Introduction

Pneumoconiosis is a term used to describes a range of interstitial lung diseases caused by inhalation of mineral dusts, resulting in interstitial fibrosis.

They are usually occupational diseases (but not always).

Pneumoconiosis can vary greatly in severity, from diseases that cause death, to those that never cause any significant symptoms.

Common types include¬†asbestosis, silicosis¬†and¬†coal worker’s¬†pneumoconiosis.¬†

In the UK and to some extent in Australia, financial compensation is available to patients of they can prove their lung disease is the result of industrial exposure.

Most exposure to the causative agents occurred int he 1950s and 1960s in the developed world and thus these diseases are on the decline in these societies. In the developing world, or in mining communities, incidence is higher.

Epidemiology

  • Asbestosis causes about 5,000 deaths per year in the UK
    • It is the most common work-related cause of death in the UK
    • Asbestos related lung cancer (rather than pneumoconiosis) is under-diagnosed, as it is indistinguishable from that caused by smoking
  • There are about 250 cases of coal workers pneumoconiosis and about 40 cases of silicosis in the UK every year
  • It is thought that about 15% of cases of COPD are a result of industrial disease – usually coal mining

The three most common causes of pneumoconiosis are:

Asbestos

  • Asbestos was widely used as an insulating and fireproofing material in the middle of the 20th century, before its disease-causing effects were known
  • It was available in various forms, including sheets (which were often sawn to size), as a paste-like substance which was applied around pipes, and even as a powder that was mixed to make a paste to insulate other objects.
  • Particular occupations with exposure include:
    • Plumbers
    • Roofers
    • Mechanics
    • Shipyard workers
  • Asbestosis is correlated to the level of exposure, but the disease can take 10-60 years to develop from the time of exposure
  • Asbestos has been banned fro many decades, but lots of asbestos remains in the environment in older buildings.
  • Asbestos is also an important cause of lung cancers, both the asbestos specific¬†mesothelioma¬†and other types of lung cancer.

Silica

  • The main component of sand and rock
  • Types of workers who might be exposed to silica include:
    • Miners
    • Sandblasters
    • Stonemasons
  • Pneumoconiosis risk correlates to the length of exposure
  • Chronic simple silicosis
    • Caused by long periods of low level exposure
    • Multiple nodules throughout the lungs
    • Mild symptoms (sometimes none)
  • Progressive massive fibrosis (PMF)
    • Develops from chronic simple silicosis
    • The nodules enlarge and coalesce into large masses
    • Severe respiratory symptoms
  • Acute silicosis
    • Large exposure over a short period of time
    • Rapidly advancing silicosis – often results death

Coal

  • Often co-exists with silicosis
  • Takes on average about 10 years from exposure to the development of pneumoconiosis
  • Causes¬†coal-workers pneuomoconiosis
  • Similar disease pattern to silicosis – most cases are¬†chronic simple pneumoconiosis
  • Generally cases are mild, but just like silicosis – in some cases it can progress to¬†progressive massive fibrosis

Pathology

The most important factor of the inhaled dust particles is their size. Particles in the 1-5um range are most dangerous as these get stuck at the bifurcations of the airway

  • Smaller particles pass right into and out of the alveoli
  • Larger particles get stuck higher up the airway
  • Most dust particles are cleared by the normal mucocilliary clearance of the lungs
  • Those that remain – particularly those that are stuck at the bifrucations, become encased in macrophages and set off localised inflammatory responses
    • This leads to an inflammatory cascade that ultimately leads to fibroblast proliferation and collagen deposition
  • The level of immune response always depends on the chemical make-up of the dust
    • Coal is not very reactive and large amounts of coal dust are required to cause pneuomoconiosis
    • Asbestos, silica and beryllium are much more reactive
  • Where the process of pneumoconiosis occurs alongside rheumatoid arthritis, it is called¬†Caplan’s syndrome.¬†

Presentation

  • Shortness of breath – particularly on exertion
  • Cough – with or without sputum production

Differentials

Diagnosis

  • CXR –¬†may demonstrate evidence of fibrotic nodule in simple pneumocosis, or larger masses in PMF
    • High resolution CT is then often used to further quantify the extent of the disease
  • Spirometry

Treatment

  • There is no specific treatment and no cure
  • Most interventions are aimed at reducing the risk of further lung damage
  • Other treatments are often similar to those used in COPD
    • Pulmonary rehabilitation
    • Inhaled corticosteroids
    • Inhaled bronchodilators
    • O2 if sats / symptoms indicate it is required
    • Smoking cessation
  • Lung transplant may be considered in more severe cases (but finding a suitable donor is difficult and in reality only a small number of patients undergo transplant)

References

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