics

• •5 to 10 new cases per 100,000 persons per yr in the U.S.
• •Prolonged interval (20-30 yr) between exposures to inhaled fibers and clinical manifestations of disease.
• •Most common in workers over age 40 yr involved in the primary extraction of asbestos from rock deposits and in those involved in the fabrication and installation of products containing asbestos (e.g., naval shipyards in World War II; installation of floor tiles, ceiling tiles, acoustic ceiling coverings, wall insulation, and pipe coverings in public buildings).
• •Smokers and heavy drinkers have the greatest risk of developing this disease.

Physical Findings & Clinical Presentation

• •Insidious onset of shortness of breath and dry cough with exertion is usually the first sign of asbestosis.
• •Dyspnea becomes more severe as the disease advances; with time, progressively less exertion is tolerated.
• •Cough is frequent and usually paroxysmal, dry, and nonproductive. Hemoptysis is rare but reported. Scant mucoid sputum may accompany the cough in the later stages of the disease.
• •Fine end-respiratory crackles (rales, crepitations) are heard more predominantly in the lung bases.
• •Digital clubbing, edema, and jugular venous distention may be present.
• •Advanced cases may have signs of right heart failure.

Etiology/Pathogenesis

Inhalation of asbestos fibers. The pathogenesis of pulmonary interstitial inflammation and fibrosis is related to immune mechanisms.

Asbestosis is known to be associated with positive serum antinuclear antibody (ANA) and rheumatoid factor (RF).

An important role of interleukin-1beta (IL-1beta) in the pathogenesis of asbestosis and its systemic autoimmune manifestations has been reported.

Differential Diagnosis

• •Silicosis
• •Siderosis, other pneumonoconioses
• •Interstitial lung disease
• •Lung cancer

Workup

Documentation of exposure history

Pulmonary function testing

Diagnostic imaging studies

Laboratory Tests

• •Generally not helpful
• •Arterial blood gases: May show hypoxemia and/or hypercarbia in advanced stages

Pulmonary function testing:

• •Most often shows decreased vital capacity (VC), decreased total lung capacity (TLC), and decreased carbon monoxide gas transfer (DLco)
• •FEV1 might be reduced in concomitant smokers

Bronchoscopy with bronchoalveolar lavage:

• •Clinical utility of bronchoscopy is limited. It can be helpful in ruling out infection, or hypersensitivity pneumonitis. Asbestos bodies are found in sputum and BAL fluid of asbestos workers but utility in diagnosis of asbestos-related lung disease and progression is limited.

Imaging Studies

• •Chest x-ray: Imaging findings associated with asbestos exposure may vary from benign pleural disease (including discrete plaques, pleural calcification, diffuse pleural thickening with blunting of costophrenic angles, and thickening of the interlobar fissure) to asbestosis (diffuse interstitial pulmonary fibrosis).
• •CT scan of chest: Typical findings of asbestosis on high-resolution CT of the chest include increased interstitial markings found mainly at the bases. As the disease progresses, honeycombing is noted.

Treatment

Nonpharmacologic Treatment

• •Smoking cessation
• •Exercise program to maximize available lung function. Pulmonary rehabilitation can be considered in advanced cases for improved cardiopulmonary capacity
• •Supplemental oxygen on a PRN basis
• •Removal of patient from further asbestos fiber exposure
• •Prompt identification and treatment of respiratory infections
• •Pneumococcal vaccination and annual influenza vaccination

Pharmacologic Therapy

• •There is no specific pharmacologic treatment for asbestosis
• •Some new data are coming out targeting IL-1beta therapy on the progression of lung fibrosis that suggest a new perspective for the treatment of systemic autoimmune features of asbestosis and, possibly, of lung involvement. 

Disposition

• •Death is usually from respiratory failure from cor pulmonale.
• •Survival in patients after development of mesothelioma is 4 to 6 yr.
• •Benign asbestos pleural effusions (BAPEs) are usually small and unilateral and occur yr before the onset of interstitial disease.
• •Diffuse pleural thickening and asbestosis are associated with increased risks of malignant peritoneal mesothelioma beyond the risk calculated to be associated with the degree of asbestos exposure. 
• •None of the benign pleural diseases or ARPD was associated with an increased risk of malignant pleural mesothelioma.
• •Asbestos increases the risk for development of lung cancer regardless of smoking status. The joint effect of asbestos and smoking is additive and depends in part on the presence of asbestosis. Patients with a history of tobacco smoking who have diffuse parenchymal disease secondary to asbestos, have a 40-fold increased risk of lung cancer compared to never-smokers. Asbestos workers who stop smoking experience a dramatic decline in lung cancer risk, which approaches that of nonsmokers after 30 yr.
• •Low-dose chest CT scanning offers an excellent opportunity to detect early-stage lung cancers in asbestos-exposed workers.
• •Computed tomography is more sensitive than radiography, computed tomography without contrast generally suffices for evaluation, and PET scan (fluorodeoxyglucose-positron emission tomography) may have utility in patients with mesothelioma.

References

• American Thoracic Society: Diagnosis and initial management of nonmalignant diseases related to asbestos. Am J Respir Crit Care Med 2014; 170 (691):
• Expert Panel on Thoracic Imaging, et al.: ACR appropriateness criteria review ACR Appropriateness Criteria® occupational lung diseases. J Thorac Imaging 2016; 31 (1):
• Reid A et al: The additional risk of malignant mesothelioma in former workers and residents of Wittenoom with benign pleural disease or asbestosis, Occup Environ Med 62:665-669, 2005.
• Niccoli L et al: Systemic autoimmune disease in asbestosis rapidly responding to anti-interleukin-1beta antibody canakinumab: a case report, BMC Musculoskelet Disord 14(16):146, 2015.