Idiopathicpulmonaryfibrosisisprototypicofrestrictivelungdiseases.Itischaracterizedbypatchyinterstitialfibrosis,fibroblasticfoci,andformationofcysticspaces(honeycomblung).Thishistologicpatternisknownasusualinterstitialpneumonia(UIP).
Pneumoconiosis is a term originally coined to describe lung disorders caused by inhalation of mineral dusts. The term has been broadened to include diseases induced by organic and inorganic particulates, and some experts also regard http://ebooksmedicine.net
Table 13.3 Mineral Dust–Induced Lung Disease
CoaldustSimplecoalworker’spneumoconiosis:maculesandnodulesCoalminingComplicatedcoalworker’spneumoconiosis:PMF
SilicaSilicosisSandblasting,quarrying,mining,stonecutting,foundrywork,ceramics chemical fumeand vapor-induced lung diseases as pneumoconioses. The mineral dust pneumoconioses—the three most common of which are caused by inhalation of coal dust, silica, and asbestos—usually stem from exposure in the workplace. Asbestos is the exception, as with this mineral the increased risk for cancer extends to family members of asbestos workers and to individuals exposed outside of the workplace.
Table 13.3 indicates the pathologic conditions associated with each mineral dust and the major industries in which the dust exposure may produce disease.
The reaction of the lung to mineral dusts depends on many variables, including the size, shape, solubility, and reactivity of the particles. For example, particles greater than 5 to 10 µm are unlikely to reach distal airways, whereas particles smaller than 0.5 µm move into and out of alveoli, often without substantial deposition and injury. Particles that are 1 to 5 µm in diameter are the most dangerous, because they get lodged at the bifurcation of the distal airways. Coal dust is relatively inert, and large amounts must be deposited in the lungs before lung disease is clinically detectable. Silica, asbestos, and beryllium are more reactive than coal dust, resulting in fibrotic reactions at lower concentrations. Most inhaled dust is entrapped in the mucus blanket and rapidly removed from the lung by ciliary movement. However, some of the particles become impacted at alveolar duct bifurcations, where macrophages accumulate and engulf the trapped particulates.
The pulmonary alveolar macrophage is a key cellular element in the initiation and perpetuation of inflammation, lung injury and fibrosis. Following phagocytosis by macrophages, many particles activate the inflammasome and induce production of the pro-inflammatory cytokine IL-1 as well as the release of other factors, which initiates an inflammatory response that leads to fibroblast proliferation and collagen deposition. Some of the inhaled particles may reach the lymphatics either by direct drainage or within migrating macrophages and thereby initiate an immune response to components of the particulates and/ or to self-proteins that are modified by the particles. This then leads to an amplification and extension of the local reaction. Tobacco smoking worsens the effects of all inhaled mineral dusts, more so with asbestos than other particles.
Worldwide dust reduction in coal mines has greatly reduced the incidence of coal dust–induced disease. The spectrum of lung findings in coal workers is wide, ranging from asymptomatic anthracosis, in which pigment deposits without a perceptible cellular reaction; to simple coal worker’s pneumoconiosis (CWP), in which macrophages accumulate with little to no pulmonary dysfunction; to complicated CWP or progressive massive fibrosis (PMF), in which fibrosis is extensive and lung function is compromised (see