Occupational asthma and related respiratory disorders.

Occupational rhinitis is a common but generally underreported entity. Although it may occur alone, it is frequently associated with occupational asthma. Occupational asthma may have one of several presentations that are difficult to distinguish from non-work conditions. The respiratory tract acts as the final common pathway for all inhaled environmental pollutants, whether encountered in the home or at work. More than 200 chemicals have been incriminated as a cause of work-related asthma. It is said that about 2% of the 10 million Americans who have asthma acquired it as a result of some chemical irritant or immunogen in their work environment. A number of predisposing factors facilitate the development of work-related asthma. These include industrial conditions, climatic factors, atopic predisposition, smoking, recreational drug use, viral infection, nonspecific bronchial hyperreactivity, and a variety of miscellaneous factors. Pathogenetically, occupational asthma may be immunologic or nonimmunologic in nature. The immunologic variants involve sensitization to a variety of large-molecular-weight constituents. The major nonimmune variant is referred to as inflammatory bronchoconstriction or reactive airways dysfunction syndrome (RADS). There are well-defined criteria for the diagnosis of immunologic and nonimmunologic asthma. The several clinical variations of occupational asthma can be difficult to distinguish from nonindustrial disorders. The most common presentation in practice involves the worker with preexistent asthma who has been adversely affected by work exposures. Occasionally these industrial exposures precipitate permanent impairment. It is clear, however, that occupational asthma is not a single, simple, or homogeneous entity, even when a single specific causal factor can be identified in the workplace. Therefore the physician must be aware of the patient's entire medical history and the precise occupational exposures and must have convincing physiologic evidence that demonstrates a cause-and-effect relationship before making a definitive diagnosis of work-related asthma. Once the diagnosis is established, the worker should be removed from the work-place. If the diagnosis is made in a timely fashion, the patient should experience a significant improvement. The major factor in determining a poor prognosis in occupational asthma is the duration of exposure before the diagnosis is established. Prevention of the disorder is the best therapeutic intervention.