Author
Lars Grimm, MD, MHS
House Staff
Department of Internal Medicine
Duke University Medical Center
Durham, North Carolina
Disclosure: Lars Grimm, MD, MHS, has disclosed no relevant financial relationships.
Editor
Zab Mosenifar, MD
Director, Division of Pulmonary and Critical Care Medicine,
Women's Guild Pulmonary Disease Institute; Executive Vice
Chair, Department of Medicine, Cedars Sinai Medical Center;
Professor of Medicine, David Geffen School of Medicine at UCLA
Los Angeles, California
Disclosure: Zab Mosenifar, MD, has disclosed no relevant financial relationships.
Occupational lung diseases are a broad group of pulmonary disorders that develop from inhalation of specific particles. Historically, they have been a major cause of morbidity and mortality before workplace safety guidelines were rigorously established and enforced. Although each disease has a slightly unique presentation, they all lead to progressive deterioration in lung function that can cause severe respiratory compromise if appropriate measures are not undertaken. The chest radiograph shown is from a patient with asbestosis, an occupational lung disease caused by inhalation of asbestos fibers, and shows extensive pleural plaques and diffuse interstitial fibrotic disease of the lungs.
The major classifications of occupational lung diseases are hypersensitivity pneumonitis (HP) and pneumoconiosis. HP, or extrinsic allergic alveolitis, refers to lung diseases caused by inhalation of organic materials. Pneumoconiosis is the term for lung diseases caused by inhalation of mineral dust.
HP is an inflammatory disease of the lung parenchyma caused by inhalation of organic dusts. It is characterized by diffuse inflammation of the lung parenchyma in previously sensitized patients. Organic dusts can be from a variety of sources such as dairy and grain products, animal dander and protein, bark, and water reservoir vaporizers. The most common antigens are thermophilic actinomycetes species and avian proteins. The most common diseases are farmer's lung and bird fancier's lung. A table listing various hypersensitivity pneumonitis types, sources of exposure, and major antigens is shown.
The pathophysiology of HP is based on immunoglobulin G antibodies to offending inhaled antigens inducing a predominately cell-mediated immune response that causes extensive inflammation and fibrosis. There are 3 distinct pathologic forms of hypersensitivity pneumonitis: acute, subacute, and chronic. The acute form is characterized by poorly formed noncaseating peribronchial granulomas (black arrow in the light microscopy image shown) and mononuclear cell infiltration with many giant cells. In the subacute form, the granulomas become well-formed and there is bronchiolitis, interstitial fibrosis, and possibly organizing pneumonia. In the chronic form, there is progressive interstitial fibrosis and honeycombing. Chronic hypersensitivity pneumonitis may have 1 of 3 patterns of fibrosis: patchy peripheral with architectural distortion, homogenous linear fibrosis, and irregular peribronchial fibrosis. The similarity in fibrotic changes to other interstitial lung diseases, such as usual interstitial pneumonitis and nonspecific interstitial pneumonia, can be misleading.
Bird fancier's lung is the most common type of HP in children. It has been associated with a wide variety of different birds including pigeons, pheasants, turkeys, geese, and parakeets. Although the classic presentation is in individuals who have birds as pets or who raise birds for consumption, more insidious cases have been identified. Bird nests near air-conditioning intake systems, feather duvets, and bird congregations in backyard pools have all been identified as sources of HP. A high degree of suspicion is recommended for patients who present signs and symptoms of HP but lack any obvious history of bird exposure. Image courtesy of Wikimedia Commons.
Farmer's lung is caused by the inhalation of thermophilic Actinomyces or Aspergillus species in decomposing compost, hay, or sugar cane. Exposure to large quantities of contaminated hay is the most common source. This most commonly occurs during the winter months due to the cold, damp climate. The thermophilic actinomycetes include Saccharopolyspora rectivirgula (formerly Micropolyspora faeni), Thermoactinomyces vulgaris, Thermoactinomyces viridis, and Thermoactinomyces sacchari, among others. Incidence is highly variable, depending on the local climate, type of farming, and exposure history, but HP is estimated to affect 0.4%-7% of the farming population. Image courtesy of Wikimedia Commons.
The diagnosis of HP is based on history, physical examination, and radiographic findings. Patients may report fever, chills, malaise, cough, dyspnea, and headaches 4-6 hours after heavy exposure to an inciting agent in acute HP. Subacute and chronic forms are characterized by cough, progressive dyspnea, fatigue, anorexia, and weight loss. On examination, patients may present with fever, tachypnea, and diffuse fine basilar crackles; with muscle wasting, clubbing, and respiratory distress in severe cases. Chest radiographs may show micronodular or reticular opacities (shown) in acute or subacute HP and progressive fibrosis with lung volume loss in chronic HP.
High-resolution computed tomography scans will show ground-glass opacities in acute disease, focal air-trapping with diffuse micronodules in subacute HP, and extensive fibrosis with honeycombing and air-trapping in chronic HP (shown). Inhalation challenges, bronchoalveolar lavage, pulmonary function testing, and lung biopsy are adjunctive tests that may facilitate a diagnosis or identify a specific etiologic agent. Treatment is focused on antigen avoidance. Corticosteroids may be helpful in severe disease to accelerate the initial phase of recovery, but the long-term prognosis is not affected. Most patients will recover the majority of lung function, but it may take several years. Patients with significant fibrosis have a poorer prognosis.
Asbestosis is a pneumoconiosis fibrotic lung disease caused by inhalation of asbestos fibers. Asbestos fibers are naturally occurring long, thin fibers of silicon that come in 1 of 2 major varieties. The curved fibers are serpentine and the straight fibers are amphiboles (scanning electron micrograph shown). Due to their heat-resistant properties they were extensively used to insulate heating and cooling units in World War II ships and buildings. Image courtesy of Wikimedia Commons.
The carcinogenicity and fibrinogenicity of asbestos fibers are related to the type of fiber, duration of exposure, and associated host risk factors. Although both types of asbestos fibers are fibrogenic, amphiboles are markedly more carcinogenic because their straight shape allows for better penetration of cell membranes. Smaller fibers penetrate cells inducing fibrosis, while long fibers are incompletely phagocytosed and stay in the lungs inducing cycles of inflammation and cytokine release. Damage to the lung parenchyma is the result of chronic, repetitive release of oxygen free radicals, plasminogen activators, and growth factors by the macrophages. Individuals who smoke have an increased risk for asbestosis progression because of their impaired mucociliary clearance mechanisms. The Prussian blue stained micrograph shows an asbestos body (arrow) within the lung parenchyma surrounded by macrophages; this is called a ferruginous body. Image courtesy of the Centers for Disease Control.
Asbestos-related diseases may develop after a latency of up to 20 years. The most common presenting symptom is a dry nonproductive cough or nonspecific chest discomfort in advanced cases. On physical examination, persistent and dry inspiratory rales are the most important finding. Clubbing and reduced chest expansion may also be present. Formal diagnosis requires an exposure history, evidence of fibrosis on imaging, physical examination, and pulmonary function findings particularly low forced vital capacity and a low carbon monoxide diffusing capacity consistent with fibrosis, and the absence of another cause of interstitial fibrosis. Chest radiographs are the most commonly used radiographic test. Classic findings include reticulonodular infiltrates at the lung bases (shown), shaggy heart borders (shown), and calcified diaphragmatic pleural plaques that are commonly called "holly leaf."
High-resolution computed tomography may show intralobular opacities (black arrow), thickened septa (white arrows), subpleural curvilinear lines, parenchymal bands, peribronchial fibrosis, honeycombing, and calcified diaphragmatic pleural plaques (red arrow), depending on the extent of disease. Treatment focuses on removal of any ongoing asbestos exposure. Patients are advised to quit smoking. Prompt treatment of any subsequent respiratory infections and timely immunizations against influenza and pneumococcal pneumonia are warranted. Some patients may require supplemental home oxygen therapy. Corticosteroids and immunosuppressive drugs do not alter the course of the disease.
Patients with asbestosis are at increased risk of developing bronchogenic carcinoma and malignant mesothelioma. The majority of mesothelioma cases are preceded by asbestos exposure, but the latency period may be up to 50 years. Tumor growth usually occurs along the lower part of the chest. With disease progression, the tumor often extends into the pulmonary parenchyma, brachial plexus, and superior vena cava. Treatment options have limited success and are based on the extent of disease progression. Combinations of chemotherapy, radiation therapy, and surgery are utilized. Median survival is only 11 months and the disease is almost always fatal. The computed tomography scan shown is of a 58-year-old patient who presented with shortness of breath and was found to have mesothelioma with extensive pleural thickening, effusion, and lung volume reduction in the affected hemithorax.
Silicosis is a fibronodular lung disease caused by inhalation of dust containing crystalline silica. It is perhaps the oldest known occupational lung disease, referred to by both Hippocrates and Pliny. Crystalline silica, most commonly quartz, is found in granite, slate, sandstone, and other common building materials. Individuals who work in mining, sandblasting, cement manufacturing, masonry, construction, or grinding are at risk of developing disease without appropriate protection. The historical image from 1939 depicts workers shoveling finely ground quartz for the creation of clay without respiratory protection before the dangers of silicon inhalation were known. Small silicon particles are inhaled into the distal alveoli where they generate silicon-based radicals that lead to the production of oxygen and hydrogen-based free radicals that damage cell membranes. Alveolar macrophages ingest the particles and release their own inflammatory mediators. The end result is inflammation that damages cells and the extracellular matrix leading to fibrosis. Silica particles outlive the alveolar macrophages, thus continuing the cycle of injury. Image courtesy of the Centers for Disease Control.
Acute silicosis occurs following a brief massive exposure to silica while chronic silicosis develops after years of exposure. In both forms, physical examination findings are typically benign with respiratory difficulty and signs of hypoxemia only in severe cases. Diagnosis is based on a history of exposure, clinical symptoms, physical examination findings, and chest radiographic appearance. Chest radiographs are essential to the diagnosis of silicosis. Typical findings include bilateral alveolar filing, multiple diffuse small nodules predominately in the upper lung findings, calcification of hilar lymph nodes (red arrow), and rarely cavitation of coalescing nodules. Treatment focuses on exposure avoidance, smoking cessation, immunization, and prompt treatment of respiratory infections. Corticosteroids may benefit individuals with acute silicosis. Infection of cavities by fungal organisms is a potential complication. Overall mortality is quite low, with reports of only 2 per million people in 1991 in the United States.
Inhalation of beryllium causes 2 distinct pulmonary syndromes: an acute chemical pneumonitis and a chronic granulomatous lung disease known as berylliosis. It is often confused with sarcoidosis as they have very similar chest radiographs. In acute beryllium disease, the metal acts as a direct chemical irritant causing an inflammatory reaction. Due to improved industrial hygiene measures, the incidence in the United States has virtually disappeared. Berylliosis occurs after exposure to beryllium dust or fumes, which can be found in numerous manufactured products: computer or automotive electronics, nuclear reactors, aircraft components, and nuclear reactors. The pathogenesis is a result of delayed-type hypersensitivity reaction stimulating proliferation of T cells leading to inflammatory, fibrosis, and granuloma formation. Patients may report cough, chest pain, arthralgias, fatigue, and weight loss. Other than inspiratory crackles, physical examination findings are uncommon. Diagnosis is made by a beryllium lymphocyte proliferation test from blood or bronchoalveolar lavage and non-necrotizing granulomas on lung biopsy (black arrow on hematoxylin-and-eosin histopathology slide shown). Treatment focuses on exposure avoidance and corticosteroid therapy for 4-6 weeks. Prognosis is highly variable and ranges from complete recovery to lung transplantation.
Coal worker's lung is a fibrotic pulmonary condition caused by the accumulation of coal dust in the lungs. Anthracosis in comparison is the asymptomatic accumulation of coal pigment without cellular reaction found in urban dwellers and tobacco smokers. Coal dust enters the alveoli and is ingested by macrophages which expel the particles through mucus or via the lymphatic system. When the system is overwhelmed, the accumulation of macrophages triggers an immune response leading to inflammation and fibrosis (shown). Periarterial fibrosis can lead to strangulated vessels and ischemic necrosis. Focal areas of coal deposition produce coal macules, the hallmark or coal worker's pneumoconiosis, which can extend into one another leading to focal emphysematous changes. The degree of fibrosis is related to the duration of exposure, age at first exposure, and the quantity of inhaled silica within the coal dust. Patients with early disease are typically asymptomatic but may eventually report productive cough and dyspnea. Diagnosis is typically made based on history, physical examination findings, and evidence of fibrosis on radiographic imaging. Treatment is largely supportive and preventative. Mortality is related to the degree of fibrosis and oxygen requirement.
Author
Lars Grimm, MD, MHS
House Staff
Department of Internal Medicine
Duke University Medical Center
Durham, North Carolina
Disclosure: Lars Grimm, MD, MHS, has disclosed no relevant financial relationships.
Editor
Zab Mosenifar, MD
Director, Division of Pulmonary and Critical Care Medicine,
Women's Guild Pulmonary Disease Institute; Executive Vice
Chair, Department of Medicine, Cedars Sinai Medical Center;
Professor of Medicine, David Geffen School of Medicine at UCLA
Los Angeles, California
Disclosure: Zab Mosenifar, MD, has disclosed no relevant financial relationships.
