Asbestos
From Pharmpedia
Asbestos is a Greek derived term meaning ‘inextinguishable’ and ironically the disease caused by it slowly extinguishes the breathing capacity of the asbestosis patient.
Asbestosis is a slowly progressive, chronic disease of the lungs caused by inhalation of asbestos fibers. The inhaled fibers cause irritation and inflammation, ultimately leading to fibrosis (scarring) of the lung tissue. Progressive and extensive fibrosis cause defective oxygen transfer (gas exchange), which causes dyspnea (difficulty in breathing), and other sequelae ranging from chronic bronchitis to respiratory tract cancers.
Asbestosis is also called as pulmonary fibrosis or idiopathic interstitial pneumonitis or pneumoconiosis from asbestos exposure.
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Incidence
The risk of getting asbestosis depends upon the concentration, duration, frequency, size, shape and type of asbestos fibers.
The exact incidence of asbestosis is not known but it is estimated that around 10 million may be affected and another 0.25 million at risk in US alone (and these are people who got exposed before 1970s). From late 70s the production of all asbestos-containing materials for home construction and other use was strictly regulated in developed countries.
Mortality and morbidity
The exact mortality and morbidity data are not available. Smokers exposed to asbestos have a greater chance of developing chronic bronchitis, hear failure, respiratory infections, mesothelioma and bronchogenic carcinoma.
Pathophysiology
Asbestos is a group of microscopic, naturally occurring minerals that was earlier commonly used in variety of applications like construction, fireproofing, ship building, insulation etc. It takes about 1 to 2 decades for the onset of asbestosis, after the initial exposure. Principally the lung parenchyma and pleura are affected.
Normally the inhaled asbestos fibers are either filtered at the nose or cleared by mucus but when these defenses fail, the particles get deposited in the distal airways (respiratory bronchioles and alveolar duct). Then the macrophages come in to play. Since the fibers are too big to engulf and resist break down the macrophages also fail to clear them. However the macrophages release chemical mediators (various growth factors, plasminogen activator and oxygen free radicals) which initiate the process of damage and fibrosis. Fibrosis begins in the peribronchiolar area and extends to the adjacent alveoli. The fibrosed lung is stiff with very much diminished capacity for gas transfer which makes the patient to put in more effort to breathe.
There is also compression of pulmonary blood vessels leading to pulmonary hypertension. This in turn makes the heart difficult to pump blood to lungs (right heart failure).
The asbestos fibers that affect the parietal pleura are surrounded by abnormal collections of collagen which later get calcified. These are called as pleural plaques.
Clinical features
The disease can vary from asymptomatic (no symptoms) to potentially fatal condition.
Symptoms
Symptoms usually appear after the 2nd decade of initial exposure of asbestos and the severity varies with the amount and duration of exposure.
No symptoms (asymptomatic)
or
Shortness of breath (exertional dyspnea) is the primary symptom.
A persistent dry cough or productive (with mucus) if concomitant infection
Chest tightness
Chest pain
Loss of appetite
Signs
Clubbing of the fingers
Reduced chest expansion
An inspiratory dry crackle over the lung fields (in the posterior, lower zones). In advanced cases, additional signs and symptoms pertaining to complications like Cor pulmonale (right heart failure- cyanosis, edema of legs), pleural effusion etc. may be seen.
Diagnosis
Diagnosis depends on 1) History of asbestos exposure 2) X-ray findings and when in doubt HRCT (fibrous bands in lung parenchyma, honey comb appearance, pleural plaques and rounded atelectasis).
Plain X-ray chest – detects pleural plaques (seen as linear, irregular opaque areas), pleural thickening, and pleural
calcification. Pleural thickening with calcification is a reliable radiographic marker for asbestos exposure.
HRCT (High-resolution computed tomography) provides greater detail than and detects cases even before the plain x-ray shows.
Pulmonary function tests using spirometry (reduced vital capacity) – but the findings are not typical to asbestosis since they can be seen in other restrictive respiratory disorders.
Arterial blood gas analysis and Pulse oximetry may be needed to detect the level of hypoxemia in advanced cases.
Bronchoalveolar fluid lavage (asbestos bodies may be identified) and lung biopsy (fibrosis) are rarely necessary, but will confirm the diagnosis.
Differential Diagnosis
Allergic pneumonitis
Coal worker’s pneumoconiosis
Collagen vascular diseases
Interstitial pulmonary disease due to other causes
Complications
Asbestosis can lead to many complications like
Cor pulmonale (disease of heart secondary to disease of lungs or their vessels – there is right heart failure)
Pleural effusion
Malignant mesothelioma (malignant tumor of the mesothelium which may be pleura, peritoneum or pericardium, but with asbestosis pleura is commonly affected) is a difficult to treat cancer. The only known cause of mesothelioma is prior exposure to asbestos.
Other cancers (esophagus, biliary system, renal)
Treatment
There is neither a cure, nor any specific drug to treat asbestosis. Supportive treatment may be offered for distressing symptoms.
Supportive treatment also involves measures to remove secretions from the lungs which include postural drainage, chest percussion, and vibration. If there is any suspected respiratory bacterial infection, appropriate antibiotics have to be administered.
If the oxygen status of the patient is poor, administer oxygen. Advice the patients regarding periodic followup (X-ray chest, Lung function tests).
Surgery
Occasional cases may be treated with lung transplantation.
General measures
Stop smoking. Immunize asbestosis patients against diseases for which they are more prone; that includes influenza and pneumococcal pneumonia.
Prognosis
Prognosis is directly proportional to the extent and duration of asbestos exposure. Mesothelioma can occur many years long after the exposure is terminated.
Prevention
Control of asbestos exposure is the best single measure to prevent asbestosis. Asbestos related job should best be left to the concerned professional. For self protection face mask is better.
Screening of the susceptible population (those with history of exposure) may detect the cases for early intervention.
Future
Due to rigorous enforcement of laws in many developed countries the possibility of occurrence of new cases of asbestosis is extremely thin. If at all cases may still arise in developing or under developed countries, though the exact figures are not available.
References
- Asbestosis: From the American Lung Association
- Galvin JR and D'Alessandro MP. The Diagnosis of Diffuse Lung Disease
- Asbestosis
- Asbestosis Varkey B and Varkey AB.
- Asbestosis MyaoClinic
- Mesothelioma information: Available at, the asbestos cancer resource
Author
This is original article by Dr.Gurusamy Sivagnanam
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