OCCUPATIONAL ASTHMA: WHAT ARE THE MECHANISMS?

Occupational asthma may be defined as asthma induced by acquired hypersensitivity to an agent inhaled at work. A lot of agents in the workplace have been shown to cause asthma and the list is growing as new materials and processes are introduced. There are two major types of occupational asthma. Sensitizer-induced asthma is characterized by specific responsiveness to the etiologic agent. The mechanism of irritant-induced asthma is unknown, but there is no clinical evidence of sensitization. Two other mechanisms by which variable airway obstruction due to workplace exposure can occur are reflex and pharmacological bronchoconstriction. Occupational asthma can be a challenging diagnosis to make and to prove. Tests which are used and are helpful include nonspecific pulmonary function tests, specific or bronchoprovocative pulmonary function test, serial pulmonary function tests (most commonly using the peak flow meter), and immunologic tests. Each test has its own drawbacks and none is perfect. Early diagnosis of occupational asthma and early removal of patients from exposure are important.