Black Lung Disease

Black lung disease, also known as coal workers' pneumoconiosis (CWP), is an occupational condition that—while once declining—is now increasing in both incidence and severity in the United States. Most often occurring in coal miners, the greatest increase has been seen in central Appalachia, though the disease is increasing in other regions as well.

CWP is caused by the inhalation of fine dust particles that cause scarring, which is followed by the development of scar tissue (fibrosis). Since the condition is irreversible, treatment is focused on managing symptoms and preventing further lung damage.

This article discusses the types of black lung disease, as well as the symptoms and causes. It also addresses the diagnosis, treatment, and prevention of the disease.

Black Lung Disease Overview

Black lung disease gets its name from the black appearance of the lungs of 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 (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: Also called progressive massive pulmonary fibrosis, or PMF, complex disease is more severe. It can lead to severe disability and death.

Black Lung Disease 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). Sometimes the coughing may bring up black 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 (the 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).

Other complications may include:

• Chronic bronchitis
• Chronic obstructive pulmonary disease (COPD)
• Respiratory failure

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 people 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. A meta-analysis suggested an increased risk of lung cancer in coal miners with CWP but not in miners of unknown CWP status.

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. It's estimated that 35% of coal miners have chronic bronchitis due to dust exposure.

Incidence of Black Lung Disease

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.

Black lung disease is present in over 10% 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% 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 during the mid to late 1990s was 0.37%. This rose to 3.23% (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 of Black Lung Disease

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 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 also play a role in who is most at risk. 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% of coal miners work in regions outside of central Appalachia).

A 2017 study found that, overall, 2.1% of miners had black lung disease. The prevalence was highest in the East (3.4%) and lowest in the interior (0.8%), with a prevalence in between these in the West (1.7%).

How Is Black Lung Disease Diagnosed?

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 1 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

A number of conditions need to be considered in the differential diagnosis of black lung disease, especially if there have been less than 10 years of exposure to coal mine dust. Some of these include:

• Silicosis (also occurs in miners and can appear quite similar to PMF)
• Asbestosis
• Hypertrophic osteoarthropathy
• Idiopathic pulmonary fibrosis (IPF)
• Interstitial (nonidiopathic) pulmonary fibrosis
• Lung cancer
• Metastatic disease
• Tuberculosis (TB)/Miliary tuberculosis
  

Black Lung 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.

How Long Can Someone Live With a Black Lung?

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 (preventing exposure in the first place) and secondary prevention—preventing further damage and complications 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 reduced the maximum allowable exposure and added protections to previous guidelines.

Secondary prevention for managing black lung disease includes:

• Reducing exposure to coal dust by wearing a mask, washing areas of skin that come in contact with dust
• Reducing exposure to other metal dusts
• Stopping smoking and avoiding secondhand smoke
• Safe removal of dust from clothing

The pneumonia vaccine and flu vaccines are important to reduce the risk of pneumonia.

Surveillance

Surveillance, or attempting to diagnose black lung disease in the early, simple stage of the disease, is 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.

Summary

Black lung disease is increasing in both prevalence and severity. This condition is caused by the inhalation of dust particles during coal mining. These particles lead to the development of inflammatory nodules in the lung and can progress to fibrosis and other complications. Treatment focuses on controlling symptoms and preventing the disease from worsening. Early diagnosis and prevention are key elements to lowering the prevalence and severity of black lung disease.