Other Occupational Lung Diseases

WHAT lS OCCUPATIONAL LUNG DISEASE?

Most respiratory disease is caused by breathing in some potentially noxious material such as bacteria, viruses, cigarette smoke, allergens and dusts. Nowhere is respiratory vulnerability more evident than with the constant air pollution occurs in some jobs. Although information about occupational hazards goes back to antiquity (for instance, in mining), doctors have only recently come to realize the magnitude of the problem in all areas of employment, from manufacturing (e.g., asbestos inhalation) to white collar jobs (e.g., "sick building syndrome").

Occupational medicine is now a major part of medicine in general; it has its own specialty journals and training programs for doctors who want to specialize. Occupational lung disease, a major aspect of this field, is a significant cause of respiratory problems in all industrial nations. It is caused by inhaling noxious agents in the workplace, mainly dusts, fumes, gases, and vapors. There are two broad categories of occupational lung disease:

1. Diseases that are not occupation­specific. This group includes people with common medical conditions as emphysema, bronchitis, asthma, and interstitial lung disease. Although these conditions could be caused by workplace exposure, they are more commonly due to factors unrelated to the job, such as cigarette smoking. They may also be due to causes that can't be discerned. Although not occupation­specific, these conditions can definitely be aggravated by conditions at work. Emphysema, bronchitis and asthma are discussed in their respective sections. In addition, Section D is devoted to occupational asthma. This chapter will concentrate on occupation­specific lung diseases.

2. Diseases related to a specific occupation, such as asbestosis in asbestos workers (pipe fitters), silicosis in people exposed to silica dust (sandblasters) and coal workers' pneumoconiosis in coal miners. These diseases and many others like them have a specific cause and effect relationship with the inhaled material and would not occur if the workers did not have the specific exposures.

HOW COMMON IS OCCUPATIONAL LUNG DISEASE?

Surprisingly common. Although there are no exact figures, thousands of Americans are adversely affected by their workplace, the majority from lung damage. The Department of Health and Human Services estimates that every year 400,000 people develop a disease caused by their jobs. An estimated 100,000 deaths each year are caused by occupational diseases. More than half of these diseases and deaths are due to lung disease.

Many occupations are associated with some form of illness. Liver cancer in vinyl chloride workers, lung cancer in asbestos workers, deafness in jackhammer operators, bronchitis in toll­booth workers – these are but a few examples. The economic costs are staggering. Some $5 billion is paid out in workers' compensation annually for job­related illness and injuries.

The sad fact is that much of the human misery behind these statistics is preventable. Unfortunately, the connection between the patients illness and the job is often not made until too late. This delay in recognition is related to several factors, one of which is the slow and insidious progress of most occupational diseases.

WHAT ARE THE SPECIFIC OCCUPATIONAL LUNG DISEASES?

The list of all known occupational lung diseases would fill several volumes and be incomplete anyway since new ones are frequently being discovered. This fact reflects the amazing number of new compounds and industrial methods introduced yearly, as well as improved detection methods. For simplicity we can divide occupational lung disease into three main groups based on the type of material inhaled:

• mineral dusts
• organic dusts
• smoke, fumes, vapors, mists, and sprays.

Mineral dusts come from rocks, stones, and ores in the earth's crust. Diseases arising from inhalation of mineral dusts are called pneumoconioses. The most common are coal workers' pneumoconiosis (black lung), silicosis, and asbestosis.

Organic dusts come from living materials such as plants, animals, and microorganisms. A common example is farmers lung.

Smoke comes from burning organic material such as cigarettes, wood, trash, and so forth.

Fumes are formed when very hot vapors cool rapidly and condense into very fine solid particles; this occurs in welding, smelting, and furnace work.

Gases are found apart from liquids and can be defined as a liquid that will expand to fill any size space.

Vapors are essentially the same as gases except that they are encountered only in the presence of the parent liquid.

Mists and sprays are terms used interchangeably; they are fine suspensions of liquid droplets in air or some other propellant gas.

WHAT lS BLACK LUNG DISEASE?

Black lung refers to lung disease caused by inhaling coal dust. The medical term coal workers pneumoconiosis (CWP). Black lung comes from the fact that the lungs of deceased coal miners often appear black from the heavy deposits of coal. The normal human lung has a healthy pink appearance. Although people living in an around cities will have some black deposits in their lungs, coal workers may have much more extensive involvement.

CWP or black lung disease is diagnosed by two simple criteria:

1. History of working in coal mines, and

2. Abnormal chest X­ray showing the characteristic spots in the lungs caused by coal dust deposits.

Only a small percentage of ex­coal miners, perhaps fewer than 10 percent, have any x­ray evidence of coal dust deposits; when present, they usually show up as small spots, less than one centimeter in diameter. Such a chest x­ray pattern, in an ex­coal miner, is called simple CWP (see Figure 1 ).

Figure 1. Drawing of chest x­ray picture showing simple coal workers pneumoconiosis ("black lung"). Dust deposits, represented by black dots, are scattered throughout both lungs. See Section I for further discussion of chest x­ray drawings.

Simple CWP causes no symptoms and does not lead to respiratory disability In fact, epidemiologic studies show that coal miners who have breathing impairment, but have only simple CWP on their chest x­ray, are invariably heavy cigarette smokers; smoking, not coal dust, is responsible for the breathing problem.

Although coal dust can certainly infiltrate the lungs and make them black, coal dust by itself ever causes major breathing impairment. How then to account for severe black lung disease, which has claimed many victims in the past? This more virulent form of black lung disease is manifested by progressive fibrosis (scarring) of the lungs and shows a very different x­ray picture from simple CWP. It is not due to cigarette smoking, but also doesn't seem due to coal dust per se. Some investigators think it is due to silica dust mixed in with the coal in the particular mine that was worked. Silica is much more fibrogenic (likely to lead to scarring) than coal. The cause for progressive fibrosis seen in coal miners is not known with certainty, but fortunately it is much less common than simple CWP.

A far greater threat to the health of most miners is cigarette smoking. Added to the inhaled coal dust, the smoking miner is at much greater risk for bronchitis emphysema and lung cancer than his nonsmoking co­worker (see Figure 2).

WHAT IS SILICOSIS?

Inhalation of silica dust which is sometimes inhaled in pure form during sandblasting causes much more severe disease than inhalation of pure coal dust. This type of pneumoconiosis is called silicosis. Silica may also be responsible for the severe cases of black lung disease seen in coal workers. Pure silica dust can lead to widespread scarring of the lungs and can be extremely disabling. In addition, silicosis makes the patient more susceptible to tuberculosis and lung cancer.

Sandblasting is a term for abrasive cleaning in which a stream of sand is projected by compressed air under high pressure. Sandblasting is used to clean metal surfaces in shipyards and steel fabrication plants, as well as facades of buildings. It is only one of many occupations that may lead to silicosis.

Given the presence of pneumoconiosis on the chest x­ray, silicosis can usually be separated from coal workers, pneumoconiosis by work history and appearance of the chest x­ray (see Figure 2). If the patient worked in coal mines, he may have silicosis along with CWP, but he most certainly has CWP. Patients who have never worked in coal mines, but have worked as sandblasters or in other silica dust areas have characteristic findings on their chest x-rays – usually widespread scarring in the upper parts of the lungs.

Figure 2 Chest x­ray appearance of silicosis. Silicosis, caused by inhaling silica dust, affects mainly the upper parts of the lungs.

Not everyone who works around silica and coal dust gets silicosis or coal worker's pneumoconiosis. Contraction of either disease is related to the intensity and duration of dust exposure; the longer one works with these dusts and the more dense the air concentration, the better the chance that the disease will occur. Cigarette smoking also contributes to any impairment that results from dust inhalation .

WHAT ARE THE HEALTH HAZARDS FROM ASBESTOS?

Asbestos is a family of naturally occurring minerals that are widely used as insulating material. Asbestos has over 3,000 uses, including insulation for boilers and pipes, automobile brake linings, and, until recently, insulating hair dryers. An estimated 30 million tons has been used in the United States since 1900.

Asbestos can cause serious disease when inhaled over a period of time. Minute asbestos fibers are taken up by the lung cells; unlike many ordinary dust particles, these fibers cannot be removed by the lung defenses. The physical property of the fibers (small size, thin, and narrow) allows them to penetrate the deepest lung tissues where they reside throughout life. Many years later, even two to three decades after exposure, one of several diseases can show up, including asbestosis, lung cancer, mesothelioma, and some less common conditions.

Asbestosis

Asbestosis is the most common form of asbestos­related lung disease. It occurs in only a small number of people who have worked with asbestos, and is diagnosed by a typical appearance on the chest x­ray plus a history of occupational exposure (see Figure 3). Asbestosis is really a lung tissue reaction to the inhaled asbestos dust and is, therefore, a type of pneumoconiosis, comparable to silicosis or other mineral dust diseases. Asbestosis is not cancer (though it may lead to cancer) and is not invariably fatal, although patients can die from severe forms of. the disease. The usual picture is scarring and fibrosis of the lung tissue. The reason why only some of the people exposed to asbestos dust get asbestosis is not known. There is no effective treatment for asbestosis. Complications, such as pneumonia or lung cancer, can be fatal in patients with asbestosis. If the patient smokes, he or she should quit forever; smoking tremendously increases the risk of developing lung cancer in people with underlying asbestosis.

Lung Cancer

This is the most dreaded result of chronic asbestos inhalation. It is usually found in patients who also smoke; the combination of smoking and asbestos exposure sharply increases the risk of lung cancer over that of people who only smoke or only have chronic asbestos exposure. Smoking and asbestos exposure are synergistic for the development of lung cancer. X­ray findings of asbestosis don't have to be present to develop asbestos­related lung cancer. The cancer can begin growing in a patient whose chest x­ray has been negative for years following exposure to asbestos dust. The cure rates for any lung cancer are dismal and asbestos­related lung cancer is no exception.

Figure 3. Typical x­ray appearance of asbestosis. The disease affects mainly the lower parts of the lungs.

Mesothelioma

This is a tumor of tissues that cover either the lungs (the pleural membranes) or the contents of the abdominal cavity (the peritoneal membranes) and is related to asbestos exposure. Although occasionally these tumors can be benign, when they occur due to asbestos exposure they are usually malignant. Unlike lung cancer, their occurrence is not related to cigarette smoking. There is no effective treatment for malignant mesothelioma.

Other Conditions

Other diseases have been linked to asbestos exposure, including cancer of the larynx (voice box) and cancer of the stomach,colon, and rectum. The association of asbestos exposure with these tumors is not as strong as with lung cancer, but asbestos workers contract these tumors more often than the general public.

HOW WAS ASBESTOS FOUND TO BE DANGEROUS?

Asbestos has been mined since the late 1800s, with industrial uses expanding greatly after the turn of the century. In the 1930s and 40s several investigators made the association between asbestos exposure and an increased incidence of lung cancer. Further recognition of this association occurred in the 1960s when Dr. Irving Selikoff and colleagues at New York City's Mt. Sinai Hospital published data on 632 members of the International Association of Heat and Frost Insulators and Asbestos Workers. They found a much higher than average number of deaths from lung cancer in these workers as well as a much larger than expected number of mesotheliomas. This and other studies have also demonstrated that cigarette smoke adds a synergistic effect to asbestos exposure so that the rate of lung cancer is far greater than with either exposure alone. People who smoke and work with asbestos are in a potentially very dangerous situation.

Dr. Selikoff also published data on asbestos insulation workers who had been at their job for at least 20 years. This large group (12,051 workers) was compared with another large group of men followed by the American Cancer Society and in whom smoking habits were known. They reported the following risks for developing lung cancer:

The nonsmoker not exposed to asbestos has a very low risk of ever getting lung cancer. This risk is arbitrarily assigned a value of 1. Work with asbestos increases the risk of lung cancer 5­fold. People who smoke but are not exposed to asbestos have an almost 11­fold greater chance of getting lung cancer than nonsmokers. Add smoking to the asbestos exposure and the risk is enormous. Asbestos exposure increases the risk of lung cancer 5­fold over the already large risk from smoking alone.

Anyone who smokes is inviting lung cancer; any asbestos worker who smokes is making sure the invitation is answered. According to Dr. Selikoff, among asbestos workers one in every five deaths is due to lung cancer!

IS THERE ASBESTOS EXPOSURE APART FROM THE WORKPLACE?

Yes. If carefully searched for under the microscope, asbestos fibers are often found in lungs of non­asbestos workers. This is considered a normal finding in most people, and differs from the disease asbestosis mainly in the small numbers of fibers present. Thus, healthy lungs may have a few fibers in lung tissue whereas people with asbestosis have tremendously more fibers, enough to form scar tissue. If it is absolutely unavoidable that you work with asbestos, then a special mask and filter should be worn at all times to avoid inhaling these fibers.

WHAT OTHER DUSTS CAN CAUSE PNEUMOCONIOSIS?

Actually the list is long. Virtually any mineral dust inhaled to excess over a long period of time can cause some pulmonary reaction and a resulting abnormal chest x­ray. For unknown reasons some dusts tend to be relatively inert and almost never cause severe lung scarring. Examples of the more benign mineral dusts are tin, iron and aluminum. Exposed workers can show extensive x­ray evidence of inhaled tin for example, yet have no pulmonary impairment or symptoms. The more commonly inhaled dusts such as coal, asbestos, and silica can be very damaging especially the latter two, although exposure usually has to be prolonged (years). It is likely that a one­time exposure will have little if any harmful effect in most individuals.

WHAT IS ORGANIC DUST DISEASE?

We have just discussed lung diseases that may occur from inhaling mineral dusts; these are the pneumoconioses. Lung disease may also occur from inhaling living or organic dusts. Such dusts include spores, fungi, and other tiny organisms that may be inhaled in occupations dealing with plants, trees, animals, crops, and so forth. Aside from the material inhaled, this group differs from the pneumoconioses in one important aspect: patient symptoms.

Patients suffering from organic dust disease generally manifest one of two acute syndromes: a diffuse pneumonia accompanied by shortness of breath and fever (so­called hypersensitivity pneumonitis) or an acute asthma­bronchitis problem. With chronic exposure the patient may end up with chronic obstructive or restrictive lung disease.

There is a diversity of occupations and materials that may lead to organic dust disease, Table 1 lists many of the jobs and associated conditions that have been reported. Only a minority of workers in each occupation suffer from inhalation lung disease; why this is so is not known.

When patients present with an asthma­bronchitis picture, the chest x­ray is usually clear and the patient complaints are coughing, wheezing, and shortness of breath. This is also known as occupational asthma (see Section D). Classically, the symptoms are worse on returning to work after a weekend off and abate after stopping work at the end of the week. One of the best studied of such diseases is found in cotton workers; it is called byssinosis or brown lung.

The second major manifestation of organic dust exposure is called hyper-sensitivity pneumonitis (HP). In HP the patients are clinically sick with pneumonia and the x­ray shows an infiltrate. In contrast to infectious pneumonia, HP is not an infection and is not treated with antibiotics. HP is caused by an allergic reaction to the inhaled dust. One of the best studied examples of HP is farmer's lung. Farmers who work around moldy hay may inhale the fungal spores that make the hay moldy. They may become sick within a few hours of inhaling the fungal dust and develop fever, cough, and shortness of breath. The chest x­ray shows a stringy infiltrate. Hyper-sensitivity pneumonitis usually responds to treatment with corticosteroids.

There is still much to learn about all of the various occupational diseases, and active research is underway on many of them. Over a period of time repeated exposure and reaction to organic dusts can definitely lead to chronic lung disease and chronic airway obstruction. Anyone suspected of suffering from occupational dust exposure should be thoroughly evaluated and, if necessary, undergo a change in job or alter his or her work pattern to avoid dust exposure.

It should be noted that not everyone exposed to organic dusts becomes ill. Many organic dust reactions are allergic in nature and only affect a small percentage of the exposed population. Other reactions are perhaps due to the bulk load of inhaled dust and may affect a greater percentage of people. Unless large scale screening studies are done on all exposed workers, the only way these diseases can be identified is by patient symptoms. For this reason, it is imperative for any worker to report symptoms that could possibly be related to dust exposure.

WHAT IS BYSSINOSIS?

Byssinosis is the medical term for brown lung, the lung disease that comes from inhaling cotton dust. Byssinosis occurs mainly in people who work with hemp, flax, or cotton dust and thus is prevalent in the textile industry. In the early stages byssinosis can lead to shortness of breath and cough while at work (so­called acute byssinosis). When the worker is removed from the dusty environment, as at home or on vacation, these symptoms improve or disappear. After about five years or longer of constant exposure, the worker may develop chronic byssinosis, leading to permanent breathing trouble.

Byssinosis differs from other occupational dust diseases in that there are no characteristic chest x­ray findings and a lung biopsy does not reveal any evidence of the cotton dust. Except for the work history, chronic byssinosis is indistinguishable from chronic obstructive pulmonary disease. Byssinosis is diagnosed by the work history and the presence of breathing impairment. If clear worsening of symptoms or airflow obstruction can be demonstrated after arriving at work, the diagnosis is more secure.

No one knows for sure how cotton dust ideas to lung disease. The term brown lung comes from the brown dust of the leaves surrounding the cotton balls. But what in the cotton dust is responsible for byssinosis? Is it a chemical? bacteria? fungus? The answer is not known,

Like all occupational diseases the symptoms attributable to byssinosis are worse and more prevalent in cotton workers who smoke, compared to nonsmoking workers. This is particularly true of chronic byssinosis with irreversible airways obstruction. Perhaps something in cotton dust hastens the damaging effects of cigarettes, or vice versa.

Regardless of the cause of byssinosis, the advice is the same for anyone potentially exposed to dust at work. Avoid dusty areas as much as possible, Wear whatever protective devices or masks are available. And above all, don't smoke--on or off the job.

WHAT DISEASES OCCUR FROM INHALING SMOKE, FUMES, GASES, VAPORS, MISTS, AND SPRAYS?

These gaseous­type products are given off in many industrial processes; some of the better characterized diseases, and their causes, are given in Table 2.

Inhaling these noxious materials can lead to a wide variety of clinical reactions. For example, metal fume fever, which comes from inhaling fumes of hot, burning metal, can lead to nausea, vomiting, headaches, and general malaise. TDI, an industrial solvent, can cause asthma in some individuals. Meat wrappers, asthma occurs from inhaling the fumes given off when the plastic used to wrap meat is cut with a hot wire. Arc welders can get a form of chronic lung scarring.

There are many examples and the list grows longer with the addition of new or exotic industrial processes. The advice given in the previous section holds here as well. Anyone suffering symptoms suspected from inhaling industrial products should be evaluated medically and, if necessary, change his or her job or the workplace situation.

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