Basics
Black lung disease gets its name from the black appearance of lungs in miners who have inhaled coal dust particles. The medical term for black lung disease is coal workers’ pneumoconiosis, which is actually a spectrum of diseases.
Definitions and Types
Black lung disease is caused by the inhalation of dust particles during coal mining. It begins with a mild condition known as anthracosis that does not have symptoms (is asymptomatic). Evidence of anthracosis related to air pollution can be found in many people who live in urban areas and not just coal miners.
Black lung disease, or coal mine dust lung disease (CMDLD), can be divided into two categories:
Simple: Simple black lung disease is most common, with the development of inflammatory nodules in the lung. Complex: Complex disease (PMF) is more severe. It can lead to severe disability and death.
Symptoms
Early on, many people will have no symptoms of black lung disease. When symptoms begin, shortness of breath only with activity (exercise intolerance) may easily be dismissed as being simply due to age.
With time, shortness of breath may worsen and include a sensation of chest tightness. A persistent cough may also occur, which can be either dry or wet (productive of mucus).
The particular symptoms a person experiences can vary based on the makeup of the dust at their particular place of employment, other medical conditions, and general health.
Complications
One of the most serious complications of severe black lung disease is right heart failure. Due to extensive fibrosis in the lungs, the blood pressure in the pulmonary artery (blood vessel that carries blood from the right side of the heart to the lungs) increases. This increased pressure subsequently leads to enlargement of the right side of the heart and right-sided heart failure (cor pulmonale).
An uncommon complication of black lung disease is Caplan syndrome. In this syndrome, on top of the background of a black lung, inflammatory nodules appear in the lung as well (rheumatoid nodules), and patients develop joint inflammation as seen in rheumatoid arthritis.
An older study also noted an increased risk of lung cancer (specifically squamous cell carcinoma of the lungs) with simple black lung disease. Lung cancer does appear to be more common among coal mine workers even without black lung disease.
Other Lung Diseases Caused by Coal Dust Exposure
Coal dust exposure is also associated with other lung diseases that may have their own symptoms. In addition to fibrosis, coal miners are at risk for developing obstructive lung diseases such as emphysema and chronic bronchitis, and it’s estimated that at least 15 percent of coal miners have chronic bronchitis due to dust exposure (industrial bronchitis).
Incidence
The incidence of black lung disease had actually declined to record lows in the 1990s due to the Coal Act. Since that time, the prevalence of black lung disease (combining both simple and complex) has increased significantly according to a 2018 study reported in the American Journal of Public Health. At the current time, black lung disease is present in over 10 percent of miners who have worked in or near the mines for 25 or more years. This number is higher in central Appalachia, with 20.6 percent of long-term miners having black lung disease. (Central Appalachia includes Kentucky, Virginia, and West Virginia.) In this study, black lung disease was defined as the presence of small opacities or the presence of an opacity larger than 1 centimeter on imaging.
The prevalence of severe (complex) black lung disease has also increased significantly since the mid to late 1990s. The average annual prevalence of PMF in the mid to late 1990s was 0.37 percent. This rose to 3.23 percent (an 8.6-fold rise) between 2008 and 2012. Data was derived from the Coal Workers’ Health Surveillance Program in Kentucky, Virginia, and West Virginia.
A cluster of cases of PMF not discovered through the surveillance program was reported by a single radiology practice in eastern Kentucky. The single practice found 60 cases of PMF in current and former coal miners between January 2015 and August 2016.
The proportion of people with PMF who have claimed federal black lung benefits has also increased considerably since 1996, especially in Virginia.
Why Are Incidence and Severity Increasing?
The increase in black lung disease may be partly linked to the recent increase in coal mining, but this does not explain the worsening severity and the finding of severe black lung disease even in young miners. There are a number of factors that may be contributing, such as mining thin coal seams (with greater exposure to silica), the depth of mining, and more.
The Problem Persists After Exposure Is Done
Of great importance is that negative health effects persist even after a person is no longer exposed to coal mine dust. A 2015 study compared the prevalence of black lung disease in former and active miners. The former miners had a greater prevalence of black lung disease than the current miners.
Causes and Risk Factors
Many coal miners are at risk for black lung disease, with some exposures to coal dust posing more risk. For example, stone cutters have very high exposure rates, as do people who work downwind from dust-generating equipment.
Pathophysiology
When coal dust enters the lungs, it settles in the small airways where it cannot be removed or degraded. Immune cells called macrophages (essentially the “garbage trucks of the immune system”) engulf the particles, where they remain indefinitely. The presence of these particles in macrophages causes the lungs to appear black, hence the name black lung disease.
It is actually the substances released by macrophages (such as cytokines) that lead to inflammation. Inflammation, in turn, leads to the formation of scar tissue (fibrosis).
Black lung disease differs from some lung diseases in that it is primarily a disease of the small airways. Due to the small size of the dust particles, they “land” in the distal bronchioles near the sacs where the exchange of oxygen and carbon dioxide takes place (alveoli). Larger particles are often caught in the cilia in the large airways where they can be moved upward in the airways and coughed up or swallowed.
Genetic differences may play a role in who is most at risk as well. Genome-wide association studies (studies that look for common variants in the entire genome) in China have shown associations that may increase the risk as well as associations that may be protective.
Where Are People Most at Risk?
Though coal miners in central Appalachia appear to have the highest risk of black lung disease, the disease occurs in all U.S. mining regions across the country (and roughly 57 percent of coal miners work in regions outside of central Appalachia). A 2017 study reported in the American Journal of Industrial Medicine found that, overall, 2.1 percent of miners had black lung disease. The prevalence was highest in the East (3.4 percent) and lowest in the interior (0.8 percent), with a prevalence between these in the West (1.7 percent).
Diagnosis
The diagnosis of black lung disease begins with a careful history to evaluate risk factors and a physical exam.
Imaging
A chest X-ray is most often the first test, but a CT scan is usually needed to find smaller abnormalities. Findings may include “coal macules,” or tiny nodules 2 to 5 millimeters (mm) in diameter scattered diffusely in the upper lobes of the lungs. (Of note is that a chest X-ray cannot usually detect nodules less than 10 mm in diameter).
PMF is diagnosed if there are lung nodules larger than 1 centimeter in diameter (roughly 0.4 inches), or 2 centimeters (0.8 inches), depending on the criteria of different organizations.
Other studies (such as an MRI or PET scan) may be needed at times, primarily to rule out other diagnoses.
Procedures
Pulmonary function tests are commonly done, but due to the presence of disease in the small airways, these tests may not show significant changes until the disease is fairly advanced. A bronchoscopy and/or lung biopsy may be needed to rule out other diagnoses.
Differential Diagnosis
There are a number of conditions that need to be considered in the differential diagnosis of black lung disease. Some of these include:
Silicosis (also occurs in miners and can appear quite similar to PMF)AsbestosisBerylliosisChronic bronchitis (can occur along with black lung disease, but symptoms may also mimic the disease)
Treatment
There is currently no cure for black lung disease, and the goal of treatment is to prevent worsening of the disease and control symptoms.
Medications such as inhalers may be needed, especially for those who also have chronic bronchitis. Oxygen may be needed, especially with PMF. Pulmonary rehabilitation can be helpful by providing breathing techniques and teaching people how to cope with the symptoms of black lung disease.
A lung transplant is the only option with end-stage black lung disease, and the rate of lung transplants that are done for black lung disease has been increasing. The increasing rate of lung transplants also supports the rising prevalence of severe black lung disease.
Measures to prevent worsening or complications are critical in managing black lung disease. This includes not only reducing exposure to coal dust but also to other metal dusts. Smoking cessation and avoidance of secondhand smoke are, of course, important. The pneumonia vaccine and flu vaccinations are important to reduce the risk of pneumonia.
Prognosis
The prognosis of black lung disease depends on the extent of the disease (simple or complex) as well as further exposures. Simple black lung disease can progress slowly over a long period of time, whereas PMF can progress rapidly.
Years of potential life lost (YPLL), a measure of the toll the disease takes, has been increasing, likely due to the increased severity of black lung disease in recent years.
Prevention
Prevention encompasses both primary prevention, meaning preventing exposure in the first place, and secondary prevention, or preventing further damage once evidence of black lung disease is present.
Primary prevention includes better methods of dust control, limits on exposure, and the use of protective equipment (such as respirators) when indicated. The Federal Coal Mine Health and Safety Act of 1969 (amended in 1977) defined dust limits and created the Coal Workers’ Health Surveillance Program (NIOSH).
In 2014, new rules (Lowering Miners’ Exposure to Respirable Coal Mine Dust) reduced the maximum allowable exposure and added protections to previous guidelines.
Surveillance
Surveillance, or attempting to diagnose black lung disease in the early, simple stage of the disease, is also very important. At the current time, The National Institute for Occupational Safety and Health has guidelines that recommend miners have imaging studies done every five years to look for evidence of disease related to coal mine dust. These are only guidelines, and some people may need to be monitored more frequently. These guidelines are also in place for people who do not have symptoms. Those who have symptoms or findings on imaging studies that suggest black lung disease will need further evaluation.
A Word From Verywell
Black lung disease is increasing in both prevalence and severity, which is disheartening as it is, in a sense, a preventable disease. Efforts to increase surveillance are vital. Fortunately, studies are in place attempting to determine why progressive massive fibrosis is increasing so that measures can be taken to reduce risk.
