(See also Overview of Environmental Pulmonary Disease Overview of Environmental Pulmonary Disease Environmental pulmonary diseases result from inhalation of dusts, allergens, chemicals, gases, or environmental pollutants. The lungs are continually exposed to the external environment and... read more .)
Etiology of Coal Workers’ Pneumoconiosis
Coal workers' pneumoconiosis is caused by chronic inhalation of dust from high-carbon coal (anthracite and bituminous) and rarely graphite, typically over ≥ 20 years. Inhalation of silica contained in coal may also contribute to clinical disease.
Pathophysiology of Coal Workers’ Pneumoconiosis
Alveolar macrophages engulf the dust, release cytokines that stimulate inflammation, and collect in lung interstitium around bronchioles and alveoli (coal macules). Coal nodules develop as collagen accumulates, and focal emphysema develops as bronchiole walls weaken and dilate. Fibrosis can occur but is usually limited to areas adjacent to coal macules. Distortion of lung architecture, airflow obstruction, and functional impairment are usually mild but can be highly destructive in some patients.
Two forms of coal workers' pneumoconiosis are described:
Simple, with individual coal macules
Complicated, with coalescence of macules and progressive massive fibrosis
Patients with simple coal workers' pneumoconiosis develop progressive massive fibrosis at a rate of about 1 to 2% /year. Recently, rapid progression of coal workers' pneumoconiosis to progressive massive fibrosis has been recognized in young miners, especially in the eastern US compared to the rest of the United States (1 Key Points Coal workers’ pneumoconiosis is caused by inhalation of coal dust. Deposition of dust produces dust-laden macrophages around bronchioles (coal macules), occasionally causing focal bronchiolar... read more ).
In progressive massive fibrosis, nodules coalesce to form black, rubbery parenchymal masses usually in the upper posterior lung fields. The masses may encroach on and destroy vascular supply and airways or may cavitate. Progressive massive fibrosis can develop and progress even after exposure to coal dust has ceased. Despite the similarity of coal-induced progressive massive fibrosis and conglomerate silicosis, the development of progressive massive fibrosis in coal workers is unrelated to the silica content of the coal. However, exposure to silica in coal is required for progression from coal workers' pneumoconiosis to progressive massive fibrosis, and exposure to graphite alone can cause coal workers' pneumoconiosis but not progression to progressive massive fibrosis.
A small percentage of patients with coal workers' pneumoconiosis develop diffuse pulmonary fibrosis.
An association between coal workers' pneumoconiosis and features of rheumatoid arthritis Rheumatoid Arthritis (RA) Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease that primarily involves the joints. RA causes damage mediated by cytokines, chemokines, and metalloproteases. Characteristically... read more is well-described. It is unclear whether coal worker's pneumoconiosis predisposes miners to developing rheumatoid arthritis, whether rheumatoid arthritis takes on a unique form in patients with coal workers' pneumoconiosis, or whether rheumatoid arthritis alters the response of miners to coal dust. Multiple rounded nodules in the lung appearing over a relatively short time (Caplan syndrome) represent an immunopathologic response related to rheumatoid diathesis. Histologically, they resemble rheumatoid nodules but have a peripheral region of more acute inflammation.
Patients with coal workers' pneumoconiosis are at a slightly increased risk of developing active tuberculosis Tuberculosis (TB) Tuberculosis is a chronic, progressive mycobacterial infection, often with an asymptomatic latent period following initial infection. Tuberculosis most commonly affects the lungs. Symptoms include... read more and nontuberculous mycobacterial infections Nontuberculous Mycobacterial Infections There are over 170 recognized species of mycobacteria, mostly environmental. Environmental exposure to many of these organisms is common, but most exposures do not cause infection and many infections... read more . Weak associations have been reported between coal workers' pneumoconiosis and progressive systemic sclerosis Systemic Sclerosis Systemic sclerosis is a rare chronic disease of unknown cause characterized by diffuse fibrosis and vascular abnormalities in the skin, joints, and internal organs (especially the esophagus... read more and stomach cancer Stomach Cancer Etiology of stomach cancer is multifactorial, but Helicobacter pylori plays a significant role. Symptoms include early satiety, obstruction, and bleeding but tend to occur late in the... read more .
1. Almberg KS, Halldin CN, Blackley DJ, et al: Progressive massive fibrosis resurgence identified in U.S. coal miners filing for black lung benefits, 1970-2016. Ann Am Thorac Soc 15(12):1420–1426, 2018. doi: 10.1513/AnnalsATS.201804-261OC
Symptoms and Signs of Coal Workers’ Pneumoconiosis
Coal workers' pneumoconiosis does not usually cause symptoms. Most chronic pulmonary symptoms in coal miners are caused by other conditions, such as industrial bronchitis Occupational Asthma due to coal dust or coincident emphysema Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease (COPD) is airflow limitation caused by an inflammatory response to inhaled toxins, often cigarette smoke. Alpha-1 antitrypsin deficiency and various occupational... read more due to smoking. Cough can be chronic and problematic in patients even after they leave the workplace, even in those who do not smoke.
Progressive massive fibrosis causes progressive dyspnea. Occasionally, patients cough up black sputum (melanoptysis), which occurs when progressive massive fibrosis lesions rupture into the airways. Progressive massive fibrosis often progresses to pulmonary hypertension Pulmonary Hypertension Pulmonary hypertension is increased pressure in the pulmonary circulation. It has many secondary causes; some cases are idiopathic. In pulmonary hypertension, pulmonary vessels may become constricted... read more with right ventricular failure Cor Pulmonale Cor pulmonale is right ventricular (RV) enlargement secondary to a lung disorder that causes pulmonary artery hypertension. Right ventricular failure follows. Findings include peripheral edema... read more and respiratory failure Overview of Respiratory Failure Acute respiratory failure is a life-threatening impairment of oxygenation, carbon dioxide elimination, or both. Respiratory failure may occur because of impaired gas exchange, decreased ventilation... read more .
Diagnosis of Coal Workers’ Pneumoconiosis
History of exposure to coal dust
Chest CT or chest x-ray
Diagnosis of coal workers’ pneumoconiosis is based on a history of exposure to coal dust and chest x-ray or chest CT appearance.
In patients with coal workers' pneumoconiosis, chest x-ray or CT reveals diffuse, small, rounded opacities or nodules. The finding of at least one opacity > 10 mm suggests progressive massive fibrosis. The specificity of the chest x-ray for progressive massive fibrosis is low because up to one third of the lesions identified as being progressive massive fibrosis turn out to be cancers, scars, or other disorders. Chest CT is more sensitive and specific than chest x-ray for detecting coalescing nodules, early progressive massive fibrosis, and cavitation.
Diffuse pulmonary fibrosis is characterized by lower lobe predominant reticular opacities. Honeycomb changes have also been reported.
Pulmonary function tests Overview of Tests of Pulmonary Function Pulmonary function tests provide measures of airflow, lung volumes, gas exchange, response to bronchodilators, and respiratory muscle function. Basic pulmonary function tests available in the... read more are nondiagnostic but are useful for characterizing lung function in patients in whom obstructive, restrictive, or mixed defects may develop. Because abnormalities of gas exchange occur in some patients with extensive simple coal workers' pneumoconiosis and in those with complicated coal worker's pneumoconiosis, baseline and periodic measures of diffusing capacity for carbon monoxide (DLCO) and arterial blood gas levels at rest and during exercise are recommended.
Because patients with coal workers' pneumoconiosis often have had exposure to both silica dust and coal dust, surveillance for tuberculosis Tuberculosis (TB) Tuberculosis is a chronic, progressive mycobacterial infection, often with an asymptomatic latent period following initial infection. Tuberculosis most commonly affects the lungs. Symptoms include... read more (TB) is usually done. Patients with coal workers' pneumoconiosis should have annual tuberculin skin testing. In those with positive test results, sputum culture and cytology, CT, and bronchoscopy may be needed to confirm TB.
Treatment of Coal Workers’ Pneumoconiosis
Sometimes supplemental oxygen and pulmonary rehabilitation
Restriction from further exposure
Treatment is rarely necessary in simple coal workers' pneumoconiosis, although smoking cessation Smoking Cessation Most smokers want to quit and have tried doing so with limited success. Effective interventions include cessation counseling and drug treatment, such as varenicline, bupropion, or a nicotine... read more and TB surveillance are recommended. Patients with pulmonary hypertension, hypoxemia, or both are given supplemental oxygen therapy.
Pulmonary rehabilitation Pulmonary Rehabilitation Pulmonary rehabilitation is the use of supervised exercise, education, support, and behavioral intervention to improve functional capacity and enhance quality of life in patients with chronic... read more can help more severely affected workers carry out activities of daily living. Workers with coal workers' pneumoconiosis, especially those with progressive massive fibrosis, should be restricted from further exposure, especially to high concentrations of dust. TB is treated Treatment Tuberculosis is a chronic, progressive mycobacterial infection, often with an asymptomatic latent period following initial infection. Tuberculosis most commonly affects the lungs. Symptoms include... read more in accordance with current recommendations.
Prevention of Coal Workers’ Pneumoconiosis
Preventive measures include eliminating exposure, stopping smoking, and giving pneumococcal and influenza vaccinations. Coal workers' pneumoconiosis can be prevented by suppressing coal dust at the coal face. Despite long-standing regulations, exposures continue to occur in the mining trade, resulting in increased rates of disease, including severe forms.
Respiratory masks provide only limited protection.
Coal workers’ pneumoconiosis is caused by chronic inhalation of dust from high-carbon coal (anthracite and bituminous) and rarely graphite, typically over ≥ 20 years.
Most patients have simple coal workers' pneumoconiosis, with small, asymptomatic nodules seen on imaging.
Some patients with coal workers' pneumoconiosis develop progressive massive fibrosis, with deterioration of pulmonary function, dyspnea, and marked abnormalities on imaging studies.
Base the diagnosis on history of exposure as well as chest imaging.
Treat supportively, encourage smoking cessation, and restrict further exposure.