Introduction to Occupational immunologic lung disease (OILD) (Ref: Patterson’s Allergic Diseases, Sixth Edition; Lippincott Williams and Wilkis Publication)
A wide variety of occupational respiratory disorders are caused by immunologic mechanisms. Increasing industrialization has also led to the production of numerous materials capable of inducing immunologically mediated lung disease in the working population. This is a matter of concern for physicians who diagnose and treat these diseases and to labor, management and various governmental agencies.
There are two major subdivisions of diseases that constitute OILD: immunologically mediated asthma and hypersensitivity pneumonitis. There is also an asthma syndrome that can occur after one high irritant exposure called reactive airways dysfunction syndrome (RADS).
Various overlaps and uncertainties exist in OILD. First, some exposures can cause more than one disease. For instance some antigens such as trimellitic anhydride (TMA) and various fungal antigens can cause more than one immunologic pulmonary disease including asthma or hypersensitivity pneumonitis. Secondly many reactive chemicals such as toluene diisocyanate (TDI) can cause disease by inducing either RADS or immunologic asthma. And finally pulmonary responses to some antigens have not been definitely established as immunologically or nonimmunologically mediated. An example of this would be Western red cedar.

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Prevalence and Medicolegal Aspects of OILD:

It has been estimated that 2% of all cases of asthma in industrialized nations are occupationally related. In a US Social Security Disablility survey, about 15% of asthma cases were classified as occupational in origin. In another study of adult asthma in general medical practice, it was reported that more than 1 in 10 patients has a work history strongly suggestive of a potential relationship between work exposure and asthma. The European Community Respiratory Health Survey Group reported the highest risk for asthma was in farmers (odds ration, 2.62), painters (2.34), plastic workers (2.20), cleaners (1.97) and spray painters (1.96).

Most sensitizing agents that have been reported to cause occupational asthma are proteins of plants, animal or microbial derivation and are therefore not specifically regulated by Occupational Safety and Health Administration (OSHA). Some of the low-molecular-weight sensitizers, such as isocyanates, anhydrides, and platinum, are regulated by OSHA; published standards for airborne exposure can be found in the Code of Federal Regulations.

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Diagnosis, Treatment and Prevention of OILD:

The diagnosis of OILD is not complex in the individual worker if symptoms appear at the work place shortly after exposure to a well-recognized antigen. However, the diagnosis can be very difficult in patients whose symptoms occur many hours after exposure, for instance, late asthma from TMA. Because of the increasing importance of OILD, it has now become essential to evaluate patients with respiratory syndromes for a possible association between their present disease states, their pulmonary function test results, and their immunologic exposure in the work environment. In the case or the well-established OILD syndrome, a careful history and physical examination with corroborative immunology and spirometry will suffice. A negative methacholine test can almost exclude occupational asthma. Immunologic evaluations may provide important information about the cause of the respiratory disease. Skin tests with antigens determined to be present in the environment may detect igE antibodies and suggest a casual relationship. Haptens maybe coupled to carrier proteins, such as human serum albumin, and used in skin tests or radioimmunoassays.

The management of OILD consists of controlling the workers exposure to the offending agent. To accomplish this, the worker can be moved to another station; efficient dust and vapor extraction can be instituted; or the ventilation be improved in other ways so that a total job change is not required. Pharmacologic management of OILD is rarely helpful in the presence of continued exposure on a chronic basis. The key principle in OILD is that prevention, rather than treatment must be the goal. There should be efforts to educate individual workers and managers in high risk industries so that affected workers can be recognized early.

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