Study Syllabus for Classification of Radiographs of Pneumoconioses
Major Occupational Lung Diseases
Silicosis refers to a spectrum of lung diseases caused by inhalation of free crystalline silica. Workers from a broad range of industries are exposed to crystalline silica, with some of the more common industries including coal and hard rock mining, hydraulic fracturing, foundries, tunneling, stone and countertop cutting, sandblasting, construction and masonry, glass manufacturing, concrete and ceramics production, and agriculture.
Several clinical presentations of the disease have been described. Acute silicosis, also known as silicoproteinosis, results from exposure to high concentrations of respirable silica, with symptoms occurring within weeks to a few years after exposure onset. The diagnosis of acute silicosis is based on a history of acute, high-dose silica exposure; imaging findings may include diffuse nodular opacities (Fig. 1) as well as ground glass and patchy consolidative opacities; a milky lipoproteinaceous bronchoalveolar lavage effluent; and exclusion of other potential explanations (e.g., infection, pulmonary edema, alveolar hemorrhage). Accelerated silicosis is also associated with high-level exposure to respirable silica and develops within 10 years. Chronic simple silicosis is characterized radiographically by small rounded opacities (Fig. 2) composed pathologically of hyalinized collagenous nodules. Chest radiograph with detail view (Fig. 2) shows extensive p/q opacities. CT shows primarily centrilobular distribution of nodules characterized by relative uniformity of nodule size, spacing, and sparing of the immediate subpleural area. Chronic complicated silicosis, or progressive massive fibrosis (PMF), is characterized by nodular lung lesions of one centimeter or greater in diameter, usually in the upper lung zones on chest radiograph and CT (Fig. 3). Depending on the stage and severity of disease, resting lung function abnormalities may include reduced lung volumes and diffusion capacity.
Excessive silica exposure is associated with an increased risk for lung cancer, autoimmune disorders (including rheumatoid arthritis, systemic sclerosis and increased serum autoantibodies), chronic kidney disease, chronic airflow obstruction (including emphysema and chronic bronchitis), and lung infections from mycobacteria and some fungal species.
There is no specific treatment sub-acute or chronic. Lung transplantation may be an option for patients with progressive respiratory failure. Medical management is targeted towards controlling ongoing exposure, bronchodilators if airflow limitation is present, monitoring and treatment of infection, pulmonary rehabilitation, supplemental oxygen if hypoxia is present, appropriate vaccinations, and smoking cessation if applicable.
Silicosis, like all of the occupational pneumoconioses, is a preventable disease. Primary prevention through monitoring exposures and maintaining effective controls must be the highest priority. Respiratory protection programs may provide temporary protection of workers but are not a long-term solution to controlling dust levels. Medical monitoring of at-risk workers using chest radiographs and spirometry may help with early detection of those at risk for worsening lung disease with ongoing exposure.