Asbestosis

Occupational medicine

Asbestosis is a diffuse interstitial lung fibrosis due to respiratory exposure to asbestos fibers.

Asbestos has excellent thermal and noise insulating properties, strength and durability against mechanical, thermal and chemical stress. It has therefore been in wide use in industry until increased awareness on the side effects on workers health discontinued its use in many western countries.

Workplaces associated with a high risk of asbestos exposure: asbestos production, asbestos transportation, manufacture of insulating products, end-use of asbestos containing materials, other occupations.

There is a linear relationship between exposure and risk for asbestosis. A regular, continuous exposure and an inefficiency of lung clearance mechanisms are factors likely to contribute to asbestosis.

Exposure to asbestos may lead to a variety of lung diseases such as: asbestosis, lung cancer, benign pleural diseases and malignant mesothelioma.

The symptoms of asbestosis are nonspecific, common to other interstitial disease of the lung.

The lung function tests indicate a restrictive ventilatory dysfunction, but the sensitivity of such methods is quite low. The posteroanterior chest radiograph shows small irregular opacities in the lower lung fields, and a fine reticulation progressing to a coarse linear pattern or honeycombing, according to the disease stage. The pleural plaques are also important radiographic findings supporting the diagnosis of asbestosis. However, the overall sensitivity and specificity of this method is rather weak. The high-resolution computed tomograph (HRCT) scan with 1 mm thin sections has an increased accuracy in diagnosing asbestosis showing septal lines, intralobular lines, subpleural curvilinear lines and honeycombing. Bronchoscopy with bronchoalveolar lavage (BAL) may show a number of characteristic cellular, biochemical and mineralogical features in asbestos-exposed workers or asbestosis patients, such as asbestos bodies which are asbestos fibers covered with an proteinaceous material containing iron.

American Thoracic Society criteria for asbestosis:

* reliable history of asbestos exposure
* appropriate time interval between exposure and detection
* clinical criteria
* chest radiograph evidence of type s, t, u, small irregular opacities of a profusion of 1/1 or greater
* restrictive pattern of lung impairment with an FVC below the lower limit of normal
* diffusing capacity below the limit of normal
* bilateral inspiratory crackles at the posterior lung bases not cleared by cough

There is no specific therapy for asbestosis, only symptomatic and palliative treatments.

In the last decades, the prevention of asbestos exposure within tight exposure limits is the main concern. Asbestos is replaced in industry with alternative materials, wherever this is possible, so that in many industrialized countries, the greatest risk remained in occupations involving asbestos removal. Wherever asbestos has to be used or has to be removed and the estimated exposure levels are higher that the statutory limits, the asbestos exposure should be minimized by local exhaust ventilation wit adequate filters and workers should be provided with appropriate respirators and clothing.

Reference for this article: P. de Vuyst, P.A. Gevenois - "Asbestosis", chapter in D.J. Hendrick, P.Sherwood Burge, W.S.Beckett, A.Churg - "Occupational Disorders of the Lung", WB Saunders, Harcourt Publishers Limited, 2002