1. Silicosis

    1. Fibrotic disease of the lungs caused by inhalation of crystalline silicone dioxide.

    2. Occupations at risk: mining, manufacturing (glass, pottery, porcelain), sandblasting.

    3. Pathogenesis: Macrophages exposed to silica release chemotactic and fibrogenic factors.

    4. Pathology: Hyaline nodule having concentric whorls of connective tissue with an acellular central zone of free silica.

    5. Clinical presentations

      1. Chronic Silicosis: apparent 20 or more years after exposure.

      2. Accelerated Silicosis: apparent 5-15 years after exposure.

      3. Acute Silicosis: develops in 6 months to 2 years after massive exposure; fulminant course.

      4. Silicoproteinosis: a variant characterized by intra-alveolar lipoproteinaceous material similar to that of pulmonary alveolar proteinosis.

    6. CXR findings

      1. Simple: reticular and nodular patterns predominantly in the upper lobes; hilar adenopathy common, occasionally with "eggshell" calcifications.

      2. Progressive massive fibrosis: coalescence of larger nodules.

      3. Silicoproteinosis: alveolar filling pattern.

    7. Higher incidence of mycobacterial disease.

    8. Dx: Compatible history and characteristic CXR.

    9. Rx:  None; INH for patients with positive PPD.

  2. Asbestos-Related Disease

    1. Asbestosis is a fibrous silicae containing silicon and oxygen.

    2. Industries at risk: construction, manufacturing, shipbuilding, insulation

    3. Chrysotile fibers (serpentine group) account for 95% of world's production of asbestos; amphibole group considered more pathogenic (fibers with greatest length-to-diameter ratio are cost carcinogenic).

    4. Clinical conditions

      1. Parenchymal Pulmonary  Fibrosis (asbestosis)
        - After 10-20 years of inhalational exposure.
        - Fibers and asbestos bodies (fibers coated with protein-iron complexes) in lung biopsy.
        - Interstitial changes usually at lung bases with progression to upper lobes.

      2. Pleural Plaques
        - Thickened fibrotic areas of pleura (visceral and parietal); may coalesce to involve large areas of the lung.
        - Occasionally plaques calcify and are sometimes seen along the diaphragm.

      3. Exudative Pleural Effusion
        - Recurrent, blood-tinged; associated with pleural thickening or parenchymal fibrosis.

      4. Malignancy
        - Increased risk of lung cancer with asbestos exposure; dose-related.
        - Smoking multiples this risk.
        - Increased risk of pleural and peritoneal mesothelioma (smoking does not add to the risk of mesotheliomas).
        - Increased risk of cancers of the GI tract, larynx, kidney, pancreas, ovary, and eye with asbestos exposure.

  3. Coal Worker's Pneumoconiosis

    1. Associated with coal dust exposure.

      1. Risk increases with intensity, duration and higher ranks (hardness) of coals. Anthracite is the hightest rank (mined in eastern U.S.) followed by bituminous and lignite.

      2. Although there are immunologic abnormalities (elevated IgG, IgA, C3), the pathogenesis remains unknown.

    2. Clinical manifestations (develop over 10-20 years)

      1. Simple Coal Worker's Pneumoconiosis (SCWP)
        - Few symptoms.

      2. Progressive Massive Fibrosis
        - Associated with anthracite coal.
        - May see melanoptysis due breakdown of lesions.
        - Can appear after expsoure stops.

      3. Caplan's Syndrome (Rheumatoid Pneumoconiosis)
        - Associated with rheumatoid arthritis.
        - Nodules (0.5-5cm) on CXR in individuals with SCWP; nodules may cavitate.
        - Also occurs with other pneumoconioses.
        - Rheumatoid factor positive in 70% of patients.

    3. No increased risk of TB.

    4. Dx: History of dust exposure and characteristic CXR.

  4. Berylliosis

    1. Exposures: fluorescent light industry, ceramics, nuclear control equipment, electronics

    2. Acute disease (rare): toxic, dose-related, bronchiolitis, pulmonary edema, chemical pneumonitis.

    3. Chronic disease: multisystemic granulomatous disorder which involves the lung; course variable.