TABLE 58.1 Pneumoconioses | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Miscellaneous Pneumoconioses
Miscellaneous Pneumoconioses
Allen P. Burke, M.D.
Background
Pneumoconiosis is defined as a restrictive lung disease resulting from occupational inhalation of dust, usually inorganic particulates. It differs histologically and pathogenetically from hypersensitivity pneumonitis, which may initially have an obstructive component and which results from an immune-mediated reaction to inhaled organic material. Hypersensitivity pneumonitis may also result from occupational exposure, however (see Chapter 23).
Pneumoconioses are characterized histologically by bronchiolocentric aggregates of dust-laden macrophages forming macules or nodules. The macrophages may track along lymphatic routes (bronchovascular bundles, pleural surfaces, and interlobular septa).
The distinction between pneumoconiosis and hypersensitivity becomes somewhat blurred for some conditions. For example, berylliosis is believed to be an immune-related disease with a sarcoid-like reaction that does not resemble other types of pneumoconiosis.
Epidemiology
Worldwide, pneumoconiosis represents the second leading cause of death among the chronic respiratory diseases (second to chronic obstructive lung disease), resulting in over 250,000 deaths annually.1 Nearly one-half are caused by silicosis, asbestosis, and coal workers’ pneumoconiosis (in descending order). Asbestosis and silicosis are discussed in Chapters 56 and 57, respectively. Other pneumoconioses are relatively uncommon (Table 58.1).
Coal Miners’ (Workers’) Pneumoconiosis
The prevalence of coal workers’ pneumoconiosis has declined to 2% among underground coal miners in the U.S. Appalachia, with a similar rate among aboveground miners.2 The disease is assessed radiographically and is staged based on the numbers of rounded opacities and presence of consolidation or diffuse fibrosis.
Grossly, there are black-stained nodules or masses that are predominantly centrally located. Histologically, coal dust is present within macrophages or the interstitium, beginning around airways. There may be occasional ferruginous bodies with a black core. The smallest lesion is called a macule (0.5 to 6 mm), which may progress to a fibrotic nodule. Coalescing fibrous nodules are termed progressive massive fibrosis, which can result in diffuse interstitial fibrosis.3
Caplan Syndrome
Caplan syndrome, or rheumatoid pneumoconiosis, was first identified in coal workers with rheumatoid arthritis and lung nodules and later found in other types of pneumoconiosis, especially silicosis. The opacities range from 0.5 to 5 cm in diameter and, unlike pneumoconiosis, are well defined, numerous, and predominantly peripheral, presumably representing rheumatoid nodules.4
There are few histologic descriptions of the pulmonary nodules of Caplan syndrome. Both silicotic nodules and rheumatoid nodules have been documented histologically in the same patient.5 The precise relationship between the pneumoconiosis and rheumatoid nodules is unknown, but they may represent a chance coincidence, or a predisposition to form rheumatoid nodules when there is inhalation of particulate matter.
Cobalt Pneumoconiosis
Hard metal pneumoconiosis is sometimes used synonymously with cobalt pneumoconiosis.6 Cobalt is used as a binder in producing hard metals composed of carbon, tungsten, and other elements. The cobalt elicits a fibrotic reaction that initially manifests as inflammatory small airway disease. Workers at risk include machinists and other employees in the metal industry and previously dental technicians.
Symptoms include cough and hemoptysis. Computed tomograms show diffuse bilateral ground-glass attenuation and interstitial linear markings.
Histologically, there are inflammatory bronchiolar infiltrates, peribronchiolar fibrosis with peribronchiolar metaplasia, and macrophages within peribronchiolar alveoli containing tight aggregates of macrophages and giant cells without well-formed granulomas.7 The multinucleated giant cells are characteristic and led to the former designation giant cell interstitial pneumonia.
