Asbestosis

Asbestosis - asbestos-related lung diseases caused by inhalation of asbestos fibers. Diseases include asbestosis; lung cancer; benign focal pleural lesions and thickening; benign pleural effusions and malignant pleural mesothelioma. Asbestosis and mesothelioma result in progressive shortness of breath.

Diagnosis is based on history and chest X-ray or CT and, in the case of malignancy, tissue biopsy. Treatment of asbestosis is effective, except for malignancy, which may require surgical and/or chemotherapy.

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What causes asbestosis?

Asbestos is a naturally occurring silicate whose heat-resistant and structural properties have made it useful for construction and shipbuilding, and it is used in automobile brakes and some textiles. Chrysotile (snake fiber), chrocidotile, and amosite (amphibole, or straight fiber) are the three main types of asbestos fibers that cause disease. Asbestos can affect the lungs and/or pleura.

Asbestosis, a form of interstitial pulmonary fibrosis, is much more common than the malignant diseases. Shipbuilders, construction and textile workers, housing remodelers, and workers and miners exposed to asbestos fibers are among the many groups at risk. Secondary infection may occur among family members of affected workers and among those living close to mines. The pathophysiology is similar to that of other pneumoconioses—alveolar macrophages attempting to ingest inhaled fibers secrete cytokines and growth factors that stimulate inflammation, collagen deposition, and ultimately fibrosis—except that asbestos fibers themselves may also be directly toxic to lung tissue. Disease risk is generally related to the duration and intensity of exposure and the type, length, and thickness of inhaled fibers.

Symptoms of asbestosis

Asbestosis is initially asymptomatic, meaning there are no symptoms of asbestosis, but may cause progressive dyspnea, nonproductive cough, and malaise; the disease progresses in more than 10% of patients after exposure has ceased. Long-term asbestosis may cause clubbing of the terminal phalanges of the fingers, dry basilar rales, and, in severe cases, symptoms and signs of right ventricular failure (cor pulmonale).

Pleural lesions, a hallmark of asbestos exposure, include pleural plaques, calcification, thickening, adhesions, effusions, and mesothelioma. Pleural lesions are associated with effusion and malignancy but few symptoms. All pleural changes are diagnosed by chest radiography or HRCT, although chest CT is more sensitive than chest radiography in detecting pleural lesions. Treatment is rarely required except in cases of malignant mesothelioma.

Discrete superimpositions, which occur in 60% of asbestos-exposed workers, typically involve the parietal pleura bilaterally at the level between the fifth and ninth ribs adjacent to the diaphragm. Calcification of the spots is common and may lead to misdiagnosis of severe lung disease if they are superimposed on the lung fields radiographically. HRCT can differentiate between pleural and parenchymatous lesions in such cases.

Diffuse thickening occurs in both the visceral and parietal pleura. It may be an extension of pulmonary fibrosis from the parenchyma to the pleura or a nonspecific reaction to a pleural effusion. With or without calcification, pleural thickening may cause restrictive abnormalities. Rounded atelectasis is a manifestation of pleural thickening in which invagination of the pleura into the parenchyma may trap lung tissue, causing atelectasis. It typically appears on chest radiography and CT as an irregularly marginated scar mass, often in the lower lung regions, and may be mistaken radiographically for pulmonary malignancy.

Pleural effusion also occurs, but is less common than the other pleural lesions it accompanies. The effusion is an exudate, often hemorrhagic, and usually resolves spontaneously.

Diagnosis of asbestosis

The diagnosis of asbestosis is based on a history of asbestos exposure and chest CT or radiography. Chest radiography shows linear reticular or patchy infiltrates reflecting fibrosis, usually in the peripheral lower lobes, often accompanied by pleural involvement. Honeycombing reflects more advanced disease, which may involve the middle lung fields. As with silicosis, severity is graded according to the International Labour Organization scale based on the size, shape, location, and extent of the infiltrates. Unlike silicosis, asbestosis causes reticular changes primarily in the lower lobes. Hilar and mediastinal adenopathy are unusual and suggest another diagnosis. Chest radiography is not helpful; high-resolution chest CT (HRCT) is helpful when asbestosis is suspected. HRCT is also superior to chest radiography in identifying pleural lesions. Pulmonary function tests, which may show reduced lung volumes, are nondiagnostic but help characterize changes in lung function long after the diagnosis is made. Bronchoalveolar lavage or lung biopsy is indicated only when noninvasive methods fail to establish a definitive diagnosis; detection of asbestos fibers indicates asbestosis in people with pulmonary fibrosis, although such fibers may occasionally be found in the lungs of exposed people without the disease.

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Treatment of asbestosis

There is no specific treatment for asbestosis. Early detection of hypoxemia and right ventricular failure leads to the use of supplemental 02 and treatment of heart failure. Pulmonary rehabilitation may be helpful for patients with worsening disease. Preventive measures include avoidance of exposure, reduction of asbestos in non-working areas, smoking cessation, and vaccination against pneumococcus and influenza. Smoking cessation is especially important given the multifactorial risk of lung cancer in those exposed to both asbestos and tobacco smoke.

What is the prognosis for asbestosis?

Asbestosis has a variable prognosis; many patients live happily with no or mild symptoms, while some suffer from progressive dyspnea, and a few patients develop respiratory failure, right ventricular failure, and malignancy.

Lung cancer (non-small cell) occurs in patients with asbestosis at a rate 8-10 times higher than in patients without asbestosis, and is particularly common in workers exposed to amphibole fibers, although all forms of inhaled asbestos are associated with an increased risk of cancer. Asbestos and smoking have a synergistic effect on lung cancer risk.