Before discussing work-related asthma I will briefly define asthma in general. Asthma is a pulmonary condition characterized by episodic airflow obstruction that is at least partially reversible. Obstruction to flow of air occurs in the bronchial tubes within the lungs. In asthmatics these air passages become inflamed when affected by various triggers; the inflammation in turn leads to narrowing (broncho constriction) and resultant respiratory symptoms. Asthma symptoms typically manifest as wheezing, chest tightness, cough and shortness of breath. Wheezing is a high pitched sound generated by air going through the constricted passages. Shortness of breath is typically felt with exertion, but in severe cases can be at rest. Symptoms are highly variable, from mild and non-limiting, to disabling and, rarely, fatal. Overall, asthma is a common condition, affecting in some fashion an estimated 5-10% of the general population (1, 2).

At a basic level the cause of asthma is unknown. Given an individual's predisposition to asthma, a variety of factors can trigger symptoms (Table 1). Perhaps the most common trigger in adults is respiratory viral infections, including the common cold. Less common, but very important, are allergens, substances that when inhaled can react with the host's antibodies to generate an allergic response. Allergens include various plant pollens, animal furs, excreta from house mites, proteins in shellfish, and some metals. Allergens play a major role in many cases of occupational asthma. Irritants can also trigger an asthma attack through a non-allergic mechanism, by directly injuring cells within the lungs. Other triggers of an asthma attack include climate changes; exercise, particularly in cold weather; certain medications such as aspirin; and acid-reflux from the stomach. Although everyone is subjected to the types of triggers listed in Table 1, only the 5-10% of the population with asthma are prone to develop symptoms when so exposed.

Table 1

• Respiratory viral infections.
• Allergies (e.g., to pollen, animal fur, grain dust, dust mites, shell fish, diisocyanates, etc.)
• Irritants (smoke, fumes, gases, other pollutants)
• Climate changes
• Exercise (particularly in cold air)
• Sinus infections
• Drug reactions, e.g., aspirin
• Stomach acid reflux

There are two basic types of work-related asthma (3).

Work-related asthma
1. Occupational asthma
With latency period - allergic
Without latency period - irritant (RADS)
2. Work-aggravated asthma

The first type - also called 'occupational asthma' is when the asthma first begins on the job, and is directly related to the job. Two types of occupational asthma are distinguished by whether symptoms appear after a latency period, i.e., a period of time (weeks to years) between the very first exposure and first development of symptoms.

• With latency period. This is 'allergic' or 'immunologic' asthma. With repeated exposure over time to an 'allergen', such as latex in hospital gloves, the worker becomes 'sensitized' to the allergen. The next exposure after sensitization might lead to symptoms diagnosed as asthma.
• Without a latency period. This is 'non-allergic' or 'non-immunologic' asthma, and is better known as 'irritant-induced' asthma. It is also sometimes called reactive airways dysfunction syndrome, or RADS. The irritant - typically a chemical fume - inflames the airways and the worker has symptoms immediately.

In both types of 'occupational asthma' symptoms can range from mild to life-threatening, and leave the worker chronically disabled. Generally, once a worker is 'sensitized' he or she must no longer be exposed to the allergen, as even tiny amounts can trigger renewed symptoms.

The second type of work-related asthma is called 'work-aggravated asthma'. This is when pre-existing asthma (such as childhood or teenage asthma) flares up because of exposure to some allergen or irritant on the job. Distinction between true 'occupational asthma' and 'work-related asthma' is often important because workers' compensation agencies may handle them differently; to the individual patient, though, asthma is asthma, and overall management should be no different.

Many people mistakenly equate all asthma with 'allergy', but in fact allergy is only one of the potential triggers of an asthma reaction (Table 1), including work-related asthma. However, on the job, allergy is an important cause of asthma. Over 250 substances have been identified in the workplace that can elicit an antigen-antibody response and cause occupational asthma. These allergens are typically categorized as high or low molecular weight compounds (1-3, 5), but the two groups cannot be distinguished on clinical grounds. Generally, high molecular weight compounds are mostly proteins from animals and plants; low molecular weight compounds include numerous chemicals. Examples of these compounds and the occupations at risk are given in Table 2.

Table 2
Some Antigens Responsible for Work-related Asthma

High MW antigens
Occupation animal danders, animal handlers insect scales entomologists, lab workers egg white proteins egg producers grain dusts farmers, grain store workers wood dusts saw mill workers, carpenters latex health care workers

Low MW antigens
diisocyantes workers in printing and painting industry anhydrides workers in plastics and drug industries metallic salts tool and dye workers antibiotics pharmaceutical workers.

Low molecular weight diisocyanates are the leading causes of occupational asthma (5); they are used in many different manufacturing processes and their fumes can sensitize the worker. Occupational asthma can also occur in 'clean' environments, such as in the pharmaceutical industry, where workers may develop sensitization after repeated exposed to low molecular weight antibiotics; an example is latex allergy.

Latex allergy is an example of occupational asthma in a clean environment. Latex allergy in health care workers appears to be increasing in incidence (6-9). Latex, or natural rubber, is found in many medical products, particularly gloves. Latex allergy is also seen in patients repeatedly exposed to health care workers= gloves and other latex-containing products. Allergic reactions range from contact hives (skin reaction only) to asthma and in some extreme cases, shock (anaphylaxis). For this reason many hospitals and dental offices have switched to non-latex gloves and other products. (Note that latex is not just confined to gloves, but is a component of numerous other hospital products, including intravenous lines and ventilation bags.)

Factors predisposing to latex allergy include a history of other allergies (such as hives or hay fever) and frequent exposure to latex products. 'Sensitization' to latex doesn't happen after a single exposure; instead, the worker becomes sensitized to the latex after repeated exposures, over time. Antibodies gradually build up until there is sufficient amount to produce an antigen (latex)-antibody reaction that produces bronchial inflammation and symptoms. Asthma from latex allergy is thought to arise from repeated inhalation of airborne latex particles that adhere to the cornstarch used to powder gloves (10-11). (Cornstarch is placed in gloves to make them easy to slip on and off.)

RADS, or reactive airways dysfunction syndrome, was first described in the 1985, is now a well-recognized form of occupational asthma. It is non-immunologic, i.e., unrelated to allergy. The exposure is obvious and the symptoms are usually immediate, although they may gradually worsen over the first 24 hours (see Table 4). The inhaled irritant (e.g., fumes from a chemical spill), causes direct irritation of the lining of the bronchial tubes, leading to asthma symptoms. Symptoms can persist long after exposure, and indeed become chronic and disabling.

Table 3
Reactive Airways Dysfunction Syndrome (RADS) (12-13)

• Exposure to a high concentration of irritant gas, smoke, fume, or vapor
• Immediate onset of symptoms after single exposure to the irritant, although symptoms may not peak for several hours
• Documented absence of preceding respiratory complaints
• Symptoms (cough, wheeze and/or dyspnea) persist at least 3 months
• Presence of airflow obstruction on pulmonary function testing
• Presence of non-specific bronchial hyper-responsiveness
  Other pulmonary diseases ruled out

Sometimes it's obvious, sometimes very difficult to know. While there are a variety of sophisticated tests (including blood and breathing tests) to help physicians diagnose this condition, perhaps the most important is the medical history. Medical history includes information about your medical condition before the job began and the specific relationship of your symptoms to job activities.

For example, an obvious case of occupational asthma would be a 30-year-old woman who:

• never smoked;
• never had asthma or respiratory symptoms before starting a new job;
• after working on a new job for months to years, develops wheezing, cough and shortness of breath;
• notes that her symptoms get better away from work (weekends, or vacation), and flare again back at work;
• works with a specific chemical that is known to cause occupational asthma (e.g., toluene diisocyante);
• is diagnosed with asthma by breathing tests.
  

A much more difficult case would be a 35-year-old man who:

• currently smokes, and has smoked a pack a day for 15 years;
• has a history of episodes of Abronchitis@ before taking a new job in a factory at age 34;
• develops a respiratory infection with fever, and then notes trouble breathing;
• gets more short of breath when he returns to work after recovering from the infection. This patient may in fact have smoking-related chronic obstructive disease exacerbated by infection, and not work-related asthma. Only by testing and further history could a physician make a reasonable determination.

Every state runs a worker's compensation agency, and work-related asthma is certainly compensable. The worker will have to satisfy some stringent medical criteria. Usually, an exam will be ordered with a state physician (i.e., someone other than your treating physician).
More often than not, the employer will dispute the diagnosis, and may ask for yet another exam with a physician they designate. Conflicting reports are common, making it difficult for a workers' compensation agency to decide on a case's merits. In truth, these agencies were originally set up to compensate 'injured' workers, and this meant broken limbs and other external injuries. It is much more difficult to adjudicate a medical diagnosis like asthma:

• where the cause is often not obvious;
• in which symptoms can be extremely variable, and
• that is also very common in the general population. Given the potential for disagreement, it is not surprising that the decision of the compensation agency is often appealed

If you think you have work-related asthma, by all means get it checked out, but don't expect a speedy resolution. And remember: your health comes first.

Treatment of work-related asthma is no different from asthma unrelated to the job, with one important exception: advice about continued working. If a worker has developed an allergic reaction to something in the environment (i.e., is Asensitized to it), he or she must leave that environment. The quicker they remove themselves, the better the outcome; studies have shown that continued exposure to the sensitizing agent is associated with further deterioration of lung function (14-15). Masks and other devices to minimize the exposure are of no help, and should not be relied on. Even tiny amounts of allergen can trigger a reaction if the worker is sensitized to it.

On the other hand, if the asthma was due to a one-time irritant exposure, and the irritant is removed completely, than there should be no contraindication to continued working in that environment. Sometimes, though, other pollutants in the environment may bother the worker more than before, even though the specific agent causing the asthma is removed.

Although stopping exposure generally results in clinical improvement, this is not invariable, particularly if the worker is a smoker or has co-existing sinusitis (which can also trigger asthma exacerbation. Even without these other conditions, the patient may continue to manifest asthma symptoms and require medication for months or years after leaving the job (15).

Lawrence Martin, M.D. FACP, FCCP
University Mednet
Mednet Health Center

9000 Mentor Avenue
Mentor, Ohio 44060
440-974-4400
Email: martin@lightstream.net
Dr Martin's web site is www.mtsinai.org/pulmonary.

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