Asbestos

Exposure to asbestos may cause asbestosis—a common form of ILD. Asbestos fibers are a mixture of fibrous minerals composed of hydrous silicates of magnesium, sodium, and iron in various proportions. There are two primary types: the amphiboles (crocidolite, amosite, and anthophyllite) and chrysotile (most commonly used in industry). Asbestos fibers typically range from 50 to 100 µm in length and are about 0.5 µm in diameter. The chrysotiles have the longest and strongest fibers. Box 25-1 lists common sources associated with asbestos fibers.

As shown in Figure 25-1, B, asbestos fibers can be seen by microscope within the thickened septa as brown or orange baton-like structures. The fibers characteristically stain for iron with Perls’ stain. The pathologic process may affect only one lung, a lobe, or a segment of a lobe. The lower lobes are most commonly affected. Pleural calcification is common and diagnostic in patients with an asbestos exposure history.

Coal dust

The pulmonary deposition and accumulation of large amounts of coal dust causes what is known as coal worker’s pneumoconiosis (CWP). CWP also is known as coal miner’s lung and black lung. Miners who use cutting machines at the coal face have the greatest exposure, but even relatively minor exposures may result in the disease. Indeed, cases have been reported in which coal miners’ wives developed the disease, presumably from shaking the dust from their husbands’ work clothes.

Simple CWP is characterized by the presence of pinpoint nodules called coal macules (black spots) throughout the lungs. The coal macules often develop around the first- and second-generation respiratory bronchioles and cause the adjacent alveoli to retract. This condition is called focal emphysema.

Complicated CWP or progressive massive fibrosis (PMF) is characterized by areas of fibrotic nodules greater than 1 cm in diameter. The fibrotic nodules generally appear in the peripheral regions of upper lobes and extend toward the hilum with growth. The nodules are composed of dense collagenous tissue with black pigmentation. Coal dust by itself is chemically inert. The fibrotic changes in CWP are usually caused by silica.

Silica

Silicosis (also called grinder’s disease or quartz silicosis) is caused by the chronic inhalation of crystalline, free silica, or silicon dioxide particles. Silica is the main component of more than 95% of the rocks of the earth. It is found in sandstone, quartz (beach sand is mostly quartz), flint, granite, many hard rocks, and some clays.

Simple silicosis is characterized by small rounded nodules scattered throughout the lungs. No single nodule is greater than 9 mm in diameter. Patients with simple silicosis are usually symptom-free.

Complicated silicosis is characterized by nodules that coalesce and form large masses of fibrous tissue, usually in the upper lobes and perihilar regions. In severe cases the fibrotic regions may undergo tissue necrosis and cavitate. Box 25-2 lists common occupations associated with silica exposure.

Beryllium

Beryllium is a steel-gray, lightweight metal found in certain plastics and ceramics, rocket fuels, and x-ray tubes. As a raw ore, beryllium is not hazardous. When it is processed into the pure metal or one of its salts, however, it may cause a tissue reaction when inhaled or implanted into the skin. The acute inhalation of beryllium fumes or particles may cause a toxic or allergic pneumonitis sometimes accompanied by rhinitis, pharyngitis, and tracheobronchitis. The more complex form of berylliosis is characterized by the development of granulomas and a diffuse interstitial inflammatory reaction.

Hypersensitivity pneumonitis

Hypersensitivity pneumonitis (also called allergic alveolitis or extrinsic allergic alveolitis) is a cell-mediated immune response of the lungs caused by the inhalation of a variety of offending agents or antigens. Such antigens include grains, silage, bird droppings or feathers, wood dust (especially redwood and maple), cork dust, animal pelts, coffee beans, fish meal, mushroom compost, and molds that grow on sugar cane, barley, and straw. The immune response to these allergens causes production of antibody and an inflammatory response. The lung inflammation, or pneumonitis, develops after repeated and prolonged exposure to the allergen. The term hypersensitivity pneumonitis (or allergic alveolitis) is often renamed according to the type of exposure that caused the lung disorder. For example, the hypersensitivity pneumonitis caused by the inhalation of moldy hay is called farmer’s lung. Table 25-2 provides common causes, exposure sources, and disease syndromes associated with hypersensitivity pneumonitis.

Medications and illicit drugs

As the list of medications and illicit drugs continues to grow, so does the list of possible side effects (Box 25-4). Unfortunately, the lungs are major target organs affected by these side effects. Although it is impossible to discuss in detail the various lung-related side effects of every drug, it is possible to describe some of the general concerns related to drug-induced lung disease and to list some of the pharmacologic agents that may be responsible.