Occupational lung diseases- Asbestosis

Pathology

Asbestosis is lung fibrosis caused by prolonged exposure to asbestos dust, a mineral fibre of silicate origin. Occupations classically associated with asbestos exposure are shipbuilding, construction, plumbing and welding. There are three types of asbestos fibres: crocidolite (blue), amosite (brown), and chrysotile (white). Chrysotile is thought tube the most pathogenic. Histologically, asbestos bodies may be seen; these originate from asbestos fibres coated with brown phagocyte ferritin consequent upon being engulfed by macrophages. Asbestos exposure also causes benign pleural plaques, pleural effusion and mesothelioma, and greatly increases the risk of lung cancer, especially in smokers.

Clinical features

Shortness of breath and a productive cough are the usual non-specific symptoms. Patients may also present with symptoms of a mesothelioma or lung cancer . On examination clubbing may be seen and crepitations may be heard in the bases.

Investigations

Chest X-ray

Initially linear opacities are seen in the lower zones progressing to fibrotic changes in the costophrenic and cardiophrenic angles. Fibrosis begins in the lower lobes subpleurally and progresses proximally. Calcified pleural plaques may be seen on the diaphragmatic or lateral pleural surfaces . Pleural thickening or effusions can occur, but should not be assumed to be benign. Fibrosis that occurs in the absence of pleural plaques is unlikely to be due to asbestos exposure.

CT Thorax

The findings on CT are peripheral septal lines, bronchiolar thickening, honeycombing of the lung, pleural thickening and plaques . The density of parenchymal abnormalities correlates well with the severity of symptoms.

Pulmonary function tests

A restrictive defect occurs with reduced gas transfer (Tlco).

Management

Supportive management

The management is essentially supportive. Occupational exposure should stop. In the UK, mesothelioma and asbestosis are recognized as industrially related. Patients or their estate are entitled to compensation from the state and may also resort to the law to sue their former employers.

Prognosis

The prognosis is variable and can range from stable disease with mild symptoms to progressive deterioration and respiratory failure. Usually, disease progression slows over a period of a decade after cessation of exposure. Lung cancer is the commonest cause of death in patients with asbestosis.